6.5 Protein synthesis
6 exam questions worth 13 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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How many bases code for one amino acid?
Mark scheme
three / a triplet
Model answer
Three bases (a triplet).
Explain why a copy of the gene (mRNA) has to be made before a protein can be made.
Mark scheme
- DNA is too large to leave the nucleus (1)
- proteins are made at ribosomes in the cytoplasm (1)
Model answer
DNA cannot leave the nucleus, but proteins are made at the ribosomes in the cytoplasm, so a smaller mRNA copy carries the code out.
Describe how a protein is made at a ribosome.
Mark scheme
- mRNA attaches to ribosome (1)
- ribosome reads the bases in triplets / codons (1)
- carrier molecules / tRNA bring specific amino acids (1)
- amino acids joined in the order coded (1)
- chain folds into a specific shape (1)
Maximum 4 marks
Model answer
The mRNA attaches to a ribosome, which reads its bases in triplets. Carrier molecules bring the matching amino acids, which are joined together in the order coded for by the mRNA. The chain then folds into the protein's unique shape.
A gene is 900 bases long. How many amino acids does it code for?
Mark scheme
300
Model answer
900 ÷ 3 = 300 amino acids.
Give two examples of types of protein and their functions.
Mark scheme
Any two from:
- enzymes: catalysts (1)
- hormones: carry messages (1)
- structural proteins / collagen: strength (1)
- antibodies: bind to antigens (1)
Model answer
Enzymes act as biological catalysts, and structural proteins such as collagen give strength to tissues.
Explain why the order of bases in a gene affects the function of a protein.
Mark scheme
- base order determines order of amino acids (1)
- which determines how the chain folds / its shape (1)
- shape determines function, e.g. active site (1)
Model answer
The order of bases decides the order of amino acids, which decides how the chain folds and so the shape of the protein. Its shape, such as the active site of an enzyme, decides its function.
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