Genetics Notes Exam 3 Chapter 15-21

Genetics Notes Exam 3 Chapter 15-21 - Chapter 15:...

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Unformatted text preview: Chapter 15: Translation 1. C-value paradox a. Why does genome size vary so much? b. Numbers of genes i. Humans 24,000 genes ii. Fruit fly 13,525 genes iii. Nematode 20, 598 genes iv. Mustard 25, 706 genes v. Mouse 26 ,762 genes c. Nobrega i. Deleted two large areas of mouse genome with no known genes ii. Homologous regions in human genome iii. No differences detected. 2. Gene Expression a. Large, noncoding regions of DNA not essential, but may be some abnormalities 3. Genes & Proteins a. Archibald Garrodgenes code for protein b. Beadle & Tatumone gene-one enzyme hypothesis i. Developed method for isolating auxotrophic [nutritionally deficient] mutants in Neurospora. Mutant grew only when supplemented with arginine. c. Cistron-sequence of nucleotides that codes for one polypeptide chain. d. Srb & Horowitz established that each step in a pathway is controlled by a different enzyme. Spores of auxotrophic mutants whose growth requires arginine are placed on minimal medium + supplement. e. The common amino acids have similar structure [see fig] i. Joined by peptide bonds ii. Structural organization: 1. Primarysequence of amino acids 2. Secondaryfolding, alpha helix 3. Tertiaryfurther folding 4. Quaternaryseveral polypeptide chains 4. Genetic Codehow base sequences code for amino acid sequences a. Watson & Crickgenetic info in sequence of bases. b. Codonssequence of nucleotides that specify one amino acid [code word] i. 20 common amino acids ii. 3 bases/codon=4^3=64 codons iii. Genetic code is a t riplet code iv. Nirenburg & Matthaei developed a method for identifying the amino acid specified by a homopolymer c. Redundancy in Code i. 3 stop codons ii. 61 sense codons [specify amino acid] iii. Wobble: one anticodon pairs with more than one codon 1. Occurs at 3 rd position of codon d. Reading Frame i. 3 potential reading frames for a sequence ii. Set by initiation codon AUG methionine e. Stop Codons i. UAA ii. UAG iii. UGA iv. No corresponding tRNAs f. Universality of Codeall life uses same genetic code i. Exceptions 1. Most in mRNA [Table 15.3] g. Characteristics of Code i. Triplet code ii. Comma free iii. Nonoverlapping iv. Degenerate [redundant] 64 codons but only 20 acids v. Universal [almost] vi. 4 letters [AGCU] vii.Wobbleisoaccepting tRNAs 5. mRNA protein 6. requires 4 steps a. tRNA charging i. tRNA loaded with appropriate amino acid ii. requires aminoacyl-tRNA synthetase iii. a two-step process 1. AA+syn+ATP complex (AA-syn-AMP)+PiPi 2. Complex+tRNA AA-tRNA+syn+AMP b. Initiation i. Two IF associate with small subunit of ribosome, and IF2+GTP associate with small subunit. The complex attaches at Shine-Dalgarno sequence on mRNA....
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Genetics Notes Exam 3 Chapter 15-21 - Chapter 15:...

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