1. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition Solomon Berg Martin Chapter 12 Gene Expression

2. 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

3. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression An “inborn error of metabolism”

4. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Mutations affecting biochemical pathways

5. 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

6. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Nucleotide structure of RNA

7. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Overview of transcription and translation

8. 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

9. 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

10. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Transcription

11. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Synthesis of mRNA

12. 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

13. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Three representations of a tRNA molecule

14. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Ribosome structure

15. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Initiation of translation in bacteria

16. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Elongation cycle in translation

17. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Termination of translation

18. 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

19. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Coupled transcription and transla- tion in bacteria

20. 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

21. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Infection cycle of an RNA tumor virus

22. 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

23. 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

24. Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 12 Gene Expression Mutations