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Chapter 8. Microbial Genetics. Structure and Function of Genetic Material. Learning Objectives. 8-1 Define genetics, genome, chromosome, gene, genetic code, genotype, phenotype, and genomics. 8-2 Describe how DNA serves as genetic information.

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chapter 8

Chapter 8

Microbial Genetics

structure and function of genetic material
Structure and Function of Genetic Material

Learning Objectives

  • 8-1 Define genetics, genome, chromosome, gene, genetic code, genotype, phenotype, and genomics.
  • 8-2 Describe how DNA serves as genetic information.
  • 8-3 Describe the process of DNA replication.
  • 8-4 Describe protein synthesis, including transcription, RNA processing, and translation.
  • 8-5 Compare protein synthesis in prokaryotes and eukaryotes.
  • Genetics: The study of what genes are, how they carry information, how information is expressed, and how genes are replicated
  • Gene: A segment of DNA that encodes a functional product, usually a protein
  • Chromosome: Structure containing DNA that physically carries hereditary information; the chromosomes contain the genes
  • Genome: All the genetic information in a cell
  • Genomics: The molecular study of genomes
  • Genotype: The genes of an organism
  • Phenotype: Expression of the genes
e coli
E. coli

Figure 8.1a

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

Figure 8.3b

dna synthesis
DNA Synthesis

Figure 8.4

dna synthesis1
DNA Synthesis
  • DNA is copied by DNA polymerase
    • In the 5\' 3\' direction
    • Initiated by an RNA primer
    • Leading strand is synthesized continuously
    • Lagging strand is synthesized discontinuously
    • Okazaki fragments
    • RNA primers are removed and Okazaki fragments joined by a DNA polymerase and DNA ligase
dna synthesis2
DNA Synthesis

Figure 8.5

Give a clinical application of genomics. 8-1
  • Why is the base pairing in DNA important? 8-2
  • Describe DNA replication, including the functions of DNA gyrase, DNA ligase, and DNA polymerase. 8-3
  • DNA is transcribed to make RNA (mRNA, tRNA, and rRNA)
  • Transcription begins when RNA polymerase binds to the promoter sequence
  • Transcription proceeds in the 5\' 3\' direction
  • Transcription stops when it reaches theterminator sequence

Figure 8.7

the process of transcription1
The Process of Transcription

ANIMATION Transcription: Overview

ANIMATION Transcription: Process

Figure 8.7

  • mRNA is translated in codons (three nucleotides)
  • Translation of mRNA begins at the start codon: AUG
  • Translation ends at nonsense codons: UAA, UAG, UGA

Figure 8.2

the genetic code
The Genetic Code
  • 64 sense codons on mRNA encode the 20 amino acids
  • The genetic code is degenerate
  • tRNA carries the complementary anticodon

Figure 8.2

What is the role of the promoter, terminator, and mRNA in transcription? 8-4
  • How does mRNA production in eukaryotes differ from the process in prokaryotes? 8-5
mutation change in the genetic material
Mutation: Change in the Genetic Material

Learning Objectives

  • 8-8 Classify mutations by type.
  • 8-9 Define mutagen.
  • 8-10 Describe two ways mutations can be repaired.
  • 8-11 Describe the effect of mutagens on the mutation rate.
  • 8-12 Outline the methods of direct and indirect selection of mutants.
  • 8-13 Identify the purpose of and outline the procedure for the Ames test.
  • A 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
Change in one base

Result in change in amino acid

  • Base substitution (point mutation)
  • Missense mutation

Figure 8.17a, b

Results in a nonsense codonMutation
  • Nonsense mutation

Figure 8.17a, c

the frequency of mutation
The Frequency of Mutation
  • Spontaneous mutation rate = 1 in 109 replicated base pairs or 1 in 106 replicated genes
  • Mutagens increase to 10–5 or 10–3 per replicated gene

ANIMATION Mutations: Types

chemical mutagens
Chemical Mutagens

Figure 8.19a

chemical mutagens1
Chemical Mutagens


Figure 8.19b

  • Ionizing radiation (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone
  • UV radiation causes thymine dimers

Figure 8.20

  • Photolyases separate thymine dimers
  • Nucleotide excision repair

ANIMATION Mutations: Repair

Figure 8.20