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Glycolysis, Gluconeogenesis, and thePentose Phosphate Pathway
Chapter 14
LehningerPrinciples of Biochemistry
5th edition
By Nelson & Cox
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1. Good fuel ( ___ standard free energy).
2. Storage: starch or glycogen
(high MW polymers): - does not affect cytosolic _________
could be used in future when energydemand increases.
3. Oxidation via __________________________
Glucose
1
2
3
Major fates in animals and vascular plants:
•Central place in metabolism
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Oxidation of glucose
C6H
12O
6 + 6O
2 6CO
2 + 6H
2O
Glycolysis
•During this reaction some of the free energyis conserved as _____ or _______.
Fermentation: Anaerobic breakdown of glucose andothers to obtain energy as ATP.
Most ______ form of energy obtaining process?
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Glycolysis
-Breakdown of 6-C glucose into-two molecule of the 3-C __________
-occurs in 10 steps.
- First five (1-5) are ________ phase- energy investment
- Last five (6-10) are ________ phase
aerobic
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Hexokinase – ATP & Mg2+ - ______ reversible (under intracellular condition).
- Hexokinase kinase transfers terminal phosphoryl group from _____ to an acceptor.
- Hexokinase is present in ______ of all organisms.
p532
1. Phosphorylation of Glucose
negative charged sugar: cannot _____ the cell.
Preparatory Phase of Glycolysis
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Phosphohexose isomerase – Mg2+
- Isomerization reaction - Freely __________ If slight ______ in product, reverses reaction.
2. Conversion of Glucose 6-Phosphate to Fructose 6-Phosphate
Preparatory Phase of Glycolysis
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Phosphofructokinase 1 (PFK-1) – ATP & Mg++
– Essentially ___________ / first __________ step
• Fructose 1,6-bisphosphate is targeted forglycolysis.
- It is a major point of _________ in glycolysis.- ATP & PEP __________ regulate PFK1
3. Phosphorylation of Fructose 6-P to Fructose 1,6-bisphosphate
p526
Fructose 6-phosphate
G´°
= –14.2 kJ/mol
Preparatory Phase of Glycolysis
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4. Cleavage of Fructose 1,6-bisphosphate
AldolaseFreely _________ : yields two ________ trioses
- Lower concentration of reactants for reverse reaction.
(Products are _____________up by subsequent reaction) p533
Preparatory Phase of Glycolysis
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5. Interconversion of Triose Phosphates
Triose phosphate isomerase- Only G3-P (Glyceraldehyde 3-phosphate) can be ________
degraded.
- Dihydroxyacetone phosphate is readily converted into
_______ .
- Freely __________ reaction but moves in forward direction
because product is readily used up.
Preparatory Phase of Glycolysis
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Glyceraldehyde 3-phosphate dehydrogenase - Ist step in payoff phase (energy conserving) leading to
ATP formation later on.
- Freely ________
- Acceptor of hydrogen is ________ yielding NADH.
6. Oxidation of G3-P to 1,3-Bisphosphoglycerate
p535
G’̊ = 6.3 kJ/mol
Payoff Phase of Glycolysis
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Phosphoglycerate kinase – Mg2+• ___________ level phosphorylation.
(different from respiration-linked synthesis of ATP)• Freely reversible, but highly _______________
7. Phosphoryl transfer from 1,3-Bisphosphoglycerate to ADP
p536
Payoff Phase of Glycolysis
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Phosphoglycerate mutase – Mg2+
- Freely reversible
- Shifts phosphoryl group between C-3 and C-2
8. Conversion of 3-Phosphoglycerate to 2-Phosphoglycerate
Payoff Phase of Glycolysis
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Enolase (dehydratase) - Freely reversible,
- Removes _____ from 2-Phosphoglycerate to yield ___.-
9. Dehydration of 2-Phosphoglycerate to Phosphoenolpyruvate
Sets up ____ substrate-level phosphorylation
Payoff Phase of Glycolysis
PEP
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Pyruvate kinase (PK) – ADP & Mg2+
Yield is ________ per glucose molecule.(substrate-level phosphorylation)
PK is ____ reversible
10. Transfer of phosphoryl group from PEP to ADP
Pyruvatekinase
Mg 2+ , K+
p538
Payoff Phase of Glycolysis
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Products of Glycolysis?
• ________
• ________ • ________
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What happens to these three products?
– ATP is ________ source.– NADH makes more ATP if Oxygen is
_________.
– Pyruvate is further _____ if Oxygen isavailable
- contains majority of the energy.
–
Anaerobic conditions produce _______ result.
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Other carbohydrates:
1.Storage polysaccharides: ____________ & __________.
2. disaccharides: _________, ______, _______ & ________.
3. monosaccharides:
__________, mannose, galactose
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Feeder pathways for Glycolysis
The trick is to make:
Glycolytic _______________
may involve one or more specific _______.
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Feeder pathways for Glycolysis
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1. Catabolism of Polysaccharides
•Digestive tract or sprouting seeds- hydrolyzed by __________
- maltose & glucose released
•Intracellular- transfer of glucose to Piby
___________
- glucose 1-phosphate released
Starch (______), and Glycogen (______) can be used
in the same _________.
Dietary glycogen/starch (similar structure) is brokenby hydrolysis through use of _________ not Pi.
http://en.wikipedia.org/wiki/File:Amylose2.svg
t ll l
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Glycogen and Starch
Two enzymes needed
1. Glycogen Phosphorylase :catalyzes an attack by Pi onthe ____________ bond that joins last two glucose
residues at the _____________ end.
- glucose 1-phosphate
This enzyme works until itreaches a glucose that is within _____residues of an:
_______ branch point.(glycogen & amylopectin).
tracellular
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• Debranching enzyme has 2 activities– Transferase – moves
______ glucose unitsfrom the _____ branch
to the ______ branch
– Glucosidase – releases afree _______ byhydrolyzing the
-1,6-glycosidic bond
Glycogen and StarchDebranching
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Glycogen and Starch Detail
2. Phosphoglucomutase
- Converts Glucose 1-phosphateto Glucose ___-phosphate
Glucose 1-phosphate
Glucose ___-phosphate
- Freely ________ reaction
GlycogenPhosphorylase
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Hydrolysis of dietary polysaccharide: (breakdown of starch)
•Salivary -amylase: smaller _______________(digestion begins in mouth).
•Pancreatic -amylase : maltose & maltotriose
(di- and trisaccharides of glucose) and dextrins.
•Maltose and dextrins are further degraded byenzymes
into ___________.
•Disaccharides must be hydrolyzed to ____saccharides
before entering cells.
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2. Catabolism of Disaccharides
•Maltose – from breakdown of starches Maltase – 2 ________ units are released
•
Lactose – milk sugar, major source of energy forinfants in mammals.
________ (intestine) – Glucose & Galactose
•Sucrose (glucose + fructose) – cane or beet sugarTable sugar, sweetener in all regular soft drinks
________ – Glucose & Fructose
Disaccharides are hydrolyzed by specific __________
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Lactose intolerance ?
ommon among adults of most humans except___________ and parts of _______ ?
ctase (or -galactosidase) is low or missing in manyArabian,Jewish,Bantu,Japanese,Native Americans, and
Filipinoadults – are all _______________.
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3. Catabolism of Monosaccharides
•Mannose – from breakdown of complex ________________.
•Galactose – from breakdown of _______.
•Fructose – from breakdown of sucrose.- Main sugar in _______ and _______
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Mannose catabolism
Two enzymes convert mannose to __________________
1.hexokinase - Same enzyme that acts
on glucose
2. phosphomannoseisomerase
Fig 14.9
G l b li(From Lactose)
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Three enzymes convert galactose to
_______________
1. Galactokinase 2. UDP-glucose: galactose 1-
phosphate uridylyltransferase 3. UDP-glucose 4-epimerase
Defect in any of the enzymesis cause of __________________.
Galactose catabolism( )
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Problems in Galactose Metabolism
Infants lacking: hexose 1-phosphate uridylyltransferase
- have a form of _____________ - Must _______ milk and other sources of galactose.
Adults have galactose 1-phosphate uridylyltransferase which can metabolize galactose.
Some infants lack galactokinase– 2nd type of galactosemia
– _________ overcome as adults
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Fructose (fruits) first getsconverted to Fructose 6-
phosphate and then enters ___________ .
Enzyme: ___________
This is major way of entry of Fructose in glycolysis in _____ and _________.
But different in _______ ,where most of Fructose iscatabolized.
Fructose catabolism
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3 enzymes make glycolyticmetabolites
– ___________
– Fructose 1-PhosphateAldolase
– _____________
Fructose catabolismin Liver
C t b li f t f P t
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Catabolic fates of Pyruvate
First route:Pyruvate _______.
Acetyl group is then oxidizedcompletely to CO2 by _______
_________________
Second route:Reduction to lactate via lactic
acid ___________
Third route:
leads to formation of _______ via ethanol ______________
1
23
F t f P t d A bi C diti
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•Under hypoxic condition, NADH from glycolysis cannot be ______________ by O2.
•
•Non-availability of _____ as an electronacceptor for oxidation of G3-P can
__________ the Glycolysis.
Fate of Pyruvate under Anaerobic Conditions
F t f P t d A bi C diti
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•Under these conditions, NAD+ is regenerated from _______ byreduction of pyruvate to _________ .
Lactate formationfavored ( ______ – G´)
______change inNAD+ or NADH
Fate of Pyruvate under Anaerobic Conditions
Fate of P ate nde Anae obic Conditions
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Fermentation – 2 steps- I st step- Pyruvate decarboxylase requires Thiamin
pyrophosphate (TPP) (co-enzyme) and Mg2+
TPP is a coenzyme derived from vitamin ____ .
- Vitamin deficiencies leads to? ______- TPP has role in cleavage of bonds adjacent tocarbonyl group.
-
II nd step - Alcohol dehydrogenase requires - _____
Freely reversible
Fate of Pyruvate under Anaerobic Conditions
Fate of Pyruvate under Anaerobic Conditions
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Summary
Glucose + 2ADP + 2Pi
__ lactate + 2 ATP + 2H2Oor
__ ethanol + 2 ATP + 2H2O
Fate of Pyruvate under Anaerobic Conditions
A b li f t f P t
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Anabolic fate of Pyruvate
Pyruvate can also providecarbon skeleton for the synthesis of theamino acid ________ .
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Gluconeogenesis
•Some mammalian tissue depend ________
glucose for their metabolic energy.
e.g. Human _____, nervous systems, renal medulla,
erythrocytes, embryonic tissue.
All need glucose from the blood as major /sole source of fuel.
Brain needs ~ _____ glucose/day whichis half of all the stored glucose.
Gl
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Gluconeogenesis
•Body fluids carry only:
•~ ___g free glucose
• glycogen can provide 180-200 g of free
glucose.- Little more then a ___-day supply.
•Glucose if not obtained from the diet, body
must make _________ from the ____-carbohydrate precursors:
Gluconeogenesis
Gl i
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Gluconeogenesis
•Gluconeogenesis occurs in _____- animals,- plants,- fungi and
- microorganisms.•Reactions are essentially ____ in all tissues
and all species.
Gl i
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Gluconeogenesis
Biosynthesis of
carbohydrates
Glucogenicmolecules
Storage of
carbohydrates
S bst ates of Gl coneogenesis
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Substrates of Gluconeogenesis
•Pyruvate, lactate and other non-carbohydrate
precursors can be substrates:•most of the ____________ ,• _______ and all the• _______cycle intermediates.
• Fatty acids are _____ the substrates in animals. • Lysine and Leucine are the only amino acids that
are ____ substrates.
Site of Gluconeogenesis in Animals
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Site of Gluconeogenesis in Animals
•The organ which consumesmost of the
glucose e.g. brain and muscle,- carry out very little glucose __________.•
•Major site of gluconeogenesis in animals:
Liver : ___% Kidney : ___%
The synthesized glucose is released into
_____ which gets transported to the placeof need.
Gluconeogenesis Not merely of Glycolysis
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Gluconeogenesis Not merely _____ of Glycolysis
In some ways gluconeogenesis
is reverse of glycolysis but not all steps are similar.
What is different?
Both are _____________ andoccur largely in _______ .
Reactions specific to Gluconeogenesis
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Reactions specific to Gluconeogenesis
___ different reactions in
gluconeogenesis.- Other ______ are same
as glycolysis.
Three different enzymecatalyzed reactions areutilized.
start here
Reactions specific to Gluconeogenesis
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Reactions specific to Gluconeogenesis
1.First: Conversion of pyruvate to ____ : initiates gluconeogenesis.
Occurs in two unique steps: A.Pyruvate carboxylase
catalyzes first convertingpyruvate to oxaloacetate.
- First pyruvate is transportedto _____________.
Reactions specific to Gluconeogenesis
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Reactions specific to Gluconeogenesis
Oxaloacetate + NADH + H+ L-malate + NAD+
Malate + NAD+ oxaloacetate + NADH + H+
Malate is transported out to _________ and isreoxidized to oxaloacetate.
Since oxaloacetate is required in cytosol but
it _________ be transported to cytosol. -so it is converted to_________by malate dehydrogenase.
Reactions specific to Gluconeogenesis
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Reactions specific to Gluconeogenesis
B. Then PEP carboxykinase catalyzes the conversion of oxaloacetate to PEP in cytosol.
Reversible reaction buteffectively irreversibledue to ______ effectiveconcentration of PEP.
2nd specific reaction: Gluconeogenesis
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2 specific reaction: Gluconeogenesis
Conversion of:
Fructose 1,6-bisphosphate to
Fructose 6-P
Catalyzed by _________ - Irreversible hydrolysis of
C-1 phosphate
3rd specific reaction : Gluconeogenesis
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3. Conversion of Glucose 6-P to Glucose
catalyzed by Glucose 6-phosphatase requires Mg2+
Glucose is transported via _____ to brain and muscle.
3 specific reaction : Gluconeogenesis
Gluconeogenesis is a expensive but essential step
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Gluconeogenesis is a expensive but essential step
2 Pyruvate + __ ATP+ ___ GTP+ __NADH + 2 H+ + 4 H2O
glucose + 4ADP + 2GDP + 6Pi + 2NAD+
P 556
P t Ph h t P th
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Pentose Phosphate Pathway
- A __________ for producing NADPH: needed in synthesis of
• _________• _________
-Provides a pool of ribose5-phosphate for
synthesis of •
________ . 1
2
3
Pentose Phosphate Pathway: Starting point
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Hexokinase – ATP & Mg2+
- ___ reversible (under intracellular condition) - Hexokinase is present in _______ of all organisms.
From Glycolysis: Phosphorylation of glucose
Pentose Phosphate Pathway: Starting point
Pentose Phosphate Pathway
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Pentose Phosphate Pathway
Pentose phosphate pathway
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1. Glucose 6-P dehydrogenase– requires _______ & Mg2+
Makes 6-phosphogluconolactone and ________ (1st molecule)
Genetic defect causes disease? Read. Common!
2. Lactonase– Mg2+
Makes 6-phosphogluconate
Oxidative Phase
Pentose phosphate pathway
Pentose phosphate pathway
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Fig14
.21bottom
3. 6-Phosphogluconatedehydrogenase :
- requires NADP+ & Mg2+
- Products:
- ribulose 5-phosphate- _______ (2nd molecule)
4. Pentose phosphate isomerase:
- converts Ribulose 5-Pto itsisomer ________________
Oxidative Phase
Pentose phosphate pathway
Non-oxidative phase
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Non oxidative phase
Pentose phosphate pathway: Non-oxidative phase
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In tissue which primarily require NADPH:Pentose-P are recycled into ____________ .
-First step: epimerization of Ribulose 5-P to Xylulose 5-P- enzyme ribose 5-phosphate epimerase
Epimers?
Recycles PP to G6-P
Pentose phosphate pathway: Non oxidative phase
Non-oxidative phase Recycles PP to G6P
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-Series of rearrangements of carbon skeletons:Six , 5-C sugar phosphates are converted to
_____ , 6-C sugar phosphates.
Non-oxidative phase Recycles PP to G6P