cells21-translation-RNA-2009 - Bio 106 Cells – Professor...

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Unformatted text preview: Bio 106 Cells – Professor Owen 10/27/2009 If only 4 nucleotides make up the genetic code, how do we get proteins made from combinations of 20 amino acids? Translation From mRNA to Protein A. You can’t! B. Use combinations of nucleotides – 1 at a time Use combinations of nucleotides at time C. Use combinations of nucleotides – 2 at a time D. Use combinations of nucleotides – 3 at a time E. The amino acids directly read the nucleotide bases Nucleotides Amino Acids Ponder: DNA and RNA are each composed of only 4 nucleotides, but proteins are made from combinations of 20 amino acids. • 1 nucleotide : 1 aa not enough variability • 2:1 (42=16) still not enough • 3:1 (43=64) 64 possible amino acids using sequences of 3 nucleotides (Enough) Thus, the genetic code translates into groups of 3 nucleotides for 1 amino acid = codons UUU Cooper 4.12 The Genetic Code: Codons tRNA the anticodon binds to the codon on the mRNA Codons are written with the 5’-end on the left ECB3 7-24 Cooper 8.1 tRNAs link amino acids with the mRNA codons Lecture 21 – Translation & RNA 1 Bio 106 Cells – Professor Owen 10/27/2009 Aminoacyl tRNA Synthetase tRNA Acts as an adapter – its anticodon base pairs with mRNA ECB3 7-29 • An aminoacyl tRNA synthetase enzyme links a specific amino acid to its specific tRNA. tRNA. • There are 20 of these enzymes, one per amino acid. ECB3 7-29 movie 7.6 Ribosomes Ribosomes A ribosome is a large complex of four RNAs and more than 80 proteins proteins. The mRNA is decoded on ribosomes, a molecular machine which travels along the mRNA capturing complementary tRNAs and holding them in position for peptide bond formation. Ribosomes attached to the ER ECB37-30, 32 ECB37-31 Overview of Translation Where to Start? Consider the following sentence: Start reading at this letter 5’– GDO 5’– GDOGDOGDOGDOGDOG – 3’ is translated to OGDOGDOGDODG GDOGDOGDOGDOG DOGDOGDOGDOG 5’– GDOG 5’– GDOGDOGDOGDOGDOG – 3’ is translated to 5’– GDOGD 5’– GDOGDOGDOGDOGDOG – 3’ is translated to Cooper 8.9 movie 7.7 Does one make more sense than the others? Lecture 21 – Translation & RNA 2 Bio 106 Cells – Professor Owen 10/27/2009 Three Possible Reading Frames The sequence of mRNA nucleotides is read from the 5’ to the 3’ direction in sequential sets of th three nucleotides. Where the translation starts determines the final 1º protein structure. The stages of translation are: (1) initiation; (2) __________, and (3) termination. A. elevation B. elongation C. elation D. emanation E. ebonite ECB2 7-22 special initiator tRNA Initiation movie 7.8 movie 7.11 ECB3 7-35 AUG is the “start” codon ECB3 7-37 When the complex finds the AUG codon, the eIFs are released. Termination Initiation of Translation Now the large subunit (60S) binds to the small. Initiation is complete. modified from Cooper 8.11 Lecture 21 – Translation & RNA 3 Bio 106 Cells – Professor Owen 10/27/2009 Translation During protein synthesis, the growing polypeptide is transferred from …. movie 7.7 A.The A. The tRNA in the E site to a tRNAtRNAamino acid in the P site B. The tRNA in the P site to a tRNAThe tRNA in the site to tRNA amino acid in the E site C.The C.The tRNA in the P site to a tRNAtRNAamino acid in the A site D. The tRNA in the A site to a tRNAtRNAamino acid in the P site Polyribosomes The first stage of translation is called _____________. A series of ribosomes can simultaneously translate the same mRNA. ECB3 7-38 movie 7.10 A. elongation B. orientation C. initiation D. termination E. cessation Know this plant? Ricin, a toxic protein isolated from the castor bean seeds, is the best-known bestmember of a class of plant polypeptides known as ribosome-inactivating proteins ribosome(RIPs). It removes an adenine on the RIPs). 28S rRNA. RIPs are being investigated as potential therapeutic agents that could be targeted to kill malignant cells. Antibiotics Ricinus Ricinus communis Ricin was made famous as the poison used by the Bulgarian secret police to assassinate the defector Georgi Markov in A dart-tipped umbrella was used dartLondon in 1978. to deliver the toxin (450 g). http://news.bbc.co.uk/1/hi/uk/2636459.stm Lecture 21 – Translation & RNA 4 Bio 106 Cells – Professor Owen 10/27/2009 What determines the human population on earth? Protein Degradation RNA Interference RNA World World What happens to some of the proteins and mRNAs? • birth & death rates – many societies need a high number of kids for factory or field work • duration of life of life Population birth rate death rate duration Cell – protein function protein synthesis (transcription/translation) proteolysis half-life on/off (phosphorylation) Many Steps in Eucaryotic Protein Synthesis The concentration of a protein depends upon the regulation of each step. Even after a protein is translated, its activity can it be controlled by degradation, by binding, or by modification. current topic ECB3 7-40 Lecture 21 – Translation & RNA 5 ...
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