imp_key_pts_4_net

8/6/2019 imp_key_pts_4_net

1/219

Biochem

Acidic dissociation

1


2/219

Biochem

1. General expression: HA is the acid (proton donor) andA- is the conjugate base (proton acceptor):

2. An acid dissociates in water to yield a hydrogen ion (H+) andits conjugate base

3. A base combines with H+ in water to form its conjugate acid

k1[HA] = forward rate, k-1[H+][A-] = reverse rate

2

Acid (acetic acid) Conjugate base (acetate)

CH3COOH --> H+ + CH3COO-

Ammonia (base) Ammonium ion (conjugate acid)

NH3 + H+ --> NH4

+

k1

HA --> H+

+ A-

k-1


3/219

Biochem

Measures of acidity

3


4/219

Biochem

1. pKa

When forward & reverse rates are equal, acidic dissociationconstant, Ka, is defined by:

o k1/k-1 = [H+][A-] / [HA] = Ka

Expresses the STRENGTH OF AN ACID

pKa = -log[Ka] Strong acid has pKa of2 (H+ binds loosely to conjugate base)

Weak acid has a pKa of10 (H+ binds tightly to conjugate base)2. pH Henderson-Hasselbalch equation: pH = pKa + log [A-]/[HA] A measure of the ACIDITY OF A SOLUTION pH = -log[H+]

Neutral solution has a [H+] of 10-7 pH = 7

4


5/219

Biochem

Acidic solution has a [H+] > 10-7 pH < 7 Alkaline solution has a [H+] < 10-7 pH > 7

Buffers and Buffering capacity

5


6/219

Biochem

1. A solution that contains a mixture of a weak acid and its

conjugate base2. It resists changes in [H+] on addition of acid or alkali

3. The buffering capacity of a solution is determined by th

acid-base concentration and the pKa of the weak acid

Maximum buffering effect occurs when:o [weak acid] = [conjugate base]

When the buffer effect is at its maximum:o pH of the solution = pKa of the acid

4. Buffering effect is seen on a titration curve for a weak ac

The shape of the curve is the same for all weak acids

6


7/219

Biochem

At the midpoint of the curve, the pH = pKa The buffering region extends one pH unit above and belo

the pKa

What acid-base pair is an effective buffer in physiologic fluid

What acid-base pair is the principal buffer in plasma and

extracellular fluid (ECF)?

7


8/219

Biochem

1. What acid-base pair is effective buffer in physiolog fluids?

H2PO4- and HPO42-2. What acid-base pair is the principal buffer in plasma and ECF?

CO2-H2CO3-HCO3- system (carbon dioxide-carbonic acid-bicar

CO2 + H2O carbonic anhydrase H2CO3 H+ + HCO3-

Note : carbonic anhydrase converts CO2 to H2CO3 in RBCs In this system, CO2 is an acid, so H-H equation is:

o pH = 6.1 + log [HCO3-] / (0.0301)PCO2

This system is effective around physiologic pH of 7.4, even thouthe pKa is only 6.1, for 4 reasons:

8


9/219

Biochem

o Supply of CO2 from oxidative metabolism is unlimited, so

effective concentration of CO2 is very high

o Equilibration of CO2 with H2CO3 is very rapid

o CO2 removal by lungs allows for rapid changes in [H2CO3]

o Kidney can retain or excrete HCO3-, thus changing the concentrat

of the conjugate base

Acid-Base Disorders:Acidosis and Alkalosis

9


10/219

Biochem

1. Acidosis

Occurs when pH of blood and ECF falls < 7.35 Results in CNS depression When severe, can lead to coma and death Respiratory acidosis: pCO2 as a result of hypoventilati Metabolic acidosis: [HCO3-] as a result of the addition o

an acid stronger than H2CO3 to the ECF

2. Alkalosis

10


11/219

Biochem

Occurs when pH of blood and ECF is >7.45 Leads to neuromuscular hyperexcitability When severe, can result in tetany

Respiratory alkalosis: pCO2as result of hyperventilatio Metabolic alkalosis: [HCO3-] as a result of excess acid

loss (e.g., vomiting) or addition of a base (e.g., oral antacid

Diabetic ketoacidosis

11


12/219

Biochem

1. Combination of high blood levels of ketone bodies and ametabolic acidosis

2. Pathogenesis

Uncontrolled insulin-dep DM (type 1)glucose utilization,hyperglycemia fatty acid oxidation

fatty acid oxidation excessive production of acetoacetic an3-hydroxybutyric acids and acetone (ketone bodies)

Acids dissociate at body pH and release H+metabolic acido

12


13/219

Biochem

3. Clinical picture Dehydration Lethargy

Vomiting Drowsiness

Coma

4. Therapy: correct the hyperglycemia, dehydration, & acidosis Insulin to correct the hyperglycemia Fluids (physiologic saline) to treat dehydration In severe cases: sodium bicarbonate to correct acidosis

Amino acids grouped by the properties of their R-groups

13


14/219

Biochem

1. Aliphatic, nonpolar (hydrophobic)

Glycine Alanine

Valine Leucine

Isoleucine Proline

2. Aromatic, nonpolar

Phenylalanine Tyrosine Tryptophan

14


15/219

Biochem

3. Sulfer-containing

Cysteine Methionine4. Hydroxyl, mildly polar (uncharged, hydrophilic)

Serine Threonine5. Basic, polar

Lysine Arginine Histidine6. Acidic, polar

Aspartic acid Asparagine

Glutamic acid Glutamine

Secondary structures of proteins and collagen

15

Pg. 7 for

structures


16/219

Biochem

1. Secondary structure = arrangement of H bonds between peptid

nitrogens & carbonyl oxygens of different amino acids

2. Helical coils

Hydrogen-bonded nitrogens & oxygens are on nearby amino aci

Right-handed alpha helix most common

16


17/219

Biochem

o Alpha-keratin in hair and nails

o Myoglobin has several alpha-helical regions

Proline, glycine, and asparagine helix breakers

3. Beta sheets (pleated sheets) may run parallel or antiparallel Hydrogen bonds between residues on neighboring peptide chain4. Left-handed helical strands

Wound into a supercoiled triple helix in collagen Collagen major structural protein in the body

o Primary structure : repeating glycine-X-Y sequences

o X and Y are freqeuntly proline or lysine

o Contains hydroxyproline & hydroxylysine

17


18/219

Biochem

Protein Denaturation Agents

1. Extremes of pH (e.g., strong acid or alkali)

2. Ionic detergents (e.g., sodium dodecylsulfate/SDS)

3. Chaotropic agents (e.g., urea, guanidine)

18

i h


19/219

Biochem

4. Heavy metal ions (e.g., Hg++)

5. Organic solvents (e.g., alcohol or acetone)

6. High temperature

7. Surface films (e.g., as when egg whites are beaten)

19

Bi h 20


20/219

Biochem

Sickle cell anemia

1. Caused by mutant sickle cell hemoglobin (Hgb S)

Hydrophobic valine replaces hydrophilic glutamate at position 6 of thbeta-chain of normal hemoglobin A (Hgb A)

20

Bi h 21


21/219

Biochem

2. Sickle cell disease Individuals with homozygous genotype (SS) Have only Hgb S in their RBCs Symptoms

o Severe anemia: deoxy Hgb S produces fibrous precipitates

formation of sickle cells shorter life span severe anemia

o Acute episodes of vaso-occlusion sickle cell crisis

Sickle cells cant pass thru capillaries vasocclusion Disabling pain that requires hospitalization

3. Sickle cell trait Individuals with heterozygous genotype (AS) Have both Hgb A and Hgb S in their RBCs Symptoms

o Usually asymptomatico Episodes ofhematuria

21

Bi h 22


22/219

Biochem

Scurvy

22

Biochem 23


23/219

Biochem

1. Defective collagen synthesis resulting from a

vitamin C (ascorbic acid) deficiency

2. Consequences of abnormal collagen

Defective wound healing Defective tooth formation Loosening of teeth

Bleeding gums Rupture of capillaries

3. Ascorbic acid is required for hydroxylation of proline and

lysine during post-translational modification of collagen

4. Pathogenesis

Hydroxylating rxn requires hydroxylase, O2, & Fe2+

Vit C is required to maintain iron in its oxidation state (Fe Hydroxyproline forms H-bonds that stabilize collagen heli

23

Biochem 24


24/219

Biochem

Symptoms of scurvy are thus the result of weakendcollagen when these hydrogen bonds are missing

Free energy change

24

Biochem 25


25/219

Biochem

1. The quanitity of energy from chemical reactions that is

available to do work ( G)2. The G of a rxn A + B C + D is:

G = G0 + RTln ([C][D]) / [A][B])o where G0 is the standard free-energy change

(when concentrations of all reactants and productare 1M and pH = 7), R is the gas constant (1.987

cal/molK) and T is the absolute temperature

3. When the rxn has reached equilibrium:

G0 = RTlnKeq

25

Biochem 26


26/219

Biochem

Thermodynamic spontaneity: Exergonic and Endergonic Rxn

26

Biochem 27


27/219

Biochem

1. Exergonic rxns are spontaneous (rxn goes to the right)

Keq > 1 G0 is negative Final concentration of the products, C and D, is greater tha

that of the reactants, A and B

2. Endergonic rxns are nonspontaneous (rxn goes to the left)

Keq < 1 G0 is positive Final concentration of the reactants, A and B, is greater tha

that of the products, C and D

27

Biochem 28


28/219

Biochem

3. Note: G0 CANNOT predict spontaneity underintracellular conditions

Intracellular spontaneity is a function of actual

concentrations as well as Keq, G, NOT G0

Enthalpy, entropy, and free-energy change

28

Biochem 29


29/219

oc e

1. Enthalpy ( H) The amount of heat generated or absorbed in a rxn

2. Entropy ( S) Measure of the change in randomness or disorder of system when a salt crystal dissolves, when a solute diffuses fro

a more concentrated to a less concentrated solution, and

when a protein is denatured

when a complex molecule is synthesized from smaller

substrates

29

Biochem 30


30/219

3. Free-energy change ( G) Is related to enthalpy and entropy as follows:

o G = H - T S (where T = absolute temp in

Kelvins)

Catalysts and the Rate of Reaction

Biochem 31


31/219

1. Rate of reaction

The G0 provides no info concerning the rate ofconversion from A to B

When A is converted to B, it first goes through anenergy barrier called the transition state, A-B

The activation energy ( G) = energy required to

scale the energy barrier and form the transition state

Biochem 32


32/219

The greater the G, the lower the rate of therxn converting A to B

2. Catalysts (mostly enzymes) result in a:

Lower G Faster reaction rate

Michaelis-Menten equation

Biochem 33


33/219

1. Describes the kinetics of enzyme rxns2. In enzyme-catalyzed rxns:

k1 k3E + S ES E + P

k2

Where E=enzyme, S=substrate, P=product, k1-3 = rate constant3. Velocity (v) of product formation is related to [ES]:

o v = k3[ES] where k3 is also called kcat

Biochem 34


34/219

4. Michaelis-Menten eq predicts velocity if [enzyme] is

constant:

Where Vm = max velocity & Km is the Michaelis constant5. Km = [substrate] at which v = Vm ([S] = Km)

6. A plot of velocity versus [S] is a rectangular hyperbola

Lineweaver-Burk Equation

Vm[S]

v = Km+[S]

Biochem

35


35/219

1. Form of the Michaelis-Menten eq, which is sometimes

known as the double-reciprocal equation:1 = Km + [S] = Km x 1 + 1

v = Vm[S] Vm [S] Vm

2. The slope is Km/Vm

Biochem 36


36/219

3. The Y-intercept = 1/Vm4. The X-intercept is 1/Km

Enzyme Regulation:

How doe Inhibitors affect the Lineweaver-Burk plots?

Biochem 37


37/219

1. Competitive inhibitors

apparent Km Vm remains the same slope X-intercept has smaller absolute value

Y-intercept is unchanged

Biochem

2 N i i i hibi38


38/219

2. Noncompetitive inhibitors

Vm Km unchanged

slope X-intercept is unchanged Y-intercept is larger

3. Uncompetitive inhibitors (bind only to ES complex)

Both Km & Vm are different lines on the plot are paral

Allosteric regulation of enyzmes: Definition, How do they

affect Km, and Example of Hexokinase

Biochem 39


39/219

1. Low-molec wgt effector binds to enzyme at a specific site oththan active site (the allosteric site) & alters its activity

2. Allosteric enzymes usually have >1 subunit and >1 active site

Active sites that interact cooperatively: velocity vs, [S] = sigmoi Binding of 1 substrate facilitates binding of substrate at other sit

3. Effectors may have a + or effect on activity

Biochem

40


40/219

Positive effectors the apparent Km Negative effectors the apparaent Km

4. Example: muscle hexokinase

Hexokinase catalyzes 1st

rxn in use of glucose my muscle cells:o Glucose + ATP glucose-6-P + ADP

Hexokinase has a low Km compared to blood [glucose], so it issaturatedand operates at its Vm

When glycolysis slows down, gluc-6-P accumulates gluc-6-Pallosterically inhibits hexokinase (keeps gluc-6-P in balance)

Other mechanisms of enzyme regulation:

1. Induction/repression of enzyme synthesis

Biochem

2 C l t difi t i41


41/219

2. Covalent modificataion

3. Protein-protein interaction

1. Induction/repression of enzyme synthesis

Cytochrome P450 enzymes in the liver (degrade anddetoxify drugs) are induced by the drugs themselves

2. Covalent modificataion

Biochem

Ph h l ( th t b k d l )

42


42/219

Phosphorylase (enzyme that breaks down glycogen)is activated by phosphorylation of a specific hydroxyl grou

This phosphorylation is stimulated by hormones that elevablood glucose, such as glucagon and Epi

3. Protein-protein interactionbetween enzyme & regulatoryprotein

Pancreatic lipase (digests dietary fat) is assisted by colipas Colipase anchors lipase to the surface of fat droplets

Mechanism and Treatment of Methanol & Ethylene glycol

Poisoning

Biochem 43


43/219

1. Mechanism of poisoning

Toxicity is caused by the action of their metabolites In both cases, the 1st oxidation is carried out by alcohol

dehydrogenase

Biochem

o M th l f ld h d + f i id

44


44/219

o Methanol formaldehyde + formic acid

Eyes very sensitive to formaldehydeblindneso Ethylene glycol glycoaldehyde, oxalate, and lacta

Deposition of oxalate crystals in kidneykidnefailure

2. Treatment

Initial infusion of ethanol competitive substratedisplaces methanol or ethylene glycol from active site of

alcohol dehydrogenase Prevents continued production of toxic metabolites

Citric acid cycle:

Biochem

Location Pathway and Initial Substrate45


45/219

Location, Pathway, and Initial Substrate

1. Location

Mitochondria (found in all cells except RBCs)

2. Pathway

Biochem

It is the final common pathway of oxidiative46


46/219

It is thefinal common pathway of oxidiativemetabolism

3. Initial Substrate: Acetyl Coenzyme A (ACETYL CoA)

Condenses with oxaloacetate (OAA) to begin the cyc4. Where does acetyl CoA come from? The catabolism of carbs, fats, & proteins

o Glucose catabolism eventually produces pyruvate

acetyl CoA via pyruvate dehydrogenase

o Fatty acids generate acetyl CoA via -oxidationo Some amino acids are degraded to acetyl CoA

Biochem

What are the products of one revolution of the citric47


47/219

What are the products of one revolution of the citric

acid cycle?

1. 2 CO2 (most CO2 from metabolism)

Biochem

2 Regeneration of one mole of OAA48


48/219

2. Regeneration of one mole of OAA

3. 3 NADH & 1 FADH2 11 ATPs (via oxidative

phosphorylation)

4. 1 GTP 1 ATP

TOTAL OF 12 ATPs/acetyl CoA

Oxidative Phosph:

1 NADH = 3 ATP

1 FADH2 = 2 ATP

Biochem 49


49/219

Describe the anaplerotic rxns that provide OAA and other

citric acid cycle intermediates

1. Pyruvate carboxylase in the liver & kidney:

Biochem

Pyruvate + ATP + HCO3- OAA + ADP + Pi50


50/219

Pyruvate + ATP + HCO3 OAA + ADP + Pi2. Phosphoenolpyruvate (PEP) carboxykinase in heart an

skeletal muscle:

PEP + CO2 + GDP OAA + GTP3. Malic enzyme in many tissues: Pyruvate + HCO3- + NAD(P)Malate + NAD(P)+

4. Glutamate dehydrogenase in the liver:

Glutamate + NAD(P)+ + H2O -ketoglutarate +NAD(P)H + NH4+

Biochem 51


51/219

Regulation of the citric acid cycle

Biochem

1. Step: Acetyl CoA + OAA citrate52


52/219

1. Step: Acetyl CoA OAA citrate

Enzyme: citrate synthase Inhibitors: ATP ( Km), long-chain acyl-CoA

2. Step: Isocitrate + NAD+

-ketoglutarate + NADH + CO2 Enzyme: isocitrate dehydrogenase Allosteric activator: ADP Inhibitors: ATP, NADH

3. Step: -ketoglutarate + NAD+ + CoASH succinyl CoA +NADH + CO2

Enzyme: -ketoglutarate dehydrogenase (note: requiressame cofactors as the pyruvate dehydrogenase complex)

Inhibitors: succinyl CoA, NADH

Regulated mainly by need for ATP, & therefore by supply of NAD+

Biochem 53


53/219

Electron Transport Chain (ETC) & Oxidative Phosphorylatio(BOTH in MITOCHONDRIA)

Biochem 54


54/219

NADH Q cytochrom

ATP ATP synthase-- Proton gradientO2

H2O

NADH

dehydrogenase

Ubiquinone-c

oxidoreductase

(Cytochrome bc1)

Cytochrome

oxidase

1. ETS: electrons pass from NADH or FADH2 to ultimately reduO2 and produce H2O

2. Oxidative phosphorylation: uses energy derived from flow oelectrons thru ETS to drive synthesis of ATP from ADP and P

Biochem

NADH dehydrog. = Complex I, Succinate dehydrog. = Complex55


55/219

II (where FADH2 enters not pictured here), Cytochrome bc1 = Comple

III, Cytochrome oxidase = Complex IV

Chemiosmotic hypothesis

Biochem 56


56/219

1. Describes coupling of electron flow thru ETS to ATP

2. Respiratory complexes as proton pumps:

As electrons (e-) pass thru complexes I, III, & IV, hydrogeare pumped across inner membrane to intermembrane spac

The [H+] in the intermembrane space relative to matrix This generates a proton-motive force as result of 2 factor

o Difference in pH ( pH)o Difference in electrical potential ( ) between the

intermembrane space and the mitochondrial matrix

3. ATP synthase complex (complex V)

Biochem

Hydrogen ions pass back into the matrix thru57


57/219

y g pcomplex V, and in doing so, drive the synthesis of ATP

o Passage of pair of e- from NADH to O2 3ATP

o

Passage of e

-

pair from FADH2 to O2 (bypass I)

2A

Uncouplers and Inhibitors of ETS

Biochem 58


58/219

1. Uncoupling

Carry H+ across inner mit membrane w/o going thru complex V

This short-circuits the proton gradient and uncouples electron

flow from ATP synthesis Energy, instead of used to make ATP, is dissipated as heat Uncoupling agents :

o Dinitrophenol (2,4-DNP) former diet drug

Caused blindness (retina has rate of oxidativmetblism)

Biochem

o Thermogeninhelps to maintain normal body

59


59/219

temp

Found normally in brown fat of newborn mammals2. Inhibitors (via blocking e- flow thru complexes ordirect actio

Complex I Amobarbital (barbiturate), Rotenone (insecticide),Piericidin A (antibiotic), Amytal

Complex II Antimycin A (antibiotic)

Complex IV Cyanide, Hydrogen sulfide, Carbon monoxide

ATP synthase Oligomycin

Carbohydrate digestion and absorption

Biochem 60


60/219

1. Digestion

Disacharides (sucrose),oligosacharides (dextrins),& polysachari(starch) are cleaved into monosaccharides (glucose, fructose)

Starch : storage from of carbs in plants

Biochem

o Hydrolyzed to maltose, maltotriose, and -dextrins61


61/219

by -amylase in saliva and pancreatic juice Disaccharides & oligosaccharides

o Hydrolyzed to monosaccharides by enzymes on the surfac

of epithelial cells in the small intestine

2. Absorption

Monosaccharides absorbed directly by carrier-mediated transpor These sugars (primarily glucose) travel via portal vein to liver fo

o

Oxidation to CO2 and H2O for energyo Storage as glycogen

o Conversion to triglyceride (fat)

o Release into general circulation (as glucose)

Biochem

Glycogen metabolism62


62/219

[Glycogen: carb storage, found chiefly in liver & muscle]

1. Glycogenesis (glycogen synthesis)

Biochem

Activated substrate: Uridine diphosphate-glucose63


63/219

Glycogen synthaseadds to nonreduc end of chains in -1,4 lin Branching enzyme amylo (14) to (16) transglycosylase

creates branches w/ -1,6 linkages Stimulator: insulin (via dephosphorylation in muscle, liver, & f Inhibitors: glucagon (liver), Epi (muscle & liver), phosphorylas

(liver), cAMP, Ca2+ (muscle)

2. Glycogenolysis (glycogen breakdown)

Phosphorylasereleases units of glucose 1-P from nonreducingend

Phosphoglucomutase converts glucose 1-P to glucose 6-P Debranching system releases glucose residues from -1,6 bond Stimulators: sames as inhibitors of glycogenesis

Biochem

Inhibitor: insulin (via dephosphorylation in muscle, liver,d f )

64


64/219

and fat)

Glycolysis:

Location, Anaerobic and Aerobic

Biochem 65


65/219

1. Location: cytosol in most tissues of the body

2. Anaerobic (without oxygen)

Glucose 2Lactate + 2ATP Characteristic of skeletal muscle after prolonged

exercise

Lactate dehydrogenase converts pyruvate to lactate

3. Aerobic: Glucose + 6O2 6CO2 + 6H2O + 36-38 ATP Charactersitic of the brain NADH produced is oxidized by the mitochondrial ET

ATP is generated by oxidative phosphorylation

Biochem 66


66/219

Describe the first step in glycolysis

Biochem 67


67/219

1. Phosphorylation involves rxn of glucose in presence ofhexokinase OR glucokinase to form glucose 6-phosphate

Hexokinase is found in the cytosol of most tissues:o Low specificity (catalzyes phosphorylation of a wide

variety of hexoses)

o Low Km (its saturated at normal blood [glucose])

o Inhibited by glucose 6-P (prevents cells fromaccumulating too much glucose since phosphorylatio

traps glucose inside cells)

Glucokinase is present in the liver & pancreas ( -cells):o High specificity for glucose

Biochem

o High Km (above the normal blood [glucose])

i i f 6 ( l ill b

68


68/219

o Inhibited by fructose 6-P (ensures glucose will be

phosphorylated only as fast as it is metabolized)

What happens in the 2 phases of glycolysis?

Biochem 69


69/219

1. In the first phase (5 reactions):

1 mole of glucose is converted to 2 moles ofglyceraldehyde 3-P

2 moles of ATP are consumed for each mole of gluco2. In the second phase (5 reactions):

Two moles of glyceraldehyde 3-P are oxidized to 2moles of pyruvate

4 moles of ATP and 2 moles of NADH are generatedfor each mole of glucose

Biochem 70


70/219

What do the following do:

1. Glycerol phosphate shuttle

2. Malate-aspartate shuttle

Biochem 71


71/219

NADH produced in the cytosol DOES NOT pass through the

mitochondrial inner membrane, but is instead shuttled in by:1. Glycerol phosphate shuttle (most tissues)

Transfers electrons from cytosolic NADH to mitoch FADH It generates 2 ATP/cytosolic NADH = 36 moles of

ATP/glucose2. Malate-aspartate shuttle (heart, muscle, & liver)

Transfers electrons to mitochondrial NADH It generates 3 ATP/cytosolic NADH = 38 ATP/glucose

Biochem 72


72/219

Gluconeogenesis

Biochem 73


73/219

1. Occurs primarily in the liver & kidney2. Synthesis of glucose from small noncarb precursors (such as lactate a

alanine)

3. Involves the reversible rxns of glycolysis

4. To bypass nonreversible steps of glycolysis, separate rxns occur:

Conversion of pyruvate to PEP bypasses pyruvate kinase Conversion of fructose 1,6-bisphosphate to fructose 6-phosphateby fructose 1,6-bisphosphatase bypasses phosphofructokinase

Conversion of glucose 6-P to glucose by glucose 6-phosphatasebypasses hexokinase

Biochem5. Glucose from gluconeogenesis is released into the

bloodstream for transport to tissues such as the brain and exercising

74


74/219

p g

muscle

6. Gluconeogenic substrates:

Lactate Pyruvate Glycerol Substances that can be converted to oxalacetate via the citric acicycle (such as amino acid carbon skeletons)

Cori cycle

Biochem 75


75/219

1. Shuttling of gluconeogenic substrates between RBCs and

muscle to liver, allowing muscle to function anaerobically(net 2 ATP)

2. Lactate from exercising or ischemic muscle is carried by

the circulation to the liver and serves as a substrate for

gluconeogenesis

Biochem

3. The liver releases the resynthesized glucose into the

circulation for transport back to the muscle

76


76/219

circulation for transport back to the muscle

Regulation of glycolysis

Biochem 77


77/219

1. All are the irreversible steps:

Fructose 6-P fructose-1,6-BP via phosphofructokinao Stimulators : AMP, fructose 2,6-BP (in liver)

o Inhibitors : ATP, citrate

o Rate-limiting step

D-glucose glucose-6-P via hexokinase/glucokinase*

Biochem

o Inhibitors : glucose-6-P

PEP pyruvate via pyruvate kinase

78


78/219

PEP pyruvate via pyruvate kinaseo Inhibitors : ATP, alanine

o Stimulators : fructose-1,6-BP (in muscle)

Pyruvate acetyl CoA via pyruvate dehydrogenaseo Stimulators : CoA, NAD, ADP, pyruvate

o Inhibitors : ATP, NADH, acetyl CoA

2. Induced by insulin

Gluconeogenesis regulation

Biochem 79


79/219

1. All are the irreversible steps: Pyruvate OAA via Pyruvate carboxylase (mitochondo Requires biotin, ATP

o Activated by acetyl CoA

OAA PEP via PEP carboxykinase

Biochem

o Requires GTP

Fructose-1,6-BP fructose-6-P via Fructose-1,6-BPas80


80/219

, ,

Glucose-6-P glucose via Glucose-6-phosphatase2. These enzymes are only found in liver, kidney, intestinal epith

3. Muscle cannot participate in gluconeogenesis4. Hypoglycemia is caused by a deficiency of these key enzymes

5. Induced by glucocorticoids, glucagon, cAMP6. Suppressed by insulin

Pnemonic: Pathway Produces Fresh Glucose

Pyruvate dehydrogenase complex

Biochem 81


81/219

1. Contains 3 enzymes that require 5 cofactors: Pyrophosphate (from thiamine) Lipoic acid CoA (from pantothenate) FAD (riboflavin)

Biochem

NAD (niacin)2. Reaction:

82


82/219

Pyruvate + NAD+ + CoA acetyl-CoA + CO2 + NADH3. The complex is similar to the a-ketoglutarate dehydrogenase

complex (same cofactors, similar substrate and action)4. Cofactors are the first 4 B vitamins plus lipoic acid:

B1 (thiamine; TPP) B2 (FAD)

B3 (NAD)

B5 (pantothenate CoA Lipoic acid

Pentose phosphate pathway

Biochem 83


83/219

1. Sites: lactating mammary glands, liver, adrenal cortex all site

of fatty acid or steroid synthesis

2. Begins with glucose 6-P

3. The irreversible oxidative portion generates NADPH

Biochem NADPH needed for: fatty acid and cholesterol

(steroid) synthesis, maintaining reduced glutathione inside

84


84/219

RBCs

4. The reversible nonxidative portion rearranges the sugars s

they can reenter the glycolytic pathway5. Ribose 5-P, which is needed for nucleotide synthesis, can be

formed from glucose 6-P by either arm

6. Major regulatory enzyme: glucose 6-P dehydrogenase

Glucose 6-P 6-phosphogluconolactone7. Stimulators : NADP+, insulin8. Inhibitors : NADPH

Sucrose and Lactose Metabolism

Biochem 85


85/219

1. Sucrase converts sucrose to glucose and fructose

Hexokinase can convert fructose fructose 6-P (muscle,kidney)

Biochem Fructose enters glycolysis by a different route in the

liver

86


86/219

Dihydroxyacetone phophate (DHAP) enters glycolysisdirectly

After glyceraldehyde is reduced to glycerol, it isphosphorylated and then reoxidized to DHAP

2. Lactase converts lactose to glucose + galactose

Galactokinase converts galactose galactose 1-P Galactose 1-P glucose 1-P glycolysis

BiochemGlycogen Storage Diseases

87


87/219

Result in abnl glycogen metabolism & glycogen in cells

DEFFECT TISSUE SIGNS, ETC.

BiochemVon Gierkes

(type I)

Glucose 6-P Liver &

kidney

Hepatomegaly,

Failure to thrive, Hypoglyc

Ketosis, Hyperuricemia,

H li id i

88


88/219

Hyperlipidemia

Pompes

(type II)

-1,4-glucosidase Lysosomes,All organs

Failure of heart & lungs

Death


89/219

1. Hereditary enzyme deficiences in sucrose metablism:

Biochem

Fructokinase deficiency essential fructosuriao Benign disorder

90


90/219

Fructose 1-P aldolase deficiency hereditary fructose intolerano Characterized by severe hypoglycemia after ingesting

fructose (or sucrose), jaundice, cirrhosis2. Inherited enzyme deficiencies in lactose metabolism:

Lactase deficiency milk intoleranceo Develops in adult life (age-dep) or hereditary (blacks, Asia

Galactokinase deficiency mild galactosemiao Early cataract formation

Galactose 1-P uridyltransferase deficiency severe galactosem(AUTOSOMAL RECESSIVE)

o Cataract, hepatosplenomeg, growth failure, retardation, dea

o Treatment: exclude galactose & lactose from diet

Biochem 91


91/219

Pyruvate dehydrogenase deficiency

Biochem

1. Pyruvate dehydrogenase deficiency neurologic defects

2 C b k f b ( & l i ) l i

92


92/219

2. Causes backup of substrate (pyruvate & alanine), resultin

in lactic acidosis

3. Treatment: intake of ketogenic nutrients (Lysine &Leucine are the only purely ketogenic amino acids)

Biochem

Gl cose 6 phosphate deh drogenase deficienc

93


93/219

Glucose-6-phosphate dehydrogenase deficiency

Biochem1. X-linked recessive

2. Background:

G6PD i th t li iti i HMP (h

94


94/219

G6PD is the rate limiting enzyme in HMP (hexosemonophosphate) shunt, which includes the pentose

phosphate pathwy (which yields NADPH) NADPH is necessary to keep glutathione reduced, which i

turn detoxifies free radicals and peroxides

3. Manifestations of disease:

NADPH in RBCshemolytic anemia4. Pathogenesis:

Poor RBC defense against oxidizing agents (fava beans,sulfonamides, primaquine) and antituberculosis drugs

5. More prevalent among blacks

6. Heinz bodies: altered Hemoglobin precipitates w/in RBC

Biochem

Lipid digestion

95


95/219

Lipid digestion

Biochem1. In mouth:

Medium-chain triacylglycerol (TGs) are hydrolyzed by lipase Continues in stomach, producing a mix of diacylglycerols & FFAs

96


96/219

, p g y g y

2. In the duodenum: Lipids are emulsified by bile salts (made from cholesterol in liver)

3. In small intestine: Emulsified fats are hydrolyzed by pancreatic lipase Phospholipids are hydrolyzed by phospholipase A Cholesterol esters are hydrolyzed by cholesterol esterase

4. Mixed micelles form, which contain: Fatty acids Diacylglyc

Monoacyl Phospholipi

Cholesterol VitA,D,E, K

Bile acid

5. Micelles absorbed in small intestine further metabolized Medium-chain TGs are hydrolyzed Medium-chain fatty acids (8-10 carbons) pass into portal vein

Biochem Long-chain fatty acids (>12 carbons) are reincorporated intoTGs

TGs go into chylomicrons lymphatics circulation via thoracic duc

97


97/219

g y y p

How are lipids transported to tissues?

Biochem 98


98/219

1. Lipids are transported to tissues in the blood plasma

primarily as lipoproteins: Spherical particles w/a core that contain varying

proportions of hydrophobic triacylglycerols &

cholesterol esters

Outer layer of cholesterol, phospholipids, and specificapoproteins

Biochem 99


99/219

Lipoprotein absorption

Biochem 100


100/219

1. Exogenous lipid (from intestine), except for medium-chain fatty aci

is released into the plasma as chylomicrons Chylomicrons contain a high proportion of TGs

TG is hydrolyzed to FFAs and glycerol by lipoprotein lipase onthe surface of capillary endothelium in muscle and adipose tissu

The cholesterol rich chylomicron remnants travel to the liver,

where they are taken up by receptor-mediated endocytosis (RME2. Endogenous lipid (from liver) is released into blood as VLDLs

VLDL TG is hydrolyzed by lipoprotein lipase to FFAs andglycerol, yielding low-density lipoproteins (LDLs)

Biochem LDLs are removed from circulation by RME in tissues

that contain LDL receptors (tissues that need cholesterol, but

mostly in liver)

101


101/219

y )

LDL cholesterol:

o Inhibits HMG CoA reductase (RLS in cholesterol synthesio Down-regulates LDL receptor synthesisLDL uptake

High density lipoproteins (HDLs) are made in the liver

Lipoprotein functions and associated apolipoproteins:Chylomicrons

Biochem 102


102/219

1. Delivers dietary triglycerides to peripheral tissues and

dietary cholesterol to liver

2. Secreted by intestinal epithelial cells

3. Excess causes pancreatitis, lipemia retinalis, eruptive

xanthomas

4. Associated apolipoproteins:

Biochem B-48 mediates secretion As are used for formation of new HDL C II activates lipoprotein lipase

103


103/219

C-II activates lipoprotein lipase E mediates remnant uptake by liver

Lipoprotein functions and associated apolipoproteins:

VLDL

Biochem 104


104/219

1. Delivers hepatic triglycerides to peripheral tissues

2. Secreted by liver

3. Excess causes pancreatitis


B-100 mediates secretion C-II activates lipoprotein lipase

Biochem

E mediates remnant uptake by liver 105


105/219


LDL

Biochem106


106/219

1. Transports hepatic cholesterol to peripheral tissues

2. Formed by lipoprotein lipase modification of VLDL in

peripheral tissue

3. Taken up by target cells via RME

4. Excess causes atherosclerosis, xanthomas, and arcus

corneaa (senilis?)

Biochem


B-100 mediates binding to cell surface receptor forendocytosis

107


107/219

y


HDL

Biochem 108


108/219

1. Mediates centripetal transport of cholesterol (i.e. reverse

cholesterol transport, from periphery to liver, i.e. transpor

cholesterol from periphery to liver)

2. Acts as a repository for apoC & apoE (which are needed

for chylomicron and VLDL metabolism)

3. Secreted from both liver and intestine

Biochem


As help form HDL structure A-I in particular activates LCAT (which catalyzes

109


109/219

p ( y

esterification of cholesterol)

CETP mediates transfer of cholesteryl esters to otherlipoprotein particles

Pneumonic: HDL is Healthy, LDL is Lousy

Oxidation of fatty acids

Biochem 110


110/219

1. Occurs in mitochondrial matrix. The overall process is:RCH2CH2COOH -oxidation CH3COSCoA Citric acid cycle CO2+H2O

2. Fatty acids must first be activated to their acyl CoA thioesters

Long-chain (LC) fatty acids (>12) activated in cytosol LC acCoAs are shuttled into mitoch matrix by carnitine transport sy

Biochem

MCFAs pass directly into the mitoch & are activated inthe matrix

3. Fatty acyl CoA is then oxidized to CO2 and H2O by -id i

111


111/219

oxidation:

Continues in cycle until its completely converted to acetyl CoA Each cycle generates 5 ATPs via ETS and 12 ATPs via combinaction of citric acid cycle and ETS

Terminal 3 carbons of odd-numbered fatty acids yield propionyCoA as the final product, which can:

o Enter the citric acid cycle (after carboxylation to succinylCoA in a 3-rxn sequence requiring biotin and Vit B12)

o Be used for gluconeogenesis

Biochem

Ketogenesis112


112/219

1. The formation ofacetoacetate and -hydroxybutyratefrommetabolism of acetyl CoA in the liver


113/219

Biochem

Fatty acid synthesis114


114/219

1. Carried out by fatty acid synthase, a cytosolic complex

Biochem

2. Primary substrates :

Acetyl CoA: formed in mitoch, mainly by pyruvate dehydrogeno Its transported to cytosol by citrate-malate-pyruvate shuttl

115


115/219

Malonyl CoA: formed by biotin-linked carboxylation of actyl C

3. The acetyl and malonyl moieties are transferred from the sulfuof CoA to activate sulfhydryl groups in the fatty acid synthase

4. 7 cycles lead to production of palmityl:enzyme, which ishydrolyzed to yield products palmitate & fatty acid syntha

5. Palmitate is the precursor for longer & unsaturated fatty acids

Chain-lengthening occurs in the mitoch and ER (C16C18etc) Desaturating system is also present in the ER

o Requires NADPH and O2

o Inserts double bonds no further than 9 carbons from the

carboxylic acid group

Biochem

What do the limitations of the desaturating system result in?

116


116/219

Biochem

1. The limitations of the desaturating system impose a

dietary requirement for essential fatty acids (those

w/double bonds >10 carbons from the carboxyl end)

Li l i id

117


117/219

Lineoleic acid

o Precursor for arachidonic acid (which is beginninof cascade that synthesizes prostaglandins,

thromboxanes, and eicosanoids)

Linolenic acids

Biochem

Glycerolipid synthesis

118


118/219

Biochem

1. This process is carried out by the liver, adipose tissue,

and the intestine

2. Pathways begin w/glycerol 3-P, which is mainly produced byreducing dihydroxyacetone phosphate w/NADPH

119


119/219

reducing dihydroxyacetone phosphate w/NADPH

3.Succesive transfers of acyl groups from acyl CoA to carbons 1

and 2 of glycerol 3-phosphate produce phosphatidate, which

can then be converted to a variety of lipids:

Triacylglycerol (from transfer of acyl group from acyl CoA Phosphatidyl choline & phosphatidyl ethanolamine (from

transfer of base from its cytidine diP/CDP derivative) Phosphatidylserine (from exchange of serine for choline) Phosphatidylinositol (from reaction of CDP-diacylglycero

with inositol)

Biochem

Sphingolipid synthesis

120


120/219

Biochem

1. Begins with palmityl CoA and serine

Produces dihydrosphingosine and sphingosine2. Sphingosine can then by acylated to produce ceramide

Additi l b dd d t th C OH f

121


121/219

Additional groups may be added to the C1-OH of

ceramides

Biochem

Cholesterol synthesis

122


122/219

Biochem

1. Cholesterol is made by the liver and intestinal

mucosa from acetyl CoA in a multistep process

2. Key intermediate = HMG CoA

HMG CoA reductase: regulatory enzyme that

123


123/219

HMG CoA reductase: regulatory enzyme that

catalyzes HMG CoA + NADPH mevalonic acid Increasing amounts of intracellular cholesterol lead to

inhibition of HMG CoA reducate and accelerated

degradation of the enzyme

3. Overall reaction:

Acetoacetyl CoA + acetyl CoA HMG CoA synthase HMG CoA

HMG CoA reductase mevalonic acidcholesterol

Biochem

What are the fates of the products of cholesterol synthesis?

124


124/219

Biochem

1. Mevalonic acid

Precursor of a number of natural products calledterpenes, which include vit A, vit K, coenzyme Q, an

natural rubber

125


125/219

natural rubber

2. Cholesterol Converted to steroid hormones in the adrenal cortex,

ovary, placenta, and testes

Majority is oxidized to bile acids in the liver 7-dehydrocholesterol is the starting point for synthesi

ofvit D

Biochem

Lipid malabsorption

126


126/219

Biochem

1. Leads to excessive fat in the feces (steatorrhea)2. Occurs for a variety of reasons:

Bile duct obstructiono ~50% of dietary fat appears in the stools as soaps

127


127/219

o ~50% of dietary fat appears in the stools as soaps

(metal salts of LCFAs)o Absence of bile pigments leads to clay-colored stool

o Deficiency of the ADEK vitamins may result

Pancreatic duct obstructiono Stool contains undigested fat

o Absorption of ADEK vitamins is not sufficiently

impaired to lead to deficiency symptoms

Diseases of the small intestine(e.g., celiac disease,abetalipoproteinemia, nontropical sprue, IBD)

Biochem

Hyperlipidemias

128


128/219

Biochem

1. Familial hypercholesterolemia

Results from defective LDL receptors Findings: severe atherosclerosis, early death from CAD

129


129/219

g , y

Tx: HMG CoA reductase inhibitors (statins)2. Hypertriglyceridemia Can result from either overproduction of VLDL or defectiv

lipolysis of VLDL triglycerides

Findings: cholesterol levels may be mildly

3. Mixed hyperlipidemias BOTH serum cholesterol & serum triglycerides are

Biochem

There is both overproduction of VLDL and defectivelipolysis of triglyceride-rich lipoproteins (VLDL and

chylmicrons)

There is a danger of acute pancreatitis

130


130/219

g p

Inheritied defects and deficiencies that disrupt fatty acid

oxidation

Biochem

1. Inherited defects in the carnitine transport system, which hav

131


131/219

p y ,

widely varying symptoms: Hypoglycemia Muscle wasting w/accumulation of fat in muscle Feeding fat w/medium-chain triacylglycerols (e.g., butterfa

is helpful in some cases, b/c MCFAs can bypass carnitine

transport system2. Inherited deficiencies in the acyl CoA dehydrogenase, the mo

common being medium-chain (C6-C12) acyl CoA

dehydrogenase deficiency

Biochem

Hypoketotic hypoglycemia and dicarboxylic aciduriaoccur, with vomiting, lethargy, and coma

This is believed to account for the condition called Reye-like syndrome

132


132/219

Sphingolipid Storage Diseases

Biochem 133


133/219

Disease

Accumulated

Substance Clinical Manifestations

Tay-SachsGanglioside GM2 Mental retardation (MR), blindness, r

spot on macula, death by 3rd yr

Gauchers Glucocerebroside Hepatosplenomeg, bone erosion, MR

FabrysCeramide

trihexoside

Rash, kidney failure, lower extremity

painNiemann-Pick Sphingomyelin Hepatosplenomegaly, MR

Globoid cell

leukodystrophy

Galactocerebroside MR, myelin absent

(also called Krabbes disease)

Metachromatic Sulfatide MR, metachromasia, nerves stainyellowish brown w/crystal violet

Biochem

leukodystrophy

Gen gangliosidosisGanglioside GM1 MR, hepatomegaly, skeletal

abnormalities

SandhoffsGanglioside GM2,

globoside

Same as Tay-Sachs, but more rapid

course

134


134/219

Fucosidosis

Pentahexosylfuco-

glycolipd

Cerebral degeneration, spasticity, thic

skin

Urea Cycle

Biochem 135


135/219

1. Converts NH4+ (which is toxic, esp to CNS) to urea

2. Occurs in the liver

3. Urea is excreted in the urine

4. NH4+ + CO2 carbamoyl phosphate synthetase I

carbamoyl P + ornithine ornithine transcarbamoylasecitrulline + aspartate + ATP argininosuccinate synthetase

argininosuccinate argininosuccinate lyase fumarate +

arginine + H20 arginaseUREA + ornithine

Biochem

Urine byprodu

136


136/219

How does detoxification of NH4+ occur in peripheral tissues?

Biochem 137


137/219

1. In most tissues:

Glutamine synthetase incorporates NH4+ into glutamate toform glutamine, which is carried by circulation to the liver

In the liver, glutaminase hydrolyzes glutamine back to NH

and glutamate2. In skeletal muscle:

Glutamate dehydrogenase and glutamate-pyruvateaminotransferase incorporate NH4

+ into alanine

Biochem

Alanine is carried to the liver, wheretransdeamination results in converstion of alanine back to

pyruvate and NH4+

138


138/219

Hyperammonemia

Biochem 139


139/219

1. May be caused by insufficent removal of NH4+, resulting fromdisorders that involve one of the enzymes in the urea cycle

2. Signs and Symptoms Blood NH4+ concentrations above the normal range (30-60 M Mental retardation, seizure, coma, and death

3. Enzyme defects

Biochem

Low activity of carbamoyl P synthetase or ornithine-carbamoyl transferase [NH4

+] in blood & urine NH4+

intoxication

Defective argininosuccinate synthetase, argininosuccinase, ORi bl d l l f t b lit di d f t

140


140/219

arginase blood levels of metabolite preceding defect

o NH4+ levels may also rise

4. Treatment Restriction of dietary protein Intake of mixes of keto acids that correspond to essential amin a

Eating benzoate & phenylacetate: alternate path for NH4+

excret

Carbon skeletons of amino acids

Biochem 141


141/219

1. Amino acids can be grouped into families based on the point wheretheir carbon skeletons enter the TCA cycle

2. AcetylCoA/Ketogenic fam(blue:keto-& glucogenic; red:ketogen on

Isoleucine, leucine, lysine,phenylalanine, tryptophan, and tyros Phenylalanine tyrosine via phenylalanine hydroxylase

Biochem

Tyrosine is starting compound for:o Epi and NE, T3 and T4, Dopamine, Melanin

3. -Ketoglutarat fam (arginine,histidine,glutamate,gluatmine,prolin Histidine precursor of histamine Glutamate excitatory neurotransm can be converted to GABA

142


142/219

Glutamate excitatory neurotransm, can be converted to GABA

4. Succinyl CoA family (isoleucine, methionine, valine) Methyl of methionine participates in methylation rxns as S-

adenosylmethionine (SAM)

5. Fumarate family (phenylalanine and tyrosine)

6. Oxaloacetate family (asparagine and aspartate)

7. Pyruvate fam (alanine,cysteine,glycine,serine,threonine, tryptophan

Essential amino acids

Biochem 143


143/219

1. Isoleucine

2. Leucine

Biochem

3. Lysine4. Phenylalanine

5. Tryptophan

6. Histidine

7 Methionine

144


144/219

7. Methionine

8. Valine

9. Threonine

Biochem

Phenylketonuria (PKU)

145


145/219

1. Results from a deficiency of:

Phenylalanine (Phe) hydroxylase OR

Biochem

Dihydropteridine reductase2. Findings

Phe in the blood (hyperphenylalaninemia) Phe builds up to toxic concentrations in body fluids,

146


146/219

resulting in CNS damage with mental retardation Phe inhibits melanin synthesis hypopigmentation3. An alternative pathway for Phe breakdown produces

phenylketones, which spill into th eurine

4. In those affected, tyrosine is an essential amino acid

5. Treatment: restricting dietary protein (phenylalanine)

Biochem

Albinism

147


147/219

1. No tyrosinase (1st enzyme on pathway to melanin)

2. Have little or no melanin and are:

Biochem

Easily sunburned Very susceptible to skin carcinoma Photophobic b/c of lack of pigment in iris of eye

148


148/219

Biochem

Homocystinuria

149


149/219

1. May result from several defects:

Cystathionine synthase (CS) deficiency

Biochem

affinity of CS for its coenzyme, pyridoxal phosphate(PLP) (may respond to megadoses of pyridoxine/vit B6)

Methyl tetrahydrofolate homocyst methyltransferase deficie Vit B12 coenzyme deficiency (may respond to vit B12)

2 Finding: homocysteine accumulation in blood appears in urin

150


150/219

2. Finding: homocysteine accumulation in blood, appears in urin3. Pathologic changes

Dislocation of optic lens Mental retardation Osteoporosis and other skeletal abnormalities Atherosclerosis and thromboembolism

4. Pts unresponsive to vitamin therapy may be treated with: Synthetic diets low in methionine Betaine (trimethylglycine) alternative methyl group donor

Biochem

Maple-syrup urine disease

151


151/219

Biochem

1. Results from a deficiency in the branched-chain 2-keto acid decarboxylase

2. Findings: branched chain keto acids derived from

isoleucine, leucine, and valine appear in the urine, giving

a maple syrup-like odor

152


152/219

a maple syrup like odor

3. Elevated keto acids cause severe brain damage, with

death in the first year of life

4. Treatment

A few respond to megadoses of thiamine (vitamin B1)

Those that dont: synthetic diets low in branched-chaiamino acids

Biochem

Histidinemia

153


153/219

Biochem

1. Deficiency in histidine- -deaminase (the 1stenzyme in histidine catabolism)

2. Characterized by elevated histidine in blood plasma and

excessive histidine metabolites in urine

3. Symptoms:

154


154/219

3. Symptoms:

Mental retardation and speech defects (both are rare)4. Treatment: not usually indicated

Biochem

Origin of the atoms in the purine ring

155


155/219

N

te

C

C

NH

C

N3, N9: glutamine

Biochem 156


156/219

Biochem

PURINE nucoleotide synthesis

157


157/219

Biochem

De novo synthesis:

158

PATHWAY: (remember: purines = adenine and guanine)

Ribose 5-P PRPP synthetase PRPPglutamine PRPP amidotransferase 5

phosphoribosyl-1-amine 9 rxns IMP + Asp + GTP AMP

IMP + Gln + ATP + NAD GMP


158/219

1. Inosine monophosphate (IMP), AMP, & GMP inhibit PRPP syntheta2. Committed step: conversion of PRPP to 5-phosphoribosyl-1-amine

PRPP activates glutamine PRPP amidotransferase Inhibited by end products (IMP, GMP, AMP) of the pathway

Purines made by salvage of preformed purine bases:

1. Involves 2 enzymes: Hypoxanthine-guanine phophoribosyltransferase (HGPRT)

o Comp inhibited by IMP and GMP

Adenine phosphoribosyl transferaseo Inhibited by AMP

Biochem

Regulation of purine synthesis

159


159/219

Biochem

1. Regulation provides a steady supply of purinenucleotides

2. GMP and AMP inhibit 1st step in their own synthesis from IMP

3. Reciprocal substrate effect: GTP is a substrate in AMPsynthesis, and ATP is a substrate in GMP synthesis

160


160/219

Balances supply of adenine and guanine ribonucleotides4. Interconversion among purines ensures control of their levels

AMP deaminase converts AMP back to IMP GMP reductase converts GMP back to IMP IMP is the starting point for synthesis of AMP and GMP

Biochem

Origin of the atoms in the pyrimidine ring

161


161/219

N

N

C

C

Biochem 162


162/219

Biochem

De novo pyrimidine synthesis

163


163/219

Biochem

1. In mammals, 1st

3 steps occur on one multifunctionalenzyme called CAD, which stands for the names of the enzym

CO2 + glutamine CAP synthetase II carbamoyl-P (CAP) Synthesis of dihydroorotic acid is a 2-step process:

o Committed step: aspartate + CAP aspartate

164


164/219

transcarbamoylase carbamoyl aspartate

o Carbam aspartate dihydrorotase dihydroorotic acid + H

2. Dihydroorate forms UMP

Dihydroorate orotic acid

Orotic acid + PRPP

orotidylate (OMP) Decarboxylation of OMP uridylate (UMP) These 2 steps occur on 1 protein (if defected: orotic acidur

3. Synthesis of remaining pyrimidines involves UMP

Biochem

Phosphorylation of UMP UDP + UTP Addition of amino group from glutamine to UTP CTP

Regulation of pyrimidine synthesis

165


165/219

Biochem

1. CAP synthetase II regulation

Inhibited by UTP Activated by ATP and PRPP

166


166/219

2. CTP itself inhibits CTP synthetase

Biochem

Salvage of pyrimidines

167


167/219

Biochem

Accomplished by the enzyme pyrimidine phosphoribosyl

transferase, which can use orotic acid, uracil or thymine, bu

NOT CYTOSINE

168


168/219

Biochem

Deoxyribonucleotide synthesis

169


169/219

Biochem

Formation of deoxyribonucleotides (for DNA synthesis) involvesreduction of sugar of ribonucleoside diphosphates:

1. Ribonucleotide reductase

L d t d ti f ADP GDP CDP UDP t d ib

170


170/219

Leads to reduction of ADP, GDP, CDP, or UDP to deoxyribonu Its reducing power is from 2 sulfhydryl groups on thioredoxin Using NADPH + H+, thioredoxin reductase converts oxidized

thioredoxin back to the reduced form

Regulation controls the overall supply of deoxyribonucleotideo Rxn proceeds only in presence of nucleotide triphosphate

o dATP: allosteric inhibitor

o Other deoxynucleosides interact w/enzyme to alter specific

2. Thymidylate synthase

Biochem

Catalyzes formation of dTMP (deoxythymidylate) fromdUMP

Coenzyme : N5, N10-methylene tetrahydrafolate (regenerated afteeach rxn by dihydrofolate reductase)

N l tid d d ti

171


171/219

Nucleotide degradation

Biochem

1. Purine degradation (product: Uric acid is exreted in urine) Sequential actions of 2 groups of enzymes (nucleases and

nucleotidases) lead to hydrolysis of nucleic acids to nucleosides

172


172/219

nucleotidases) lead to hydrolysis of nucleic acids to nucleosides Deaminase converts adenosine/deoxyadenosine to deoxy-/inosin Purine nucleoside phosphorylase splits inosine and guanosine to

ribose 1-P and free bases hypoxanthine and guanine

Guanine is deaminated to xanthine

Hypoxanthine & xanthine xanthine oxidaseuric acid2. Pyrimidine degradation (products = -amino acids, CO2,

NH4+)

Degraded to free bases uracil or thymine

Biochem

A 3-enzyme rxn (reduction, ring opening, deamination-decarboxylation) converts uracil to CO2, NH4+, and -alanine anthymine to CO2, NH4

+, & -aminoisobutyrate

THUS: urinary -aminoisobutyrate is an indicator of DNAturnover (may be during chemo or radiation therapy)

173


173/219

Disorders caused by deficiencies in enzymes involved in

nucleotide metabolism

Biochem

Hereditary

orotic

Orotate

phosphoribosyl

Retarded growth,

Anemia

Synthetic cytdi

or uridine (UT

174


174/219

oroticaciduria

phosphoribosyltransferase

and/or OMP

decarboxylase

Anemia or uridine (UTformed acts as

inhib of carbam

P synthetase II

Purine

phosphorylas

deficiency

purine

uric acid

formation

Impaired T-cell

function

SCID Adenosinedeaminase

T- & B-cell dysfunction

w/early death from

infection

Gene therapy

Lesch-Nyhan HGPRT purine synthesis, Allopurinol -

Biochem

(deficient or

absent)

hyperuricemia, severe

neuro problem (spastic,

MR, self-mutilation)

deposition ofsodium urate

crystals, but

doesnt amelio

neuro symptom

Anticancer drugs that interfere w/nucleotide metabolism

175


175/219

Anticancer drugs that interfere w/nucleotide metabolism

Biochem

1. Hydroxyurea

Inhibits nucleoside diphosphate reductase (enzyme th

176


176/219

Inhibits nucleoside diphosphate reductase (enzyme thconverts ribonucleotides to deoxyribonucleotides)

2. Aminopterin and methotrexate

Inhibit dihydrofolate reductase (enzyme that converts

dihydrofolate to tetrahydrofolate)3. Fluoredeoxyuridylate

Inhibits thymidylate synthetase (enzyme that convertsdUMP to dTMP)

Biochem 177


177/219

Gout

Biochem

1. May result from a disorder in purine metabolism

2 Is associated w/hyperuricemia

178


178/219

2. Is associated w/hyperuricemia3. Primary gout: overproduction of purine nucleotides

Mutations in PRPP synthetase loss of feedback inhibitiby purine nucleotides

A partial HGPRT deficiency less PRPP is consumed bysalvage enzyes PRPP activates PRPP amidotransfera

4. Secondary gout

Due to radation therapy, CA chemo (b/c they cell death

Biochem

5. Treatment: allopurinol Xanthine oxidase catalyzes oxidation of allopurinol toalloxanthine, which is a potent inhibitor of the enzyme

Result: uric acid levels fall, hypoxanthine & xanthine leverise (is OK, b/c they dont form crystals)

179


179/219

Energy expenditure (3 components)

Biochem

1. Basal energy expenditure (BEE)

resting energy expenditure

180


180/219

resting energy expenditure Energy used for metabolic processes at rest Represents >60% of total energy expenditure Related to the lean body mass

2. Thermic effect of food Energy required for digesting and absorbing food Amounts to ~10% of energy expenditure

3. Activity-related expenditure

Biochem

20-30% of daily energy expenditure

181


181/219

Caloric yield from foods and what % they should be in diet

Biochem

1. Carbs: 4 kcal/g

50-60% of caloric intake

182


182/219

50 60% of caloric intake2. Proteins: 4 kcal/g

10-20% of caloric intake (0.8 g/kg body weight/day)3. Fats: 9 kcal/g

No more than 30% of caloric intake4. Alcohol: 7 kcal/g

Biochem 183


183/219

Fats:

Essential fatty acids, Deficiency, and Excess storage

Biochem

1. Essential fatty acids (EFAs):

Linoleic acid

184


184/219

Linoleic acid Linolenic acid

2. Deficiency

Mainly seen in low-birth-weight infants maintained o

artificial formulas and adults on TPN Characteristic system: scaly dermatitis3. Excess fat

Stored as triacylglycerol

Biochem 185


185/219

Marasmus vs. Kwashiorker

Biochem

Marasmus Kwashiorker

Insufficient food, including bothcalories and protein

Starvation with edema often due protein deficient diet

186


186/219

, gcalories and protein protein deficient diet

Depleted subQ fat Pitting edema

Flaky paint dermatosis: dark patch

on skin that peel

Liver ketogenesisbrain&heart fuel Large liver due to fatty infilatratio

Muscle wasting (breakprotein forgluconeogenesis & protein synthes)

Muscle wasting less severe

Frequent infections Frequent infections

Low body temp

Biochem

Micronutrient deficiencies Other nutrient deficiencies

Slowed growth(60% expected w

Death when energy & protein

reserves exhausted

Poor appetitie (anorexia)

Watery stools w/undigested food

Mental changes (apathetic)

187


187/219

Vitamin A

Biochem

1. Functions:

11-cis-retinal prosthetic group of rhodopsinB i id NOT TOXIC hi h d

188


188/219

p g p p Beta-carotene antioxidant NOT TOXIC at high doses Retinyl phosphate mannose acceptor/donor in glycoprotein syn Retinol & retinoic acid regulate tissue growth & differentiation

2. Deficiency signs and symptoms:

Night blindness, Xerophthalmia (cornea keratinizes: Bitot spotso Leading cause of child blindness in 3rd world nations

Follicular hyperkeratosis (rough, tough skin) Anemia

Biochem

resistance to infection susceptibility to cancer3. Toxicity (prolonged ingestion of 15,000-50,000 equivalents/da

Bone pain, scaly dermatitis, hepatosplenomegaly, nausea, diarrh4. Clinical usage: For acne and psoriasis

189


189/219

Vitamin D

Biochem

1 Functions: regulation of Ca+ metabolism

190


190/219

1. Functions: regulation of Ca+ metabolism

Stimulates synth of Ca+-binding protein aids absorption In combo w/PTH, blood Ca+ by:

o bone demineralization by stimulating osteoblastic activity

o Simulates Ca+ reabsorption by distal renal tubules2. Sources:

Major: skin (UV: 7-dehydrocholesterol Vit D3/cholecalciferol) Diet (vit D3) and foods fortified w/vit D2

Biochem

3. Activation

Liver: Vit D3 25(OH)D3 Kidney: 25(OH)D3 active 1,25(OH)2D3 (stimulated by PTH)

4. Deficiency

Rickets (kids): soft bones, stunted growth

Osteomalacia (adults): pathologic fractures B d i li l lt f it D i ti f b t

191


191/219

Bone demineraliz may also result from vit D inactive forms by stero5. Toxicity: (hyperCa+, metast calcification, bone demineraliz, kidney stones)

Seen in sarcoidosis (epithelioid macroph convert vit.D to its active form

Vitamin E

Biochem 192


192/219

1. Function

Protection of membranes & proteins from free-radical damage

Includes isomers of tocopherol:o Tocopherol + free radicals tocopheroxyl radical vit C

reduces tocopheroxyl radical tocopherol is regenerated

2. Deficiency

Biochem

Secondary to impaired lipid absorption (cystic fibrosis,celiac disease, chronic cholestasis, pancreatic insufficiency,

abetalipoproteinemia)

Signs & Symptoms :o Ataxia

o Impaired reflexes

o Myopathy

193


193/219

o Muscle weakness

o Hemolytic anemia (b/c of fragility of RBCs)

o Retinal degeneration

Vitamin K

Biochem 194


194/219

1. Function

Post-translational carboxylation of glutamyl residues in Cabinding proteins: factors VII, IX, & X

2. Deficiency ( PT, aPTT, but nl bleeding time)

Biochem

Impaired blood clotting

bruising,

bleeding Causes:o Fat malabsorption

o Drugs that interfere w/vit K metabolism (warfarin)

o Antibiotics that suppress bowel flora

3. Vitamin K in infants Neonates are born w/low stores of vit K

195


195/219

Neonates are born w/low stores of vit K Vit K crosses placental barrier poorly Newborns given single injection of vit K High doses: anemia, hyperbilirubinemia, kernicterus

The B vitamins

Biochem 196


196/219

1. B1 = Thiamine2. B2 = Riboflavin

3. B3 = Niacin

Biochem

4. B5 = Pantothenate (pantothenic acid)

5. B6 = Pyridoxine (pyridoxamine, pyridoxal)

6. B12 = cobalamin

197


197/219

Thiamine (vitamin B1)

Biochem 198


198/219

1. Thiamine pyrophosphate (TPP): required for nervetransmission & is coenzyme for several key enzymes:

Biochem

Pyruvate & -ketoglutaratedehydrogenase(glycolysis, TCA)

Transketolase (pentose phosphate pathway) Branched-chain keto-acid dehydrogenase (valine, leucine,

isoleucine metabolism)

2. Deficiency leads to beriberi, which occurs in 3 stages: Early: loss of appetite constipation nausea periph

199


199/219

Early : loss of appetite, constipation, nausea, periphneuropathy, irritability, fatigue

Moderately severe : Wernicke-Korsakoff syndrome (mentaconfusion, ataxia, ophthalmoplegia)

Severe (in addtion to polyneuritis):o Dry: atrophy & weakness of muscles

o Wet:edema,high-output cardiac failure,pulm congesti

Biochem

Riboflavin (vitamin B2)

200


200/219

Biochem

1. Function:

Converted to re-dox coenzymes FAD & FMN2. Deficiency signs & symptoms:

Angular cheilitis Glossitis (red and swollen tongue)

Scaly dermatitis (esp at nasolabial folds & aroundt )

201


201/219

scrotum)

Corneal vascularization

Biochem

Niacin (vitamin B3)

202


202/219

Biochem

1. Function:converted to redox coenzymes NAD & NADP2. Deficiency

Causes :o Hartnup disease

o Malignant carcinoid syndrome

o INH Mild deficiency: glossitis

203


203/219

Mild deficiency : glossitis

Severe deficiency : pellagra the 3 Dso Dermatitis

o Diarrhea

o Dementia

3. High doses

Vasodilation (very rapid flushing)

Biochem

Metobolic changes: blood cholesterol & LDLs

Vitamin B6 (pyridoxine, pyridoxamine, & pyridoxal)

204


204/219

Biochem

1. Function

Coenzyme involved in transamination (e.g., ALT & AST)decarboxylation, and trans-sulfuration (rxns of amino acid

metabolism)

2. Deficiency (inducible by INH)

Mild: irritability, nervousness, depression

205


205/219

Severe: periph neuropathy, convulsions, occasionalsideroblastic anemia

Other symptoms: eczema, seborrheic dermatitis around ear

nose, and mouth; chapped lips; glossitis; angular stomatiti3. Clinical usefulness:

High doses: tx homocystinuria (defective cystathione -synthase)

Biochem

Vitamin B6: Pantothenic acid

206


206/219

Biochem

1. Function

Essential component of coenzyme A (CoA) and of fatacid synthase

Cofactor for acyl transfers

2. Deficiency (very rare) Vague presentation little concern to humans

207


207/219

Vague presentation, little concern to humans

Dermatitis, enteritis, alopecia, adrenal insufficiency

Biochem

Biotin

208


208/219

Biochem

1. Function

Covalently linked biotin = prosthetic group for carboxylatenzymes (e.g. pyruvate carboxylase, acetyl CoA

carboxylase) (NOT decarboxylations)

2. Deficiency (rare)

Signs and symptoms:D titi P th l

209


209/219

o Dermatitis

o Hair loss

o Atrophy tongue papilla

o Gray mucous memb

o Paresthesa,muscle pa

o Hypercholesterlemia

o ECG abnormalities

Causeso Antibiotic use (since intestinal bacteria make biotin)

o Eating Avidin (raw egg whites)

Biochem

Binds biotin in a nondigestible form If you eat >20 eggs/day

Folic acid

210


210/219

Biochem

1. Function

Polyglutamate derivatives of tetrahydrofolate serve as coenzymein 1-carbon transfer rxns:

o Purine & pyrimidine synthesis

o Thymidylate synthesis

o Conversion of homocysteine to methionine

211


211/219

o Conversion of homocysteine to methionine

o Serine-glycine interconversion

2. Deficiency

Signs & symptoms :o Megaloblastic anemia

o Neural tube defects

o blood homocysteine associated w/atherosclerotic disea

Biochem

Can be caused by several drugs :o Methotrexate (chemo)

o Trimethoprim (antibact)

o Pyrimethamin(antimalari)

o Diphenylhydantoin

(anticonvulsant)

o Primidone (anticonvul

Vitamin B12 (cobalamin)

212


212/219

Biochem

1. Functions

Coenzyme for methylmalonyl CoA

succinyl CoA(methylmalonyl CoA mutase) in propionyl CoA metabolism

C f th l t f b t t t h d f l t &

213


213/219

Coenzyme for methyl transfer between tetrahydrofolate &methionine (homocysteine methyl transferase)

2. Deficiency:

Signs & Symptoms :o Megloblastic anemia

o Paresthesia, optic neuropathy, subacute combined degener

o Prolonged deficiency irreversible nervous system dama

Biochem

Causes :o Intake of no animal products (vegans)

o Achlorhydria, intrinsic factor (impaired absorption)

o Malabsorption (impaired pancreatic function, sprue, enterit

D. latum, absence of terminal ileum/Crohns)

3. Use Schilling test to detect deficiency

Vitamin C (ascorbic acid)

214


214/219

Vitamin C (ascorbic acid)

Biochem

1. Functions

C f d i l di

215


215/219

Coenzyme for re-dox rxns, including:o Post-translational hydroxylation of proline & lysine in

maturation of collagen

o

Carnitine synthesiso Tyrosine metabolism

o Catecholamine neurotransmitter synthesis

Antioxidant

Biochem

Facilitator of iron absorption2. Deficiency

Signs & symptoms :o Mild: capillary fragility w/easy bruising & petechiae

(pinpoint hemorrhages in skin), immune function

o Severe: scurvy (wound healing, osteoporosis,hemorrhage, anemia, swollen gums, teeth may fall ou

216


216/219

y

Symptoms of Mineral Deficiencies

Biochem

Mi l D fi i A i t d C diti

217


217/219

Mineral Deficiency-Associated ConditionsCalcium Paresthesia

Tetany

Bone fractures, bone painOsteomalacia (as in vit D deficiency)

Iodine Goiter

Cretinism

Biochem

Iron Anemia

Fatigue, tachycardia, dyspneaMagnesium Neuromusc excitability, paresthesia

Depressed PTH release

Phosphorus (as phosphate) Deficiency rarely occurs

Zinc Growth retardation & hypogonadism

Dry, scaly skinMental lethargy

Imparied taste & smell poor appetite

218


218/219

Imparied taste & smell, poor appetite

Biochem 219


219/219

Documents

imp_key_pts_4_net