Chapter 16 - Exam 3

Question 1

The conversion of pyruvate.

Answer 1

pyruvate is oxidized to Acetyl-CoA and CO2

Question 2

Enzyme components of the enzyme complex.

Answer 2

PDH complex: highly ordered cluster of enzymes and cofactors that oxidizes pyruvate
E1: pyruvate dehydrogenase
E2: dihydrolipyl transacetylase
E3: dihydrolipoyl dehydrogenase

Question 3

Coenzyme components of the enzyme complex.

Answer 3

Thiamine pyrophosphate (TPP)
Lipoate
Coenzyme A
Flavin adenine dinucleotide (FAD)
Nicotinamide adenine dinucleotide (NAD)

Question 4

Cellular Respiration Basic Pathway.

Answer 4

Steps 1 and 2: oxidation of fuels to acetyl-CoA (generates ATP, NADH, and FADH2)
Step 3: oxidation of acetyl groups to CO2 in the citric acid cycle (generates NADH, FADH2, and 1 GTP)
Step 4: electron transfer chain and oxidative phosphorylation (generates the vast majority of ATP from catabolism)
Step 5: the conversion of pyruvate (pyruvate is oxidized to Acetyl-CoA and CO2)

Question 5

Conversion of Pyruvate Basic Pathway.

Answer 5

Step 1: decarboxylation of pyruvate to the hydroxyethyl derivate (rate-limiting step)
Step 2: oxidation of the hydroxyethyl derivate to an acetyl group (electrons and the acetyl group are transferred from TPP to the lipoyllysyl group of E2
Step 3: the acetyl moiety is transferred to Coenzyme A to form acetyl CoA
Step 4: electron transfer to regenerate the oxidized form of the lipoyllysyl group
Step 5: electron transfer to regenerate the oxidized FAS cofactor, forming NADH

Question 6

Citric Acid Cycle

Answer 6

Breakdown of acetyl-CoA

Question 7

Breakdown of acetyl-CoA: What is Released?

Answer 7

3 NADH, 1 FADH2, 1 GTP, and 2 CO2

Question 8

Know which steps of the TCA are regulated and what the regulators are.

Answer 8

1. Pyruvate dehydrogenase – allosteric regulation by substrates and products (activated by pyruvate and NAD+; inhibited by acetyl-CoA and NADH)
2. Citrate synthase – succinyl-CoA is a competitive inhibitor (activated by acetyl-CoA and oxaloacetate; inhibited by NADH and citrate)
3. Isocitrate dehydrogenase – activated by the binding of citrate and ADP to the alpha and gamma subunits of the enzyme
4. Alpha-ketoglutarate dehydrogenase – 3 enzyme subunits (E1: activated by ADP, Pi, and Ca2+; inhibited by NADH and ATP, E2: inhibited by succinyl-CoA and ATP, E3: inhibited by NADH and ATP)

Question 9

Similarities between PDH and alpha-ketoglutarate dehydrogenase.

Answer 9

Pyruvate and alpha-ketoglutarate are keto acids. Both complexes are similar as have 3 enzyme subunits (E1, E2, and E3). Also, both bind an alpha- keto acid to a thiamine pyrophosphate coenzyme, followed by decarboxylation. Lastly, both require TPP, lipoic acid, and FAD to function correctly.

Question 10

Understand the regulation of PDH through phosphorylation by PDH-kinase

Answer 10

The PHD complex is inhibited by reversible phosphorylation of residues of E1 by PDH kinase, a part of the PDH complex. PDH kinase is activated by the products of the PDH complex (ATP, NADH, and acetyl-CoA). PDH kinase is inhibited by the substrate for the PDH complex (ADP, NAD+, and pyruvate). PDH kinase is regulated by metabolites that signal the energetic state of the cell. Metabolites that accumulate in the energy-sufficient state activate the PDH kinase, which phosphorylates and inactivated PDH. Then, pyruvate is diverted away from the citric acid cycle keeping PDH kinase active and sending acetyl-CoA into the citric acid cycle.