lecture 12 pyruvate dehydrogenase

Question 1

after glycolysis, what occurs?

Answer 1

pyruvate –> acetyl coA to power the citric acid cycle

Question 2

where does the oxidation of glucose occur

Answer 2

mitochondria

Question 3

Conversion of pyruvate to acetyl CoA occurs in the ___

Answer 3

Conversion of pyruvate to acetyl CoA occurs in the mitochondrial matrix

Question 4

how does pyruvate dehydrogenase link glycolysis with cellular respiration?

Answer 4

by converting pyruvate into acetyl coA

Question 5

describe where glycolysis occurs

Answer 5

cytoplasm

Question 6

where is glycolysis vs pyruvate oxidation?

Answer 6

pyruvate —> acetyl coA (we call this pyruvate oxidation) occurs in mitochondrial matrix

Question 7

once we have oxidized pyruvate, where do we need to send our acetyl coA for the citric acid cycle?

Answer 7

the citric acid cycle takes place in the matrix of themitochondria

Question 8

why is pyruvate oxidation a crucial junction in metabolism?

Answer 8

This reaction is an irreversible link between glycolysis and the citric acid cycle

Question 9

describe what pyruvate dehydrogenase does

Answer 9

the pyruvate dehyrogenase complex, a complex mitochondrial matrix enzyme, oxidatively decarboxylates pyruvate to form acetyl CoA.

Question 10

how many enzymes comprise the pyruvate dehydrogenase complex?

Answer 10

3

Question 11

T/f: pyruvate dehydrogenase complex has multiple enzymes, each with its own co-factor and prosthetic group

Answer 11

true

Question 12

The synthesis of acetyl CoA from pyruvate consists of three steps:

Answer 12

1. Decarboxylation to remove CO₂
2. Oxidation to form an energy-rich (thioester with lipoic acid chain) bond
3. Transfer onto Coenzyme A (also a thioester). Co A carries acetyl units with a high energy bond (high transfer potential)

Question 13

what happens to acetyl coA once in the TCA

Answer 13

Acetyl CoA will either be oxidized to CO₂ (catabolic fate) or be used to synthesize lipids (anabolic fate).

Question 14

Co A carries acetyl units with a ___ energy bond due to ___

Answer 14

high energy bond; high transfer potential

Question 15

Overall reaction pyruvate oxidation

Answer 15

pyruvate + coA + NAD+ –> acetyl coA + CO2 + NADH + H+

Question 16

describe what happens to pyruvate in this process

Answer 16

remove COO group, then remove some electrons to give it a positive charge. now its an ‘acetyl’ group : O=C-CH3. stick it on coA to make acetyle coA

Question 17

what’s special about the bond formed when you put acetyl on coA?

Answer 17

forms a high energy thioester bond

Question 18

what is the lipoamide arm and what does it do?

Answer 18

a long arm in the pyruvate dehydrogenase that is covalently attached to the amide group of lysine

it reacts with the acetate that was formed by the decarboxylation and carries it from active site to active site so that the reactions are made more efficient and occur more quickly

Question 19

T/F: The PDG is regulated by covalent modification and by allosteric effectors

Answer 19

true

Question 20

Regulation of the PDG enzyme has to do with :

Answer 20

Energy charge and availability of pyruvate and acetyl coA

Question 21

Response of the pyruvate dehydrogenase complex to the energy charge

Answer 21

The pyruvate dehydrogenase complex is regulated to respond to the energy charge of the cell. (A) The complex is inhibited by its immediate products, NADH and acetyl CoA, as well as by the ultimate product of cellular respiration, ATP. (B) The complex is activated by pyruvate and ADP, which inhibit the kinase that phosphorylates PDH.

Question 22

T/F: The transformation of malate to oxaloacetate can occur in the cytoplasm as well as the matrix of the mitochondrion.

Answer 22

true! you have to turn OA into malate to get it back to OA. you have it in the cytoplasm and need it back in the matrix