Citric Acid Cycle

Question 1

How the three stages in glucose metabolism – glycolysis, citric acid cycle, oxidative phosphorylatin - are connected

Answer 1

1. Glycolysis is the first step - ends in pyruvate
2. Followed by the citric acid cycle - Acetyl-CoA enters
3. then Oxidative phosphorylation - uses e- from reduced NADH and FADH2 to produce ATP

Question 2

Where glycolysis takes place

Answer 2

in the cytoplasm, outside the outer membrane of the mitochondrion

Question 3

Structure and properties of the membranes in the mitochondrion

Answer 3

• a mitochondrion has two bilayer membranes - an outer and an inner membrane
• the outer is quite porous and there is easy equilibration of material from the cytoplasm across this membrane to the inter membrane space
• the inner membrane is completely closed and transporters are needed for movement of molecules.

Question 4

Where the citric acid cycle takes place

Answer 4

inside the inner membrane of the mitochondria; the reduced e- carriers (NADH, FADH2) will accumulate inside the inner membrane

Question 5

Overall ATP , NADH and QH2 production in glycolysis and citric acid cycle

Answer 5

Glycolysis - 2 ATP, 2 NADH
Bridge Step, 2 from pyruvate to Acetyl CoA
Citric Acid Cycle - 2 ATP, 6 NADH, 2 QH2

Question 6

Inhibitors and activators of Krebs

Answer 6

• inhibitors are energy rich by law of mass action. Other inhibitors are not participants in the reaction and must act as allosteric effectors.
• activators are associated with energy-poor state and they are activators because they are substrates or work through allosteric effects.

Question 7

anaplerotic reaction

Answer 7

• reactions that replenish the metabolites in the citric acid cycle
• a main anaplerotic reaction is the replenishment of oxaloacetate

Question 8

oxaloacetate transport

Answer 8

• a way to get oxaloacetate to leave the mitochondrial matrix and get into the cytoplasm so it can be a substrate for gluconeogenesis
• converts oxaloacetate to phosphoenolpyruvate through PEPCK
• inefficient to transport oxaloacetate directly because its concentration in the mitochondria is very low compared to its concentration in the cytoplasm

Question 9

citrate transport

Answer 9

• export of acetyl-CoA
• no transport system, but convert to citrate and export
• citrate converted to oxaloacetate and acetyl-CoA in the cytoplasm