A gene codes for an enzyme.
The Table shows the amino acids coded for by some DNA base triplets.
Table
| DNA base triplet | Amino acid |
|---|---|
| AAA | lysine |
| CAT | histidine |
| CCT | proline |
| GAA | glutamic acid |
| GAG | glutamic acid |
| GTA | valine |
Part of the gene has this base sequence:
CCT GAA GAA AAA
Scientists found two different changes to this part of the gene in different people.
Explain why change 1 has no effect on the enzyme.
Change 2 stops the enzyme working.
Use the Table to explain why.
In a third person, one extra base is added to the gene after the third base.
Suggest why this is likely to have a bigger effect on the enzyme than change 2.
184 exam-style questions on OCR GCSE Biology 1.2 What happens in cells (and what do cells need)?, covering 1.2.1 Structure of DNA, 1.2.2 Nucleotides and complementary bases, 1.2.3 Protein synthesis, 1.2.4 DNA structure and the proteins made, 1.2.5 Investigating enzymatic reactions, and 1.2.6 Mechanism of enzyme action. Each one has a worked solution and a mark scheme showing where the marks go.