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MCAT-BIOCHEMISTRY > Carbohydrates & Carbohydrate Metabolism > Flashcards

Carbohydrates & Carbohydrate Metabolism Flashcards

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MCAT flashcards
1
Q

what is the bond between two sugar molecules?

A

glycosidic linkage; a covalent bond formed in a dehydration reaction that requires enzymatic catalysis

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2
Q

what does glycogen consist of?

A

thousands of glucose units joined in alpha-1,4 linkages or alpha-1,6 branches

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3
Q

what bonds exist in cellulose

A

beta-glycosidic bonds

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4
Q

what are the two high energy electron carriers involved in cellular respiration?

A

NADH and FADH2

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5
Q

what is the four step process in cellular respiration?

A

glycolysis (produces pyruvic aid molecules), pyruvate dehydrogenase complex (PDC) (pyruvate is decarboxylated to form an acetyl group that is then attached to coenzyme A), the Krebs cycle (acetyl group from PDC is added to oxaloacetate to form citric acid which is then decarboxylated and isomerized to regenerate oxaloacetate, produces more NADH and FADH2), and electron transport/oxidative phosphorylation (high energy electrons carriers are oxidized by electron transport chain to finally reduce water, electron energy is used to pump protons into intermembrane space. protons allowed to flow back in to produce ATP)

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6
Q

coenzyme A

A

a carrier that attaches to the acetyl group formed in PDC and transfers the acetyl group into the Krebs cycle

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7
Q

what are the other names for the Krebs cycle?

A

tricarboxylic acid cycle (TCA cycle), citric acid cycle

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8
Q

hexokinase

A

catalyzes the first step in glycolysis, the phosphorylation of glucose to G6P. G6P feedback inhibits hexokinase

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9
Q

phosphofructokinase

A

phosphorylates F-6-P to F-1,6-bP, committed step, thermodynamically very favourable, irreversible, allosteric inhibition by ATP

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10
Q

reducing power

A

reduction potential

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11
Q

aerobic

A

in the presence of oxygen

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12
Q

anaerobic

A

without oxygen

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13
Q

fermentation

A

regenerates NAD+ in anaerobic conditions, allowing glycolysis to continue in the absence of oxygen by using pyruvate as the acceptor of the high energy electrons from NADH

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14
Q

what are two examples of fermentation?

A

1) reduction of pyruvate to ethanol in yeast

2) reduction of pyruvate to lactate in human muscle cells

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15
Q

what is the difference between ethanol and lactate production in fermentation?

A

ethanol production includes loss of a carbon dioxide, both oxidize NADH to produce one NAD+

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16
Q

where do lactate molecules go?

A

exported from muscle to liver

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17
Q

cofactors

A

additional non-protein compounds that are required by enzymes for their biological activity

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18
Q

prosthetic group

A

if a cofactor is very tightly or covalently bound to the enzyme

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19
Q

what are some examples of cofactors?

A

thiamine (part of thiamine pyrophosphate and is required in the PDC and Krebs cycle)

20
Q

what does the oxidation of one glucose create in steps 1-3?

A

1) 2 ATP and 2 NADH
2) 2 NADH
3) 6 NADH, 2 FADH2, 2GTP

21
Q

mitochondrial outer membrane

A

smooth and contains very large pores formed by porin proteins

22
Q

mitochondrial inner membrane

A

impermeable and folded into dense structures called cristae

23
Q

matrix

A

the innermost space of the mitochondrion

24
Q

intermembrane space

A

the space between the two membranes in the mitochondria

25
Q

what are the goals of electron transport/oxidative phosphorylation?

A

1) reoxidize all the electron carriers that were reduced

2) store energy in the form of ATP in the process

26
Q

how does electron transport work in prokaryotes?

A

proton gradient is created across the bacterial membrane and by the ATP synthase (this produces 2 more ATP than eukaryotes because it does not need to transport cytoplasmic electron carriers across the inner mitochondrial membrane)

27
Q

oxidative phosphorylation

A

the oxidation of the high-energy electron carriers NADH and FADH2 coupled to the phosphorylation of ADP to produce ATP

28
Q

what is the source of energy used to drive the phosphorylation of ADP to ATP

A

the proton gradient

29
Q

electron-transport chain

A

a group of five electron carriers located on the inner mitochondrial membrane

30
Q

cytochrome

A

large protein complexes embedded in the inner mitochondrial membrane and are part of the electron transport chain; contains a heme group

31
Q

what does the electron transport chain consist of?

A

3 cytochromes (NADH dehydrogenase/coenzyme Q reductase, cytochrome C reductase, cytochrome C oxidase) and two mobile electron carriers (ubiquinone/coenzyme Q, cytochrome C)

32
Q

how many ATP is produced per NADPH in matrix?

A

2.5

33
Q

how many ATP is produced per FADH2 in matrix?

A

1.5

34
Q

how many ATP is produced per cytosolic NADH?

A

1.5

35
Q

glycerol phosphate shuttle

A

the pathway by which cytosolic NADH is transported directly to ubiquinone

36
Q

why is NADH and FADH2 producing only 1.5 ATP?

A

because they are transported directly to ubiquinone, bypassing NADH dehydrogenase

37
Q

what is the theoretical maximum amount of ATP that can be produced from a single molecule of glucose?

A

30 in eukaryotes, 32 in prokaryotes

38
Q

gluconeogenesis

A

occurs when dietary sources of glucose are unavailable and the liver has depleted glycogen and glucose stores: coverts non-carbohydrate precursor molecules into intermediates of glycolysis pathway to ultimately become glucose; reverse of glycolysis

39
Q

futile cycling

A

running both pathways at the same time, results in net loss of energy

40
Q

reciprocal control

A

the same molecule regulates two different (and opposite) enzymes in opposite ways

41
Q

what are the two enzymes regulated in regulation of glycolysis and gluconeogenesis?

A

phosphofructokinase (PFK-glycolysis) and fructose-1,6-biphosphatase (F-1,6-BPase gluconeogenesis), both are allosterically regulated by glycolytic intermediates

42
Q

what is another metabolic intermediate that exerts reciprocal control in regulation of glycolysis and gluconeogenesis?

A

fructose-2,6-biphosphate, stimulates PFK (glycolysis) and inhibits gluconeogenesis that is controlled by insulin and glucagon levels; increased insulin = activated PFK and glycolysis, increased glucagon=activated fru-1,6-bisPase, increased gluconeogenesis

43
Q

those enzymes which catalyze irreversible (exergonic) reactions are frequently sites for?

A

regulation

44
Q

glycogenesis

A

the formation of glycogen

45
Q

glycogenolysis

A

breaks down glycogen to form a single glucose molecule (glycogen phosphorylase)

46
Q

pentose phosphate pathway (PPP)

A

diverts glucose-6-phosphate from glycolysis in order to form NADPH, ribose-5-phosphate, (oxidative) and glycolytic intermediates (non-oxidative)

47
Q

what is the primary point of regulation in PPP?

A

the first enzyme: glucose-6-phosphate dehydrogenase (G6PDH), its product is NADPH and negatively inhibits G6PDH

MCAT-BIOCHEMISTRY (3 decks)

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