The genetic code and mRNAAQA A-Level Biology: Mind map

Exam questions on The genetic code and mRNA

1. Bacteria have been genetically modified to make human insulin by inserting the human insulin gene into their DNA. Mature insulin consists of two polypeptide chains: the A chain has 21 amino acids and the B chain has 30 amino acids.
   Explain why a code of two bases per amino acid could not code for all of the amino acids used to make proteins, and why a triplet code can.2 marks
2. A short region of mRNA has the base sequence AUG GCU UCC AAG UAA. Part of the genetic code is as follows: AUG codes for methionine (and starts translation); GCU and GCC both code for alanine; UCC and UCU both code for serine; AAG and AAA both code for lysine; UAA is a stop codon.
   Give the base sequence of the DNA template strand that was transcribed to make the first two codons (AUG GCU), written in the same order.2 marks
3. A student is comparing the two types of RNA that take part in making a polypeptide from the genetic information in a gene: messenger RNA (mRNA) and transfer RNA (tRNA).
   Describe the structure of a molecule of mRNA.3 marks