Microbial Genetics

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Microbial Genetics

To know the genetic properties of microorganisms;

In the investigation of gene functions,

Reproduction of some special genes in other organisms in microorganisms,

Production of some industrially important products in large quantities,

In the treatment of microbial diseases and

It is extremely important in determining how genes are transferred between

organisms.

Genetically modified microorganisms are used in these studies.

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MUTATION

 All kinds of base number and sequence changes that occur in the DNA structure of an organism and are hereditary are called mutations.

 A mutant is defined as a live mutant that carries a different DNA from the ancestor type (wild type) and the causative agent is defined as mutagen.

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Mutant types

 Oxotrophic mutants: They cannot develop on minimal media. They have lost some enzymes in the biosynthetic pathways.

 Resistant mutants

 Immobilized mutants

 Non-pigmented mutants

 Mutants without capsules

 Mutants that cannot use sugars

 Viruses resistant mutants

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Mutation types

Spontaneous mutations

Point mutation A mutation in a base pair

Transition  purine  purine, or primidine  primidine

Transversion  purine  primidine, or primidine  purine

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Mutation types

Point mutation in the ATG codon of ancestral strain results in:

If the ATA codon occurs, the tyrosine codon

 silent mutation

If the ATC codon occurs, the stop codon

nonsense mutation

If the TTG codon occurs, asparagine  missense mutation

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Mutation types

Frame shift mutations, reading pattern shift or frame shift

Extraction of a base pair from the DNA (microdeletion)

or insertion of a base pair into the DNA (microinsertion)

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Translocation of DNA fragments on the genome to a different region of DNA by translocation

It was determined that the DNA fragment that was broken by inversion was

inverted and adhered to the same region again.

Reversal: Point mutations are reversible.

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 Mutations in RNA genomes: Viruses with genomes consisting of RNA have more

(approximately 1000 times) mutations than DNA genomes.

 The RNA polymerase enzyme in RNA viruses can correct replication errors such as DNA polymerase.

 However, many repair systems found in DNA

genomes are not found in RNA genomes. Therefore, mutations are repaired at a higher rate in DNA

genomes.

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Mutagens

1. Chemical mutagens

 Base analogs  Timine  5-Bromurasil

 Chemicals that react with DNA

 Nitrous acid (HNO2)  (deamination)

Alkylating agents: They alkylate the guanine nitrogen at position N 7.

Dyes entering between base pairs such as acridine and ethidium bromide cause microdeletions and microinsersion.

2. Physical mutagens

Radiation: Non-ionizing radiation  ultraviolet (UV) Rays (260nm wavelength)  primidine dimers Short wavelength rays such as cosmic rays, X rays and gamma rays are ionizing radiation agents.

3. Biological mutagens

Transposons, Bacteriophage Mu, Mutagenic DNA repair systems:

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Mutagens

Physical mutagens

Radiation: Non-ionizing radiation 

ultraviolet (UV) rays (260nm wavelenght

 primidine dimers

Short wavelength rays such as cosmic

rays, X rays and gamma rays are ionizing radiation agents..

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Microbial Genetics