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Biochemistry > Module 6: V1 - V6 > Flashcards

Module 6: V1 - V6 Flashcards

1
Q

What do anabolic pathways involve?

A

building cell macromolecules from simpler precursor molecules

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2
Q

What do catabolic pathways involve?

A

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

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3
Q

What is the function of CoA?

A

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

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4
Q

Where is Acetyl-CoA used?

A

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

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5
Q

What is Acetoacetyl-CoA used for?

A

the switch to “ketone bodies” during starvation

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6
Q

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

A

dietary vitamins

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7
Q

What are the two phases of glycolysis?

A

preparatory and payoff phase

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8
Q

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

A

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

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9
Q

Is the first reaction of glycolysis reversible or irreversible?

A

irreversible

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10
Q

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

A

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

phosphohexose isomerase

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11
Q

Is the second reaction of glycolysis reversible or irreversible?

A

reversible

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12
Q

What is the third reaction of glycolysis?

A

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

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13
Q

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

A

irreversible

rate limiting step of glycolysis

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14
Q

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

A

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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15
Q

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

A

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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16
Q

How many ATP are produced during the preparatory phase?

A

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

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17
Q

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

A

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

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18
Q

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

A

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

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19
Q

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

A

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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20
Q

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

A

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

21
Q

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

A

dehydration of 2-phosphoglycerate to phosphoenolpyruvate

enolase converts 2-PG to PEP

22
Q

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

A

production of ATP from the conversion of PEP to pyruvate

pyruvate kinase

23
Q

What is gained per glucose during glycolysis?

A

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

24
Q

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

A

because glycolysis proceeds up to 10x faster in cancer cells

25
Q

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

A

by injecting isotopically labelled glucose followed by PET scanning

26
Q

What is the Warburg Hypothesis?

A

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

27
Q

Is gluconeogenesis the reverse of glycolysis? Why?

A

no

because irreversible steps occur in glycolysis and different enzymes need to be used

28
Q

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

A

pyruvate carboxylase

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

29
Q

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

A

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

30
Q

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

A

fructose-1,6-bisphosphatase

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

31
Q

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

A

glucose-6-phosphatase

converts glucose-6-phosphate to glucose

32
Q

What is the final product of glycolysis?

A

pyruvate

33
Q

What are the five major fates of pyruvate?

A

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

34
Q

What is the important role of lactase dehydrogenase?

A

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

35
Q

What are typical energy stores in humans?

A

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

36
Q

What is glycogen?

A

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

37
Q

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

A

no

used to power muscle contraction for extended periods of time

38
Q

What is glycogenolysis? Which enzymes does this process involve?

A

the breakdown of glycogen

glycogen phosphorylase, debranching enzyme and phosphoglucomutase

39
Q

What is glycogenesis? Which enzymes does this process involve?

A

the synthesis of glycogen

UDP-glucose pyrophosphorylase, glycogen synthase and amylo transglycosylase (glycogen-branching enzyme)

40
Q

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

A

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

41
Q

What is the role of phosphoglucomutase?

A

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

42
Q

What causes marathon runners to “hit the wall”

A

body runs out of available glycogen storages

43
Q

What is the role of UDP-glucose pyrophosphorylase?

A

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

44
Q

What is the role of glycogen branching enzyme?

A

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

45
Q

What is the role of glycogenin?

A

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

46
Q

Is glucose oxidised during glycolysis?

A

yes, glucose is oxidised into two molecules of pyruvate

47
Q

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?

A

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

48
Q

Why do we export lactate from the muscles?

A

prevents lactic acidosis during anaerobic conditions in the muscle

49
Q

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

A

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

Biochemistry (30 decks)

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