translation

translation purpose

rna - directed synthesis of a polypeptide

where does translation occur

on free ribosomes and rough ER (euk) or can happen while being transcribed (prok)

tRNA

1. transcribed in nucleus

2. specific to each amino acid

3. transfers AA to ribosome

ribosome

1. rRNA + protein

2. made in nucleolus

3. 2 subunits

active sites of ribosomes

a site: holds AA to be added

p site: holds growing polypeptide chain

e site: exit site for tRNA

steps in translation

1. initiation

2. elongation

3. termination

initiation

1. small subunit binds to start codon on mRNA

2. tRNA carrying start codon attaches to P site

3. large subunit attaches

elongation

1. codon recognition

2. peptide bond formation

3. tRNA in A site moves to P site; tRNA in P site moves to E site (then exits)

codon recognition

tRNA anticodon matches codon in A site

peptide bond formation

AA in A site forms bond with peptide in P site

termination

stop codon reached and translation stops

polypeptide is released

retroviruses

1. genetic info flows from RNA → DNA

2. dna integrates into host genome and is transcribed and translated for the assembly of the new viral progeny