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Metabolism > Electron Transport Chain > Flashcards

Electron Transport Chain Flashcards

1
Q

What is the site of oxidative phosphorylation?

A
  • Electron transport chain in the mitochondria
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2
Q

What is oxidative phosphorylation?

A
  • Mechanism by which most cellular ATP is generated
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3
Q

Describe the structural components of ATP

A
  • Matrix
  • Cristae
  • Inner membrane
  • Intermembrane space
  • Outer membrane
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4
Q

What is the use of NADH in the electron transport chain?

A
    • Energy produced by the oxidation of NADH is used by ETC to pump protons into the inter-membrane space of mitochondria
  • Electrochemical gradient
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5
Q

What happens when protons released by NADH re-enter the mitochondrial matrix?

A
  • Produce energy

- Used to produce ATP by oxidative phosphorylation

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6
Q

What is actually pumping protons into the inter-membrane space?

A
  • Protein complexes

- Creates EC gradient

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7
Q

How does NADH produced in the cytosol during carbohydrate metabolism cross the inner mitochondrial membrane?

A
  • Glycerol phosphate shuttle
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8
Q

What happens in the glycerol phosphate shuttle?

A
  • Enzyme cytosolic glycerol-3-phosphate dehydrogenase
  • Oxidises NADH to NAD and passes electrons to FAD
  • Results in reaction: cycle of glycerol 3-phosphate dihydroxyacetone
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9
Q

What happens to the electrons in FADH after the glycerol phosphate shuttle?

A
  • Transferred to Q and Complex III of the ETC
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10
Q

What carries protons and electrons from various sources to ETC?

A
  • NADH and FADH2
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11
Q

Describe how the electrochemical gradient leads to ATP production

A
  • Accumulation of protons follow EC gradient back across membrane through ATP synthase complex
  • High to low conc in order to equilibrate
  • H+ passes through ATP synthase
  • Provides energy for this molecule to produce ATP from ADP + Pi
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12
Q

What is the final electron acceptor?

A
  • Oxygen

- ‘Aerobic’ respiration

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13
Q

What are the first 3 electron transport chain components?

A
  • Complex I- NADH dehydrogenase
  • Complex II- Succinate dehydrogenase
  • Ubiquinone- Complex Q
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14
Q

Describe what happens at complex I- NADH dehydrogenase

A
  • Accepts electrons from NADH
  • Flavoprotein, containing FMN- electron carrier components
  • Oxidises mitochondrial NADH to NAD+ and transfers electrons through FMN and iron-sulphur (FeS) complexes to ubiquinone (Q)
  • Pumps H+
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15
Q

Describe what happens at complex II-succinate dehydrogenase

A
  • Same enzyme that acts within the TCA cycle

- Flavoprotein that oxidises succinate to fumarate and reduces FAD to FADH2

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16
Q

Describe what happens at ubiquinone- complex Q

A
  • Ubiquitous, mobile, lipid-soluble co-enzyme
  • Accepts one electron - half reduced to semiquinone
  • Accepts 2 electrons- fully reduced to quinone from complexes I and II and then donates electrons to complex III
  • Mobile shuttle
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17
Q

Describe succinate dehydrogenase

A
  • Bound to inner mitochondrial membrane
  • Big, bulky enzyme with many subunits
  • Oxidises succinate to fumarate (and passes electrons to FAD) as part of TCA cycle and passes these electrons to ubiquinone in mitochondrial electron transport chain
18
Q

What are the next 4 ETC components (Complex III onwards)?

A
  • Complex III- cytochrome 3 reductase
  • Cytochrome C
  • Complex IV- cytochrome C oxidase
  • Complex V- ATP synthase
19
Q

What happens at complex III- cytochrome C reductase?

A
  • Reduces cytochrome C and oxidises quinone and takes electrons from ubiquinone
  • Electrons are transferred through cytochrome b to an FeS centre then cytochrome C
  • And then to cytochrome C
  • Pumps H+ ions
20
Q

What happens at cytochrome C?

A
  • Small haem protein which shuttles electrons one at a time from complex III to complex IV
21
Q

What happens at complex IV- cytochrome C oxidase?

A
  • Haem-containng dimer which pumps H+ ions to inter membrane space
  • Oxidises cytochrome C and conducts electrons through cytochrome a and a3
  • Finally reducing oxygen to water
22
Q

What do iron and copper ions facilitate in the ETC?

A
  • Collection and transfer of 4 electrons

- Reduction of oxygen

23
Q

What is the reaction that occurs at cytochrome c that produces water?

A

4 e from cytochrome C +4 H+ + oxygen –> 4 cytochrome C (now oxidised) +2 H2O

24
Q

Describe the structure of complex V ATP synthase

A
  • Comprises of a motor (F0) embedded in the inner membrane

- And a generator (F1) which extends into the matrix

25
Q

How efficient if ATP synthase?

A
  • Almost 100%

Makes around 100 ATP molecules per second

26
Q

What are the three different states of ATP synthase?

A
  • 1st state binds ADP and Pi
  • 2nd state synthesised ATP
  • 3rd state releases ATP- requires most of proton metic energy
  • One complete turn produces 3 ATPs
27
Q

Describe respiratory control involving ATP synthase

A
  • ADP taken up by mitochondria, ATP synthase stimulated to covert it to ATP
  • Acts as signal that a lot energy has been used ip
  • Lowers proton gradient and so respiration increases to re-establish proton gradient
  • Oxygen uptake declines when conc. of ADP depleted and ATP synthase terminated
28
Q

What are uncouplers?

A
  • Hydrophobic compounds which can accept protons from the inertmembrane space and then diffuse back into the mitochondrial matrix
29
Q

What is the consequence of uncouplers?

A
  • Avoid those protons having to go through ATP synthase
  • Make inner membrane leaky
  • Diminish H+ gradient
  • Stimulate respiration as system attempts to restore proton gradient through fuel oxidation
30
Q

What happens if a gradient cannot be re-established due to continued uncoupling?

A
  • Metabolic energy is wasted as heat
31
Q

What is dinitrophenol and how does it inhibit oxidative phosphorylation?

A
  • Uncoupler seen to lead to weight loss for munitions making dynamite
  • Massive side effects
  • Cataracts, blindness, kidney and liver damage and death
  • Cells die due to excess heat and lack of ATP
  • Sold illegally as a weight loss pill- used legally in herbicides and insecticides
32
Q

What is rotenone and how does it inhibit oxidative metabolism?

A
  • Common insecticide inhibiting complex I- inhibits oxidation of NADH
33
Q

What is antimycin and how does it inhibit oxidative metabolism?

A
  • piscicide inhibits the transfer of electrons to Complex III
34
Q

How do cyanide and carbon monoxide inhibit oxidative metabolism?

A
  • Inhibit complex IV by blocking access of oxygen to cyt-a3
35
Q

What is oligomycin and how does it inhibit oxidative metabolism?

A
  • Macrolide produced by streptomyces
  • Inhibits ATP synthase by blocking its proton channel
  • Oxidative phosphorylation of ADP to ATP cannot occur
36
Q

Give examples of some inhibitors of oxidative metabolism

A
  • Dinitrophenol
  • Ronetone
  • Antimycin
  • Cyanide and CO
  • Oligomycin
37
Q

How many subunits in oxidative phosphorylation are coded for by mtDNA?

A

13

38
Q

Give examples of oxidative phosphorylation diseases caused by mutations in mtDNA

A
  • LHON (Leber hereditary optic neuropathy) mutation in NADH dehydrogenase
  • Leigh disease (subacute necrotising encephalopathy) mutation in F0 subunits of F0F1-ATPase
39
Q

What is the consequence of a magnesium deficiency in oxidative phosphorylation?

A
  • ATP readily forms a complex with Mg ion (stabilises it when not used)
  • Complex required in all reactions in all reactions requiring ATP
  • Deficiency impairs all metabolism because ATP can neither made or used
40
Q

What is the consequence of an iron deficiency in oxidative phosphorylation?

A
  • Part of iron-sulphur complexes as well as oxygen transport haem systems
41
Q

What is the consequence of riboflavin dietary deficiency?

A
  • Both FMN and FAD contain it

- Can seriously impair function of these and other flavoproteins

42
Q

What is the consequence of a copper deficiency?

A
  • Rare in adult but premature infants have low stores
  • Impair ATP production by inhibiting terminal ETC reaction
  • Leads to pathology of heart where ATP demand is high
  • Therefore, dietary preparations for premature babies contain copper

Metabolism (9 decks)

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