BIOM-360 Lecture Notes - Lecture 24: Ribosome-Binding Site, Start Codon, Pyrrolysine
2 May 2018
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Shine-Dalgarno → The leader section that helps to get things started.
Translation
Final step in expression of protein encoding in genes
Genetic Code
Codon
3 base pairs long
Specifies an AA
Anticodon on tRNA is complementary
Start codon
Start side for translation
Always AUG
Organization of the Code
Sense codons
61 codons that specify AAs
Stop (nonsense) codons
3 codons used as translation termination signals
Do not encode AAs
Code degeneracy
Up to 6 different codons can code for a single AA
Wobble
Loose base pairing
3rd position of codon less important than 1st or 2nd
A little bit of forgiveness
Eliminates need for unique tRNA for each codon
Exceptions to the Code
Several exceptions exist.
Some protists use a single stop codon
The other 2 code for AAs instead
Some microbes incorporate two rare AAs into polypeptides
Selenocysteine
Pyrrolysine
Document Summary
Shine-dalgarno the leader section that helps to get things started. Final step in expression of protein encoding in genes. Up to 6 different codons can code for a single aa. 3rd position of codon less important than 1st or 2nd. Eliminates need for unique trna for each codon. Some microbes incorporate two rare aas into polypeptides. Synthesis of polypeptide directed by sequence of nucleotides in mrna. Direction of synthesis n terminal c terminal. Gtp the secondary energy source for protein sythesis. Each specific for single aa and its cognate trna. Need to activate aas before building can get off the ground. Binds to shine dalgarno site on mrna for protein synthesis initiation. Binds protein needed for initiation of translation (initiation factor 3) and aminoacyl-trna. N-formylmethionine-trna fmet-trna bound to the p site of 50s + 30s + mrna complex. Holds the rna to be attached to the growing polypeptide.
