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Lecture 14

biology lecture 14

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Biology 1202B
Brenda Murphy

Lecture 14: Chapter 13&14—Translation (mRNAProtein) Structure of RNA rRNA  About 80% of RNA in a cell is rRNA (ribosomal)  rRNA protein complexes—where translation occurs o Consists of large and small subunits o Each subunit is made of rRNA and ribosomal proteins o Translates mRNA into amino acid which are joined together to make a peptide chain mRNA  Template for translation  100s of nucleotides long  Single stranded  Any errors in mRNA will affect the protein you make  Read in 5’3’ direction tRNA  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  Wobble hypothesis—Watson and Crick said there don’t need to be as many tRNAs as there are codons  Non-Watson and Crick bindings—there are some unusual binds in tRNA compared to DNA  This gives it some wiggle room tRNA and mRNA bind in an antiparallel manner 3 sites in rRNA complex: A site (aminoacyl)—where the incoming next amino acid to be added to the chain binds P site (peptidyl)—where the tRNA carrying the growing peptide chain is bound E site (exit)—where exiting tRNA binds as it leaves the ribosome Translation  Using mRNA to create polypeptide chains (long amino acid chains)  3 stages: 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 Met  Methionine never binds to the A site—it binds to the P site Elongation  An aminoacyl-tRNA binds to the A site  GTP provides the energy when an aminoacyl-tRNA binds to A site—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)  The empty E site is released and the cycle is ready to occur again  Growing polypeptide moves through the exit tunnel of the large unit  1-3 cycles/sec in eukaryote  15-20 cycles/sec in prokaryote  Prokaryotes a
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