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Bad Girl's MCAT Club > Biochemistry 10: Carbohydrate Metabolism II > Flashcards

Biochemistry 10: Carbohydrate Metabolism II Flashcards

1
Q

acetyl-coA

A

contains a high-energy thioester bond that can be used to drive other reactions when hydrolyzed

can be formed from…

  • pyruvate dehydrogenase
  • fatty acids
  • carbon skeletons of ketogenic amino acids, ketone bodies, and alcohol
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2
Q

pyruvate dehydrogenase

A

enzyme of pyruvate dehydrogenase complex

oxidizes pyruvate, creating CO2

requires thiamine pyrophosphate (TPP) and Mg2+

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3
Q

dihydrolipoyl transacetylase

A

enzyme of pyruvate dehydrogenase complex

oxidizes the remaining 2-carbon molecule after CO2 release using lipoic acid

transfers the acetyl group to CoA, forming acetyl-CoA

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4
Q

dihydrolipoyl dehydrogenase

A

enzyme of pyruvate dehydrogenase complex

uses FAD to reoxidize lipoic acid, making FADH2

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5
Q

pyruvate dehydrogenase phosphatase

A

enzyme of pyruvate dehydrogenase complex

dephosphorylates PDH when ADP levels are high, turning the enzyme on

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6
Q

pyruvate dehydrogenase kinase

A

enzyme of pyruvate dehydrogenase complex

phosphorylates PDH when ATP or acetyl-CoA levels are high, turning off the enzyme

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7
Q

how does fatty acid oxidation (beta-oxidation) contribute to the formation of acetyl CoA?

A
  1. in cytosol, fatty acid + CoA –> fatty acyl-CoA, which moves into the intermembrane space
  2. fatty acid (acyl) group is transferred to carnitine –> acyl-carnitine, which crosses the inner membrane
  3. acyl group transferred to mitochondrial CoA –> fatty acyl-CoA
  4. fatty acyl-CoA undergoes beta-oxidation to form acetyl CoA
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8
Q

how does amino acid catabolism form acetyl-CoA?

A

ketogenic amino acids lose their amino group via transamination and their carbon skeletons form ketone bodies

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9
Q

how does alcohol form acetyl-CoA?

A

enzymes alcohol dehydrogenase and acetaldehyde dehydrogenase

alcohol —> acetyl CoA

reaction also builds up NADH, which inhibits the citric acid cycle

acetyl-CoA formed through this process is usually used to make fatty acids

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10
Q

Control Points of the Citric Acid Cycle

A

Citrate synthase

Isocitrate dehydrogenase,

alpha-Ketoglutarate dehydrogenase complex

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11
Q

Citrate synthase

A

enzyme in citric acid cycle

acetyl-CoA + oxaloacetate —>—> citrate + CoA-SH

ATP and NADH function as allosteric inhibitors

high levels of ATP and NADH imply that the cell is energetically satisfied

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12
Q

aconitase

A

enzyme in the citric acid cycle

isomerizes citrate to isocitrate

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13
Q

Isocitrate Dehydrogenase

A

enzyme in the citric acid cycle; rate-limiting step

oxidizes and decarboxylates isocitrate –> a-ketoglutarate

creates the first CO2 and NADH of the cycle

inhibited by ATP and NADH

ADP and NAD+ function as allosteric activators

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14
Q

a-Ketoglutarate dehydrogenase complex

A

enzyme in the citric acid cycle

a-ketoglutarate —> succinyl-CoA

creates the second CO2 and NADH of the cycle

inhibited by succinyl-CoA, NADH, and ATP

stimulated by ADP and Ca2+

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15
Q

succinyl-CoA synthetase

A

enzyme in the citric acid cycle

hydrolyzes the thioester bond in succinyl-CoA –> succinate + CoA-SH

creates GTP

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16
Q

fumarase

A

enzyme in the citric acid cycle

hydrolyzes the alkene bond of fumarate —> malate

17
Q

malate dehydrogenase

A

enzyme in the citric acid cycle

oxidizes malate —> oxaloacetate

denerates the third NADH of the cycle

18
Q

what is the order of the substrates in the citric acid cycle?

A

Pyruvate

Citrate

Isocitrate

a-Ketoglutarate

Succinyl-CoA

Succinate

Fumarate

Malate

Oxaloacetate

Please Can I Keep Selling Sea Shells For Money, Officer?

19
Q

what is the net yield of acetyl-CoA formation and the citric acid cycle per pyruvate?

A

PDH:

1 NADH

Citric acid cycle:

3 NADH

1 FADH

1 GTP

net ATP production -

4 NADH(2.5) = 10 ATP

1 FADH(1.5) = 1.5 ATP

1 GTP = 1 ATP

total = 12.5 ATP per pyruvate

20
Q

why is the formation of ATP coupled to electron transport?

A

ADP + Pi –> ATP is endergonic

electron transport is exergonic since electrons move through the complexes up their reduction potential gradient (spontaneous) until reaching O2 (highest reduction potential)

coupled so that energy from one rxn can fuel the other

21
Q

Complex I (NADH-CoQ oxidoreductase)

A

includes an iron-sulfur cluster and flavoprotein covalently bonded to flavin mononucleotide (FMN)

movement of electrons:

NADH —-> FMN

Flavoprotein becomes reoxidized while the iron-sulfur subunit is reduced

iron-sulfur subunit —> coenzyme Q

pumps 4 protons

22
Q

Complex II (Succinate-CoQ oxidoreductase)

A

includes an iron-sulfur cluster an is covalently bonded to FAD

movement of electrons:

succinate + FAD —-> fumarate + FADH2

FAD becomes reoxidized while the iron-sulfur subunit is reduced

iron-sulfur subunit —> coenzyme Q

does not pump any protons

transfers electrons to coenzyme Q; receives electrons from succinate succinate is oxidized and FAD is reduced to FADH2 FAD2 is oxidized to FAD as it reduces an iron-sulfur protein The iron-sulfur protein is reoxidized as coenzyme Q is reduced No hydrogen pumping occurs here to contribute to the proton gradient

23
Q

Complex III (CoQH2-cytochrome c oxidoreductase) (cytochrome reductase)

A

includes an iron-sulfur cluster

movement of electrons:

CoQH2 —-> cytochrome c + 2H+

4 protons are pumped

main contribution to the proton-motive force is via the Q cycle

24
Q

Q cycle

A

linked to complex III

cycle of moving electrons from coenzyme Q to cytochrome c

two electrons are shuttled from a molecule of CoQH2 to a molecule of CoQ

another two electrons attach to heme moieties on cytochrome c

moves 4 protons into the intermembrane space

continues to increase the gradient of the proton-motive force across the inner mitochondrial membrane

25
Q

Complex IV (cytochrome c oxidase)

A

movement of electrons:

cytochrome c —> oxygen, the final electron acceptor

includes subunits of cytochrome a, cytochrome a3, and Cu2+ ions

pumps 2 protons across the membrane

26
Q

Cytochrome oxidase

A

made up of cytochromes a and a3

this gets oxidized as oxygen becomes reduced and forms water

this is the final location on the transport chain where proton pumping occurs

27
Q

The increase of hydrogen ions in the intermembrane space causes:

A

pH of the intermembrane space to drop

voltage difference between the intermembrane space and matrix increases due to proton pumping

28
Q

what two shuttle mechanisms help NADH enter the mitochondrial matrix from glycolysis?

A

shuttle mechanism: transfers high-energy electrons of NADH to carrier that can cross the inner mitochondrial membrane, making ATP in the process

glycerol 3-phosphate shuttle

malate-aspartate shuttle

29
Q

Glycerol 3-phosphate shuttle

A

electrons transferred from NADH to DHAP —> G3P by the cytosolic enzyme glycerol 3-phosphate dehydrogenase

electrons are then transferred to FAD, Complex II and eventually CoQ using mitochondrial glycerol 3-phosphate dehydrogenase

the enzyme recreates DHAP to continue the cycle

NADH makes 1.5 ATP by using this shuttle mechanism

30
Q

Malate-aspartate shuttle

A

electrons are transferred from NADH to OAA —> malate

malate is able to cross the inner mitochondrial membrane and transfer electrons back to NAD+ recreating NADH and reforming OAA in mitochondria

OAA can be transaminated —> aspartate, which can cross into the cytosol and be reconverted to OAA

malate dehydrogenase exists in both the cytosol and the mitochondria, can perform both reactions

more efficient because it produces 2.5 ATP for each NADH

31
Q

F0

A

the portion of ATP synthase that spans the inner mitochondrial membrane

functions as an ion channel, so protons travel through F0 along their gradient back into the matrix

32
Q

F1

A

portion of atp synthase that utilizes the energy released from the electrochemical gradient to phosphorylate ADP to ATP

33
Q

what regulates oxidative phosphorylation?

A

when O2 limited, electrons can’t leave the ETC

also increases NADH levels (backs up everything up to the citric acid cycle)

when ADP is limited, there isn’t enough to be phosphorylated into ATP

ADP also activates isocitrate dehydrogenase, pushing the citric acid cycle forward

34
Q

respiratory control

A

the coordination of the citric acid cycle and oxidative phosphorylation

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