Chemistry IIMILBANK HIGH SCHOOL

Ch. 24Metabolism and Energy

Introduction

Photosynthesis 6CO2 + 6H2O + 686kcal C6H12O6 + 6O2

Metabolism Entire series of chemical reactions that

keep cells alive Catabolism

Breaking down of molecules to provide energy

AnabolismBuilding up of molecules of living

systems

Introduction Con’t

Respiration All metabolic processes in which oxygen is used

to oxidize organic matter to carbon dioxide, water, and energy

Carbohydrate oxidation C6H12O6 + 6O2 6CO2 + 6H2O + 686 kcal

Lipid oxidation C16H32O2 + 23O2 16CO2 + 16 H2O + 2340 kcal

Sec. 24.1 ATP: Universal Energy Currency

ATP Adenosine triphosphate Figure 24.2 Most important phosphate compound in

metabolism Energy rich compound (energy currency of

the cell) Lead to a release of energy upon

hydrolysis

ATP Con’t

ATP hydrolyis ATP ADP + Pi + 7.5 kcal/mol Reaction is reversible

ATP is produced by processes that supply energyRadiant energy in plants, breakdown of food in

animals) ATP is hydrolyzed by processes that require

energySynthesis of carbs, lipids, and proteins;

transmission of nerve impulses, muscle contractions, etc

Sec. 24.2Digestion and Absorption of Major

NutrientsCatabolism

Three stages (Fig. 24.5)Digestion (stage 1)

Hydrolytic process that breaks down food molecules into simpler chemical units

Absorption occurs mainly in small intestine

Alimentary tract

Digestion Con’t

Mechanical Aspects Chewed Saliva

α-amylase Stomach

Broken down by pepsin Chyme Moves into small intestine

Digestion of Carbohydrates (Fig. 24.7)

Mouth α-amylase attacks α-glycosidic linkages in

starchSmall Intestine

α-amylase converts remaining starch to maltose, broken down by maltase to form two glucose units

Sucrose and lactose broken down by sucrase and lactase; form glucose, fructose, and galactose

Digestion of Proteins (Fig. 24.9)

Stomach Gastric juice Hydrochloric acid opens up folds in protein

molecule Pepsin

Endopeptidase that catalyzes the hydrolysis of peptide linkages

Amino Acids Absorbed through lining of small intestine

Digestion of Lipids (Fig. 24.13)

Small intestine Bile salts from gallbladder act as

emulsifiers Break down large molecules into small

globules (more surface area) Lipases

Mono and diglycerides absorbed Triglycerides transported by

chylomicrons

Absorption of Digested Nutrients

Villi Small molecules

Passive Transport Fatty acids, monoglycerides

Active Transport Requires energy Monosaccharides and amino acids

Sec. 24.3 Overview of Stage II of Catabolism

Metabolic Pathway Series of biochemical reactions that enables

us to explain how an organism converts a given reactant to a desired end product

Stage II Conversion of subunits to a form that can be

completely oxidizedAcetyl-CoA

Enzyme used in many biochemical pathways Starting material for biosynthesis of lipids

Sec. 24.4The Kreb’s Cycle

Kreb’s Cycle Stage III of catabolism AKA citric acid cycle, tricarboxylic acid cycle Produces ATP, NADH, FADH2, and metabolic

intermediates for the synthesis of needed compounds during the cycle

Occurs in mitochondria of the cell Essential for the breakdown of glucose and other simple

sugars Very complex

Utilizes condensation, dehydration, hydration, oxidation, decarboxylation, and hydrolysis reactions

Each reaction is catalyzed by an enzyme

Kreb’s Cycle Con’t

http://www.johnkyrk.com/krebs.htmlStarts when pyruvate produces Acetyl-CoA1. Acetyl-CoA is the starting reactant—

supplies the 2 carbons needed Acetic acid molecule linked to coenzyme A

2. Acetyl-CoA condenses with oxaloacetate to produce citrate (citric acid cycle)

Kreb’s Cycle Con’t

3. Isocitrate is reduced to NAD which leads to the NADH (nicotinamide adenine dinucleotide) (NADH used by Electron Transport Chain to create

further ATP) 3 total NADH produces per 1 Acetyl-CoA

4. Alphaketogluterate produced—more NAD and acetyl-CoA added to produce two more NADH+ along with succinyl CoA

5. GTP is produced from GDP when another phosphate group is added. GTP (guanosine triphosphate) is easily converted to ATP…1=1 ratio

Kreb’s Cycle Con’t

6. FAD (flavin adenine nucleotide) added to succinate which readily accepts and transfers electron pairs to Electron Transport Chain where FADH2

which is converted to ATP…each FAD yields 2 ATP

7. Water added to fumerate to produce malate. NAD added, electrons are transferred to produce NADH+ and oxaloacetate

8. Two more pyruvate are added to start the Kreb’s Cycle all over again

Sec. 24.5Cellular Respiration

Occurs in mitochondria Mitochondria

Power plants of the cell 100 to 5000 in a particular cell Outer and inner membranes that are folded into a

series of ridges known as cristae Contains all of the enzymes and coenzymes needed for

the Kreb’s cycle

The Electron Transport Chain

Sequence of enzymes used to oxidize coenzymes and transfer the resulting electrons to oxygen Coenzymes involved: NADH and FADH2

Closely linked to the Kreb’s cycle Very little ATP actually produced in Kreb’s

Aids in oxygen participationAssists significantly in ATP productionETC consists of four complexes (I, II, III, IV)

Each complex contains several enzymes, other proteins, and metal ions that each have different tasks

Electron Transport Chain Con’t

CoQ (coenzyme quinone, or ubiquinone) Mobile electron carrier that acts as an electron shuttle

between Complexes I and II and Complex IIIReactions of the ETC are a series of

oxidation/reduction reactions involving cytochromes Cytochromes: iron-sulfur proteins and other molecules that

ultimately reduce oxygen to water in Complexes III and IVPasses electrons through a series of protein

complexes, moving towards increasing electron potential Electrons flow from molecules that easily transfer electrons

to those that easily accept them Reduction Potential

Oxidative Phosphorylation

Metabolic pathway that uses energy released by the oxidation of nutrients to produce ATP

Tightly coupled with ETCUsed by almost all forms of lifeHighly efficient way of storing energyNADH and FADH2 only work if ADP is

phosphorylated to ATP

Oxidative Phosphorylation Con’t

Electrons are transferred from electron donors to electron acceptors such as oxygen, in a redox reaction

Reactions release energy, which is used to form ATP

http://www.wiley.com/legacy/college/boyer/0470003790/animations/electron_transport/electron_transport.htm

Theoretical YieldsStep Coenzym

e YieldATP Yield

Source of ATP

Glycolysis preparatory phase

-2 Phosphorylation of glucose and fructose uses 2 ATP

Glycolysis pay-off phase

4 Substrate level phosphorylation

2 NADH 4 (6) Oxidative Phosphorylation

Oxidative decarboxylation of pyruvate

2 NADH 6 Oxidative Phosphorylation

Krebs Cycle 2 Substrate level phosphorylation

6 NADH 18 Oxidative Phosphorylation

2 FADH2

4 Oxidative Phosphorylation

Total Yield 36 (38) ATP

Complete oxidation of one glucose molecule to CO2 and oxidation of all the reduced coenzymes

ATP and Fibromyalgia

Fibromyalgia Chronic pain in muscular system Afflicts 7-10 million Americans Mainly women ages 20-50 (3.4% of all women in US)

Possible Cause: Unable to process ATP and abnormally low levels of

ATP

Sec. 24.6Muscle Power

Exercise Prolongs life Lowers chance of disease Makes muscles stronger, more flexible, more efficient

in use of oxygen

Muscles 600 in human body Strong muscles can do more work than weak Heart is a muscle…exercise pulse and blood pressure

usually decline Training Effect

Person who exercises regularly is able to do more physical work with less strain

Muscle Power Con’t

Muscle stimulation and contraction requires energy (ATP)

Two proteins that play important roles in muscle movement Actin Myosin

Acts as an enzyme for removal of phosphate group from ATP

Directly liberates the energy required for contraction

Actomyosin Contractile protein of which muscles are made

Muscle Power Con’t

Aerobic In presence of oxygen Respiration is aerobic under usual conditions and

during moderate exerciseAnaerobic

Absence of oxygen Oxygen debt

Not enough oxygen available during strenuous exercise

Energy obtained from carbohydrates through the breakdown of glycogen and anaerobic glycolysis

Muscle Power Con’t

Muscle Tissues Slow twitch (Type I)

Light and moderate activity Respiratory capacity is high

Can provide much energy via aerobic pathways Geared to oxidative phosphorylation

High myoglobin Heme-containing protein in muscle that stores oxygen

obtained from hemoglobin Needs high levels of oxygen Many mitochondria in Type I muscle cells

Long, sustained activities (marathon runners)

Muscle Power Con’t

Muscle Tissues Con’t Fast-twitch (Type IIB)

Opposite characteristics of slow twitch Low respiratory capacity Low myoglobin levels Fewer mitochondria Generates ATP rapidly

Short bursts of activity, muscles fatigue rapidly Sprinters, weightlifters

Muscle Power Con’t

Training Endurance

Increases size and number of mitochondria Increases level of enzymes required for transport and

oxidation of fatty acids, the Kreb’s cycle, and oxidative phosphorylation

Doesn’t increase muscle size significantly Strength

No increase in mitochondria Causes neovascularization which increases efficiency of

lactic acid removal Lactic acid inhibits ATP production and use

Creatine Phosphate

Storage form of energy in muscles of vertebratesAs ATP is utilized, creatine phosphate reacts

with ADP to produce more ATP and creatineConcentration limited—used up after about 10-

15 seconds of strenuous exerciseFound in high amounts in meat and fishNaturally produced in body in synthesis of

arginineCreatine supplements may increase muscle

performance and body mass