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Biochem II > Aerobic Catabolism > Flashcards

Aerobic Catabolism Flashcards

1
Q

Where does aerobic catabolism take place?

A

mitochondria

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2
Q

How does pyruvate become acetyl-coA?

A

-catalyzed by the pyruvate dehydrogenase complex, in the mitochondria
-large, highly regulated multi-enzyme complex
-OXIDATIVE DECARBOXYLATION

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3
Q

What are the 3 subunits of the PDH complex?

A

E1- pyruvate dehydrogenase
E2- dihydrolipoyl transacetylase
E3- dihydrolipoyl dehydrogenase

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4
Q

How is acetyl co-A oxidized? GENERAL

A

-requires oxygen
-releases acetyl carbons as CO2
-generates lots of ATP

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5
Q

What are the two phases of oxidation of acetyl-CoA?

A

-Krebs cycle: releases CO2 and passes electrons to NAD+ and FAD to generate NADH and FADH2
-Electron transfer and oxidative phosphorylation: passes electrons from NADH and FADH2 to oxygen, uses energy to generate ATP

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6
Q

What is the function of the Krebs cycle in aerobic respiration?

A

-oxidation of the acetyl group of acetyl-CoA
-the acetyl group of acetyl-CoA is oxidized to CO2
– results in reduction of NAD+ to NADH and FAD to FADH2
–these are fed into the electron transfer chain provide energy for ATP synthesis

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7
Q

How is acetyl-CoA made?

A

-low concentration
-produced from:
–carbohydrate degradation via glucose and glycolysis (plus PDH reaction)
–triglyceride degradation via fatty acids and B-oxidation
–protein degradation (some amino acids)

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8
Q

What are the 8 steps of glycolysis? GENERAL

A
  1. Citrate synthase
  2. Aconitase
  3. Isocitrate dehydrogenase
  4. a-ketoglutarate dehydrogenase complex
  5. succinyl-CoA synthetase
  6. Succinate dehydrogenase
  7. Fumarase
  8. Malate dehydrogenase
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9
Q

What type of pathway is the Krebs cycle?

A

Amphibolic, involved In both catabolic and anabolic pathways:
Catabolic- aerobic respiration
Anabolic- intermediates for fatty acid and amino acid synthesis, gluconeogensis

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10
Q

What is a competitive inhibitor of succinate dehydrogenase?

A

malonate

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11
Q

What is gifblaar?

A

-South African plant contains fluroracetate, which can be metabolized to flurocitrate in the mitochondria
-potent competitive inhibitor of aconite

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12
Q

Give an overview of acetyl-CoA oxidation.

A

-electrons from reduced co-enzymes are passed through the electron transfer chain
-each passes electrons to the next member of the chain, which becomes reduced as the donor becomes oxidized
-the energy released is used to pump protons across the inner membrane
-the proton gradient drives ATP synthesis
-source of reduced co-enzymes mostly Krebs, some from cytoplasm

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13
Q

Where does oxidative phosphorylation occur?

A

mitochondria

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14
Q

What are the key points of the mitochondria?

A

-outer membrane freely permeable to small molecules
-inner membrane permeable
-Krebs cycle occurs in the matrix (except step 6)
-electron transfer and oxidative phosphorylation in the inner membrane

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15
Q

What are the two phases of oxidative phosphorylation?

A

-electron transfer reactions
– electrons passed from NADH and FADH2 to oxygen- generates a proton gradient
-proton gradient used to drive ATP synthesis

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16
Q

How do electron transfer reactions in the Mitochondria occur?

A

-electrons are funneled to universal electron acceptors (NAD+->NADH etc.)
-electrons pass through a series of membrane-bound electron carriers
-oxygen is the final electron acceptor

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17
Q

What are the 3 electron acceptors in the electron transfer chain?

A

-Ubiquinone (coenzyme Q/Q)
-Cytochromes
-Iron-sulfur proteins

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18
Q

Explain ubiquinone.

A

-hydrophobic, stays buried in the mitochondrial membrane
-accepts one e- at a time

19
Q

Explain cytochromes.

A

Three types in mitochondria:
-A
-B
-C
tightly or covalently bound heme group (prosthetic group)

20
Q

What is a heme?

A

-contain porphyrin ring
–4 5-carbon rings, containing nitrogen with a central Fe atom to accept and give up electrons

21
Q

Explain Iron-sulfur proteins.

A

-contain iron as iron-sulfur centers
-various arrangements of cys-S, inorganic S, and Fe

22
Q

What is the order of electron carriers?

A

NADH
Q
Cyt b
Cyt C1
Cyt C
Cyt A
Cyt A3
O2

23
Q

What are electron carrier inhibitors?

A

Rotenone: backs up at Q
Antimycin A: backs up at Cyt C1
CN- or CO: backs up at O2

24
Q

What are the carriers function in multienzyme complexes? (4 complexes)

A

1: NADH to Q
2: Succinate to Q
3: Q to Cyt C
4: Cyt C to O2

25
Q

Explain complex 1:

A

-also known as NADH dehydrogenase
-at least 43 polypeptides
-contains FMN and at least 6 iron-sulfur centers
-pumps 4 protons from matrix to the inter membrane space

26
Q

Explain complex II:

A

-succinate dehydrogenase (krebs enzyme)
-located in inner mitochondrial membrane (all others in matrix)
-four subunits, 5 prosthetic groups
-electrons passed to Q from QH2
-no protons pumped

27
Q

Explain complex 3.

A

-transfer of electrons from QH2 to cytochrome c
-transports protons from the matrix to the intermembrane space
-four protons transported for every two electrons transferred to cyt c
-involves a dimer of complex III

28
Q

Explain complex 4.

A

-carries electrons from cyt c to final electron acceptor, O2
-large complex of 13 subunits containing prosthetic groups, heme, iron-sulfur centers and copper
-pumps out 4 protons (two per electron pair)

29
Q

How many protons are pumped total through complexes?

A

for each electron pair, 10 protons are pumped

30
Q

How are ROS generated during oxidative phosphorylation?

A

-Reactive oxygen species
-passage of electrons from complex I to QH2, and from QH2 to complex III involve generation of ubismiquinone, this can pass an electron to O2
-creates a superoxide free radical- very reactive

31
Q

How is oxidative damage prevented from O2?

A

-superoxide dismutase:
peroxidases, remember GSH is kept in reduced state by glutathione reducaste, using NADPH from pentose phosphate pathway

32
Q

How is glutathione maintain in the reduced state?

A

NADPH from the pentose phosphate pathway

33
Q

What is the chemisomotic model of ATP synthesis?

A

mechanism of electron transfer being coupled to ATP synthesis
-How a concentration gradient of protons is transformed into ATP

34
Q

What is the basis of ATP synthesis?

A

-intact mitochondria needed
-electron transfer inhibited by inhibitors of ATP synthase
-Treatment with detergent uncouples
-Dinitrophenol uncouples

35
Q

How are electron transfer and ATP synthesis tightly coupled?

A

O2 consumption and ATP synthesis:
-only in presence of substrate
-inhibited when electron transfer inhibited

36
Q

How can electron transfer and ATP synthesis be uncoupled?

A

DNP
-dissipates proton gradient by carrying protons across the inner membrane
-allows electron transfer without ATP synthesis
-energy dissipated as heat

37
Q

What are the two functional domains of ATP synthase?

A

F0
F1
combined to perform rotational catalysis

38
Q

What are the 3 conformations of ATP synthase?

A

Open (O) low affinity
Loose-binding (L)
Tight-binding (T)
interconversions driven by rotation

39
Q

Explain ATP synthesis.

A

-ADP and Pi bind to an L site
-rotation converts L to T conformation; ATP synthesized
-further rotation converts T to conformation of O, releasing ATP
-cycle repeats

40
Q

What are ADP-ATP and phosphate translocators?

A

-for every 4 protons, one used for Pi transport, 3 for ATP synthesis
-ADP-ATP translocator drive by potential difference

41
Q

What is the P/O ratio?

A

-moles of phosphate consumed per mole of oxygen atoms consumed
-max measured: 2.5 for NADH, 1.5 for FADH2
–2.5 molecules of ATP per NADH, 1.5 molecules of ATP per FADH2

42
Q

How much ATP is produced from each acetyl-coA?

A

-3 molecules of NADH
-1 molecule of FADH2
-1 molecule of ATP
TOTAL: approximately 10 molecules of ATP for each acetyl coA

43
Q

At what age is most brown adipose tissue found? How can it be increased? What protein uncouples it?

A

newborns
cold temperatures
UCP1

Biochem II (22 decks)

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