Microbial Genetics

Terminology Genetics Genetics Study of what genes are Study of what genes are how they carry information how they carry information how information is expressed how information is expressed how genes are replicated how genes are replicated Gene Gene Segment of DNA that encodes a functional product, usually a protein Segment of DNA that encodes a functional product, usually a protein

Terminology Genome Genome All of the genetic material in a cell All of the genetic material in a cell Genomics Genomics Molecular study of genomes Molecular study of genomes Genotype Genotype Genes of an organism Genes of an organism Phenotype Phenotype Expression of the genes Expression of the genes

E. coli Figure 8.1a

Polymer of nucleotides: adenine, thymine, cytosine, guanine Polymer of nucleotides: adenine, thymine, cytosine, guanine Double helix associated with proteins Double helix associated with proteins "Backbone" is deoxyribose- phosphate "Backbone" is deoxyribose- phosphate Strands held together by hydrogen bonds between AT and CG Strands held together by hydrogen bonds between AT and CG Strands are antiparallel Strands are antiparallel DNA Figure 8.4

DNA Figure 8.3

DNA Figure 8.5

DNA is copied by DNA polymerase DNA is copied by DNA polymerase In the 5  3 direction In the 5  3 direction Initiated by an RNA primer Initiated by an RNA primer Leading strand synthesized continuously Leading strand synthesized continuously Lagging strand synthesized discontinuously Lagging strand synthesized discontinuously Okazaki fragments Okazaki fragments RNA primers are removed and Okazaki fragments joined by a DNA polymerase and DNA ligase RNA primers are removed and Okazaki fragments joined by a DNA polymerase and DNA ligase DNA

DNA Figure 8.6

DNA replication is semiconservative DNA replication is semiconservative DNA Figure 8.7

Figure 8.8

RNA processing in Eukaryotes Figure 8.12

mRNA is translated in codons (3 nucleotides) mRNA is translated in codons (3 nucleotides) Translation of mRNA begins at the start codon: AUG Translation of mRNA begins at the start codon: AUG Translation ends at a STOP codon: UAA, UAG, UGA Translation ends at a STOP codon: UAA, UAG, UGA Translation Figure 8.2

The Genetic Code Figure 8.9

Translation Figure

Translation Figure

Translation Figure

Translation Figure

Translation Figure

Translation Figure

Translation Figure

Translation Figure

Translation Figure 8.11

Change in the genetic material Change in the genetic material Mutations may be Mutations may be neutral neutral beneficial beneficial or harmful or harmful Mutagen: Agent that causes mutations Mutagen: Agent that causes mutations Spontaneous mutations: Occur in the absence of a mutagen Spontaneous mutations: Occur in the absence of a mutagen Mutation

Base substitution (point mutation) Base substitution (point mutation) Missense mutation Missense mutation Mutation Figure 8.17a, b Change in one base Result in change in amino acid Change in one base Result in change in amino acid

Nonsense mutation Nonsense mutation Mutation Results in a nonsense codon Results in a nonsense codon Figure 8.17a, c

Frameshift mutation Frameshift mutation Mutation Figure 8.17a, d Insertion or deletion of one or more nucleotide pairs Insertion or deletion of one or more nucleotide pairs

Ionizing radiation Ionizing radiation formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone. formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone. Nucleotide excision repairs mutations Nucleotide excision repairs mutations Mutagen

UV radiation causes thymine dimers UV radiation causes thymine dimers Light-repair separates thymine dimers Light-repair separates thymine dimers Mutagen Figure 8.20

Spontaneous mutation rate = 1 in 10 9 replicated base pairs or 1 in 10 6 replicated genes Spontaneous mutation rate = 1 in 10 9 replicated base pairs or 1 in 10 6 replicated genes Mutagens increase to 10 –5 or 10 –3 per replicated gene Mutagens increase to 10 –5 or 10 –3 per replicated gene The Frequency of Mutation

Selection Positive (direct) selection detects mutant cells because they grow or appear different. Positive (direct) selection detects mutant cells because they grow or appear different. Negative (indirect) selection detects mutant cells because they do not grow. Negative (indirect) selection detects mutant cells because they do not grow.

Replica Plating Figure 8.21

The Ames Test for Chemical Carcinogens Figure 8.22

Vertical gene transfer Vertical gene transfer Horizontal gene transfer Horizontal gene transfer Genetic Transfer and Recombination Occurs during reproduction, between generations of cells Occurs during reproduction, between generations of cells Transfer of genes between cells of the same generation Transfer of genes between cells of the same generation

Transformation Figure 8.24

Recombination Figure 8.25

Conjugation Figure 8.27a

Conjugation Figure 8.27b

Conjugation Figure 8.27c

Plasmids Figure 8.29

Segments of DNA that can move from one region of DNA to another Segments of DNA that can move from one region of DNA to another Contain insertion sequences for cutting and resealing DNA (transposase) Contain insertion sequences for cutting and resealing DNA (transposase) Complex transposons carry other genes Complex transposons carry other genes Transposons Figure 8.30a, b

Constitutive enzymes are expressed at a fixed rate Constitutive enzymes are expressed at a fixed rate Other enzymes are expressed only as needed Other enzymes are expressed only as needed Repressible enzymes Repressible enzymes Inducible enzymes Inducible enzymes Regulation of Bacterial Gene Expression

Repression Figure 8.13

Operon Figure

Regulation of Gene Expression Figure

Regulation of Gene Expression Figure

Regulation of Gene Expression Figure

Regulation of Gene Expression Figure

Regulation of Gene Expression Figure 8.15