Protein Synthesis (Higher tier)

1. 1 State [1 mark]

   Name the structures in a cell on which proteins are made.

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   Model answer

   Ribosomes.

   Mark scheme

   • Ribosomes — 1 mark
2. 2 Describe [3 marks]

   The diagram shows protein synthesis. Describe the job of the carrier molecules.

   

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   Model answer

   Each carrier molecule brings a specific amino acid to the ribosome. The amino acids are added to the growing protein chain in the correct order, as specified by the template.

   Mark scheme

   • Bring amino acids to the ribosome — 1 mark
   • Each carrier brings a specific amino acid — 1 mark
   • Added to the growing chain in the correct order — 1 mark
3. 3 Explain [3 marks]

   Explain how the order of bases in a gene affects the protein that is made.

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   Model answer

   The order of bases decides the order of the amino acids that the carrier molecules add to the chain. The order of the amino acids decides the shape into which the chain folds. A different base order can therefore make a different protein.

   Mark scheme

   • The base order decides the amino acid order — 1 mark
   • The amino acid order decides the shape of the protein — 1 mark
   • A different base order may make a different protein — 1 mark
4. 4 Calculate [2 marks]

   A gene has 2 100 bases. Three bases specify one amino acid. Calculate the number of amino acids in the protein.

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   Model answer

   700 amino acids

   Mark scheme

   • \(2100 \div 3\) — 1 mark
   • 700 — 1 mark
5. 5 Explain [3 marks]

   Explain why a protein must fold into the correct shape.

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   Model answer

   When the chain is complete it folds into a unique shape. The shape enables the protein to do its job, for example as an enzyme, which has to fit its substrate, as a hormone or as a structural protein such as collagen. If the shape is wrong the protein may not work.

   Mark scheme

   • The chain folds into a unique shape — 1 mark
   • The shape enables the protein to do its job — 1 mark
   • An example such as an enzyme fitting its substrate — 1 mark
6. 6 Describe [4 marks]

   Describe how a protein is made on a ribosome.

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   Model answer

   The ribosome reads the template, which is a copy of the gene. Carrier molecules bring specific amino acids to the ribosome. The amino acids are added to the growing chain in the order set by the template. When the chain is complete it folds into a unique shape.

   Mark scheme

   • Ribosome reads a template — 1 mark
   • Carrier molecules bring specific amino acids — 1 mark
   • Amino acids added to the chain in the correct order — 1 mark
   • The finished chain folds into a unique shape — 1 mark
7. 7 Explain [4 marks]

   Collagen is a structural protein. A change in the gene for collagen can make the bones weak. Explain how a change in a gene could make weak collagen.

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   Model answer

   A change in the DNA changes the order of the bases in the gene. This can change the order of the amino acids in the collagen chain. A different order of amino acids may make the chain fold into a different shape. The collagen is then not as strong, so the bones are weak.

   Mark scheme

   • The order of the bases in the gene changes — 1 mark
   • The order of the amino acids changes — 1 mark
   • The protein folds into a different shape — 1 mark
   • The collagen is not as strong — 1 mark

Quick check

1. 1

   Where does protein synthesis happen in a cell?

   1. AOn the cell membrane
   2. BOn ribosomes
   3. CInside the nucleus only
   4. DIn the vacuole
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   B: On ribosomes

   Proteins are made on ribosomes.

2. 2

   What do carrier molecules do in protein synthesis?

   1. ABring specific amino acids to the ribosome
   2. BCopy the DNA
   3. CJoin the ribosome to the nucleus
   4. DDigest the template
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   A: Bring specific amino acids to the ribosome

   Each carrier molecule brings a specific amino acid to add to the growing chain.

3. 3

   What happens to a protein chain once it is complete?

   1. AIt is broken down at once
   2. BIt turns into DNA
   3. CIt folds into a unique shape
   4. DIt stays as a straight chain
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   C: It folds into a unique shape

   It folds up to form a unique shape.

4. 4

   What decides the order of amino acids in a protein?

   1. AThe size of the ribosome
   2. BThe cell membrane
   3. CThe number of carrier molecules
   4. DThe order of bases in the gene
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   D: The order of bases in the gene

   The order of the bases in the gene decides the order of the amino acids.

5. 5

   Why must a protein fold into the right shape?

   1. ASo that it is smaller
   2. BSo that it can do its job
   3. CSo that it can be stored in the nucleus
   4. DSo that it can become DNA
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   B: So that it can do its job

   The shape lets the protein do its job, such as an enzyme fitting its substrate.

6. 6

   A gene has 900 bases. About how many amino acids does its protein have?

   1. A300
   2. B30
   3. C450
   4. D2 700
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   A: 300

   Three bases specify one amino acid, so 900 divided by 3 is 300.

7. 7

   Which of these is a structural protein?

   1. AAmylase
   2. BInsulin
   3. CCollagen
   4. DGlucose
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   C: Collagen

   Collagen is a structural protein found in skin, tendons and bones.

8. 8

   What can happen if the structure of the DNA in a gene changes?

   1. AThe cell makes more DNA
   2. BThe ribosome disappears
   3. CNothing can ever change
   4. DA different protein may be made
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   D: A different protein may be made

   The order of the amino acids may change, so a different protein may be made.