Glycolysis

Where in the cell does glycolysis take place?

• In the cytoplasm (sarcoplasm).

Does glycolysis require oxygen?

• No, it is an anaerobic process (though it happens in both aerobic and anaerobic respiration).

What is the first step of glycolysis?

• Phosphorylation of glucose.

Why must glucose be phosphorylated at the start?

• To make it more reactive (lower the activation energy) so it can be split.

• To keep it inside the cell (phosphorylated glucose cannot cross the cell membrane).

• How many ATP molecules are invested (used) during the phosphorylation stage?

Two ATP molecules.

What is formed when Hexose Bisphosphate splits?

• Two molecules of Triose Phosphate (TP).

What happens to Triose Phosphate during the oxidation step?

• It is dehydrogenated (oxidised). Hydrogen is removed and accepted by NAD to form Reduced NAD.

What is Substrate-Level Phosphorylation?

• The formation of ATP by the direct transfer of a phosphate group from a reactive intermediate (substrate) to ADP. This happens in glycolysis and the Krebs cycle.

What is the gross (total) production of ATP in glycolysis?

• 4 ATP.

What is the net production of ATP in glycolysis?

• 2 ATP (4 produced - 2 used).

What is the final product of glycolysis?

• Two molecules of Pyruvate (3C).

Where does the Pyruvate go next (if oxygen is present)?

• It is actively transported into the mitochondrial matrix for the Link Reaction.

Describe the role of ATP in the early stages of glycolysis.(3 marks)

• ATP is hydrolysed to release phosphate groups (1).

• These are used to phosphorylate glucose (forming hexose bisphosphate) (1).

• This makes the glucose more reactive (lowers activation energy) and prevents it from leaving the cell (1).

Explain why the net yield of ATP in glycolysis is different from the total amount of ATP produced.(2 marks)

• Total ATP produced is 4 molecules (via substrate-level phosphorylation) (1).

• However, 2 ATP molecules were used at the start to phosphorylate glucose, so the net yield is only 2 ATP (1).

Glycolysis involves oxidation. Explain how oxidation occurs in this process.(3 marks)

• Oxidation in this context is the removal of hydrogen (dehydrogenation) (1).

• Hydrogen is removed from Triose Phosphate (1).

• This hydrogen is accepted by the coenzyme NAD to form Reduced NAD (1).

State two differences between substrate-level phosphorylation and oxidative phosphorylation.(2 marks)

• Location: Substrate-level occurs in cytoplasm/matrix; Oxidative occurs on the inner mitochondrial membrane (cristae) (1).

• Mechanism: Substrate-level uses a phosphate from a donor molecule; Oxidative uses energy from the electron transport chain / ATP synthase (1). (Also valid: Oxidative requires oxygen; Substrate-level does not).

Explain what happens to the products of glycolysis under anaerobic conditions in mammals.(3 marks)

• Pyruvate is converted into Lactate (1).

• This reaction uses hydrogen from Reduced NAD, re-oxidising it back to NAD (1).

• This regenerates NAD so that glycolysis can continue to produce ATP (1).