Genetics: Chapter 7

1. Genetics: Chapter 7

2. What is genetics? • The science of heredity; includes the study of genes, how they carry information, how they are replicated, how they are expressed

3. What do you know about DNA? • Chromosomes made of DNA contain an organism’s entire genome • DNA codes for genes….genes code for proteins • Chemical composition is nucleotides • It exists in most cells as a double stranded structure

4. DNA is used for many things

5. DNA Structure

6. DNA Replication

7. Enzymes necessary for DNA replication • Primase • DNA Polymerase • DNA gyrase • DNA ligase • Helicase

8. Nucleotides are added to the 3’ position (OH group)

9. DNA replication…a closer look

10. DNA replication…closer look

11. Gene Expression…why is it important? • Transcription • Translation

12. What do you know about gene expression? • Work with a partner to make a list about what you already know about gene expression

13. Transcription: RNA is transcribed from DNA

14. Transcription: Promoter orients direction of transcription

15. Transcription: DNA to RNA • Requires an enzyme….. • RNA nucleotides • Base pairing rules for building RNA from a DNA template • Process proceeds in the direction 5’--->3’ • Process begins at the promoter region and ends at the terminator sequence

16. Transcription: RNA synthesis

17. What are the possible products from transcription? • Messenger RNA (mRNA) • Transfer RNA (tRNA) • Ribosomal RNA (rRNA)

18. Quick check….. • Do we have a protein yet? • What have we made? • What is next?

19. Translation: RNA to protein • What is needed for the process? • mRNA • Ribosomes • Amino acids • tRNA

20. Translation: RNA to protein • What is needed for the process? • mRNA • Ribosomes • Amino acids • tRNA

21. Translation: reading frame determines the protein

22. The Genetic code

23. Translation

24. Translation

25. Both processes occur at the same time in bacteria…why??

26. Ribosomes are different size 5’ end of mRNA has cap (methylated guanine) 3’ end of mRNA has poly A tail Introns are excised, exons spliced together Translation is monocystronic Eukaryotic cells differ in transcription and translation

27. Is it important to regulate protein synthesis? • Yes! • Three types of protein regulation • Enyme inhibition (feedback inhibition) • Repression (tryptophan operon) • Induction (lactose operon)

28. Are all genes under regulation? • No! • Genes to produce enzymes for glucose metabolism are constitutive (always made) • Other genes are induced…only made when needed • Other genes are repressed…turned off when not needed

29. Models for transcriptional regulation with repressors

30. Transcriptional regulation by activators

31. Used to understand control of gene expression in bacteria Operon consists of three genes needed to degrade lactose Repressor gene(codes for repressor protein) outside of operon coding region inhibits transcription unless something else bind to the repressor protein Lactose Operon as a model

32. Lactose Operon

33. Diauxic growth curve of E. coli

35. What conditions are needed for the lactose operon to be turned “on”? • No glucose • Lactose present • Increasing levels of cAMP • cAMP binds to CAP, then complex binds next to lactose operon promoter at the activator region • RNA polymerase binds to promoter

36. How do organisms adapt to other changes in their environment? • Some organisms turn genes on/off as needed • Some organisms alter gene expression

37. Gene regulation systems in bacteria • Signal transduction • Two component regulatory system

38. Gene regulation systems in bacteria • Signal transduction - Quorum sensing

39. Gene expression is influenced by natural selection • Random changes enhance survival of some cells in population • Antigenic variation of pathogens • Phase variation • Switching on/off of certain genes