Bacterial Genetics Question And Answers

Bacterial Genetics

Question 1. Write a short note on transduction.
Answer:

Transduction is defined as the transmission of a portion of DNA from one bacterium to another by bacteriophage. It not only transfers chromosomal DNA but may also transfer plasmid or episomal DNA.

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• During the assembly of bacterial progeny in infected bacteria errors may happen. Besides its own nucleic acid host DNA was accidentally incorporated into bacteriophage. It is known as a packaging error.
• When a bacteriophage infects another bacterium host DNA is transferred and the recipient cell acquires new characters coded by donor DNA.

Types of Transduction:

• Generalized: When transduction involves any segment of donor DNA has a roughly equal chance of being incorporated in a phage coat.
• Restricted: When a specific bacteriophage transduces any particular genetic trait.

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Mechanism of Transduction:

• Attack of bacteriophage to the bacterium.
• Bacteriophage releases their nucleic acid in bacterial cells and starts replication.
• As the maturation process of virus particles is going on a few phage heads may envelop any fragment of bacteria.
• DNA in generalized transduction or it may envelop a particular segment of bacteria.
• DNA under specialized transduction with phage DNA.
• Now when phage infects another bacterium, it introduces bacteria.
• DNA which gets incorporated inside the bacterial chromosome. In this way, the transfer of bacterial genes to other bacteria occurs.

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Importance of Transduction:

• Transduction provides an excellent tool for the genetic mapping of bacteria.
• Transduction is a method of genetic engineering in the treatment of inborn errors of metabolism.

Question 2. Write a brief on bacterial drug resistance.
Or
Write a note on drug resistance.
Or
Write a short note on drug resistance in bacteria.
Answer:

Drugs Introduction: Drug resistance is the unresponsiveness of microorganisms towards an antibiotic due to its repeated use.

Types of Drug Resistance: There are two types of drug resistance, which are as follows.

• Chromosomal or Mutational: This is the resistance to one drug at a time. It arises as a result of spontaneous mutation in a locus of a chromosomal gene that controls susceptibility to a drug. The presence of the drug acts as a selective mechanism to suppress susceptibility and promote the growth of drug-resistant mutants.
  It has low degree resistance. It is not transferable to other organisms. This is prevented by the treatment of other drugs.
• Extrachromosomal or Transferable: This is multiple drug resistance. This type of drug resistance is mediated by the R factor as an important method of drug resistance. It has a high degree of resistance to multiple drugs. It is transferable to other organisms. It cannot be prevented by treatment with a combination of drugs.

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Mechanism of Drug Resistance: Drug resistance develops by following methods:

• Gene transfer
• Mutation
• Modification in biochemical mechanism

Gene Transfer: Transposons, i.e. DNA segments undergo self-transfer between the plasmids or from plasmids to chromosomes. During gene transfer, the donor plasmid which consists of transposes gets integrated with the acceptor plasmid and during this process, the transpose may undergo replication.

Mutation:  It is the stable and heritable genetic change in the DNA of a gene that occurs spontaneously. It is of two types, i.e. single-step and multistep. A single step emerges rapidly and shows a high degree of resistance. In multistep multiple gene modifications are present and there is retardation of sensitivity in steps.

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Modification in Biochemical Methods:

• Production of antibiotic-inactivating enzyme: Chloramphenicol gets inactivated by chloramphenicol acetyltransferase which is produced by resistant strains.
• Prevention of accumulation of the drug in bacteria: Bacterial envelope may undergo biochemical accumulation neither allowing influx nor promoting effect of the drug.
• Modification or protection of target site: An example is ribosomal point mutation for tetracycline, macrolides as well as clindamycin.
• Alternative pathways for metabolism: Development of resistance to sulphonamides due to overproduction of P aminobenzoic acid.