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USMLE Biochemistry > Electron Transport Chain > Flashcards

Electron Transport Chain Flashcards

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USMLE® Step 1 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
Q

What is complex III also known as?

A

Cytochrome bc1 complex

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26
Q

What are the roles of complex III?

A
  • Transfers electrons CoQ -> cytochrome c

- Pumps H+ to intermembrane space

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27
Q

What does cytochrome C pass the electrons to?

A

Complex 4

28
Q

Where is cytochrome c found?

A

Inner membrane space

29
Q

Where are all the complexes found?

A

On the inner membrane of the mitochondria

30
Q

What are cytochromes made of?

A

Class of proteins:

  • Contain a heme group
  • Iron plus porphyrin ring
31
Q

What is the makeup of the iron in Hgb in comparison with cytochromes?

A
  • Hgb: Mostly Fe2+

- Cytochromes: Fe2+ or Fe3+ (goes back and forth)

32
Q

Why does cytochromes changing between Fe2+ and Fe3+ benefit electron transport?

A

Means oxidation state can change with electron transport (can donate electrons)

33
Q

What are cytochromes a b and c used in?

A

Electron transport

34
Q

What is cytochrome P450 used in?

A

Drug metabolism

35
Q

What are other names for complex IV?

A
  • Cytochrome a + a3

- Cytochrome c oxidase (reacts with O2)

36
Q

What element does complex IV contain?

A

Copper (Cu)

37
Q

What does complex IV do?

A
  • Pumps H+

- Combines electrons that have come at it from the other elements of the ETC with O2 to generate water

38
Q

What are the 2 ways to produce ATP?

A
  • Substrate level phsophoryation (via an enzyme)

- Oxidative phosphorylation

39
Q

Where is the only place where oxidative phosphorylation can occur?

A

Mitochondria

40
Q

What enzyme leaks H+ ions out of the inner membrane space?

A

ATP Synthase

41
Q

How does ATP Synthase create ATP?

A

H+ ions from inner membrane space travel across and are energy rich so can convert ADP to ATP
- Converts proton charge gradient -> ATP

42
Q

What is another name for ATP synthase?

A

Complex 5

43
Q

What is the process by which protons move down the gradient?

A

Chemiosmosis

  • Uses electrochemical gradient
  • Known as a proton motive force
44
Q

What is the P/O ratio?

A

Amount of ATP generated per molecule of O2

45
Q

What is the P/O ratio for NADH and FADH2?

A
  • 2.5 - 3 per NADH

- 1.5 - 2 per FADH2

46
Q

How can the 2NADHs produced from glycolysis produce ATP?

A

Malate shuttle -> 2 NADH (6 ATP)

Glycerol-3-Pi shuttle -> 2 FADH2 (4 ATP)

47
Q

How many ATPs can be produced from GTP?

A

1

48
Q

How may molcules of ATP are roughly made from one molecule of Acetyl-CoA?

A

12 ATP

  • 3 NADH -> 9 ATP
  • 1 FADH2 -> 2 ATP
  • 1 GTP -> 1 ATP
49
Q

How many molecules of ATP are made per glucose?

A

30 / 32 molecules (depending on whether malate or glycerol-3-Pi shuttle is used for the 2 NADH from glycolysis)

50
Q

What are the 2 main ways by which drugs/poisons can disrupt oxidative phsophorylation?

A
  • Block/inhibit electron transport

- Allow H+ to leak out of inner membrane space (‘uncoupling of electron trnasport / oxidative phosphorylation)

51
Q

How does rotenone (insecticide) disrupt the ETC?

A
  • Binds to complex I, preventing electron transfer (reduction) to CoQ
52
Q

How does Antimycin A (antibiotic) disrupt the ETC?

A
  • Binds to complex III (bc1 complex)
53
Q

What 2 substances bind to complex IV?

A
  • Carbon monoxide (binds to a3 in Fe2+ state - competes with O2)
  • Cyanide (bind a3 in Fe3+ state)
54
Q

What does cyanide bind to?

A

Complex IV

  • a3 in Fe3+ state
  • RBCs not affected as not in Fe3+ state mostly
55
Q

What does CO bind to?

A

Complex IV

  • a3 in Fe2+ state
  • Competes with O2
56
Q

What are the symptoms of cyanide poisoning?

A
  • Headaches, confusion
  • Tachycardia, hypertension
  • Tachypnea
  • Bright red venous blood (due to increased O2 content)
  • Almond smell
  • Lactic acidosis (anaerobic metabolism)
57
Q

What substance may cuase cyanide poisoning?

What is it used for?

A

Nitroprusside

  • Treatment of hypertnesive emergencies
  • Toxic levels woth prolonged infusions
  • Contains 5 cyanide groups per molecule
58
Q

How can cyanide / nitroprusside poisoning be treated?

A

Nitrites (amyl nitrite)

59
Q

How do nitrites (amyl nitrite) work?

A
  • Converts Fe2+ -> Fe3+ in Hgb (methemoglobin)

- Fe3+ in Hgb binds cyanide, protect mitochondria

60
Q

What do uncoupling agents do?

A

Pierce the inner membrane, making holes so H+ molecules leak out, meaning they cannot be utilised by ATP synthase

61
Q

What are examples of uncoupling agents (allow H+ to leak out of inner membrane space)?

A
  • 2,4 dinitrophenol (DNP) (weight loss med)
  • Aspirin (overdoes)
  • Brown fat
62
Q

What is a mjor sign of aspirin overdose (uncoupling agents)?

A

Fever

  • Uncoupled oxidative phosphorylation
  • H+ ions leaking out generate heat
63
Q

What substance does brown fat (found in newborns and hibernating animals) contain which gives it uncoupling capabilities?

A

Uncoupling protein 1 (UCP-1, thermoegenin)

64
Q

How does Uncoupling protein 1 (UCP-1, thermoegenin), found in brown fat, work?

A 
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
Q

How can Oligomycin A affect the ETC?

A
  • Inhibits ATP synthase
  • H+ cannot move through enzyme
  • Trapped
  • Oxidative phosphprylation stops
  • ATP not generated
66
Q

What is oligomycin A?

A

Macrolide antiB not used clinically

USMLE Biochemistry (44 decks)

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