Monomers and polymersAQA A-Level Biology: Subtopic test

1. 1
   A student is revising how cells build the large molecules they need. She lists glucose, glycine and a nucleotide containing adenine as small molecules, and starch, a protein and DNA as large molecules made from them.

   (a)

   Which of the following is a polymer?

   [1 mark]

   • AGlucose
   • BGlycine
   • CDNA
   • DAn adenine-containing nucleotide

   (b)

   Which row correctly pairs a monomer with a polymer made from it?

   [1 mark]

   • ANucleotide and DNA
   • BAmino acid and starch
   • CMonosaccharide and protein
   • DAmino acid and glycogen

   (c)

   Name the type of reaction that joins glycine molecules to form a polypeptide, and state what is released each time two glycine molecules join.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A protease enzyme is added to a solution containing a polypeptide of 120 amino acids. After incubation the solution contains only free amino acids.

   (a)

   Which type of reaction does the protease catalyse?

   [1 mark]

   • ACondensation
   • BOxidation
   • CPhosphorylation
   • DHydrolysis

   (b)

   How many water molecules are used to hydrolyse the polypeptide completely into free amino acids?

   [1 mark]

   • A120
   • B119
   • C121
   • D240

   (c)

   Explain why water is needed for the protease to break down the polypeptide.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Three amino acids, glycine, alanine and serine, are joined in that order to make a tripeptide. The relative formula masses are: glycine 75, alanine 89, serine 105 and water 18.

   (a)

   Describe how the three amino acids are joined to form the tripeptide.

   [3 marks]

   (b)

   Calculate the relative formula mass of the tripeptide. Show your working.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   After a meal, liver cells store glucose by building glycogen, a polymer. Between meals, the liver breaks glycogen down to release glucose into the blood. Biologists also find that bacteria, plants and humans all build their proteins from the same twenty amino acids using the same type of reaction.

   (a)

   Explain how liver cells make glycogen from glucose, and how the liver releases glucose from glycogen between meals.

   [6 marks]

   (b)

   Using the information given, explain why a human can digest proteins from bacteria and use the products to build human proteins. Refer to the biochemical basis of life in your answer.

   [6 marks]

   Total for question 4: 12 marks

End of questions