TCA cycle and ETC

Question 1

Acetyl-CoA formation

Answer 1

• Occurs under aerobic conditions
• irreversible step

2 pyruvate from glycolysis are transported into the mitochondria and converted into acetyl-CoA by pyruvate dehydrogenase

Question 2

TCA cycle starting point and products

Answer 2

2 pyruvate–> acetyl-CoA

acetyl-CoA (2C) +oxaloacetate (4C) –> citrate (6C)

Makes 3NADH, 1FADH2, 1GTP, 3CO2 (2 CO2 make in TCA, 1 CO2 made when pyruvate becomes acetyl-CoA) x2 because 2 acetyl-CoA is made for every 1 pyruvate

Question 3

Why does H+ fluctuate in after TCA cycle?

Answer 3

CO2 increases, shifts equilibrium to the right, increasing H+ and decreasing the blood pH

Question 4

NADH and FADH2

Answer 4

• Energy rich molecules (electron carriers)
• synthesized from micronutrients
• each carry 2e-

Question 5

General steps of the ETC

Answer 5

1. NADH and FADH2 are fed into the ETC
2. NADH is oxidized in complex I to make 2e and 1 H+ (making energy to move H+ out of cell).
   FADH2 is oxidized in complex II making 2e- and 1 H+ (H+ is not pumped out of cell) . e- are passed through Fe-S clusters to produce energy
3. e- from NADH transported by coenzyme Q; e- from FADH2 transported by coenzyme C. As they move, H+ will be pumped through complex III and complex IV.
4. e- at end of complex IV will be paired with oxygen and H+ inside matrix to form H2O.
5. Electrochemical gradient drives H+ back inside mitochondria through ATP synthase creating ATP

Question 6

NADH and FADH2 oxidized and reduced forms

Answer 6

Oxidized: NAD+ and FAD
Reduced: NADH and FADH2

Question 7

How many ATP are produced per NADH and FADH2?

Answer 7

NADH: 1e- = 3H+ total= 3ATP (because pumped through 3 complexes)

FADH2: 1e- = 2H+ = 2ATP (because pumped through 2 complexes)

Question 8

TCA and ETC inhibitors

Answer 8

1. Rotenone
2. Cyanide
3. Fluoroacetate

Question 9

Rotenone

Answer 9

• Interferes with the iron cluster in complex ! of ETC and prevents the transfer of e- to cytochrome Q
• Widely used as a pesticide, insecticide, and piscicide. Used to treat parasitic mites, fleas and ticks
• Toxicity is higher in insects than it is in mammals

Question 10

Cyanide

Answer 10

• Naturally found in pits of fruit
• Binds irreversibly to the iron cluster in complex IV, preventing the final transport of e- to oxygen to form water molecules This stalls the entire ETC as electrons are stuck
• Highly poisonous; the heart and brain are most susceptible due to aerobic respiration

Question 11

Fluoroacetate

Answer 11

• Found naturally in Gastrolobium
• Strongly binds to aconitase, competing with citrate, stalls TCA cycle with citrate accumulation. This inhibits the production of NADH and FADH2 needed for the ETC
• Tasteless, odourless; often used as bait to eradicate invasive wildlife in Australia and New Zealand. Also used as controlled rodenticide in other countries