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BIOL 2421 - Cellular Biochem > 16. fermentation and gluconeogenesis > Flashcards

16. fermentation and gluconeogenesis Flashcards

1
Q

what happens to pyruvate under aerobic conditions

A

it’s oxidized to Acetyl-CoA, centers the CAC, and is oxidized to CO2 and H2O

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2
Q

what happens to pyruvate under anaerobic conditions

A

pyruvate undergoes fermentation to either lactate or ethanol

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3
Q

what can pyruvate ferment into

A

lactate or ethanol

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4
Q

where would pyruvate ferment into lactate

A

in animal tissues

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5
Q

where would pyruvate ferment into ethanol

A

in yeast

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6
Q

what else is produced in pyruvate fermentation

A

NAD+

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7
Q

why is NAD+ produced in pyruvate fermentation

A

it is regenerated to continue being used in glycolysis as a co-substrate

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8
Q

what enzyme reduces pyruvate into lactate

A

lactate dehydrogenase

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9
Q

lactate is the ionized form of ___

A

lactic acid

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10
Q

describe the G’o value for pyruvate fermentation into lactate

A

it has a large negative G’o

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11
Q

describe why there is no net accumulation of NAD+ as it’s produced by fermentation

A

glycolysis uses NAD+ to make NADH while fermentation replenishes NAD+. So long as both are occurring, there is no net change in the NAD+ and NADH pools

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12
Q

where does fermentation to lactate occur in humans

A

active skeletal muscles, red blood cells, and a few other cell types (ie sperm, retinal, brain, and kidney cells)

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13
Q

describe fermentation in active skeletal muscles

A

O2 (temporarily) cannot be bright in from the lungs fast enough. Muscle glycogen stores provide extra glucose for lots of glycolysis

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14
Q

describe fermentation in red blood cells

A

RBCs lack mitochondria when mature, so they cannot complete aerobic respiration

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15
Q

describe fermentation in the other human cell types (sperm, retinal, brain, kidney)

A

glycolysis in these cell types is the only method of producing ATP even in aerobic conditions

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16
Q

T or F: lactate can be recycled

A

true

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17
Q

where can lactate be recycled

A

in the liver

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18
Q

describe how lactate is recycled in the liver

A

lactate is brought to the liver via blood and is slowly reconverted to pyruvate by lactate dehydrogenase working in reverse, and then to glucose by gluconeogenesis

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19
Q

how are glycogen stores refilled

A

heavy breathing after exertion repays O2 debt and allows reformation of depleted glycogen stores

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20
Q

T or F: some bacteria can undergo lactic acid fermentation

A

true

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21
Q

describe lactic acid fermentation in bacteria

A

one such bacteria ferments the lactose in milk. The resulting pH drop precipitates milk proteins = yogurt

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22
Q

describe the first step of ethanol fermentation (what is produced + enzyme used)

A

pyruvate is converted to acetaldehyde via pyruvate decarboxylase. CO2 is also produced

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23
Q

is the first step of pyruvate fermentation in yeast reversible

A

no

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24
Q

in the first step of pyruvate fermentation in yeast, what does the enzyme require

A

Mg2+ and a coenzyme called TPP

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25
Q

what is TPP

A
  • derived from vitamin B1

- we need it for synthesis of Acetyl-CoA and in the Pentose Phosphate Pathway

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26
Q

describe the second step of ethanol fermentation

A

acetaldehyde is converted to ethanol via alcohol dehydrogenase. NAD+ is also produced

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27
Q

describe what cool stuff pyruvate decarboxylase is responsible for

A

carbonation in champagne, beer, rising dough

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28
Q

describe the function of alcohol dehydrogenase in HUMANS

A

it allows us to oxidize ingested ethanol in our liver to acetaldehyde and then to acetate and water (reverse reaction of fermentation). NAD+ is reduced to NADH

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29
Q

what are the other two fates of pyruvate

A

it can be carboxylated to oxaloacetate for the CAC, or it can have an amine group added to form alanine

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30
Q

explain why tumors are initially growing under hypoxic conditions

A

in the early stages, there aren’t a lot of blood vessels around it = not a lot of oxygen = anaerobic conditions

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31
Q

describe the rate of glycolysis in a growing tumor cell

A

the rate is about 10 times as fast in a growing tumor cell since the yield of glycolysis is so low

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32
Q

describe the cellular changes that occur in a tumor cell (bad for us, good for the tumor)

A
  • disrupted mitochondrial electron transport
  • upregulation of glycolysis enzymes
  • upregulation of glucose transporters on the PM
  • upregulated lactate dehydrogenase
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33
Q

how do chemotherapeutic agents disrupt glycolysis

A

by inhibiting hexokinase

34
Q

describe the other benefit of preventing G6P formation by inhibiting hexokinase

A

G6P is used in the pentose phosphate pathway which is used to synthesize nucleotides. No G6P=not enough nucleotides to supply constant cell division and DNA doubling. Tumor growth slows

35
Q

describe what a PET scan does/what it’s used for

A

the patient is injected with a labeled glucose analog that fluoresces which is taken up by tissues but cannot be metabolized. Accumulation of the analog allows us to view/detect nascent tumors

36
Q

what is gluconeogenesis

A

synthesis of glucose from non-carbohydrate precursors

37
Q

how many carbons is the starting material of gluconeogenesis

A

can be 2C or 3C

38
Q

what is the starting material of GNG in mammals

A

lactate, pyruvate, glycerol, and some gluconeogenic amino aicds

39
Q

where does GNG occur in mammals

A

the cytosol of the liver

40
Q

which part of the GNG pathway is consistent in both plants and animals

A

PEP to G6P

41
Q

how many steps do GNG and glycolysis share

A

7 of 10

42
Q

which steps of glycolysis are not shared with GNG

A

glucose to G6P (1)
F6P to F1,6P (3)
PEP to pyruvate (10)

43
Q

which steps of GNG are irreversible: the 7 shared or the 3 unshared with glycolysis (+why)

A

the 3 unshared steps are irreversible because GNG needs three different enzymes to bypass the steps

44
Q

what are the two possible pathways to produce PEP from pyruvate

A
  • one when pyruvate is predominant

- one when lactate is predominant

45
Q

which amino acid is prevalent in skeletal muscle as it’s degrading proteins for fuel

A

alanine

46
Q

how is alanine made

A

pyruvate + amino group =alanine

47
Q

what is transamination

A

the joining of an amino group to pyruvate to make alanine (aka swapping an amine group from one molecule to another)

48
Q

what enzyme completes transamination

A

aminotransferases

49
Q

an amino group lacking its amine group is called ___

A

an a-keto acid

50
Q

what is the a-keto acid of alanine

A

pyruvate

51
Q

what do aminotransferases require

A

PLP (a vitamin B6 derivative)

52
Q

where is alanine prevalent

A

skeletal muscle

53
Q

where does alanine travel to

A

the liver

54
Q

what happens to alanine in the liver

A

it loses the amine group and becomes pyruvate

55
Q

GNG step 1, pyruvate predominant: where is pyruvate moved to from the cytosol

A

the mitochondria

56
Q

GNG step 1, pyruvate predominant: what happens to pyruvate in the mitochondria

A

it’s carboxylated to form oxaloacetate

57
Q

GNG step 1, pyruvate predominant: what enzyme converts pyruvate to oxaloacetate

A

pyruvate carboxylase

58
Q

GNG step 1, pyruvate predominant: what does pyruvate carboxylase require

A

biotin and ATP

59
Q

GNG step 1, pyruvate predominant: what is the role of bicarbonate

A

it provides the extra CO2 group in oxaloacetate formation

60
Q

GNG step 1, pyruvate predominant: what is the role of biotin

A

it serves as a long arm that swings the carboxyl group between the two enzyme sites

61
Q

GNG step 1, pyruvate predominant: what is the role of the extra carboxyl group

A

it serves to prime pyruvate

62
Q

GNG step 1, pyruvate predominant: now that we have oxaloacetate, what is the next step

A

it needs to be converted to PEP

63
Q

GNG step 1, pyruvate predominant: can oxaloacetate directly be converted to PEP

A

no

64
Q

GNG step 1, pyruvate predominant: how do we convert oxaloacetate to PEP

A

it’s reduced to malate by malate dehydrogenase in the matrix. Malate can then leave the mitochondria, enter the cytosol and be reconverted to oxaloacetate

65
Q

GNG step 1, pyruvate predominant: describe [NADH] in the cytosol and the matrix

A

NADH in the matrix is converted to NAD+, so that molecule of NAD+ is used in the cytosol to make NADH, so this process increases cytosolic NADH levels

66
Q

GNG step 1, pyruvate predominant: what happens once oxaloacetate is in the cytosol

A

it is decarboxylated and phosphorylated to from PEP

67
Q

GNG step 1, pyruvate predominant: what molecule phosphorylated OAA to become PEP

A

GTP

68
Q

GNG step 1, lactate predominant: we have lactate produced in the muscle. What happens to it

A

the Cori Cycle shuttles it to the liver

69
Q

GNG step 1, lactate predominant: once lactate is in the liver, what happens

A

it will be reconverted to pyruvate and reproduce NADH

70
Q

GNG step 1, lactate predominant: do we need the step of conversion of OAA to malate and back again? why/why not

A

no; because cytosolic NADH is immediately produced in the first step of this pathway

71
Q

GNG step 1, lactate predominant: now that lactate is converted to pyruvate, what happens

A

pyruvate is shuttled to the mitochondria and converted to OAA

72
Q

GNG step 1, lactate predominant: once pyruvate is converted to OAA, what happens

A

OAA is directly converted to PEP in the mitochondria via a mitochondrial version of PEP carboxykinase

73
Q

GNG step 1, lactate predominant: which enzyme converts OAA to PEP

A

PEP carboxykinase

74
Q

GNG step 1, lactate predominant: once PEP is produced, what happens

A

PEP leaves the mitochondria

75
Q

GNG step 8: what is the reagent and product

A

fructose 1,6-bisphosphate –> fructose 6-phosphate

76
Q

GNG step 8: how is F6P produced

A

hydrolysis of the phosphate on the C1 of F1,6P

77
Q

GNG step 8: which enzyme is used

A

fructose 1,6-bisphosphatase 1

78
Q

GNG step 10: what is the reagent and product

A

glucose 6-phosphate –> glucose

79
Q

GNG step 10: how is glucose made

A

hydrolysis of the phosphate of C6 on G6P

80
Q

GNG step 10: what enzyme is used

A

glucose 6-phosphatase

81
Q

GNG step 10: T or F: only liver hepatocytes, renal cells, and epithelial cells of the small intestine have glucose 6-phosphatase enzyme

A

true; other tissues are thus not able to complete GNG and must receive any GNG products by the bloodstream

BIOL 2421 - Cellular Biochem (21 decks)

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