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Chem 153a > week 8: glycolysis regulation, pyruvate dehydrogenase, and citric acid cycle > Flashcards

week 8: glycolysis regulation, pyruvate dehydrogenase, and citric acid cycle Flashcards

1
Q

what happens to fructose-6-phosphate in the liver at higher glucose concentration? (enzyme, energy changes, final product)

A

converted to fructose-2,6-bisphosphate by liver PFK2 (dephosphoenzyme) and converts and ATP to an ADp

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2
Q

what happens to fructose-2,6-bisphosphate in the liver at lower glucose concentrations? (enzyme, energy changes, final product)

A

converted by liver FBPase-2 (phosphoenzyme) to fructose-6-phosphate and forms Pi from H2O

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3
Q

is fructose-2,6-bisphosphate a part of glycolysis

A

no

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4
Q

what intermediate from glycolysis does fructose-2,6-bisphosphate come from?

A

fructose-6-phosphate

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5
Q

what enzyme is the main control point in glycolysis

A

phosphofructokinase

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6
Q

how does fructose-2,6-bisphosphate regulate phosphofructokinase

A

activates it – inhibits corresponding enzyme in gluconeogenesis

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7
Q

which enzymes are the three irreversible steps in glycolysis catalyzed by?

A

hexokinase
phosphofructose kinase
pyruvate kinase

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8
Q

why would we need to reverse glycolysis

A

the brain, nervous system, and red blood cells only use glucose for ATP synthesis, so need gluconeogenesis after vigorous exercise or prolonged fasting to quickly regenerate glucose levels

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9
Q

characteristics of hexokinase

A

hexokinase can catalyze a variety of reactions (nonspecific), lower km, inhibited by G6P

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10
Q

characteristics of glucokinase

A

glucokinase is hexokinase of liver and only works on glucose – much higher km (only works at high [glucose]), not inhibited by G6P

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11
Q

how are hexokinase and glucokinase related and when is one used over the other

A

they are isozymes and can catalyze the same reaction

glucokinase is enzyme in the liver and because of high km only works at higher [glucose]

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12
Q

why do most tissues use hexokinase (over glucokinase)

A

metabolize blood glucose for energy, the G6P is trapped in the cell, so there is only product inhibition once you have enough glucose for energy

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13
Q

why does the liver use glucokinase over hexokinase?

A

it must maintain blood glucose, so when there is high blood glucose is uses glucokinase to store it as glycogen, and it is not inhibited by G6P so it can take up excess glucose and store it

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14
Q

when would the liver use hexokinase? (in addition to glucokinase)

A

keeps a little hexokinase around to do glycolysis for energy when glucose levels are normal/low

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15
Q

how are glucokinase and hexokinase regulated by substrate availability?

A

glucokinase is highly regulated by substrate availability due to Km being nearer to normal glucose levels while hexokinaase has a lower km than normal levels so it’s not really affected by substrate availability

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16
Q

how does the cell know when it needs ATP? how is glycolysis regulated to respond to this condition?

A

high ADP/AMP concentrations tell the cell it needs ATP and will activate PFK-1 and pyruvate kinase

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17
Q

which of the three regulated enzymes in glycolysis is the main control point

A

phosphofructokinase

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18
Q

what enzyme is considered the secondary control point in glycolysis?

A

pyruvate kinase

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19
Q

how is pyruvate kinase regulated by the need for glycolysis

A

fructose 1,6 bisphosphate activates (strongest regulator); Acetyl-coA and NADH inhibits

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20
Q

how is pyruvate kinase regulated by ATP

A

ATP inhibits, and ADP/AMP activate

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21
Q

what inhibits phosphofructokinase

A

citrate

22
Q

what inhibits pyruvate kinase

A

acetyl coA and NADH

23
Q

what activates phosphofructokinase (PFK)

A

AMP/ADP, fructose-2,6-bisphosphate

24
Q

what inhibits PFK

A

ATP, citrate

25
Q

anaerobic glycolysis substrate/product summary

A

glucose + 2ADP + 2pi –> 2 lactacte + 2 ATP + 2H2O

26
Q

process of alcoholic fermentation in yeast

A

pyruvate –pyruvate carboxylase–> acetaldehyde –alcohol dehydrogenase–> ethanol

27
Q

what are the 2 primary sources of energy for cancer cells?

A

glucose and glutamate (but can use any of intermediates of glycolysis as well)

28
Q

how do cells get energy

A

from C atom oxidation

29
Q

where does the TCA cycle occur?

A

mitochindrion

30
Q

what are semipermeable membranes permeable to and what is mechanism

A

hydrophobic (nonpolar) molecules (O2, CO2), small, uncharged molecules (H2O) get in by diffusion

31
Q

what are semipermable membranes impermable to and how do those get across?

A

large, polar, charged molecules get across via mediated transport system

32
Q

what are 2 types of mediated transport

A

passive: facilitates diffusion
active: uses energy to go against concentration gradient

33
Q

what is a uniport

A

single channel allows single molecule to go one direction

34
Q

what is a symport

A

single channel which allows 2 substrates to go in same direction

35
Q

what us an antiport

A

single channel which allows 2 substrates to go in opposite direction

36
Q

what/how/why is the mitochondrial outer membrane permeable to?

A

has a protein called porin which punches holes in it so permeable to molecules smaller than 5Kd by diffusion

37
Q

feature of mitochondrial inner membrane

A

larger surface area due to folds (cristae)

38
Q

what do the cristae due

A

increase surface area, allow for localized buildup of concentration to control contents of matrix, provides scaffold for ETC to occur

39
Q

how is pyruvate imported into the mitochondria

A

a symport with H+

40
Q

where does the citric acid cycle occur in eukaryotes

A

the mitochondrial matrix

41
Q

how do cristae relate to respiratory activity of cell

A

more cristae = more surface area = more e- transport chain complexes which give more respiration

42
Q

what is oxidative carboxylation

A

synthesis of acetyl coa from pyruvate

43
Q

what is the use of acetyl coa

A

its a high energy compound, so cleavage can provide energy to drive the TCA cycle

44
Q

what are sources of acetyl coa and how are these used

A

amino acids (proteins), fatty acids (lipids), glycolysis (carbohydrates) are all used as sources for acetyl coa in the first stage of cellular respiration

45
Q

what components make up pyruvate dehydrogenase; what kind of enzyme is this

A

E1, E2, and E3 – a multienzyme complex

46
Q

what is E1 (in pyruvate dehydrogenase)

A

pyruvate decarboxylase

47
Q

what is E2 in pyruvate dehydrogenase)

A

dihydrolipoyl transacetylase

48
Q

what is E3 in pyruvate dehydrogenase)

A

dihydrolipoyl dehydrogenase

49
Q

what are 2 benefits of multienzyme complexes?

A
  1. enhanced reaction rates due to channeling of intermediates and limited side reactions
  2. coordinated regulation
50
Q

how does thiamine pyrophosphate (TPP) work in pyruvate dehydrogenase

A

a cofactor bound to E1 which decarboxylates pyruvate yielding a hydroxyethyl-TPP carbanion – has an acidic proton

Chem 153a (8 decks)

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