5.7.2: Glycolysis

Question 1

What is glycolysis?

Answer 1

A biochemical pathway that occurs in the cytoplasm of all living organisms that respire, including prokaryotes.

Question 2

What does glycolysis involve?

Answer 2

-A sequence of 10 reactions, each catalysed by different enzymes, some with the help of coenzyme NAD.

Question 3

What are the three main stages of glycolysis?

Answer 3

1. Phosphorylation of glucose to hexose biphosphate.
2. Splitting each hexose biphosphate molecule into two triose phosphate molecules.
3. Oxidation of triose phosphate to pyruvate.

Question 4

What do enzymes that catalyse oxidation and reduction reactions need the help of?

Answer 4

• Coenzymes that accept the hydrogen atoms removed during oxidation.

Question 5

What is NAD?

Answer 5

-A non-protein molecule that helps dehydrogenase enzymes to carry out oxidation reactions.

Question 6

What does NAD do?

Answer 6

-NAD oxidises substrate molecules during glycolysis, the link reaction and the Krebs cycle.

Question 7

What is NAD synthesised from in living cells?

Answer 7

• nicotinamide (vitamin B3)
• the five-carbon sugar ribose
• the nucleotide base adenine
• two phosphoryl groups. The nicotinamide can accept two hydrogen atoms, becoming reduced NAD.

Question 8

What happens when the nicotinamide accepts two hydrogen atoms?

Answer 8

It becomes reduced NAD.

Question 9

What does reduced NAD do?

Answer 9

Reduced NAD carries the protons and electrons to the cristae of mitochondria and delivers them to be used in oxidative phosphorylation for the generation of ATP from ADP and Pi

Question 10

What happens when reduced NAD gives up the protons and electrons that it accepted during the first three stages of respiration?

Answer 10

It becomes oxidised and can be used to oxidise more substrate, in the process becoming reduced again.

Question 11

Glucose is a hexose sugar. What does this mean?

Answer 11

It contains six carbon atoms.

Question 12

Glucose molecules are stable and need to be activated before they can split into two three-carbon compounds.
What are the two steps of this process?

Answer 12

1. One molecule of ATP is hydrolysed and the released phosphoryl group is added to glucose to make hexose monophosphate.
2. Another molecule of ATP is hydrolysed and the phosphoryl group is added to the hexose phosphate to form a molecule of hexose biphosphate. (a phosphate group at C1 and C6)

Question 13

What is formed when a molecule of hexose biphosphate is split into two?

Answer 13

Two three-carbon molecules called triose phosphate. Each with a phosphate group attached.

Question 14

What are dehydrogenase enzymes aided by?

Answer 14

-coenzyme NAD, which helps dehydrogenase to remove hydrogens triose phosphate.

Question 15

When the two molecules of NAD accept hydrogen atoms (protons and electrons), what do they become?

Answer 15

Reduced.

Question 16

At this stage of glycolysis, how many molecules of NAD are reduced?

Answer 16

-Two molecules of NAD are reduced.

Question 17

How many molecules of ATP are made for every two triose phosphate molecues undergoing oxidation?

Answer 17

-Four molecules of ATPs.

Question 18

What are the products of glycolysis?

Answer 18

2 ATP (4 made but 2 used to 'kick start' the process)
2 NADH (reduced NAD)
2 Pyruvate

Question 19

What are the four stages of respiration?

Answer 19

1. Glycolysis
2. The link reaction
3. The Krebs cycle
4. Oxidative phosphorylation

Question 20

Do the four stages of respiration take place in aerobic or anaerobic conditions?

Answer 20

Glycolysis - Aerobic
The link reaction - Anaerobic
The Krebs cycle - Anaerobic
Oxidative phosphorylation - Anaerobic

Question 21

How are the pyruvate molecules from glucose transported to the mitochondria for the link reaction?

Answer 21

• Under aerobic respiration

- Actively transported

Question 22

What happens to the pyruvate in the absence of oxygen (anaerobic)?

Answer 22

• Pyruvate is converted, in the cytoplasm, to lactate or ethanol.
• In the process, the reduced NAD molecules are reoxidised so that glycolysis can continue to run
• generating two molecules of ATP for every glucose molecule metabolised.