Lecture 24 - Glucose as a fuel molecule #2

Question 1

What are the basic steps of Glycolysis?

Answer 1

1. Splitting of glucose (one 6 Carbon glucose to two 3 Carbon pyruvate molecules)
2. Energy is conserved in ATP and NADH
3. Pyruvate may be further metabolised aerobically or anaerobically

Question 2

What is the activation of glucose?

Answer 2

Getting the molecule into a form so energy can be captured - this requires an energy input

Question 3

What are the two phases of glycolysis?

Answer 3

1. Energy Investment phase
2. Energy Payoff phase

Question 4

What happens during the energy investment phase?

Answer 4

Energy is used/invested in making the glucose molecule ready for splitting

The molecule is split (1X6C to 2X3C) at the end of the investment phase

Question 5

What two molecules are glucose split into during the energy investment phase?

Answer 5

Pyruvate

Question 6

How many ATP are spent during the energy investment phase?

Answer 6

2 ATP

Question 7

What happens during the energy payoff phase?

Answer 7

4 ADP turns into 4 ATP

2 NAD+ turns into 2 NADH

Question 8

What is the first key reaction for the activation of glucose?

Answer 8

Glucose + phosphate ➔ glucose-6-phosphate + H2O

Question 9

What enzyme adds a phosphate onto glucose

Answer 9

Hexokinase

Question 10

Is the first key reaction for the activation of glucose energetically favourable?

Answer 10

No, has +ve ΔG, but is required for glucose to be used as a fuel molecule

Question 11

How is this non-spontaneous first key reaction for the activation of glucose carried out?

Answer 11

By the coupling of the reaction (+ΔG) to ATP hydrolysis(-ΔG). Allowing the overall reaction to be spontaneous (-ΔG)

Question 12

What is the overall coupled reaction?

Answer 12

Glucose + ATP ➔ glucose-6-phosphate + ADP

Question 13

What is the second key reaction in the activation of glucose?

Answer 13

Glucosephosphate isomerase - rearrangement from glucose-6-phosphate into fructose-6-phosphate (F-6-P) (+ΔG)

Question 14

What is the third key reaction in activation of glucose?

Answer 14

Phosphofructokinase - 2nd activation of glucose that uses ATP hydrolysis to convert Fructose-6-phosphate into Fructose-1,6-biphosphate (FBP)

(addition of second phosphate)

Question 15

What occurs during the splitting (aldolase) reaction?

Answer 15

Occurs after the third key step of glucose activation.

FBP is split by aldolase forming DHAP, and G-3-P

Question 16

What phase of glycolysis is G-3-P used?

Answer 16

In the energy payoff phase

Question 17

What is the consequence of G-3-P being used up in the energy payoff phase?

Answer 17

The G-3-P concentration is low which drives the reaction from DHAP to G-3-P

Question 18

What enzyme catalyses the rearrangement of DHAP into G-3-P?

Answer 18

Triose phosphate isomerase

Question 19

What is substrate level phosphorylation? (SLP)

Answer 19

The direct use of energy from a substrate molecule to drive the synthesis of ATP (or equivalent)

Question 20

What is one way to release energy to drive a SLP?

Answer 20

By the cleavage of a high-energy phosphate ester bond on a substrate

Question 21

What is NAD?

Answer 21

A coenzyme required by some enzymes that catalyse redox reactions

Question 22

What is NAD derived from ?

Answer 22

Niacin (vitamin B3)

Question 23

What are the two forms of NAD?

Answer 23

NAD+(the oxidised form)
NADH(the reduced form)

Question 24

What is the importance of oxidising G-3-P?

Answer 24

It is a reaction for making an ATP profit

Question 25

How does oxidising G-3-P help make ATP profit?

Answer 25

it powers the addition of a phosphate to itself forming 1,3-BPG

Question 26

Does the addition of a phosphate require ATP?

Answer 26

No, phosphate from solution added to substrate

Question 27

What is reduced as G-3-P is oxidised?

Answer 27

NAD+

Question 28

Which carbon on 1,3-BPG is very reactive?

Answer 28

The first one

Question 29

What is 1,3-BPG converted into?

Answer 29

3PG

Question 30

What does occurs during the reaction from 1,3-BPG to 3PG?

Answer 30

Phosphate is cleaved from the 3-BPG by phosphoglycerate kinase this releases energy which is coupled with substrate level phosphorylation producing some ATP

Question 31

How does arsenic poison glycolysis?

Answer 31

Binds to the phosphoglycerate and formed 1-Arseno-3-phosphoglycerate instead of 1,3-BPG. So no ATP is synthesised by the phosphoglycerate kinase.

Question 32

What then happens to 3PG?

Answer 32

Rearranged to make 2PG, and then 2PG is rearranged to make PEP. This puts the molecule in a form that enables the next reactions

Question 33

What happens to PEP?

Answer 33

A phosphate is cleaved off of it by Pyruvate kinase, releasing energy which is coupled to the second substrate level phosphorylation in order to produce ATP

Question 34

How is the overall change in Gibbs free energy throughout glycolysis?

Answer 34

Negative so pathway is energetically favourable (some energy is converted into heat)

Question 35

What happens in the citric acid cycle?

Answer 35

Aerobic oxidation - Pyruvate is converted to acetyl-CoA to be further metabolized in the citric acid cycle

Question 36

What is Coenzyme A (CoA) derived from?

Answer 36

pantothenic acid (vitamin B5)

Question 37

Is CoA a carrier of electrons?

Answer 37

No (not reduced/oxidized)

Question 38

What does CoA carry?

Answer 38

Acyl groups - (2 C to long chains)

Question 39

What are the two forms of CoA

Answer 39

free coenzyme A: CoASH acyl group attached: Acyl-CoA (AcCoA)

Question 40

Where does the aerobic oxidation of pyruvate occur?

Answer 40

In the mitochondrial matrix.

Question 41

What enzyme complex is involved in the aerobic oxidation of pyruvate?

Answer 41

Pyruvate dehydrogenase complex.

Question 42

What type of reaction is the conversion of pyruvate to Acetyl-CoA?

Answer 42

Oxidative decarboxylation.

Question 43

What molecule is released during the decarboxylation of pyruvate?

Answer 43

CO₂ (carbon dioxide).

Question 44

What is added to the two-carbon chain after pyruvate is oxidized?

Answer 44

Coenzyme A (CoA).

Question 45

What happens to pyruvate in the pyruvate dehydrogenase reaction?

Answer 45

Pyruvate is oxidized, releasing energy that is captured in NADH.

Question 46

Which cofactors or coenzymes are involved in the pyruvate dehydrogenase reaction?

Answer 46

TPP (thiamine pyrophosphate), FAD, lipoic acid, NAD⁺, and Mg²⁺.

Question 47

What is the overall change in free energy (ΔG°') for the conversion of pyruvate to Acetyl-CoA?

Answer 47

ΔG°' = -33 kJ/mol.

Question 48

What happens during anaerobic glycolysis?

Answer 48

Instead of entering the citric acid cycle, pyruvate becomes lactate from the enzyme lactate dehydrogenase

Question 49

What does lactate do?

Answer 49

Causes muscle fatigue

Question 50

What happens to the energy captured in NADH during the lactate dehydrogenase reaction?

Answer 50

The energy is lost

Question 51

How is the concentration of coenzymes in cells?

Answer 51

Low

Question 52

When are coenzymes oxidised during aerobic oxidation?

Answer 52

In oxidative phosphorylation

Question 53

What does lactate formation allow?

Answer 53

Lactate formation allows for the regeneration of NAD+ as lactate dehydrogenase reaction oxidizes NAD meaning that there is enough NAD for the G-3-P dehydrogenase reaction