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2012.02.29 - Bio 1202 Lecture Review Notes.docx

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Biology 1202B
Gardiner/ Murphy

Biology Lecture Review Notes Lecture 4 Translation (mRNA  protein)  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 structure  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 o Elongation  An aminoacyl-tRNA binds to the A site  GTP provides the energy when an aninoacyl-tRNA binds to A site  Note: incoming tRNA binds to the A site  Peptidyl transferase cleaves the amino acid from the P site tRNA and bonds it to the amino acid on the A site tRNA  The ribosome translocates along the mRNA to the next codon, which moves the tRNA with the amino acids to the P site, and the empty tRNA to the E site  GTP provides energy to shift both tRNA left as ribosome translocates right  The empty tRNA in the E site is released and the cycle is ready to occur again  Gro
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