9- Bacterial Genetics

CRITICAL THINKING QUESTIONS

Why transformation as a genetic recombination method was essential to understand the role of DNA as a hereditary molecule?

Why the genetic code is considered the universal language of life?

How come we have introns in our DNA?

List the different kinds of RNA so far studied and why do you think they have different morphology?

Microbial Genetics

Genetics

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

Scope

The transmission of biological properties (traits) from parent to offspringThe expression and variation of those traitsThe 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)

Plasmids

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

Contain genes that are not essential for cell growthBear genes that code for adaptive traitsTransmissible to other bacteria

DNA also present in chloroplasts and mitochondria

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

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

The human chromosomes have about 21,000 genes distributed into 46 chromosomes. Three billion nitrogenn bases. If stretch: 1.5 m

DNA Structure

Review section on nucleic acids in Chapter 2

  • Nitrogenous bases (purines and pyrimidines)

  • Five carbon (pentose) sugars

  • Nucleotide (phosphate, sugar, and nitrogen base)

DNA Replication 

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