Citric Acid Cycle

Question 1

What does the first stage of cellular respiration, glycolysis, produce?

Answer 1

Generation of Acetyl-CoA and a pair of electrons

Question 2

What does the second stage of cellular respiration, Citric Acid Cycle, produce?

Answer 2

Oxidation of the two carbon atoms from Acetyl-CoA to form 2 molecules of CO2 and 4 pairs of electrons, and 1 ATP or GTp

Question 3

What does the third stage of cellular respiration, electron transport chain and oxidative phosphorylation, produce?

Answer 3

The reduced electron carriers from stage 1 and 3 become re-oxidized, thus providing the energy for ATP synthesis

Question 4

Where does the CAC occur?

Answer 4

Matrix of the mitochondria

Question 5

What compound enters the CAC?

Answer 5

Acetyl-CoA

Question 6

Step 1: What kind of rxn does Citrate synthase catalyze? The rxn between _ and _ to make _

Answer 6

Citrate catalyzes a condensation and then hydrolysis rxn. Acetyl-CoA and oxaloacetate to make citrate

Question 7

Step 1: The energy stored in the thioester bond us used for what?

Answer 7

To synthesize a larger molecule from smaller precursors, allowing the rxn to proceed to the right.

Question 8

Oxaloacetate binds to citrate synthase causing a _ _ so that _ _ _ can be created

Answer 8

conformational change so that the Acetyl-CoA binding site can be created

Question 9

Step 2: What does aconitase do to the newly made citrate? Why?

Answer 9

Aconitase catalyzes a hydration and dehydration rxn to turn the tertiary alcohol into a secondary alcohol to be able to make a carbonyl group later

Question 10

Step 3: What kind of rxn does isocitrate dehydrogenase catalyze?

Answer 10

Oxidative decarboxylation. Citrate loses electrons (oxidation) and release CO2 (decarboxylation). The rate limiting rxn of the cycle.

Question 11

Isocitrate turns into _ and also reduces _ to _

Answer 11

alpha-ketoglutarate, and also reduces NAD+ to NADH + H+

Question 12

Step 4: Alpha-ketoglutarate undergoes another _ /_ rxn catalyzed by _.

Answer 12

Undergoes another oxidation / decarboxylation rxn catalyzed by alpha-ketoglutarate dehydrogenase

Question 13

Step 4 yields _ and _

Answer 13

Succinyl-CoA and NADH, CO2 (decarboxylation)

Question 14

Step 5: Succinyl-CoA synthetase catalyzes a _-level _

Answer 14

Substrate-level phosphorylation

Question 15

Step 5 produces _ and _ or _ depending on what is readily available

Answer 15

Succinate and ATP or GTP depending on what is readily available.

Question 16

Steps 6,7,8 start with _ and end with _

Answer 16

Succinate to fumarate to malate and end with making oxaloacetate.

Question 17

Succinate is _ to fumarate

Answer 17

Oxidized

Question 18

Fumarate is _ to malate

Answer 18

Hydrated

Question 19

Malate is _ to oxaloacetate

Answer 19

Oxidized

Question 20

2 C atoms enter the cycle during the condensation of acetyl-CoA with oxaloacetate and 2 C atoms leave in the form of

Answer 20

CO2

Question 21

4 pairs of H atoms leave the cycle in 4 oxidation reactions to generate _ NADH and _ FADH2

Answer 21

3 NADH and 1 FADH2

Question 22

How many ATP or GTP are produced during CAC?

Answer 22

1 ATP or GTP

Question 23

How many molecules of water are consumed in CAC?

Answer 23

2 molecules of water

Question 24

How many Acetyl-CoA are generated from 1 glucose molecule?

Answer 24

2 Acetyl-CoA come from 1 glucose molecules. So 1 glucose molecule turns the CAC twice = 2x the products for 1 glucose

Question 25

Pyruvate dehydrogenase complex: Enzyme 1 function?

Answer 25

Convert pyruvate to CO2

Question 26

Pyruvate dehydrogenase complex: Enzyme 2 function?

Answer 26

Make Acetyl-CoA out of CoA-SH

Question 27

Pyruvate dehydrogenase complex: Enzyme 3 function?

Answer 27

Turn NAD+ to NADH

Question 28

How is pyruvate dehydrogenase complex regulated?

Answer 28

Enzymes 2 and 3 are regulated by feeback inhibition and enzyme 1 is regulated by covalent modification

Question 29

What signals activation of kinase in PDH (off)?

Answer 29

High levels of ATP, NADH, and Acetyl-CoA

Question 30

What signals activation of phosphatase in PDH (on)?

Answer 30

Mg 2+ Ca 2+ , Insulin, epinephrine

Question 31

is oxygen required for rxns in CAC?

Answer 31

no

Question 32

How many carbons: Citrate, a-ketoglutarate, OAA, Acetyl group?

Answer 32

6,5,4,2

Question 33

What are the two ways to regulate isocitrate dehydrogenase?

Answer 33

Allosteric inhibition or allosteric activation

Question 34

Why are citrate synthase, isocitrate dehydrogenase and, a-ketoglutarate dehydrogenase good candidates for regulation of the CAC?

Answer 34

Because they catalyze the irreversible reactions.