Translation I: basic players & an overview

What is the central dogma?

How genetic information can be stored and turned into a product within a biological system

What is the function of transfer RNA?

It is the interpreter, recognises nucleotides & amino acids

How is the amino acid added to the tRNA?

By aminoacyl-tRNA synthetase enzymes

What else is involved in addition to tRNA?

Ribosomes (small subunit reads mRNA, large reads peptide bonds between amino acids) proteins

What is the fidelity of translation?

Low rate of error in bacteria, similar accuracy to transcription but DNA replication is faster & more reliable

What are translation factors?

Used by ribosomes to complete tasks

What is the structure of tRNA?

• 75-94nt long

• Each tRNA generally specific to each amino acid

• 4 sets of ds stems/arms connected by 3 ss loops

• 5’ & 3’ ends meet at acceptor stem

• Amino acids attached on 3’ CCA tail

• Anticodon loop recognises mRNA codons

• D & T loops create elbow bend in tRNA

What can codon redundancy do?

Minimise negative effects from mutation

What does wobble base pairing allow?

One tRNA can recognise >1 mRNA codon, non-canonical base pairing

What does aminoacylation do to aminoacyl-tRNA synthetase do?

Direct attachment of a.a. to tRNA is energetically unfavourable, but attaching AMP to a.a. provides energy to permit attachment to tRNA

What is the structure of the ribosome?

Consists of an aminoacyl site, peptidyl site and an exit site

What are the 3 stages of translation?

Initiation, elongation & termination

What is initiation?

Specialised initiator tRNA^Met & initiation factors recognise AUG codon, tRNA^Met is loaded onto P site on small subunit, large subunit joins

What happens in elongation?

• Ribosome moves towards 3’ end of mRNA

• EFTu/eEF1A bring next aminoacyl-tRNA to bind to matching codon in A site

• EFs prevent amino acid from breaking off tRNA via hydrolysis & check tRNA is associating with the right codon

• Peptide chain transferred to tRNA in A site

• EFG/eEF2 moves mRNA-tRNA complex 3 nt along (translocation)

• New peptidyl-tRNA is in P site, codon on A site ready for new aminoacyl-tRNA

• Stages repeat

What happens in termination?

• UAA/UAG/UGA recognised by release factors

• Bacteria: RF1 (UAA & UAG) & RF2 (UAA & UGA)

• Eukaryotes: eRF1 for all 3

• Class I release factors promote release of peptide chain

What is ribosome recycling?

Large & small subunits separate from mRNA, can bind to initiation factors for a new round of synthesis

What is a polysome?

Many ribosomes processing one strand of mRNA all at once