1. Microbial genetics
Bios 10115
February 18, 2010
Additional reading from your book is suggested-Ch 4 pp 61-80

2. “Central Dogma” (DNARNAProtein)
 Genetic information of all
cells is in DNA
 DNA is duplicated during
the process of DNA
Replication
 Transfer of genetic
information to RNA occurs
during Transcription
 RNA is converted to protein
during translation

3. DNA
 4 nucleotides
 GATC
 Nucleotides consist of
pentose sugar (5’ and 3’
positions), phosphate and
backbone

4.  Double stranded-held together
by hydrogen bonding-base
pairs
 A-T (2 H bonds)
 G-C (3 H bonds)
 Chromosome
 Threadlike Double helix of DNA
 Prokaryotes-Circular (most)
 Eukaryotes- linear
 Virus-circular or linear

5. Double Helix – ________ strands

6. DNA higher order structure
E. coli has 1.5mm of DNA

7. Figure 10.1a: An electron micrograph of an E. coli cell immediately after
disruption. The tangled mass is the organism’s DNA.
© H. Potter-D. Dressler/Visuals Unlimited.

8. Eukaryotic DNA higher order structure
“beads on a string”

9. Information transfer
 Replication
 DNA makes new (is the template for) DNA
 Transcription
 DNA is the template for RNA
 Translation
 RNA is the template for proteins
A template is a pattern that is faithfully copied

10. DNA replication
 New strand is made as
complement of template
strand
 Each daughter double
helix has one parental
strand and one newly
synthesized strand
 DNA replication always
occurs 5’-3’
 5’ Phosphate attaches
to 3’ hydroxyl using
DNA Polymerase

11. The DNA replication fork (E. coli)
Leading and lagging strands
DNA polymerases can only move in one direction

12. http://www.dnai.org/a/index.html
(animations of replication,
E. Coli replicates 1000 bases per second

13. Replication of circular DNA
Also see fig 10.2 of your book

14. RNA
 Ribose instead of deoxyribose
 Uracil instead of Thymine
 Single Stranded (except some viruses)
 Messenger (mRNA)
 Transfer (tRNA)
All transcribed from DNA
 Ribosomal (rRNA)

15. Transcription
 An RNA copy of DNA must be made first before
proteins can be synthesized
 Transcription requires the enzyme RNA Polymerase

16. Translation
 Translation is the
process of
synthesizing
protein from RNA
 Three types of
RNA involved

17. Figure 4.8: The translation process

18. The Genetic Code
 Codon-set of 3 nucleotides
that encodes an amino
acid
 Amino acid-building block
of protein
 Start Codon - AUG-
methionine
 Stop codon- terminator-
UAA, UAG, UGA

19. Figure 4.9: A summary view of protein synthesis

20. Open reading frames

21. Mutations- changes in DNA
Genotype -genetic info
 Always changed by a mutation
Phenotype -outward appearance
 May not change with mutation
Point mutations
 A single nucleotide has been
changed
 A single codon is changed
 May or may not change amino
acid sequence (silent mutation)

23. Mutations (cont.)
Frameshift mutations
 A deletion or insertion of
one or more bases
 Changes ORF
 Usually change
phenotype

25. Mutations (cont.)
 Spontaneous mutations
 Occur in the absence of any known agent
 Arise during DNA replication
 Bacterial genes have a relatively high
spontaneous generation rate
 Induced mutations
 Caused by mutagens

26. Mutagens
 Chemical
 Many different effects
at molecular level
 Base analogs
 Alkylating agents
 Deaminating agents
 Acridine derivatives
 Radiation
 Thymine dimers

27. Plasmids
Small, circular extra-chromosomal
DNA
Do not carry essential genes
May carry helpful genes
Replicate independently of
chromosome
Over 300 naturally occurring
plasmids have been isolated
from E. coli

29. Gene transfer
 Vertical gene transfer-parents to offspring
 Lateral (or horizontal) gene transfer-passing
of genes within a generation
 Transformation
 Transduction (virus mediated)
 Conjugation
http://www.microbelibrary.org/microbelibrary/files/ccImages/Articleimages/
Mondomedia/4hirez.mov

30. Also see figs 10.5-10.9 in your book

31. Figure 10.9a: Bacterial transformation
Free DNA taken up by cell
© National Library of Medicine

32. Genetic exchange-Transformation
Streptococcus pneumoniae (pneumococcus) +/- capsule
1928-pneumococcus expt (Griffith)
1944-transforming compound is DNA
1953-structure of DNA
Also fig 4.2 of your book

33. Transduction
 Transfer of DNA by a _____________

34. Conjugation: _______ transfer of plasmids
 Ability is encoded by
_________
 Donor cell produces ____
 New population can gain
plasmid very quickly

35. Manipulation of DNA and
Genetic engineering

36. Tools to manipulate DNA
 ___________________
Sequences usually palindromic
(enzymes)
 Derived from _______
 Protect bacteria from
_______________
 Recognize specific small
sequences of DNA and ___
_________ leaving
“sticky” (staggered) or
“blunt” (straight) ends
 Bacteria’s own DNA
_________ by methylation

37. Figure 10.10a: A restriction enzyme cuts through two strands of a DNA
molecule to produce two fragments.

38. Figure 10.10b: The recognition sites of several restriction enzymes

39. Recombinant DNA technology
 Recombinant DNA
 DNA from _________
 Transgenic or recombinant
organism
 Organism derived from
recombined DNA
 _______
 Self replicating DNA
(plasmid)

40. Figure 10.11A-B: Construction of a recombinant DNA molecule

41. Figure 10.11C-E: Construction of a recombinant DNA molecule

42. Figure 10.12A-C: Developing new products using genetic engineering

43. Figure 10.12D-G: Developing new products using genetic engineering