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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

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Chapter 8

Microbial Genetics


Structure and Function of Genetic Material

Learning Objectives

  • 8-1Define genetics, genome, chromosome, gene, genetic code, genotype, phenotype, and genomics.

  • 8-2Describe how DNA serves as genetic information.

  • 8-3Describe the process of DNA replication.

  • 8-4Describe protein synthesis, including transcription, RNA processing, and translation.

  • 8-5Compare protein synthesis in prokaryotes and eukaryotes.


Terminology

  • 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


Terminology

  • Genomics: The molecular study of genomes

  • Genotype: The genes of an organism

  • Phenotype: Expression of the genes


E. coli

Figure 8.1a


Genetic Map of the Chromosome of E. coli

Figure 8.1b


The Flow of Genetic Information

Figure 8.2


DNA

  • 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


Semiconservative Replication

Figure 8.3a


DNA Synthesis

Figure 8.4


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


Table 8.1


Table 8.1


DNA Synthesis

Figure 8.5


Replication of Bacterial DNA

Figure 8.6


  • 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


Transcription

  • 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


Transcription

Figure 8.7


The Process of Transcription

Figure 8.7


The Process of Transcription

ANIMATION Transcription: Overview

ANIMATION Transcription: Process

Figure 8.7


RNA Processing in Eukaryotes

Figure 8.11


Translation

  • 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

  • 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 Code

Figure 8.8


Simultaneous Transcription & Translation

Figure 8.10


The Process of Translation

Figure 8.9


The Process of Translation

Figure 8.9


The Process of Translation

Figure 8.9


The Process of Translation

Figure 8.9


The Process of Translation

Figure 8.9


The Process of Translation

Figure 8.9


The Process of Translation

Figure 8.9


The Process of Translation

Figure 8.9


  • 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

Learning Objectives

  • 8-8Classify mutations by type.

  • 8-9Define mutagen.

  • 8-10Describe two ways mutations can be repaired.

  • 8-11Describe the effect of mutagens on the mutation rate.

  • 8-12Outline the methods of direct and indirect selection of mutants.

  • 8-13Identify the purpose of and outline the procedure for the Ames test.


Mutation

  • 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

Mutation

  • Base substitution (point mutation)

  • Missense mutation

Figure 8.17a, b


Results in a nonsense codon

Mutation

  • Nonsense mutation

Figure 8.17a, c


Insertion or deletion of one or more nucleotide pairs

Mutation

  • Frameshift mutation

Figure 8.17a, d


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

Figure 8.19a


Chemical Mutagens

ANIMATION Mutagens

Figure 8.19b


Radiation

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


Radiation

  • UV radiation causes thymine dimers

Figure 8.20


Repair

  • Photolyases separate thymine dimers

  • Nucleotide excision repair

ANIMATION Mutations: Repair

Figure 8.20


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