Week 7, Lecture 2, from gene to protein

Week 7, Lecture 2, from gene to protein - FROM GENE TO...

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1 FROM GENE TO PROTEIN Ribosomes • Ribosomes facilitate specific coupling of tRNA anticodons with mRNA 17-Oct-09 Gardiner 2 codons in protein synthesis • The two ribosomal subunits (large and small) are made of proteins and ribosomal RNA (rRNA) After rRNA genes are transcribed to rRNA in the nucleus, the rRNA and proteins form the subunits in the nucleolus. The subunits exit the nucleus via nuclear pores. The large and small subunits join to form a functional ribosome only when they attach to an mRNA molecule. While very similar in structure and function, prokaryotic and eukaryotic ribosomes have enough differences that certain antibiotic drugs (like tetracycline) can paralyze prokaryotic ribosomes without inhibiting eukaryotic ribosomes. Fig. 14.13 B I O L O G Y • A ribosome has three binding sites for tRNA: – The P site holds the tRNA that carries the growing polypeptide chain The A site holds the tRNA that carries 0 2 3 17-Oct-09 Gardiner 5 the next amino acid to be added to the chain – The E site is the exit site, where discharged tRNAs leave the ribosome
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2 Fig. 14.11 B I O L O G Y Building a Polypeptide • The three stages of translation: – Initiation – Elongation 0 2 3 17-Oct-09 Gardiner 8 – Termination • All three stages require protein “factors” that aid in the translation process Ribosome Association and Initiation of Translation • The initiation stage of translation brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits • First, a small ribosomal subunit binds with mRNA and a special initiator tRNA • Then the small subunit moves along the mRNA until it reaches the start codon (AUG) • Proteins called initiation factors bring in the large subunit so the initiator tRNA occupies the P site GTP Initiator tRNA P site Large ribosomal subunit GDP mRNA 5 3 mRNA binding site Small ribosomal subunit Start codon 5 3 Translation initiation complex E A Fig. 14.15 Fig. 14.16
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3 B I O L O G Y Polyribosomes • A number of ribosomes can translate a single mRNA simultaneously, 0 2 3 17-Oct-09 Gardiner 13 forming a polyribosome • Polyribosomes enable a cell to make many copies of a polypeptide very quickly Fig. 14.17 Completing and Targeting the Functional Protein • Often translation is not sufficient to make a functional protein 17-Oct-09 Gardiner 15
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This note was uploaded on 04/18/2010 for the course BIOLOGY 1223 taught by Professor Gardiner/lajoie during the Spring '09 term at UWO.

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Week 7, Lecture 2, from gene to protein - FROM GENE TO...

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