MICRO PPT (1)

TRANSFER OF GENETIC MATERIAL- PLASMIDS, TRANSPOSONS & TRANSDUCTION

BYJYOTHSNA BMtech BiotechnologySem-1

GENE TRANSFER

Gene transfer is the process in which the genetic material is transferred from one organism into the other organism.

There are two types of gene transfers.

a) Horizontal gene transfer(lateral gene transfer) - gene transfer from one cell to another cell which is not its offspring. b) Vertical gene transfer - gene transfer from one cell to another cell which is from its ancestors.

MECHANISM

1) Plasmids – Acts as vectors in transfer of genetic material.

2) Transformation – Genetic recombination in which a DNA fragment

from a dead, degraded bacterium enters a competent recipient bacterium and it is exchanged for a piece of the recipient's DNA.

3) Transduction – The process in which bacterial DNA is moved from one bacterium to another by a virus (Bacteriophage).4) Conjugation – A process in which a bacterial cell transfers genetic

material to another cell by cell-to-cell contact.

PLASMIDS Plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA.

They are double-stranded and circular.

Plasmid sizes vary from 1 to over 1,000kbp.

Plasmids serve as important tools in genetics and biotechnology labs, where they are commonly used to multiply or express particular genes. TYPES

conjugative plasmids non-conjugative plasmids (tra genes)

Based on their function:

1) F-plasmids – tra genes – conjugation

2) R-plasmids – genes resistance to antibiotics and toxins

3) Col-plasmids – genes for bacteriocins and toxins

4) Degradative plasmids – enable digestion of unusual substances

5) Virulence plasmids – turns bacteria into pathogen

Plasmids may carry genes that provide resistance to naturally occurring antibiotics.

TRANSPOSONS

Transposons are sequences of DNA that can move or transpose themselves to new positions within the genome of a single cell.

The mechanism of transposition can be either "copy and paste" or "cut and paste".

They were first discovered by Barbara McClinkton in maize, for which she got Noble prize in 1983. Types

Retrotransposons DNA transposons

Retrotransposons:

They are formed by RNA as intermediate.

Mechanism: Transposon (Transcription)

RNA (Reverse transcription)

DNA (Reintegration)

Retrotransposon (Transposon copy) The integration may occur randomly on the same chromosome or on different chromosome.

DNA Transposons:

No RNA intermediates, it is a direct transposition of DNA to DNA. TYPES

Replicative transposition Conservative transposition

TRANSDUCTION

The process by which foreign DNA is introduced into another cell via a viral vector. TYPES

Generalized transduction Specialised transduction

Seven steps in Generalised Transduction

1. A lytic bacteriophage adsorbs to a susceptible bacterium.

2. The bacteriophage genome enters the bacterium. The genome directs the bacterium's metabolic machinery to manufacture bacteriophage components and enzymes

3. Occasionally, a bacteriophage head or capsid assembles around a fragment of donor bacterium's nucleoid or around a plasmid instead of a phage genome by mistake.

Seven steps in Generalised Transduction (cont’d)

4. The bacteriophages are released.

5. The bacteriophage carrying the donor bacterium's DNA adsorbs to a recipient bacterium

Seven steps in Generalised Transduction (contd)

6. The bacteriophage inserts the donor bacterium's DNA it is carrying into the recipient bacterium .

7. The donor bacterium's DNA is exchanged for some of the recipient's DNA.

Six steps in Specialised Transduction

1. A temperate bacteriophage adsorbs to a susceptible bacterium and injects its genome .

2. The bacteriophage inserts its genome into the bacterium's nucleoid to become a prophage.

Six steps in Specialised Transduction (cont’d)

3. Occasionally during spontaneous induction, a small piece of the donor bacterium's DNA is picked up as part of the phage's genome in place of some of the phage DNA which remains in the bacterium's nucleoid.

4. As the bacteriophage replicates, the segment of bacterial DNA replicates as part of the phage's genome. Every phage now carries that segment of bacterial DNA.

Six steps in Specialised Transduction (cont’d)

5. The bacteriophage adsorbs to a recipient bacterium and injects its genome.

6. The bacteriophage genome carrying the donor bacterial DNA inserts into the recipient bacterium's nucleoid.

THANK YOU