AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
Glycolysis involves the following stages: phosphorylation of glucose to…
Full specification wording
Respiration (A-level only): Glycolysis involves the following stages: phosphorylation of glucose to glucose phosphate, using ATP production of triose phosphate oxidation of triose phosphate to pyruvate with a net gain of ATP and reduced NAD.
Glycolysis occurs in the cytoplasm.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 3 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Glycolysis occurs in the cytoplasm. First, glucose is phosphorylated to glucose phosphate using ATP. This makes the molecule more reactive and lowers activation energy. The glucose phosphate is then split into two molecules of the three-carbon triose phosphate. Next, each triose phosphate is oxidised to pyruvate. During this oxidation, hydrogen is removed and accepted by NAD, forming reduced NAD. This stage also produces ATP via substrate-level phosphorylation. Because two ATP are used initially and four are produced, there is a net gain of two ATP and two reduced NAD per glucose molecule.
What earns the marks
- Stating that glucose is phosphorylated to glucose phosphate using ATP to make it more reactive.
- Identifying that glucose phosphate is split into two molecules of triose phosphate.
- Describing the oxidation of triose phosphate to pyruvate.
- Explaining that NAD accepts hydrogen to form reduced NAD during the oxidation stage.
- Calculating a net gain of two ATP per glucose molecule, as four are produced and two are used.
- Naming the ATP synthesis at this stage as substrate-level phosphorylation.
Common mistakes and how to put them right
Quoting four ATP as the yield of glycolysis without subtracting the two used in phosphorylation.
Put it right: State the net gain is two ATP.
Writing that NAD is oxidised in glycolysis.
Put it right: NAD is reduced by accepting hydrogen.
Saying glucose is split straight into two pyruvate molecules.
Put it right: Include the intermediate triose phosphate stage.
Using reduced NADP instead of reduced NAD.
Put it right: Reduced NADP is used in photosynthesis, whereas reduced NAD is used in respiration.
Exam tips
- Track the carbons: six in glucose, then two lots of three in triose phosphate, then two pyruvate.
- Always use the word 'net' when quoting the ATP yield, and give both the four made and the two used when the question is worth two marks or more.
Try the lesson
The start of the Respiration (A-level only): Glycolysis involves the following stages: phosphorylation of glucose to glucose phosphate, using ATP production of triose phosphate oxidation of triose phosphate to pyruvate with a net gain of ATP and reduced NAD. lesson, made from checked teaching notes for this specification point.
Have a go first
Which molecule is used to phosphorylate glucose at the start of glycolysis?
Listen
Glycolysis occurs in the cytoplasm. First, glucose is phosphorylated to glucose phosphate using ATP. This makes the molecule more reactive and lowers activation energy. The glucose phosphate is then split into two molecules of the three-carbon triose phosphate. Next, each triose phosphate is oxidised to pyruvate. During this oxidation, hydrogen is removed and accepted by NAD, forming reduced NAD. This stage also produces ATP via substrate-level phosphorylation. Because two ATP are used initially and four are produced, there is a net gain of two ATP and two reduced NAD per glucose molecule. A strong answer earns marks for these points. Stating that glucose is phosphorylated to glucose phosphate using ATP to make it more reactive. Identifying that glucose phosphate is split into two molecules of triose phosphate. Describing the oxidation of triose phosphate to pyruvate. Explaining that NAD accepts hydrogen to form reduced NAD during the oxidation stage. A common slip: Quoting four ATP as the yield of glycolysis without subtracting the two used in phosphorylation. Instead, state the net gain is two ATP. Exam tip: Track the carbons: six in glucose, then two lots of three in triose phosphate, then two pyruvate.
Key words
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phosphorylation of glucose
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triose phosphate
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oxidation to pyruvate
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net ATP gain
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See every definition
- phosphorylation of glucose
- Glucose is phosphorylated to glucose phosphate using ATP, which makes the molecule more reactive and lowers activation energy.
- triose phosphate
- Glucose phosphate is split into two molecules of the three-carbon triose phosphate.
- oxidation to pyruvate
- Each triose phosphate is oxidised to pyruvate, during which hydrogen is removed and accepted by NAD.
- net ATP gain
- Two ATP are used initially and four are produced, giving a net gain of two ATP per glucose molecule.
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