Biology · D Continuity and change. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
A gene is a base sequence in DNA that codes for a polypeptide. The cell reads it in two stages. In transcription, RNA polymerase separates the two DNA strands and builds an mRNA molecule on one of them, the template strand, by complementary base pairing. The DNA strands then rejoin unchanged, so the same gene can be copied many times. Cells make different proteins because they transcribe different genes.
In translation, a ribosome moves along the mRNA and reads it three bases at a time. Each codon pairs with the anticodon of a tRNA that carries one specific amino acid. The ribosome joins the amino acids with peptide bonds until it reaches a stop codon.
Students read a codon table with the DNA sequence or the anticodon. Codon tables use mRNA codons, so first convert the DNA template strand to mRNA, and remember to write U instead of T.
Answer: Met–Phe–Pro, a chain of three amino acids.
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