mRNA, rRNA, and tRNA together can make protein {translation, RNA}| {RNA translation}.
template
mRNA nucleotide sequence codes for protein. mRNA is 2% of all RNA.
process
AUG or GUG codon, which codes for methionine, always starts mRNA. mRNA attaches to both smaller ribosome rRNA and larger ribosome rRNA. Ribosomes have two slots, one {peptidyl site} for current amino acid and one {aminoacyl site} for amino acid to add. Three mRNA nucleotides are in slots and lie in 5' carbon to 3' carbon direction.
process: tRNA
tRNA has amino acid on one side tip and three nucleotides on other side tip. Nucleotide tip can be complementary to three mRNA nucleotides in one slot. tRNA with complementary tip hydrogen-bonds its three tip nucleotides to the three slot nucleotides and brings one amino acid into ribosome slot. Streptomycin prevents tRNA attachment to first site.
process: peptide bonding
When amino acids are in both slots, ribosomal enzymes and GTP-protein complex join both amino acids by one peptide bond. Amino acid adds to protein chain in one second.
process: shift
Then ATP shifts both amino acids one slot. Messenger RNA also slides over one slot, leaving one slot empty. Diphtheria toxin inhibits translocation enzyme.
process: repeat
Empty slot fills with tRNA, amino acid comes in, and enzymes make peptide bond.
process: termination
The last three mRNA nucleotides are UAG, UAA, or UGA and do not pair with any tRNA tip, so slot stays empty and terminates mRNA coding. Puromycin terminates amino-acid chain early.
process: release
Enzyme releases protein and mRNA from ribosome.
modification
Enzymes can modify free-floating proteins after translation. Enzymes can remove formyl group from methionine. Enzymes can remove amino acids from amino end. Enzymes can form disulfide bonds. Enzymes can add hydroxyl to side chain. Enzymes can add sugar. Enzymes can add phosphate. Enzymes can split protein into functional parts.
Three DNA or RNA nucleotides {codon} can code for amino acids. Up to six codons can code for same amino acid. Codons coding for same amino acid have same first two bases. Coding redundancy can minimize errors. Codons are the same for all species, except for mitochondria. Mitochondrial DNA uses different genetic code for different groups.
Before initiation sites, mRNA has a purine-rich ribosome-binding site {Shine-Dalgarno sequence}, which matches rRNA molecule site. With extra ribosomal proteins, some bind to Shine-Dalgarno site and prevent or slow protein synthesis.
mRNA sites control translation rate and protein synthesis {translational control}.
Genes {suppressor gene} can make tRNA with an anticodon that matches stop codon but adds an amino acid. If DNA mutation makes a stop codon, such tRNAs allow cell to continue reading mRNA. Suppressor genes suppress such mutations.
5-Chemistry-Biochemistry-Nucleic Acid
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Date Modified: 2022.0225