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USMLE Biochemistry > Electron Transport Chain > Flashcards

Electron Transport Chain Flashcards

1
Q

What does glycolysis produce?

A
  • 2 ATP
  • Pyruvate
  • 2 NADH
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2
Q

How many molecules of NADH are made from a single Acetyl CoA molecule?

A

3 NADH (from 1 pyruvate)

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3
Q

What is produced from one Acetyl CoA molecule?

A
  • 3x NADH
  • FADH2
  • GTP
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4
Q

How many molecules of NADH are involved in the ETC?

A

8 overall

  • 2 NADH from glycolysis
  • 3 NADH from 1st Acetyl CoA
  • 3 NADH from 2nd Acetyl CoA
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5
Q

How are the 2 molecules of NADH produced from glycolysis transfered into the mitochondria?

A

Malate shuttle
NADH transfers its electrons to OAA to make malate (then becomes NAD+)

Malate crosses mitochndrial membrane then is transfered into OAA (with NAD+ becoming NADH)

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6
Q

What is oxaloacetate converted into which can then allow it to cross the mitochondrial membrane?

A

Aspartate (via Glut -> a-KG)

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7
Q

What is aspartate converted back into in the cytosol after crossing the mitochondrial membrane?

A

OAA (via a-KG -> Glut)

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8
Q

What enzyme converts Dihydroxyacetone phosphate to Glycerol Phosphate (via NADH -> NAD+), donation of electron?

A

Glycerol Phosphate Dehydrogenase

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9
Q

What does the mitochondrial membrane version of Glycerol Phosphate Dehydrogenase do?

A

Converts Glycerol phosphate back into Dihydroxyacetone phosphate

  • FAD -> FADH2
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10
Q

What does membranous Glycerol Phosphate Dehydrogenase produce / convert other than Dihydroxyacetone phosphate?

A

FADH2 (from FAD)

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11
Q

What is the disadvantage of the glycerol phosphate shuttle in comparison with the malate shuttle?

A

FADH2 (glycerol phosphate shuttle) cannot produce as many ATPs as NADH (which is produced from malate shuttle)

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12
Q

How does ETC generate energy?

A

Throigh extracting electrons from NADH and FADH2 to oxygen and in the process then generating energy (and water)

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13
Q

What is complex I also known as?

A

NADH Dehydrogenase

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14
Q

What does NADH dehydrogenase (complex I) do?

A
  • Oxidises NADH (NADH -> NAD+)

- Transfers electrons (from NADH) to coenzyme Q (ubiquinone)

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15
Q

What is coenzyme Q also known as?

A

ubiquinone

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16
Q

What does CoQ shuttle electrons to?

A

Complex III

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17
Q

Where are the Electron transport complexes found?

A

On the inner membrane of the mitochondria

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18
Q

What is pumped into the inner membrane space by complex I?

A

H+ (later used to produce ATP)

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19
Q

What are CoQ10 supplements taken in conjunction with and why?

A

Statins

  • Statins are thought to decrease CoQ levels
  • No good data to support this
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20
Q

What is Complex II also known as?

A

Succinate dehydrogenase (TCA cycle)

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21
Q

How many electron transport complexes are there?

A

4

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22
Q

What are some of the key intermeadites of complex I?

A
  • Flavin mononucleotide

- Iron sulfur compounds (FeS)

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23
Q

What does Complex II (Succinate dehydrogenase) transfer electrons to?

A

From Succinate (becomes fumarate)

  • To FADH2
  • Then to CoQ
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24
Q

What does succinate become as a result of complex II?

A

Fumarate

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25
What is complex III also known as?
Cytochrome bc1 complex
26
What are the roles of complex III?
- Transfers electrons CoQ -> cytochrome c | - Pumps H+ to intermembrane space
27
What does cytochrome C pass the electrons to?
Complex 4
28
Where is cytochrome c found?
Inner membrane space
29
Where are all the complexes found?
On the inner membrane of the mitochondria
30
What are cytochromes made of?
Class of proteins: - Contain a heme group - Iron plus porphyrin ring
31
What is the makeup of the iron in Hgb in comparison with cytochromes?
- Hgb: Mostly Fe2+ | - Cytochromes: Fe2+ or Fe3+ (goes back and forth)
32
Why does cytochromes changing between Fe2+ and Fe3+ benefit electron transport?
Means oxidation state can change with electron transport (can donate electrons)
33
What are cytochromes a b and c used in?
Electron transport
34
What is cytochrome P450 used in?
Drug metabolism
35
What are other names for complex IV?
- Cytochrome a + a3 | - Cytochrome c oxidase (reacts with O2)
36
What element does complex IV contain?
Copper (Cu)
37
What does complex IV do?
- Pumps H+ | - Combines electrons that have come at it from the other elements of the ETC with O2 to generate water
38
What are the 2 ways to produce ATP?
- Substrate level phsophoryation (via an enzyme) | - Oxidative phosphorylation
39
Where is the only place where oxidative phosphorylation can occur?
Mitochondria
40
What enzyme leaks H+ ions out of the inner membrane space?
ATP Synthase
41
How does ATP Synthase create ATP?
H+ ions from inner membrane space travel across and are energy rich so can convert ADP to ATP - Converts proton charge gradient -> ATP
42
What is another name for ATP synthase?
Complex 5
43
What is the process by which protons move down the gradient?
Chemiosmosis - Uses electrochemical gradient - Known as a proton motive force
44
What is the P/O ratio?
Amount of ATP generated per molecule of O2
45
What is the P/O ratio for NADH and FADH2?
- 2.5 - 3 per NADH | - 1.5 - 2 per FADH2
46
How can the 2NADHs produced from glycolysis produce ATP?
Malate shuttle -> 2 NADH (6 ATP) Glycerol-3-Pi shuttle -> 2 FADH2 (4 ATP)
47
How many ATPs can be produced from GTP?
1
48
How may molcules of ATP are roughly made from one molecule of Acetyl-CoA?
12 ATP - 3 NADH -> 9 ATP - 1 FADH2 -> 2 ATP - 1 GTP -> 1 ATP
49
How many molecules of ATP are made per glucose?
30 / 32 molecules (depending on whether malate or glycerol-3-Pi shuttle is used for the 2 NADH from glycolysis)
50
What are the 2 main ways by which drugs/poisons can disrupt oxidative phsophorylation?
- Block/inhibit electron transport | - Allow H+ to leak out of inner membrane space ('uncoupling of electron trnasport / oxidative phosphorylation)
51
How does rotenone (insecticide) disrupt the ETC?
- Binds to complex I, preventing electron transfer (reduction) to CoQ
52
How does Antimycin A (antibiotic) disrupt the ETC?
- Binds to complex III (bc1 complex)
53
What 2 substances bind to complex IV?
- Carbon monoxide (binds to a3 in Fe2+ state - competes with O2) - Cyanide (bind a3 in Fe3+ state)
54
What does cyanide bind to?
Complex IV - a3 in Fe3+ state - RBCs not affected as not in Fe3+ state mostly
55
What does CO bind to?
Complex IV - a3 in Fe2+ state - Competes with O2
56
What are the symptoms of cyanide poisoning?
- Headaches, confusion - Tachycardia, hypertension - Tachypnea - Bright red venous blood (due to increased O2 content) - Almond smell - Lactic acidosis (anaerobic metabolism)
57
What substance may cuase cyanide poisoning? | What is it used for?
Nitroprusside - Treatment of hypertnesive emergencies - Toxic levels woth prolonged infusions - Contains 5 cyanide groups per molecule
58
How can cyanide / nitroprusside poisoning be treated?
Nitrites (amyl nitrite)
59
How do nitrites (amyl nitrite) work?
- Converts Fe2+ -> Fe3+ in Hgb (methemoglobin) | - Fe3+ in Hgb binds cyanide, protect mitochondria
60
What do uncoupling agents do?
Pierce the inner membrane, making holes so H+ molecules leak out, meaning they cannot be utilised by ATP synthase
61
What are examples of uncoupling agents (allow H+ to leak out of inner membrane space)?
- 2,4 dinitrophenol (DNP) (weight loss med) - Aspirin (overdoes) - Brown fat
62
What is a mjor sign of aspirin overdose (uncoupling agents)?
Fever - Uncoupled oxidative phosphorylation - H+ ions leaking out generate heat
63
What substance does brown fat (found in newborns and hibernating animals) contain which gives it uncoupling capabilities?
Uncoupling protein 1 (UCP-1, thermoegenin)
64
How does Uncoupling protein 1 (UCP-1, thermoegenin), found in brown fat, work?
``` Sympathetic stimulation (NE, B receptors) leads to lipolysis, does not generate ATP as: - Electron transport does not work properly, ATP not produced, instead H+ ions released, generating heat ```
65
How can Oligomycin A affect the ETC?
- Inhibits ATP synthase - H+ cannot move through enzyme - Trapped - Oxidative phosphprylation stops - ATP not generated
66
What is oligomycin A?
Macrolide antiB not used clinically

USMLE Biochemistry (44 decks)

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