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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

Chapter 8

  • 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

Chapter 8


  • 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

The genetic code1
The Genetic Code

Figure 8.8

Chapter 8

Mutation change in the genetic material
Mutation: Change in the Genetic Material transcription?

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.

Mutation transcription?

  • 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 transcription?

Result in change in amino acid


  • Base substitution (point mutation)

  • Missense mutation

Figure 8.17a, b


Results in a nonsense codon transcription?


  • Nonsense mutation

Figure 8.17a, c


Insertion or deletion of one or more nucleotide pairs transcription?


  • Frameshift mutation

Figure 8.17a, d

The frequency of mutation
The Frequency of Mutation transcription?

  • 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 transcription?

Figure 8.19a

Chemical mutagens1
Chemical Mutagens transcription?


Figure 8.19b

Radiation transcription?

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

Radiation transcription?

  • UV radiation causes thymine dimers

Figure 8.20

Repair transcription?

  • Photolyases separate thymine dimers

  • Nucleotide excision repair

ANIMATION Mutations: Repair

Figure 8.20