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Biochemistry > Chapter 16 > Flashcards

Chapter 16 Flashcards

1
Q

What is the metabolite that links glycolysis and the citric acid cycle?

A

Pyruvate

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2
Q

Process in which cells consume O2 and produce CO2

A

cellular respiration

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3
Q

3 major stages of cellular respiration

A
  1. acetyl coA production
  2. acetyl coA oxidation
  3. electron transfer and oxidative phosphorylation
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4
Q

What molecule is required for the first step in the CAC?

A

acetyl coA

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5
Q

These types of molecules are not a permanent part of an enzyme’s structure, rather, they associate, fulfill a function and dissociate

A

Coenzymes aka cofactors

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6
Q

Advantages of multienzyme complexes

A
  • the short distance between catalytic sites allows the channeling of substrates from one catalytic site to another
  • this channeling minimizes side reactions
  • the regulation of activity of one subunit effects the entire complex
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7
Q

What is substrate channeling?

A

The passage of intermediates from one enzyme directly to another enzyme without release (no exposure to solvent)

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8
Q

Where do oxidative reactions occur in the cell?

A

In the mitochondria which contains all the enzymes, coenzyme and proteins needed to carry out oxidation

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9
Q

Citrate formed from acetyl-coA and oxaloacetate is oxidized to yield …?

A

CO2
NADH
FADH2
GTP or ATP

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10
Q

What step is the rate-limiting step of the CAC

A

Step one - citrate synthesis- acetyl coA and oxaloacetate to citrate. It is highly thermodynamically favorable - irreversible

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11
Q

What is the end goal of citrate synthesis?

A

to fully oxidize both carbons in citrate that came from pyruvate to CO2 and generate ATP and electrons (NADH and FADH2) to be used in oxidative phosphorylation

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12
Q

What are the two regulatory proteins in the PDH complex?

A

protein kinase
phosphoprotein phosphate

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13
Q

Pyruvate is oxidized into what by the PDH?

A

pyruvate gets oxidized into acetyl coA and CO2

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14
Q

where does CAC occur

A

mitochondrial matrix

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15
Q

What step in the CAC is a substrate-level phosphorylation

A

step 5. the conversion of succinyl coA to succinate, produces GTP

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16
Q

What step does the first oxidative decarboxylation occur?

A

Step 3. The redox reaction of isocitrate to alpha-ketoglutarate

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17
Q

Which enzyme in the CAC is directly associated with the ETC?

A

succinate dehydrogenase

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18
Q

What products of the CAC are fed into the ETC for the generation of ATP?

A

FADH and NADH

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19
Q

What is the coenzyme of E1 in PDH complex?

A

TPP (thiamine pyrophosphate)

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20
Q

What is the coenzyme of E2 in the PDH complex?

A

lipollysine

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21
Q

What is the coenzyme of E3 in the PDH complex?

A

FAD

22
Q

What two products are produced in the PDH complex?

A

acetyl coA and NADH

23
Q

What steps are regulation points in the CAC?

A

PDH, citrate synthase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase

  • regulated at highly thermodynamically favorable and irreversible steps
24
Q

What is the purpose of converting citrate to isocitrate?

A

citrate (tertiary alc) is a poor substrate for oxidation but isocitrate (secondary alc) is a good substrate for oxidation

25
Q

What enzyme converts pyruvate to acetyl coA

A

Pyruvate dehydrogenase complex

26
Q

what enzyme converts acetylcoA and oxaloacetate to citrate

A

citrate synthase

27
Q

what enzyme converts citrate to isocitrate

A

aconitase

28
Q

what enzyme converts isocitrate to alpha-ketoglutarate

A

isocitrate dehydrogenase

29
Q

what enzyme converts alpha-ketoglutarate to succinyl coA?

A

alpha-ketoglutarate dehydrogenase

30
Q

what enzyme converts succinyl coA to succinate

A

succinyl coA synthetase

31
Q

what enzyme converts succinate to fumarate

A

succinate dehydrogenase

32
Q

what enzyme converts fumarate to malate

A

fumarase

33
Q

what enzyme converts malate to oxaloacetate?

A

malate dehydrogenase

34
Q

what is the purpose of converting alpha-ketoglutarate into succinyl-coA?

A

alpha-ketoglutarate lacks an alcohol for oxidation so a thioester is formed on coA that can be oxidized

35
Q

All CO2 generated during the CAC is produced before _______ is made

A

succinyl-coA

36
Q

What does it mean that citrate is “pro-chiral”

A

it is not chiral but has the potential to react to generate a chiral species

can also react “stereospecifically” even though it is achiral

37
Q

What is the purpose of converting succinyl coA to succinate?

A

This reaction produced GTP and creates succinate

38
Q

What kinase converts GTP to ATP reversibly

A

Nucleoside Diphosphate kinase

39
Q

What is the purpose of converting succinate to fumarate

A

succinate needs to be oxidized to an alkene (fumarate) since an alkene is needed to form malate in the correct stereochemistry in the next step

40
Q

What molecule is a potent, competitive inhibitor of succinate dehydrogenase that blocks the CAC when added to mitochondria

A

Malonate, an analog of succinate

41
Q

what is the purpose of converting fumarate to L-malate?

A

adding water across the pi bond of the alkene allows for oxidation to a ketone in the next step
**addition of water is always ANTI and forms L-malate

42
Q

Fumarate must be (cis/trans)? in order to be recognized by fumarase

A

fumarate must be in the TRANS configuration

43
Q

What is the purpose of converting malate to oxaloacetate?

A

the oxidation regenerates oxaloacetate for citrate synthase

44
Q

What are anaplerotic reactions?

A

chemical reactions that replenish intermediates

45
Q

What is the most important anaplerotic reaction in mammalian liver, kidney and brown adipose tissue?

A

pyruvate carboxylase catalyzes the carboxylation of pyruvate by HCO3

46
Q

Explain the induced fit of citrate synthase

A

two conformations
conformational change occurs once oxaloacetate binds

open conformation: no binding site for acetyl-coA
closed conformation: binding of oxaloacetate creates a binding site for acetyl coA

47
Q

What two molecules contain high-energy thioester bonds?

A

acetyl-coA and succinyl-coA

48
Q

What coenzymes are used in all oxidative decarboxylation?

A

NAD+ and coA

49
Q

What are the overall products of the CAC pathway?

A

NADH and ATP

50
Q

How is the PDH complex regulated?

A

By phosphorylation of E1 and [ATP]

when E1 is phosphorylated it is INactive
when E1 is Dephosphorylated it is Active

High [ATP] –> PDH phosphorylated (inactive) –> less acetyl coA

Low [ATP] –> PDH DEphosphorylated (active) –> more acetyl-coA

Biochemistry (10 decks)

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