Shatha Khalil Ismael

Transformation

Certain species of Gram- negative, gram- positive bacteria and some species of Archaea are transformable .

The uptake of DNA from one bacterial cell, either as a plasmid or a fragment, by another cell is called transformation it Is a process by which free DNA is incorporated into a recipient cell and bring about a genetic change..

Since the DNA of procaryote is present in the cell as a large single molecule, when the cell is gently lysed, the DNA pours out, and because its extreme length bacterial chromosome breaks easily.

Mechanism of transformation in gram positive bacterium :

• Binding of double stranded DNA by a membrane bound DNA binding proteins

• Passage of one of the two strands into the cell while neuclease activity degrades the other strand

• The single strand in the cell is bound by a specific proteins and recombination with homologous regions of the bacterial chromosome is mediated by RecA protein

• Transformed cell

Video transformation

The end product of bacterial transformation?

DNA is degraded by the host cellintegration of the DNA by

nonreciprocal recombinationPlasmid is stably transformed into

the cell but separate from the chromosome

Bacterial conjugation:

Process of genetic transfer that involves cell-to-cell contact.

A pilus is a hairlike appendage found on the surface of many bacteria.

The terms pilus  for the appendage required for bacterial conjugation

Video conjugation

DNA transfer during conjugation:

DNA synthesis is necessary for DNA transfer to occur during conjugation a bacteriophages, called rolling circle replication ,, explains DNA transfer during conjugation

Rolling circle replication describes a process of unidirectional nucleic acid replication that can rapidly synthesize multiple copies of circular molecules of DNA or RNA, such as plasmid, the genome of bacteriophages, and the circular RNA genome of viroids . Some eukaryotic viruses also replicate their DNA via a rolling circle mechanism.

Video rolling

the formation of Hfr strains and chromosome mobilization

The F plasmid of E-coli can under circumstance, mobilize the chromosome for transfer during cell-to-cell contact. When the F plasmid is integrated into the chromosome , the chromosome becomes mobilized and can lead to transfer of chromosomal genes

Cells possessing an unintegrated F plasmid are called : F +

those that have a chromosome-integrated F plasmid are called Hfr (high frequency of recombination ) Both F+ and Hfr cells are donors and are unable to take up a second copy of the Fplasmid or genetically related plasmid

The F- recipient cell may express a new phenotype.

The conjugation between an f – and an Hfr donor lead to transfer of genes from the host chromosome because the plasmid is part of the chromosome

Plasmid integration is a mechanism for mobilizing the cells main genetic resources

The presence of F plasmid results in 3 distinct alternations in the properties of a cell:1- the ability of synthesize the F pilus 2- the mobilization of DNA for transfer to another cell 3- the alternation of surface receptors So the cell is no longer able to behave as a recipient in conjugation.

Transduction :

In transduction DNA is transferd from cell to cell by a bacterial virus ( bacteriophage ).Genetic transfer of host genes by viruses can occur by :1- generalized transduction2- specialized transduction

generalized transduction

Most DNA derived from virtually any portion of the host genome becomes a part of DNA of the mature virion in place of the viral genome

Note that the “normal” versions contain phage genes while “a transducing particle” contains host genes .

Video general

specialized transduction

Occur only in some temperate viruses .DNA from a specific region of the host chromosome is integrated directly into the virus genome , usually replacing some of the virus genes.

The transducing virion in BOTH generalized and specialized transduction is usually no infective as a virus because bacterial genes have replaced some or all necessary viral genes.

Video specialized

Thank you

A mechanism of horizontal gene transfer (HGT) in Bacteria and Archaea?

Conjugation, Transformation , Transduction

1. Aid in DNA transfer,,2. Forms sex pili,,3. Includes IS elements that assist plasmid integration into the host cell's chromosome,,

What is the role of the genes related to the F factor in conjugation

Which of the following is TRUE of conjugation?1. Requires physical contact between microbes2. Unidirectional3. Involves plasmids

Conjugation in which the donor transfers chromosomal genes with great efficiency but does not change the recipient into F+ cells is known as??HFr conjugation

What happens to donor DNA when it enters the recipient cell

Integration of the DNA into the recipient's chromosome

Replicates separately from the host DNA in a plasmid

Donor DNA remains in the cytoplasm, unable to replicate

A reciprocal exchange between a pair of DNA molecules with the same nucleotide sequence is calledHomologous recombination

insertion sequences of transposable elements..

It contains only the gene for the enzyme transposase

 replicative transposition,,Contains genes coding for transposase and resolvase

the role of the genes related to the F factor in conjugation

1. Aid in DNA transfer,,2. Forms sex pili,,3. Includes IS elements that assist plasmid integration into the host cell's chromosome,,

Conjugation in which the donor transfers chromosomal genes with great efficiency but does not change the recipient into F+ cells is known as

HFr conjugation