Chapter 9

Microbial Genetics



Genetics is the study of the inheritance, or heredity, of living things

Scope

The transmission of biological properties (traits) from parent to offspring

The expression and variation of those traits

The structure and function of the genetic material; and how this material changes


Chromosome

The genetic material of a cell that is found in several different forms, with the majority existing as large complexes of DNA and proteins

Genome

The sum total of the genetic material residing on chromosomes

Viral genomes are different (DNA or RNA)

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Plasmid

Plasmids are independently replicating, small double-stranded DNA molecules found in some bacterial species

Contain genes that are not essential for cell growth

Bear genes that code for adaptive traits

Transmissible to other bacteria

DNA also present in chloroplasts and mitochondria

 

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Gene

A site on a chromosome that provides information for a certain cell function

A specific segment of DNA that contains the necessary code to make a protein or RNA molecule

Genotype

The genetic makeup of an organism

The genotype is ultimately responsible for an organism’s phenotype, or expressed characteristics

Phenotype

The observable characteristics of an organism produced by the interaction between its genetic potential (genotype) and the environment

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Size and packing of genomes

Genomes vary in size:

Smallest virus has 4 or 5 genes

Escherichia coli (length: 1 µm) has a single chromosome containing 4,288 genes

Its chromosome measures about 1 mm if stretched out it will be about 1,000 times its length

Human has about 30,000 genes distributed into 46 chromosomes

 

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DNA structure

Review section on nucleic acids in Chapter 2


Nitrogenous bases (purines and pyrimidines)

Five carbon (pentose) sugars

Nucleotide

Other terminology

DNA replication (Figs. 9.6, 9.7)

DNA copies itself just before cellular division by the process of semiconservative replication
(each ‘old’ strand is the template upon which each ‘new’ strand is synthesized)

Leading strand

Lagging strand

The circular bacterial chromosome is replicated at two forks as directed by DNA polymerase III

At each fork, two new strands are synthesized – one continuously and one in short fragments

Mistakes are proofread and removed

 

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 Textbook: Foundations in Microbiology. K.Park Talaro. 6th edition. McGraw Hill.

Remember to read your textbook, study tables, graphs and illustrations.
Develop a strategy to administer your time so that when exams come you do not have to cram.
Attend lectures and ask questions.

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