Medical Technology Department, Faculty of Science, Islamic University-Gaza MB M ICRO B IOLOGY Dr. Abdelraouf A. Elmanama Ph. D Microbiology 2008 Chapter 8 Microbial Genetics

2008 Terminology GeneticsStudy of what genes are, how they carry information, how information is expressed, and how genes are replicated GeneSegment of DNA that encodes a functional product, usually a protein

2008 Terminology GenomeAll of the genetic material in a cell GenomicsMolecular study of genomes GenotypeGenes of an organism PhenotypeExpression of the genes

2008 E. coli Figure 8.1a

2008 Flow of Genetic Information Figure 8.2

2008 Polymer of nucleotides: adenine, thymine, cytosine, guanine Double helix associated with proteins "Backbone" is deoxyribose-phosphate Strands held together by hydrogen bonds between AT and CG Strands are antiparallel DNA Figure 8.4

2008 DNA Figure 8.3

2008 DNA Figure 8.5

2008 DNA is copied by DNA polymerase In the 5  3 direction Initiated by an RNA primer Leading strand synthesized continuously Lagging strand synthesized discontinuously Okazaki fragments RNA primers are removed and Okazaki fragments joined by a DNA polymerase and DNA ligase DNA

2008 DNA Figure 8.6

2008 DNA replication is semiconservative DNA Figure 8.7

2008 DNA is transcribed to make RNA (mRNA, tRNA, and rRNA) Transcription begins when RNA polymerase binds to the promotor sequence Transcription proceeds in the 5  3 direction Transcription stops when it reaches the terminator sequence Transcription

2008 Figure 8.8

2008 RNA processing in Eukaryotes Figure 8.12

2008 mRNA is translated in codons (3 nucleotides) Translation of mRNA begins at the start codon: AUG Translation ends at a STOP codon: UAA, UAG, UGA Translation Figure 8.2

2008 Translation Figure 8.9

2008 Translation Figure

2008 Translation Figure

2008 Translation Figure

2008 Translation Figure

2008 Translation Figure

2008 Translation Figure

2008 Translation Figure

2008 Translation Figure

2008 Translation Figure 8.11

2008 Constitutive enzymes are expressed at a fixed rate Other enzymes are expressed only as needed Repressible enzymes Inducible enzymes Regulation of Bacterial Gene Expression

2008 Repression Figure 8.13

2008 Operon Figure

2008 Regulation of Gene Expression Figure

2008 Regulation of Gene Expression Figure

2008 Regulation of Gene Expression Figure

2008 Regulation of Gene Expression Figure

2008 Regulation of Gene Expression Figure 8.15

2008 Change in the genetic material Mutations may be neutral, beneficial, or harmful Mutagen: Agent that causes mutations Spontaneous mutations: Occur in the absence of a mutagen Mutation

2008 Base substitution (point mutation) Missense mutation Mutation Figure 8.17a, b Change in one base Result in change in amino acid

2008 Nonsense mutation Mutation Results in a nonsense codon Figure 8.17a, c

2008 Frameshift mutation Mutation Figure 8.17a, d Insertion or deletion of one or more nucleotide pairs

2008 Ionizing radiation (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone. Nucleotide excision repairs mutations Mutation

2008 UV radiation causes thymine dimers Light-repair separates thymine dimers Mutation Figure 8.20

2008 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 The Frequency of Mutation

2008 Selection Positive (direct) selection detects mutant cells because they grow or appear different. Negative (indirect) selection detects mutant cells because they do not grow.

2008 Replica Plating Figure 8.21

2008 The Ames Test for Chemical Carcinogens Figure 8.22

2008 Vertical gene transfer Horizontal gene transfer Genetic Transfer and Recombination Occurs during reproduction, between generations of cells Transfer of genes between cells of the same generation

2008 Transformation Figure 8.24

2008 Recombination Figure 8.25

2008 Conjugation Figure 8.27a

2008 Conjugation Figure 8.27b

2008 Conjugation Figure 8.27c

2008 Exchange of genes between two DNA molecules Crossing over occurs when two chromosomes break and rejoin Genetic Recombination Figure 8.23

2008 Transduction Figure 8.28 Recombinant 1 Phage protein coat Bacterial chromosome 2 3 Bacterial DNA Phage DNA 4 Recipient cell 5 Donor bacterial DNA Recipient bacterial DNA Recombinant cell A phage infects the donor bacterial cell. Phage DNA and proteins are made, and the bacterial chromosome is broken down into pieces. Occasionally during phage assembly, pieces of bacterial DNA are packaged in a phage capsid. Then the donor cell lyses and releases phage particles containing bacterial DNA. A phage carrying bacterial DNA infects a new host cell, the recipient cell. Recombinant can occur, producing a recombinant cell with a genotype different from both the donor and recipient cells.

2008 Conjugative plasmidCarries genes for sex pili and transfer of the plasmid Dissimilation plasmids Encode enzymes for catabolism of unusual compounds R factorsEncode antibiotic resistance Plasmids

2008 Plasmids Figure 8.29

2008 Segments of DNA that can move from one region of DNA to another Contain insertion sequences for cutting and resealing DNA (transposase) Complex transposons carry other genes Transposons Figure 8.30a, b