Catabolism of Pyruvate

Question 1

Importance of the need to regenerate NAD+

Answer 1

• Only limited amounts of NAD+ are present in cell
• Glycolysis reduces NAD+ to NADH + H+
• NADH must be re-oxidised to let glycolysis continue

Question 2

NAD+ is regenerated through what process

Answer 2

The oxidative metabolism of pyruvate

Question 3

Stage 1 in Aerobic Metabolism (oxidation) of pyruvate

Answer 3

Citric Acid Cycle

• Pyruvate enters the mitochondria matrix
• Converted to acetyl-coA (catalysed by Pyruvate Dehydrogenase Complex PDC)

Question 4

Stage 2 in Aerobic Metabolism (oxidation) of pyruvate

Answer 4

Krebs Cycle

• Acetyl-coA condenses with 4C compound to form 6C compound
• 6C compound decarboxylated twice (yields CO2)
• 4 oxidation reactions (yield NADH + H+ and FADH2)

Question 5

Stage 3 in Anaerobic Metabolism (oxidation) of pyruvate

Answer 5

Tricarboxylic Acid (TCA) Cycle
- GTP (nucelotide) is formed
- 4C compound recreated
All enzymes of the TCA cycle are located in the matrix apart from succinate dehydrogenase (located in inner mitochondrial membrane

Question 6

How many pairs of electrons are transferred in the conversion of NAD+ to NADH + H+ ?

Answer 6

3 pairs

Question 7

How many pairs of electrons are needed to reduce FAD to FADH2 ?

Answer 7

1 pair

Question 8

Where does the TCA cycle occur?

Answer 8

In the mitochondria

Question 9

ANAEROBIC fate of pyruvate

Answer 9

alcoholic fermentation, lactic acid formation in humans

Question 10

AEROBIC fate of pyruvate

Answer 10

further oxidised in the citric acid cycle

Question 11

What are the structural features of the mitochondria?

Answer 11

• Inner membrane (proteins)
• Outer membrane
• Central matrix (containing enzyme of TCA cycle)
• Cristae folds

Question 12

From each acetyl-coA, TCA cycle generates…

Answer 12

• 3 NADH + H+
• 1 FADH2
• 1 GTP
• 2 CO2

Question 13

How is pyruvate metabolised to Acetyl-CoA

Answer 13

PDC catalyses the oxidative decarboxylation of pyruvate to acetyl-CoA
Irreversible reaction

Question 14

What is PDC?

Answer 14

Pyruvate Dehydrogenase Complex

• consists of 3 enzymes
• allosterically regulated by phosphorylation
• PDC activity determines glucose oxidation in well oxygenated tissues

Question 15

How many reactions in total are in the TCA cycle?

Answer 15

8 reactions

Question 16

TCA Cycle Overview

Answer 16

two carbon unit from acetyl-CoA condenses with a four-carbon unit

• Resulting six-carbon unit is decarboxylated twice forming CO2
• Four oxidation recations occur forming NADH + H+ and FADH2
• One GTP is formed (energy)
• Four carbon unit is recreated

Question 17

Each turn of the TCA cycle involves the uptake of two ______ atoms in the form of _________ and release of two _______ as ____

Answer 17

• carbon atoms
• acetyl-CoA
• carbon atoms
• CO2

Question 18

High ATP, NADH and acetyl-CoA means _____ energy

Answer 18

high

Question 19

High ADP and NAD+ means _____ energy

Answer 19

low

Question 20

High succinyl-CoA and acetyl-CoA means…

Answer 20

Plenty of precursor molecules for biosynthetic reactions

Question 21

All of the enzymes of the TCA cycle are associated with what structure?

Answer 21

Mitochondria