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Biochemistry > Module 6: V7 - V11 > Flashcards

Module 6: V7 - V11 Flashcards

1
Q

What is the importance of the PDH complex?

A

can be considered as the 1st control point of the Krebs cycle

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2
Q

Why are B group vitamins important?

A

used extensively in metabolism

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3
Q

What is the first reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

A

the formation of citrate from oxaloacetate and acetyl-CoA

the reaction is highly exergonic because it involves the hydrolysis of a thioester

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4
Q

What is the second reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

A

citrate is converted to isocitrate in two-steps (via a cis-aconitate intermediate) catalyzed by aconitase
unfavourable yet driven to the right by the rapid consumption of isocitrate in the cycle

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5
Q

What is the third reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

A

isocitrate is then converted to a-ketoglutarate by isocitrate dehydrogenase producing CO2 + NADH
exergonic + irreversible

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6
Q

What is the fourth reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

A

a-ketoglutarate is converted to succinyl-CoA by the a-ketoglutarate dehydrogenase complex
exergonic + irreversible

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7
Q

What is the fifth reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

A

succinyl-CoA is then converted to succinate by succinyl CoA synthetase
exergonic

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8
Q

What is the sixth reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

A

succinate is converted to fumarate by succinate dehydrogenase which produces FADH2
not exergonic or endergonic, instead = 0

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9
Q

What is the seventh reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

A

fumarate is converted to L-malate via a carbanion intermediate by the enzyme fumarase
exergonic

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10
Q

What is the eighth reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

A

conversion of malate to oxaloacetate by malate dehydrogenase which produces another NADH

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11
Q

How much energy is produced per glucose?

A

2 ATP, 10 NADH (2 cytosolic, 8 mitochondrial), 2 FADH2 and 2 GTP ~ 30-32 ATP in total

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12
Q

Where and how is redox energy (NADH + FADH2) utilised?

A

mitochondria are the sites of oxidative phosphorylation in eukaryotes

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13
Q

What is oxidative phosphorylation?

A

defined as the process of transforming redox energy formed under aerobic conditions during glycolysis and the citric acid cycle into chemical energy in the form of ATP

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14
Q

How does oxidative phosphorylation drive the unfavourable formation of ATP?

A

redox energy is converted to an electrochemical gradient which drives the unfavourable formation of ATP

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15
Q

What is the first step of phosphorylation?

A
  1. transfer of electrons from NADH to complex I and/or from FADH2 to complex II
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16
Q

What is the second step of phosphorylation?

A
  1. flow of electrons through large multi-component inner mitochondrial membrane complexes and mobile electron transporters of the electron transport chain
17
Q

What is the third step of phosphorylation?

A
  1. pumping of protons (H+) from the matrix to the intermembrane space (IMS) using the proton pumps of complex I, III, and IV as electrons flow through these complexes
18
Q

What is the fourth step of phosphorylation?

A
  1. flow of protons (H+) from the IMS through the Fo component of ATP Synthase back into the matrix resulting in the rotation of the Fo component and the ɣ subunit of F1 and the synthesis of ATP from ADP and Pi by the F1 component
19
Q

What creates the proton gradient that is used to drive ATP synthesis?

A

flow of electron through complexes in the inner mitochondrial membrane and the subsequent pumping of protons from the matrix into the intermembrane space (IMS)

20
Q

How many H+ ions are pumped across complex I? How does this occur?

A

4 H+ ions
NADH + H+ donate 2 electrons which results in a series of events that end in the reduction of coenzyme Q (movement of electrons)

21
Q

What is Coenzyme Q?

A

a lipophilic IMS dwelling mobile electron carrier that transfers electrons from complex I and II to complex III

22
Q

What is complex II known as? Is it a H+ pump?

A

also known as succinate dehydrogenase from the TCA cycle

complex II is not a H+ pump (generates ubiquinol)

23
Q

How many H+ ions are pumped across complex III? How does this occur?

A

4 H+ ions
receives ubiquinol from complex I and II
uses the electrons from ubiquinol for proton pump action

24
Q

What is Cytochrome c?

A

a small soluble protein the resides in the IMS that accepts electrons from complex III and donates them to complex IV

25
Q

How many H+ ions are pumped across complex III? How does this occur?

A

4 H+ ions

electrons on cytochrome c generates proton pump action

26
Q

What is the electron transport chain?

A

flow of electrons through complexes in the inner mitochondrial membrane and the subsequent pumping of protons from the matrix into the IMS creates a proton gradient that is used to drive ATP synthesis

27
Q

How does mitochondrial ATP synthase use the H+ gradient?

A

uses H+ gradient to drive the unfavourable synthesis of ATP from ADP + Pi -> ATP synthesis results from the rotational catalysis mechanism

28
Q

What is the structure of ATP synthase?

A

comprised of a Fo (stalk) and F1 (head) component
Fo spans the inner mitochondrial membrane and is comprised of the a, b and c subunit, subunits in mammals
F1 is located on the matrix side of the inner membrane and is comprised of α, β, ɣ, σ, ε subunits

29
Q

How many binding sites does the F1 component have?

A

three nonequivalent adenine nucleotide binding sites, one for each a/B pair
one site is in the B-ATP conformation, which binds ATP tightly, a second is in the B-ADP conformation which binds ADP + Pi and a third is in the B-empty conformation
the proton motive force causes rotation of the γ subunit (green) as H+ is pumped through the Fo component.

30
Q

How many protons are required per ATP?

A

in mammals 8 protons are required to turn the ATP
synthase through one complete cycle (only 8c subunits)
so, estimated ≈4 protons are required synthesize 1 ATP

31
Q

Why much ATP is yielded per NADH and FADH2?

A
  1. 5 ATP per NADH

1. 5 ATP per FADH2

32
Q

Why does FADH2 produce less ATP than NADH?

A

because FADH2 does not pass through complex I

33
Q

Can oxidative phosphorylation occur without the Krebs cycle and vice versa?

A

no, these processes are not able to occur without each other

34
Q

Oxidative phosphorylation seems a lot of effort. Why don’t we just use glycolysis? What is the advantage?

A

oxidative phosphorylation produces a lot more ATP

Biochemistry (30 decks)

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