L23: Acetyl CoA Synthesis and Citric Acid Cycle

Question 1

What is acetyl CoA synthesis also known as?

Answer 1

• Pyruvate processing/oxidation

Question 2

What is the citric aid cycle also known as?

Answer 2

• TCA cycle (tricarboxylic acid cycle)

- Krebs’s cycle

Question 3

What is the result of glycolysis?

Answer 3

• 2 net ATP (high energy intermediates)
• 2 NADH (high energy intermediates - carrying electrons)
• 2 pyruvates (substrates)

Question 4

What is the fate of pyruvate?

Answer 4

• In CR, pyruvate is transported into the mitochondria (via carrier protein) or maybe fermented

Question 5

What are the substrate inputs and outputs for pyruvate processing/acetyl CoA synthesis?

Answer 5

INPUTS:
- pyruvate, coenzyme A (CoA)

OUTPUTS:
- Acetyl CoA, CO2

Question 6

Summarize pyruvate processing

Answer 6

The 3 carbon pyruvate is converted to acetyl CoA by:

• giving up 2 electrons to NAD+ (becomes NADH)
• oxidizing one carbon as CO2 (decarboxylation - released as waste)
• the acetyl group (CH3OC) left has lots of potential energy. It is transferred to CoA to become Acetyl CoA.

Question 7

What do you need to know for the Citric Acid Cycle?

Answer 7

• Acetyl CoA enters the cycle
• Some NADH is made (NAD+ picks up 2 electrons)
• CO2 is released
• ATP or GTP is made
• FADH2 is made (FAD picks up 2 electrons)
• more NADH is made
• all 6 carbons have been released as a waste in the form of CO2
• Oxaloacetate is reformed and recombines w/ acetyl CoA and the cycle is restarted

Question 8

Inputs and outputs of citric acid cycle

Answer 8

INPUTS:
- Acetyl CoA, H2O, NAD+, FAD, ADP (or GDP)

OUTPUTS:
- CO2, H2O, ATP (or GTP), NADH, FADH2

Question 9

What does the cell have (in terms of ATP energy)?

Answer 9

For 1 glucose:

• 2 ATP in glycolysis
• 2 ATP in the citric acid cycle (1 ATP for every turn of the cycle and cycle takes 2 turns)
• total = 4 ATP! this is not a lot for the cell

Question 10

What is the approximate total ATP yield for the citric acid cycle?

Answer 10

• SLP: 2 ATP
• Oxphos: 18 ATP
• Total: 20 ATP

Question 11

Where does oxphos occur?

Answer 11

• inner mitochondrial membrane

Question 12

What is the process of synthesizing ATP called?

Answer 12

• oxidative phosphorylation
• oxygen accepts the electrons and ADP is phosphorylated to ATP
• also known as chemiosmosis
• Ions (H+) are moving through the ATP synthase “down their concentration gradient”

Question 13

What is the electron transport chain (ETC)

Answer 13

• the series of protein complexes and compounds