Beta-cells in the pancreas make insulin, a protein hormone. Fig. 9.1 shows the parts of a cell. Table 9.1 lists three stages in making insulin, with the loc...
Question 1 Report
Beta-cells in the pancreas make insulin, a protein hormone. Fig. 9.1 shows the parts of a cell. Table 9.1 lists three stages in making insulin, with the location of each stage missing.
| Stage | Location in cell |
|---|---|
| 1. Insulin gene copied into mRNA | ............... |
| 2. mRNA passes out to a ribosome | ............... |
| 3. Amino acids joined to form the insulin chain | ............... |
(a) State the part of the cell where the insulin gene is located [1](b) Complete Table 9.1 by naming the location in the cell of each of the three stages [3]
(c) Name the two stages of protein synthesis [2]
(d) Describe how amino acids are joined together during the making of insulin [2]
Answer Details
(a) The insulin gene is a length of DNA, and in this cell the DNA is held in the nucleus. [1]
(b) Transcription (copying the gene into mRNA) happens where the DNA is, the mRNA then leaves the nucleus, and the amino acids are joined at a ribosome in the cytoplasm:
| Stage | Location in cell |
|---|---|
| 1. Insulin gene copied into mRNA | nucleus |
| 2. mRNA passes out to a ribosome | from the nucleus to the cytoplasm (through a nuclear pore) |
| 3. Amino acids joined to form the insulin chain | cytoplasm / at a ribosome |
Marks: stage 1 nucleus [1]; stage 2 out to cytoplasm [1]; stage 3 cytoplasm/ribosome [1].
(c) The two stages of protein synthesis are transcription [1] and translation [1].
(d) At the ribosome the mRNA codons are read in order, three bases at a time, [1] and the amino acids are joined together in that coded order (by peptide bonds) to build up the insulin chain. [1]
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