1. Foundations in Microbiology
PowerPoint to accompany
Foundations in Microbiology
Fifth Edition
Talaro
Chapter 9
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2. Microbial Genetics
Chapter 9

3. Genetics – the study of heredity
transmission of biological traits from parent to offspring
expression & variation of those traits
structure & function of genetic material
how this material changes

4. Levels of genetic study

5. Levels of structure & function of the genome
genome – sum total of genetic material of an organism (chromosomes + mitochondria/chloroplasts and/or plasmids)
genome of cells – DNA
genome of viruses – DNA or RNA
chromosome – length of DNA containing genes
gene-fundamental unit of heredity responsible for a given trait
site on the chromosome that provides information for a certain cell function
segment of DNA that contains the necessary code to make a protein or RNA molecule

6. Genomes vary in size smallest virus – 4-5 genes
E. coli – single chromosome containing 4,288 genes; 1 mm; 1,000X longer than cell
Human cell – 46 chromosomes containing 31,000 genes; 6 feet; 180,000X longer than cell

8. each nucleotide consists of 3 parts
Nucleic acids are made of nucleotides similar to how proteins are made of amino acids
each nucleotide consists of 3 parts
a 5 carbon sugar (deoxyribose or ribose)
a phosphate group
a nitrogenous base (adenine, thymine, cytosine, guanine, and uracil)

9. DNA structure 2 strands twisted into a helix sugar -phosphate backbone
nitrogenous bases form steps in ladder
constancy of base pairing
A binds to T with 2 hydrogen bonds
G binds to C with 3 hydrogen bonds
antiparallel strands 3’to 5’ and 5’to 3’
each strand provides a template for the exact copying of a new strand
order of bases constitutes the DNA code

11. Significance of DNA structure
Maintenance of code during reproduction. Constancy of base pairing guarantees that the code will be retained.
Providing variety. Order of bases responsible for unique qualities of each organism.

12. DNA replication is semiconservative because each chromosome ends up with one new strand of DNA and one old strand.

13. Semi-conservative replication of DNA

14. DNA replication Begins at an origin of replication
Helicase unwinds and unzips the DNA double helix
An RNA primer is synthesized
DNA polymerase III adds nucleotides in a 5’ to 3’ direction
Leading strand – synthesized continuously in 5’ to 3’ direction
Lagging strand – synthesized 5’ to 3’ in short segments; overall direction is 3’ to 5’

15. Bacterial replicon

16. Flow of genetic information

17. What are the products that genes encode? How are genes expressed?
RNAs and proteins
How are genes expressed?
transcription and translation

18. Gene expression Transcription – DNA is used to synthesize RNA
RNA polymerase is the enzyme responsible
Translation –making a protein using the information provided by messenger RNA
occurs on ribosomes

19. Genotype - genes encoding all the potential characteristics of an individual
Phenotype -actual expressed genes of an individual (its collection of proteins)

20. DNA-protein relationship
Each triplet of nucleotides (codon) specifies a particular amino acid.
A protein’s primary structure determines its shape & function.
Proteins determine phenotype. Living things are what their proteins make them.
DNA is mainly a blueprint that tells the cell which kinds of proteins to make and how to make them.

21. DNA-protein relationship

22. 3 types of RNA messenger RNA (mRNA) transfer RNA (tRNA)
ribosomal RNA (rRNA)

24. DNA
Transcription
RNA polymerase
RNA
Translation
ribosomes
PROTEINS

25. Transcription
RNA polymerase binds to promoter region upstream of the gene
RNA polymerase adds nucleotides complementary to the template strand of a segment of DNA in the 5’ to 3’ direction
Uracil is placed as adenine’s complement
At termination, RNA polymerase recognizes signals and releases the transcript
100-1,200 bases long

26. Transcription

27. Translation Ribosomes assemble on the 5’ end of a mRNA transcript
Ribosome scans the mRNA until it reaches the start codon, usually AUG
A tRNA molecule with the complementary anticodon and methionine amino acid enters the P site of the ribosome & binds to the mRNA

28. Translation

30. Interpreting the DNA code

31. Translation elongation
A second tRNA with the complementary anticodon fills the A site
A peptide bond is formed
The first tRNA is released and the ribosome slides down to the next codon.
Another tRNA fills the A site & a peptide bond is formed.
This process continues until a stop codon is encountered.

33. Translation termination
Termination codons – UAA, UAG, and UGA – are codons for which there is no corresponding tRNA.
When this codon is reached, the ribosome falls off and the last tRNA is removed from the polypeptide.

34. Polyribosomal complex

35. Eucaryotic transcription & translation differs from procaryotic
Do not occur simultaneously. Transcription occurs in the nucleus and translation occurs in the cytoplasm.
Eucaryotic start codon is AUG, but it does not use formyl-methionine.
Eucaryotic mRNA encodes a single protein, unlike bacterial mRNA which encodes many.
Eucaryotic DNA contains introns – intervening sequences of noncoding DNA- which have to be spliced out of the final mRNA transcript.

36. Split gene of eucaryotes

37. Multiplication of dsDNA viruses

38. Multiplication of +ssRNA

39. Regulation of protein synthesis & metabolism

40. Operons
a coordinated set of genes, all of which are regulated as a single unit.
2 types
inducible – operon is turned ON by substrate: catabolic operons- enzymes needed to metabolize a nutrient are produced when needed
repressible – genes in a series are turned OFF by the product synthesized; anabolic operon –enzymes used to synthesize an amino acid stop being produced when they are not needed

41. Lactose operon: inducible operon
Made of 3 segments:
Regulator- gene that codes for repressor
Control locus- composed of promoter and operator
Structural locus- made of 3 genes each coding for an enzyme needed to catabolize lactose –
b-galactosidase – hydolyzes lactose
permease - brings lactose across cell membrane
b-galactosidase transacetylase – uncertain function

42. Lac operon Normally off Lactose turns the operon on
In the absence of lactose the repressor binds with the operator locus and blocks transcription of downstream structural genes
Lactose turns the operon on
Binding of lactose to the repressor protein changes its shape and causes it to fall off the operator. RNA polymerase can bind to the promoter. Structural genes are transcribed.

43. Lactose operon

44. Arginine operon: repressible
Normally on and will be turned off when nutrient is no longer needed.
When excess arginine is present, it binds to the repressor and changes it. Then the repressor binds to the operator and blocks arginine synthesis.

45. Repressible operon

46. Antibiotics that affect gene expression
Rifamycin – binds to RNA polymerase
Actinomycin D - binds to DNA & halts mRNA chain elongation
Erythromycin & spectinomycin – interfere with attachment of mRNA to ribosomes
Chloramphenicol, linomycin & tetracycline-bind to ribosome and block elongation
Streptomycin – inhibits peptide initiation & elongation

47. Mutations – changes in the DNA
Point mutation – addition, deletion or substitution of a few bases
Missense mutation – causes change in a single amino acid
Nonsense mutation – changes a normal codon into a stop codon
Silent mutation – alters a base but does not change the amino acid

48. Excision repair

49. Ames Test

50. Types of intermicrobial exchange
conjugation
requires the attachment of two related species & formation of a bridge that can transport DNA
transformation
transfer of naked DNA
transduction
DNA transfer mediated by bacterial virus

51. conjugation

52. transformation

53. Generalized transduction

54. Specialized transduction

55. Transposons –DNA segments that shift from one part of the genome to another