Lecture 8. Metabolic Pathways and Glycolysis

Question 1

What is glycolysis?

Answer 1

A series of reactions starting with glucose and ending with pyruvate resulting in a small gain of ATP (2 molecules ATP for each glucose molecule)

Question 2

What happens during the dialysis of yeast extract?

Answer 2

Dialysis is a fractionation method: Yeast lysate in bag (cellophane) stir in buffer for several hours
Dialysed yeast extract is inactive, activity restored by adding dialysate

Question 3

What is zymase?

Answer 3

Large molecules (non-dialysable) inactivated by heat (proteins)

Question 4

What is co-zymase?

Answer 4

Small molecules (dialysable) heat stable (substrates are coenzymes)

Question 5

What does glycolysis require?

Answer 5

Phosphate and NAD⁺

Question 6

Glycolysis equation

Answer 6

Glucose + 2 ADP + 2 Pi+ 2 NAD⁺→ 2 pyruvate + 2 ATP + 2 NADH + 2H⁺+ 2H₂O

Question 7

Advantages of studying metabolic reactions in vitro

Answer 7

Study a purified enzyme in isolation
Completely defined (and readily modifiable) conditions
Direct, quantitative results

Question 8

Disadvantages of studying metabolic reactions in vitro

Answer 8

Loss of compartmentation, spatial and temporal organisation; dilution
Instability or degradation of key components (e.g. lack of ATP consumption in H&Y extracts prevented Pi release, limiting glycolysis)

Question 9

What is required to test metabolic reaction in vivo?

Answer 9

Measuring with assays and indicators or labelled compounds
Modifying with inhibitors (pharmacological) or mutations (genetic)

Question 10

Advantages of studying metabolic reactions in vivo

Answer 10

In cells

Question 11

Disadvantages of studying metabolic reactions in vivo

Answer 11

Can be hard to get quantitive data
Many variables so careful interpretation

Question 12

What is the main difference between respiration and combustion?

Answer 12

Respiration involves a multistep energy conserving pathway, whilst all the energy from combustion is released at once

Question 13

What are control points

Answer 13

Key steps in a metabolic pathway that are irreversible (strongly negative ΔG)

Question 14

What is the key cofactor that carries energy in energy metabolism?

Answer 14

ATP

Question 15

What are the key cofactors that carries electrons for oxidation of fuels in energy metabolism?

Answer 15

NAD⁺ and FAD

Question 16

What is the key cofactor that carries electrons for reductive biosynthesis in energy metabolism?

Answer 16

NADPH

Question 17

What is the key cofactor that carries 2-carbon groups in energy metabolism

Answer 17

CoA

Question 18

What is NAD⁺?

Answer 18

Nicotineamide Adenine Dinucleotide

Question 19

What is NAD⁺ derived from?

Answer 19

Niacin / Vitamin B₃

Question 20

What is FAD?

Answer 20

Flavine Adenine Dinucleotide

Question 21

Wat is FAD derived from?

Answer 21

Riboflavin / Vitamin B₂

Question 22

How many stages of catabolism are there?

Answer 22

3

Question 23

What is anabolism?

Answer 23

Building molecules

Question 24

What is catabolism?

Answer 24

Breaking molecules

Question 25

What is stage I of catabolism?

Answer 25

Large to smaller molecules not useful for energy production

Question 26

What is stage II of catabolism?

Answer 26

Many products of stage I to Acetyl-CoA Small amount of ATP produced

Question 27

What is stage III of catabolism?

Answer 27

Acetyl group of Acetyl-CoA to CO₂ Majority of ATP produced

Question 28

What controls catabolic pathways?

Answer 28

Energy

Question 29

Are anabolic pathways simply a reversal of catabolic pathways?

Answer 29

No

Question 30

Is glycolysis aerobic or anaerobic?

Answer 30

Anaerobic - evolved before atmosphere contained significant O₂

Question 31

Where does glycolysis take place?

Answer 31

Cytosol

Question 32

How many steps are there in glycolysis?

Answer 32

10

Question 33

What is stage 1 of glycolysis also known as?

Answer 33

The investment stage

Question 34

What happens in stage 1 of glycolysis?

Answer 34

2 ATP used Phosphorylation keeps intermediates in the cell

Question 35

What is stage 2 of glycolysis also known as?

Answer 35

The payout stage

Question 36

What happens in stage 2 of glycolysis?

Answer 36

Oxidation 4 ATP produced 2 NADH produced Requires NAD⁺ and Pi

Question 37

What is the net gain of ATP per glucose

Answer 37

2

Question 38

What happens when the cofactors run out in glycolysis?

Answer 38

Glycolysis stops

Question 39

What is needed for the oxidation of G-3-P?

Answer 39

NAD⁺

Question 40

How is NAD⁺ regenerated?

Answer 40

NADH transfers electrons to O₂, forming H₂O and regenerates NAD⁺

Question 41

What is the fermentation product in animals?

Answer 41

Lactate

Question 42

What is the fermentation product in plants and yeast?

Answer 42

Ethanol

Question 43

What is glycolysis central to?

Answer 43

Glycolysis is central to carbohydrate breakdown in modern organisms

Question 44

What steps in glycolysis are have a highly negative ΔG?

Answer 44

Steps 1, 3 and 10

Question 45

Which step is the main regulatory point of glycolysis?

Answer 45

Step 3

Question 46

How is glycolysis regulated?

Answer 46

Mainly by regulation of PFK