Metabolism 5 - Mitochondria & Oxidative Phosphorylation Flashcards

1
Q

Where do the reactions of oxidative phosphorylation take place?

A

The inner mitochondrial inner membrane.

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2
Q

Discuss the possible origins of mitochondria.

A

Mitochondria are believed to be the evolutionary descendants of prokaryotes following an endosymbiotic relationship with the ancestors of the eukaryotic cells.

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3
Q

What is the supporting evidence for the endosymbiotic theory?

A
  • Mitochondria only arise from preexisting mitochondria
  • Mitochondria have their own genome in the same form as prokaryotes (a single circular molecule of DNA)
  • Mitochondria can synthesise proteins
  • The start amino acid in mitochondria is formylated methionine residue (fMet) like with bacteria
  • Antibiotics that block protein synthesis of bacteria also block protein synthesis of mitochondria
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4
Q

What are the two steps of oxidative phosphorylation?

A
  • The translocation of proteins from the mitochondrial matrix to the intermembrane space. This is controlled by the electron transport chain
  • Protons diffuse down their gradient through ATP synthase, making ATP.
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5
Q

What are the enzymes and carriers in the electron transport chain?

A

Enzymes- NADH dehydrogenase complex, cytochrome b-c1 complex, cytochrome oxidase complex
Cofactors- ubiquinone and cytochrome C

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6
Q

Why are electrons important in the ETC?

A

The electron acceptors accept electrons from NADH and FADH2 alongside H+. As the electrons lose energy travelling between the electron acceptors, protons are pumped across the membrane.

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7
Q

Why are the carriers important in oxidative phosphorylation?

A

Ubiquinone transports electrons between NADH dehydrogenase and cytochrome b c1 complex. Cytochrome C then takes the electrons to cytochrome oxidase complex. Cytochrome C has a higher affinity for electrons than ubiquinone, so the reactions are directional

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8
Q

Describe the structure of ATP synthase.

A

ATP synthase is multimeric (made of many subunits). F0 is membrane bound, while F1 is the part that projects into the matrix space.

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9
Q

How does ATP synthase work?

A
  • The enzyme rotates as protons move down rheir concentration gradient. If protons move into the matrix ATP synthesis occurs, if they move from the matrix ATP hydrolysis occurs.
  • The conformational energy of the ATP synthase changes, which promotes the formation or hydrolysis of ATP.
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10
Q

How does succinate dehydrogenase affect ATP production and why?

A

1 less molecule of ATP is made, as succinate dehydrogenase communicates directly with ubiquinone, so one less proton is pumped into the intermembrane space.

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11
Q

How does donation of electrons by FADH2 affect ATP production? When does this occur?

A

FADH2 species result in one less ATP molecule being made, as seen in the glycerol phosphate shuttle. This is because FADH2 enters the chain at a later stage than NADH.

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12
Q

How do cyanide and azide affect metabolic processes?

A
  • They bind with high affinity to the ferric form of the haem group in cytochrome oxidase
  • This blocks electron flow and consequently ATP production
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13
Q

How does malonate inhibit metabolism?

A
  • Malonate resembles succinate and acts as a competitive inhibitor of succinate dehydrogenase.
  • This slows the flow of electrons from succinate to ubiquinone ny inhibiting oxidation of succinate to fumarate
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14
Q

How does rotenone affect the rate of metabolic reactions?

A
  • It is an isoflavone

- Inhibits transfer of electrons from complex 1 to ubiquinone

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15
Q

How does ogliomycin affect metabolic processes?

A
  • An antibiotic that inhibits oxidative phosphorylation by binding to ATP synthase
  • Blocks flow of protons through the enzyme
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16
Q

How does dinitrophenol affect metabolic reactions?

A

It is a proton ionophore which shuttles protons across rhe inner mitochondrial membranes.

17
Q

How does non-shivering thermogenesis occur?

A

In hinernating animals and newborn humans.

  • Regulated uncoupling of oxidative phosphorylation occurs in the brown adipose tissue
  • This occurs by UCP-1, activated by liberation of free fatty acids and triacylglycerols.
  • Heat is released from the dissipation of the proton gradient
18
Q

What are the uses of DNP, in the past and present?

A
  • DNP induces weight loss by transporting protons across the membrane, increasing the metabolic rate and body temperature.
  • DNP was used to treat obesity, though it can also result in death.
  • DNP is now used in pesticides