A standard biochemistry book gives chain A of insulin 21 amino acids and chain B 30 amino acids…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A standard biochemistry book gives chain A of insulin amino acids and chain B amino acids. A gene for a chain needs bases for each amino acid and more bases for the stop codon.
- How many bases code for the amino acids of chain A?
- How many bases code for the amino acids of chain B?
- How many bases are needed for both genes, with a stop codon on each?
Need a reminder? The key ideaShow
Recombinant DNA technology makes safe and effective drugs in large amounts. Human insulin has two short polypeptide chains, A and B, joined by disulphide bridges. In the body it is made as a pro-hormone, which has an extra stretch, the C peptide, that is removed when the hormone matures. In 1983 the company Eli Lilly made DNA for chain A and for chain B, put them into plasmids of E. coli, made the chains separately and joined them. One A chain and one B chain make one insulin molecule. A recombinant vaccine, such as the hepatitis B vaccine, can be made in yeast.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Chain A: amino acids. Chain B: amino acids. A codon has bases.
Plan. Multiply the amino acids by , and add a stop codon to each gene.
Step 1. Chain A. bases.
Step 2. Chain B. bases.
Step 3. Both genes. Chain A: . Chain B: . Together: bases.
Answer: ; ; bases.
Check. The two chains have amino acids. , and two stop codons add , which gives .
Source. Berg, Tymoczko and Stryer, Biochemistry, the structure of insulin. NCERT does not print these counts.
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