DNA Translation

features of genetic code

universal - many organisms use same genetic code

unambiguous - each codon makes 1 amino acid

degenerate - more than one codon makes same amino acid

types of mutations

silent - no change in amino acid

missense - change in amino acid

nonsense - results in stop codon

framshift - added or deleted nucleotide

Ribosome sites

E- holds tRNA that will exit

P - holds growing polypeptide chain

A - holds aminoacyl tRNA

tRNA and aminoacyl tRNA

tRNA - brings correct amino acid to ribosome

aminoacyl tRNA synthase - loards correct amino acid onto tRNA

acceptor stem - attachment site for amino acid

anticodon loop - recognizes codon

wobble hypothesis

paradox

• 40 tRNAS, 61 codons

solution

• loose binding on 3rd position of codon that allows for nonconventional basepairing

Initiation in Prokaryotes

1. small subunit binds to mRNA at shine dalgarno sequence with 16s tRNA

2. initiator tRNA carrying fMET binds to AUG in P site

3. large subunit joins

Initiation in Eukaryotes

1. Circle of translation - forms a closed loop

   • 5’ cap binding protein binds to 5’ end

   • poly A binding protein binds to poly A tial

polysome - mRNA that contains multiple ribosomes that synthesize proteins

kozak sequence - nucleotide seuqence that helps ribosome find start codon

Elongation

1. incoming aminoacyl tRNA into A site

2. peptide bond fomration

3. transolcation - everything moves down and leaves A site empy

termination

release factor

• protein with peptide anticodon that catalyzes hydrolysis of acyl bond connecting amino acid to tRNA