Biology AS · Nucleic acids and protein synthesis. 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 sequence of nucleotides, part of a DNA molecule, that codes for a polypeptide. The code is read in triplets: each group of three bases codes for one amino acid, or for start or stop. The code is universal, so the same triplets mean the same amino acids in almost all organisms.
In transcription, RNA polymerase uses the template strand of the gene to build an RNA copy. In eukaryotes the introns are then cut out of this primary transcript and the exons are joined to make mRNA.
In translation, a ribosome moves along the mRNA. tRNA molecules bring amino acids, each anticodon pairing with a codon, and peptide bonds join the amino acids.
Counting the stop codon as an amino acid, or forgetting that introns are removed. Only the exon bases before the stop codon are translated.
Answer: 320 amino acids.
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