TCA cycle

Question 1

Where does the TCA cycle occur? Is this process aerobic or anaerobic. What is the end goal?

Answer 1

Occurs in the matrix. This is a part of aerobic respiration.

It is a series of redox reactions that generate 2 CO2, 3 NADH, 1 FADH2, per molecule of acetyl CoA

Question 2

Where is the TCA cycle most active

Answer 2

Most active in brain, heart, kidney cortex, and liver

Question 3

step 1 of the TCA cycle

Answer 3

Aldol condensation:
catalyzed by enzyme CITRATE SYNTHASE (irreversible)

Acetyl CoA (from PDH) and Oxaloacetate (prod of cycle) are with water to form water and CITRATE

Question 4

step 2 of the TCA cycle

Answer 4

Dehydration reaction:
catalyzed by enzyme ACONITASE (reversible)

Citrate is dehydrated into ISOCITRATE
It’s intermediate form “CIS-ACONITATE” forms first then gets hydrated to isocitrate.

Question 5

step 3 of the TCA cycle

Answer 5

Oxidation-Carboxylation reaction: rate limiting step
catalyzed by ISOCITRATE DEHYDROGENASE (irreversible)

reduces 6-carbon isocitrate to 5-carbon a-ketoglutarate

generates 1 NADH, releases 1 CO2 as waste

INHIBITED: ATP , ACTIVATORS: ADP, and Calcium

Question 6

What inhibits/activates the enzyme that catalyzes the 3rd step of the TCA cycle?

Answer 6

Inhibited by: ATP

Activated by: ADP and Calcium

Question 7

step 4 of the TCA cycle

Answer 7

Oxidative Carboxylation reaction:
catalyzed by a-ketoglutarate dehydrogenase

a-ketoglutarate + NAD+ and acetyl CoA are made into Succinyl CoA

(CO2, and NADH are by products)

Question 8

step 5 of the TCA cycle

Answer 8

Substrate level phosphorylation: (reversible)
Catalyzed by Succinyl-CoA synthetase

Converts Succinyl-CoA into Succinate

Converts 1 GDP into a GTP as a by product

Question 9

Step 6 of the TCA cycle

Answer 9

Oxidation reaction:

Catalyzed by Succinate Dehydrogenase

Converts Succinate into a Fumerate

FAD+ is converted into 1 FADH2

Question 10

Step 7 of the TCA cycle

Answer 10

Hydration reaction:

catalyzed by Fumerase

catalyzes Fumerate into L-Malate

Question 11

Step 8 of the TCA cycle

Answer 11

Oxidation reaction:

Catalyzed by Malate dehydrogenase (reversible)
Generate 1 NADH

Results in Malate become Oxaloacetate

Generates 1 NADH from NAD+

Question 12

What is important about the final product Oxaloacetate?

Answer 12

It is the final product of TCA, but it is sent back into the first step to react with Acetyl CoA to begin the cycle again.

Question 13

What are the irreversible steps of TCA?

Answer 13

Citrate synthetase, isocitrate dehydrogenase (major), a-ketoglutarate dehydrogenase.

Question 14

How is citrate synthase regulated?

Answer 14

NADH, succinyl-CoA, citrate, and ATP (inhibitors)

ADP (activator)

Question 15

How is isocitrate dehydrogenase regulated?

Answer 15

Succinyl-CoA and NADH (inhibitors)

calcium and ADP (activator)

Question 16

How does mutant Isocitrate dehydrogenase present in some cancers?

Answer 16

Some use NADP+ instead of NAD+

2-hydroxyglutarate accumulates to very high concentrations which inhibits the function of enzymes that are dependent on alpha-ketoglutarate. This leads to a hypermethylated state of DNA and histones, which results in different gene expression that can activate oncogenes and inactivate tumor-suppressor genes. Ultimately, this may lead to different types of cancer.

Question 17

How are mitchondria moving around the cell?

Answer 17

They are moved around on microtubles

Question 18

Why would ion transporting cells have mitochondria near them?

Answer 18

many mitochondria are located near basolateral cell membrane infoldings and provide locally needed ATP

Question 19

What creates the gradient that powers the electron transport chain?

Answer 19

The metabolism of nutrients creates a proton gradient that is used to make ATP

Question 20

What 3 substrates can become acetyl CoA destined for the TCA cycle?

Answer 20

Fatty Acids
Glucose
Amino Acids