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human metabolism - summary notes > OC3 - carbohydrate metabolism > Flashcards

OC3 - carbohydrate metabolism Flashcards

1
Q

what is glycolysis (basic)?

A

breakdown of glucose

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2
Q

what is gluconeogensis (basic)?

A

formation of glucose

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3
Q

what is glycogenesis (basic)?

A

formation of glycogen

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4
Q

what is glycogenolysis (basic)?

A

breakdown of glycogen

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5
Q

what are the subunits in carbohydrate metabolism?

A

glycolysis
gluconeogenesis
glycogenesis
glycogenolysis
TCA cycle
pentose pathway
cori cycle

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6
Q

what is carbohydrate metabolism?

A

carbohydrates are broken down through glycolysis to provide pyruvate and ATP
carbohydrates undergo glycogenesis to make glycogen as the storage substance for glucose
carbohydrates undergo the pentose pathway to produce DNA, RNA and various cofactors

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7
Q

what is glycolysis?

A

oxidation of glucose to produce ATP
glycolysis is the first step of cellular respiration
substrate-level phosphorylation
1x glucose > 2x pyruvate
net gain: 2xATP and 2x NADH + H+

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8
Q

what is pyruvate?

A

pyruvate is a key intersection in the network of metabolic pathways
the fate of pyruvate is dependent upon the availability of oxygen

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9
Q

what is the fate of pyruvate in the presence of oxygen?

A

pyruvate enters the mitochondria and is converted into acetyl CoA, before entering the TCA cycle

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10
Q

what is the fate of pyruvate in the absence of oxygen?

A

pyruvate is converted to lactate and undergoes the cori cycle
restores the NAD+ consumed in step 6 of glycolysis

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11
Q

what are the three irreversible steps in glycolysis?

A

glycolysis is an irreversible anaerobic process, due to the 3 highly exergonic (-‘ve ΔG) reactions
step one
step three
step ten

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12
Q

what is glycolysis step one?

A

hexokinase catalysed catabolism of glucose to glucose-6-phosphate
consumes 1 ATP molecule
exergonic - reverse reaction would require +16.7kJ of energy so will not proceed

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13
Q

what is glycolysis step three?

A

phosphofructokinase catalysed catabolism of fructose-6-phosphate to fructose-1,6-bisphosphate
consumes 1 ATP molecule
key regulatory enzyme - first commited step, allosteric modification by ATP
exergonic - reverse reaction would require +14.2kJ of energy so will not proceed

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14
Q

what is glycolysis step ten?

A

pyruvate kinase catalysed catabolism of phosphoenolpyruvate to pyruvate
synthesises 1 ATP molecule
exergonic - reverse reaction would require +31.4kJ of energy so will not proceed.

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15
Q

what is the TCA cycle?

A

TCA cycle is the second stage of cellular respiration
occurs in the mitochondrial matrix
TCA cycle is amphibolic
intermediates from carbohydrates, fat and amino acid metabolism meet in the citric acid cycle to be completely oxidised to carbon dioxide and water
a large amount of chemical potential energy is released in a stepwise fashion
the oxidation-reduction reactions transfer chemical energy to NAD and FAD - 3x NAD & 1x FAD
pyruvate derivatives are oxidised - lose electrons
coenzymes are reduced - gain electrons

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16
Q

what are the products of TCA cycle?

A

one molecule of GTP is produced - converted to ATP
TCA cycle = 3xNADH + FADH2 +3xH+ + GTP + 2xCO2
NADH and FADH2 - electron transport chain
no net gain of intermediates
TCA cycle is a rich source of intermediates for other biosynthetic pathways where needed

17
Q

what is the electron transport chain?

A

reduced coenzymes from the citric acid cycle travel to the inner mitochondrial membrane to the electron transport chain
ETC is a series of electron transporters embedded in the inner mitochondrial membrane that shuttles electrons from NADH and FADH2 to molecular oxygen.

18
Q

what is the process of the electron transport chain?

A

protons (H+) are pumped from the mitochondrial matrix to the intermembrane space, and oxygen is reduced to form water
ATP synthase uses the proton (H+) gradient to form ATP from ADP + Pi
energy is gained by a difference in concentration of the protons (H+) across the inner membrane of the mitochondria - electrochemical gradient
net gain of 30-32 ATP

19
Q

what is the pentose pathway?

A

makes pentoses - a class of simple sugars including deoxyribose (DNA) and ribose (RNA)
makes NADPH - provides the electrons needed for reduction in anabolic reactions (reducing potential)

20
Q

what are the end products of the pentose pathway?

A

glyceraldehyde-3-phosphate and fructose-6-phosphate that link back to glycolysis
ribose-5-phosphate to make nucleotides
glucose-6-phosphate > 6x CO2 + 12x NADPH + 12x H+ + 6x ribose-5-phosphate

21
Q

what is the function of ribose-5-phosphate?

A

leads to nucleotide biosynthesis to make DNA, RNA and various cofactors (CoA, NAD+, NADP+)

22
Q

what is the function of the pentose pathway?

A

provides the release of reducing power needed for anabolic reactions

23
Q

what is gluconeogenesis?

A

the synthesis of glucose from pyruvate, lactate, glycerol and amino acids
occurs primarily in the liver as glycogen is stored in the liver
used when glycogen stores are low
requires the input of energy
occurs in the cytoplasm
important in liver control of blood glucose homeostasis

24
Q

what regulates gluconeogenesis?

A

reciprocally regulated with glycolysis by ATP levels
low ATP = glycolysis - produces ATP
high ATP = gluconeogenesis - uses ATP

25
Q

why is gluconeogenesis used?

A

the creation of glucose in cells cannot occur by reversing glycolysis due to the three irreversible steps (1,3&10)
gluconeogenesis creates glucose using three reactions that bypass these irreversible reactions

26
Q

what is glucagon?

A

initiates gluconeogenesis
raises concenetration of glucose
produced by alpha cells in the pancreas

27
Q

what are the three steps of gluconeogenesis?

A

bypass I
bypass II
bypass III

28
Q

what is gluconeogensis bypass I?

A

converts pyruvate to phosphoenolpyruvate without using pyruvate kinase
pyruvate travels to the mitochondrial matrix where pyruvate carboxylase converts it to oxaloacetate which is then converted to malate and the malate travels to the cytoplasm where it is converted back to oxaloaetate which produces phosphoenolpyruvate

29
Q

what is gluconeogenesis bypass II?

A

convert fructose-1,6-bisphosphate to fructose-6-phosphate without using phosphofructokinase
fructose-1,6-bisphosphatase removes a phosphate group from fructose-1,6-bisphosphate to produce fructose-6-phosphate
inhibited by AMP - low ATP - glycolysis
activated by ATP - high ATP - gluconeogenesis

30
Q

what is gluconeogenesis bypass III?

A

convert glucose-6-phosphate to glucose avoiding hexokinase
glucose-6-phosphatase removes a phosphate group from glucose-6-phosphate to produce glucose

31
Q

what is the cori cycle?

A

the conversion of glucose to pyruvate to lactate in muscle cells, this lactate travels through the bloodstream to the liver where it produces pyruvate which then undergoes gluconeogenesis to produce glucose which is then recycled through the blood stream back into muscle cells.
PATHWAY

32
Q

why does the cori cycle take place in the liver?

A

the cori cycle takes place in the liver as muscle cells lack the glucose-6-phosphatase required for gluconeogenesis to occur.

33
Q

what is glycogenesis?

A

formation of glycogen from glucose.
PATHWAY

34
Q

what are the enzymes used during glycogenesis?

A

glucokinase
phosphoglucomutase
UDP-glucosepyrophosphorylase
glycogen synthase/ glycogen branching enzyme

35
Q

what is the key enzyme in glycogenesis?

A

glycogen synthase

36
Q

what is glycogenolysis?

A

breakdown of glycogen to form glucose

37
Q

what is the key enzyme in glycogenolysis?

A

glycogen phosphorylase

38
Q

how is the activity of glycogen phosphorylase controlled?

A

by phosphorylation and dephosphorylation
phosphorylase a = active (phosphorylase kinase + 2ATP)
phosphorylase b = inactive (phosphorylase phosphatase)

39
Q

what is the equation for glycogenolysis?

A

(glucose)n <> (glucose)n + glucose-1-phosphate

human metabolism - summary notes (3 decks)

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