Module 6: V1 - V6 Flashcards by Jack Wilkins

What do anabolic pathways involve?

building cell macromolecules from simpler precursor molecules

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What do catabolic pathways involve?

breaking down energy-containing nutrients into energy-depleted end products

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What is the function of CoA?

functions in acyl transfer reactions where X is an acetyl, acetoacetyl or other group which is transferred to another molecule

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Where is Acetyl-CoA used?

central to metabolism; used in Krebs cycle, fatty acid synthesis/oxidation etc.

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What is Acetoacetyl-CoA used for?

the switch to “ketone bodies” during starvation

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What are critical molecules that are involved in metabolism derived from?

dietary vitamins

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What are the two phases of glycolysis?

preparatory and payoff phase

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What is the first reaction of glycolysis? What enzymes is this reaction catalysed by?

phosphorylation of glucose
glucose -> glucose-6-phosphate
hexokinase in most tissues and glucokinase in the liver

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Is the first reaction of glycolysis reversible or irreversible?

irreversible

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What is the second reaction of glycolysis? What enzyme is this reaction catalysed by?

isomerisation of glucose-6-phosphate -> fructose-6-phosphate

phosphohexose isomerase

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Is the second reaction of glycolysis reversible or irreversible?

reversible

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What is the third reaction of glycolysis?

conversion of fructose-6-phosphate -> fructose-1,6-bisphosphate

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Is the third reaction of glycolysis reversible or irreversible? What is significant about the third reaction?

irreversible

rate limiting step of glycolysis

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What is the fourth reaction of glycolysis? What enzyme is this reaction catalysed by?

cleavage of F-1,6-bP

aldolase cuts the F-1,6-bP in the middle, producing DHAP and GA-3-P

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What is the fifth reaction of glycolysis? What enzyme is this reaction catalysed by?

isomerisation of DHAP to glyceraldehyde-3-phosphate

triose phosphate isomerase pulls a H atom off one C atom and replaces it on a neighbouring C atom

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How many ATP are produced during the preparatory phase?

there is a net loss of 2 ATP in the preparatory phase of glycolysis

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What is the sixth reaction of glycolysis or the first reaction of the payoff phase? What enzyme is this reaction catalysed by?

oxidation of glyceraldehyde-3-phosphate to 1,3-biphosphoglycerate
catalysed by glyceraldehyde 3-phosphate dehydrogenase

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What does activity of glyceraldehyde 3-phosphate dehydrogenase depend on?

the turnover of NAD+ in the cytosol of the cell under anaerobic conditions

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What is the seventh reaction of glycolysis? What enzyme is this reaction catalysed by?

conversion of 1,3-biphosphoglycerate to 3-phosphoglycerate

PGK transfers the phosphate from 1,3-BPG to ADP to form ATP

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What is the eighth reaction of glycolysis? What enzyme is this reaction catalysed by?

conversion of 3-phosphoglycerate to 2-phosphoglycerate

PG mutase shifts phosphate from C3 of the PG molecule to C2 priming it for phosphate transfer to ADP

What is the ninth reaction of glycolysis? What enzyme is this reaction catalysed by?

dehydration of 2-phosphoglycerate to phosphoenolpyruvate

enolase converts 2-PG to PEP

What is the tenth reaction of glycolysis? What enzyme is this reaction catalysed by?

production of ATP from the conversion of PEP to pyruvate

pyruvate kinase

What is gained per glucose during glycolysis?

net energy gain of 2 ATP and 2 NADH per glucose, which is equivalent to ~5 ATP per glucose

Why are some chemotherapeutic agents used to inhibit hexokinase in treating cancer?

because glycolysis proceeds up to 10x faster in cancer cells

How can high glycolytic turnover in cancer cells be used for diagnosis?

by injecting isotopically labelled glucose followed by PET scanning

What is the Warburg Hypothesis?

most cancer cells produce energy by anaerobic glycolysis rather than by oxidation of pyruvate in the mitochondria (which is common to healthy cells)

Is gluconeogenesis the reverse of glycolysis? Why?

no | because irreversible steps occur in glycolysis and different enzymes need to be used

What is the enzyme used in the 1A bypass step in gluconeogenesis? What does it do?

pyruvate carboxylase | adds a carboxylic acid to pyruvate to form oxaloacetate using biotin as a cofactor

What is the enzyme used in the 1B bypass step in gluconeogenesis? What does it do?

phosphoenolpyruvate carboxykinase which converts oxaloacetate -> phosphoenolpyruvate upon addition of GTP

What is the enzyme used in the 2 bypass step in gluconeogenesis? What does it do?

fructose-1,6-bisphosphatase | converts fructose-1,6-biphosphate to fructose-6-phosphate

What is the enzyme used in the 3 bypass step in gluconeogenesis? What does it do?

glucose-6-phosphatase | converts glucose-6-phosphate to glucose

What is the final product of glycolysis?

pyruvate

What are the five major fates of pyruvate?

ethanol, lactate, alanine + pyruvate which moves into the mitochondria and becomes either oxaloacetate or acetyl CoA

What is the important role of lactase dehydrogenase?

under anaerobic conditions plays an important role in regenerating NAD+ for STEP 6

What are typical energy stores in humans?

adipose TAG -> 84% mobilised proteins -> 15% glucose/glycogen -> 1%

What is glycogen?

storage form of carbohydrate in the body which is critical during fasting as liver glycogen provides a source of blood glucose

Can muscle glycogen give rise to blood glucose? What is it used for instead?

no | used to power muscle contraction for extended periods of time

What is glycogenolysis? Which enzymes does this process involve?

the breakdown of glycogen | glycogen phosphorylase, debranching enzyme and phosphoglucomutase

What is glycogenesis? Which enzymes does this process involve?

the synthesis of glycogen | UDP-glucose pyrophosphorylase, glycogen synthase and amylo transglycosylase (glycogen-branching enzyme)

How does debranching enzyme get rid of branches on a glycogen particle?

transfers a block of 3 glucose residues to a nearby nonreducing end and then hydrolyzes the a1->6 linkage to release free glucose

What is the role of phosphoglucomutase?

transfers phosphoryl group on glucose-1-phosphate from C1 to C6 to form glucose-6-phosphate, which is freely reversible

What causes marathon runners to "hit the wall"

body runs out of available glycogen storages

What is the role of UDP-glucose pyrophosphorylase?

synthesizes UDP-glucose form UTP and glucose-1-phosphate and also produces pyrophosphate (PPi)

What is the role of glycogen branching enzyme?

catalyses transfer of 6/7 glucose residues from the nonreducing end of a glycogen branch having at least 11 residues to the C6 hydroxyl group of a glucose residue in a more interior position within the same or a different glycogen chain

What is the role of glycogenin?

glycogen synthase cannot initiate synthesis of a new glycogen chain since it requires a primer glycogenin is both the primer on which new chains are synthesized and the enzyme that catalyses their assembly

Is glucose oxidised during glycolysis?

yes, glucose is oxidised into two molecules of pyruvate

Animals don't photosynthesise, but can we make carbohydrates? What do we make carbohydrate from and where do we get the energy to do so?

yes, carbohydrate is made from pyruvate and energy required to complete this process comes from the TCA cycle

Why do we export lactate from the muscles?

prevents lactic acidosis during anaerobic conditions in the muscle

Why don't we just transport ATP around the body? Surely this would be a lot easier?

ATP is ionized because of its phosphate groups, and therefore doesn't travel through cell walls readily