University:
Kentucky State University
Course:
CHE 315 | Biochemistry
Academic year:

2019
Views:

117

Pages:

7
Author:

MoGhoadoAnotozj10

THE GENETIC CODE 56 What is a codon? • An mRNA chain is like a coded sentence that spells out the order in which amino acid residues that form a protein. • Each word consists of a triplet of ribonucleotides, or codon, in the mRNA sentence, which in turn corresponds to a specific amino acid. • Since there are four ribonucleotides, the possible number of codons = 4 x 4 x 4 = 64 codons. 57 The genetic code • Of the 64 codons, 61 specify an amino acid. • The remaining three (UAA, UAG, and UGA) are stop codons that signal the termination of protein synthesis • Since there are 20 amino acids, some amino acids are specified by more than one codon. 58 59 60 Major types of RNA • Protein synthesis involves interactions between three types of RNA molecules: – mRNA templates – tRNAs – rRNAs 61 General process • Once made in the nucleus, mRNA is moved out of nucleus into cytosol where it binds to the ribosome, which are made of rRNA and proteins. • Amino acids are delivered one by one by tRNA molecules to be joined into a specific protein by the ribosomes. 62