Lectures 10 & 11: Electron Transport Chain and Oxidative Phosphorylation

Question 1

What is the cellular location where ETC and Oxidative Phosphorylation take place?

Answer 1

• occurs along inner mitochondrial membrane.
• H+ pumped from matrix to IMS
• This sets up a proton and electrical gradient (proton motive force)

Question 2

What is the process of transferring electron along the ETC?

Answer 2

-delta G is associated with movement from one carrier to another
-donors with low affinity—> acceptors with high affinity
~gains electrons of higher reduction potential.

Question 3

Relation of E and G:

Answer 3

E = E(acceptor) - E(donor)
G = -nFE

Question 4

Name the 5 electron carriers of ETC:

Answer 4

1. Dehydrogenase enzymes:
   
   • NADP+ obligatory 2e- hydride transfer.
2. Flavoproteins:
   
   • Transfer 1 or 2 e- at a time.
3. Coenzyme Q:
   
   • Transfer 1 or 2 electrons
4. Cytochrome C:
   
   • ONLY 1 e- at a time.
5. Fe-S protein:
   
   • ONLY 1 e- at a time.

Question 5

What is the purpose of ETC?

Answer 5

-Proton and electrical gradient drives synthesis of ATP.

Question 6

Explain the chemiosmotic model:

Answer 6

• H+ cant pass through inner membrane; only able to fross via F0 component of ATP synthase.
• F0 allows protons to flow downhill back into matrix.
• F1 synthesizes ATP

Question 7

Describe the mechanism of ATP synthesis:

Answer 7

The c subunit has a negatively charged residue (Asp or Glu) that binds protons (upon entry from proton gradient created in IMS) through the half channel. Once protonated, it becomes neutral and can no longer associate with the positive Arg on the adjacent stationary a subunit. So, the Arg reaches for the next unprotonated Asp or Glu on the c subunit and forms a salr bridge. Then the residue gets protonated again and the process repeats.

Question 8

Inhibitor and Uncoupler of ATP synthesis:

Answer 8

• Inhibitor: affect both electron transport and ATP synthesis
  ~ CN- inhibits electron transport from cyt c to O2
  ~Oligomycin inhibits F0 of ATP synthase (H+ cant flow)
• Uncoupler: allow electron transport, but inhibit ATP synthesis
  ~DNP (dinitrophenol)
  ~Adds to membranes and allows H+ to cross membrane, so gradient dissipates.
  ~ No gradient = no synthesis.

Question 9

Effects of other molecules on ATP synthase:

Answer 9

1. Metformin:
   
   • glucophage targets complex I
   • decrease NADH oxidation.
   • decrease H+ gradient —> decrease ATP production
2. Thermogenin:
   
   • Inserts into inner membrane
   • Allows H+ to cross membrane back to matrix.
   • No gradient = no ATP synthesis

Question 10

Name two other translocases involved in ATP synthase:

Answer 10

1. Adenin nucleotide translocase:
   
   • Antiports ATP (out) for ADP (in)
   • Favored by electrical gradient (net-1 exported)
2. Inorganic phosphate translocase:
   
   • symports Pi into matrix with H+
   • favored by proton gradient.

Question 11

Describe the 2 shuttle systems

Answer 11

1. Glycerol 3-phosphate:
   
   • occurs in muscle
   • G3P and DHAP cross outer membrane
   • carries cytosolic NADH electrons intro matrix
   • electrons enter ETC via FAD (skip complex I for 1.5 ATP)
2. Malate-Aspartate Shuttle:
   
   • More efficient then G3P
   • Kidney, Liver, heart of mammals.
   • Malate crosses inner mitochondrial membrane (OAA cannot)
   • Carries cytosolic NADH into matrix.
   • enters complex I for 2.5 ATP

Question 12

How is ATP producing pathways regulated?

Answer 12

-Ratio of ATP to ADP regulates PFK-1 (gkycolysis), PDC, and TCA cycle; in addition to respiration/OxPhos.