Biology 1202B Lecture Notes - Release Factor, Alternative Splicing, Protein Targeting

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30 Apr 2012
Biology Lecture Review Notes
Lecture 4
Translation (mRNA
Structure of RNA
o About 80% RNA in a cell is rRNA (ribosomal)
o rRNA-protein complexes = where translation occurs
Consists of large and small subunits
Each subunit is made of rRNA and ribosomal proteins
o mRNA template for translation
100s of nucleotides long
Single stranded
Any errors in mRNA will affect the protein you make
o tRNA (transfer RNA)
75-90 nucleotides long
Single stranded
Internal anticodon sequence is complementary to mRNA codon
Attached to 3’ end is an amino acid specific to the anticodon distinctive
Cloverleaf shape in 2D
L-shaped in 3D
non-Watson and Crick bindings - there are some unusual bindings in tRNA
compared to DNA
This gives it some wiggle room when binding they have room to move
o tRNA and mRNA bind in an antiparallel manner
o There are 3 sites in the rRNA-protein complex
E site = exit site
P site = peptidyl site
A site = aminoacyl site
o tRNA’s seek out the E, P and A sites
Translation using mRNA to create polypeptide chains (long amino acid chains)
o 3 Stages of translation
o Initiation
Met-tRNA with GTP bound to it and the small ribosomal subunit form a complex
The complex binds to the 5’ cap of the mRNA and scans along the mRNA until it
reaches the AUG start codon
GTP provides energy for large ribosome unit to bind to small unit and met-tRNA
at P site
Very first amino acid must be methionine
Note: methionine never binds to the A site it binds to the P site
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