Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition Solomon Berg Martin Chapter 12 Gene Expression
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Early evidence indicating most genes specify the structure of proteins Garrod’s work on inborn errors of metabolism in early 1900s Beadle and Tatum’s work with Neurospora mutants in the 1940s
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression An “inborn error of metabolism”
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Mutations affecting biochemical pathways
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Information flow from DNA to protein Transcription –RNA molecule complementary to the template DNA strand synthesized Translation –Polypeptide chain specified by messenger RNA (mRNA) is synthesized
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Nucleotide structure of RNA
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Overview of transcription and translation
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Structure of RNA RNA –Formed from nucleotide subunits –Each nucleotide subunit contains ribose, a base, and three phosphates –Like DNA, RNA subunits are covalently joined by a 5 ΄ —3 ΄ linkage to form alternating sugar-phosphate backbone
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Transcription Incoming nucleotides with three phosphates pair with complementary bases on the DNA strand RNA polymerase cleaves two phosphates from each nucleotide and covalently links the remaining phosphate to the 3 ΄ end of the RNA chain
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Transcription
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Synthesis of mRNA
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Translation Polypeptide chain specified by the mRNA is synthesized –Initiation –Repeating cycles of elongation –Termination Each sequence of three nucleotide bases in the mRNA constitutes a codon Requires tRNAs and cell machinery, including ribosomes
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Three representations of a tRNA molecule
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Ribosome structure
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Initiation of translation in bacteria
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Elongation cycle in translation
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Termination of translation
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Coupled transcription and translation in bacteria Unlike eukaryotic cells, in bacterial cells translation and transcription coupled Translation of the bacterial mRNA molecule usually begins before the 3 ´ end of the transcript is completed
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Coupled transcription and transla- tion in bacteria
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Retroviruses Flow of genetic information is reversed by reverse transcriptase –Enzyme associated with retroviruses –Retroviruses synthesize DNA from an RNA template –Example of retrovirus is HIV-1, AIDS virus
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Infection cycle of an RNA tumor virus
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Mutations Base substitution mutations –Often result from errors in base pairing during replication –Missense mutations –Nonsense mutations Frameshift mutations –One or two nucleotide pairs are inserted into or deleted from the molecule
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Some mutations involve larger DNA segments Due to change in chromosome structure Wide range of effects as they involve many genes –DNA sequences that “jump” into the middle of a gene –Known as transposons or transposable genetic elements –Most are retrotransposons
Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Mutations