GlycolysisEdexcel A-Level Biology B: Subtopic test

1. 1
   A biochemist adds glucose to an extract of yeast cytoplasm that contains all the enzymes of glycolysis, together with NAD, ADP and phosphate, but no ATP. No reaction takes place. When a small amount of ATP is added, glycolysis begins and pyruvate is soon detected.

   (a)

   What is the role of the ATP added at the start of glycolysis?

   [1 mark]

   • AIt donates hydrogen to reduce NAD
   • BIt acts as an enzyme to split the hexose into two molecules
   • CIt accepts electrons at the end of the pathway
   • DIt phosphorylates the hexose, making it more reactive

   (b)

   What is the net gain of ATP per molecule of glucose in glycolysis?

   [1 mark]

   • A0
   • B2
   • C4
   • D8

   (c)

   Explain why glycolysis does not begin in this extract unless ATP is added.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student supplies a cytoplasm extract with 2.0 mmol of glucose, with excess ATP, ADP, NAD and phosphate. After incubation she finds that all of the glucose has been converted to pyruvate.

   (a)

   How much pyruvate is formed in the extract?

   [1 mark]

   • A2.0 mmol
   • B8.0 mmol
   • C4.0 mmol
   • D6.0 mmol

   (b)

   Which compound is reduced during glycolysis in the extract?

   [1 mark]

   • ANAD
   • BPyruvate
   • CATP
   • DHexose bisphosphate

   (c)

   Calculate the net amount of ATP gained by the extract. Show your working.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A researcher adds an inhibitor to a yeast cytoplasm extract. The inhibitor blocks the enzyme that converts glycerate 3-phosphate (GP) to pyruvate. She supplies glucose and a limited amount of ATP, and measures the concentrations of ATP, GP and pyruvate every minute for 10 minutes.

   (a)

   Explain why the concentration of ATP in the inhibited extract falls and stays low.

   [3 marks]

   (b)

   Explain how the concentrations of GP and of pyruvate in the inhibited extract will differ from those in an uninhibited extract.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student investigates glycolysis using a cell-free extract of yeast cytoplasm. She provides the extract with 0.30 mmol of glucose, with excess ATP, NAD, ADP and phosphate, and allows all of the glucose to be converted to pyruvate. She then wants to summarise the process for her class.

   (a)

   Describe the main stages of glycolysis in this extract, from glucose to pyruvate.

   [6 marks]

   (b)

   Calculate the amount of ATP used, the gross amount of ATP made, the net gain of ATP, and the amounts of pyruvate and NADH formed, and explain why ATP is both used and made in glycolysis.

   [6 marks]

   Total for question 4: 12 marks

End of questions