Plamids role in bacterial cell

[gemma786]

Hi
I want to know about the role which plasmids play in a baterial cell.How the genes which are coded in plasmid DNA expressed themselves ? Does the transcription of plasmid DNA takes place independently of chromosomal DNA I mean to say that do the plasmids have promotor sequence for RNA polymerase to bind or plasmid first bind to chromosomal DNA forming episome inorder to express the genes which it contanins ? AND how the presence of antibiotics in the environment influence the number of plamids in a bacterial cell ?
And what is the effect of having large number of plasmid of same type in a bacterial cell ?
Please help me to find answer to these questions.
Thanks.

 

[iansmith]

How the genes which are coded in plasmid DNA expressed themselves ?
Does the transcription of plasmid DNA takes place independently of chromosomal DNA I mean to say that do the plasmids have promotor sequence for RNA polymerase to bind or plasmid first bind to chromosomal DNA forming episome inorder to express the genes which it contanins ?

Basically, expression of plasmid gene is mostly independent but it is partly dependent on the bacterial host expression apparatus. The plasmid genes have their own promoter but, in most cases, they need the bacterial host RNA polymerase for their transcription. Some plasmids have their own regulators.

AND how the presence of antibiotics in the environment influence the number of plamids in a bacterial cell ?

It depends if the plasmids codes for an antibiotic resistance genes and if a large number of the gene product encoded by the resistance genes is needed for resistance to be achieved. It will also dependent on the type of origin of replication of the plasmid. The presence of antibiotics may have no effect on the number of plasmids but in some cases it may results in increase number of plasmid copy number if the plasmids has an antibiotic resistance gene.

And what is the effect of having large number of plasmid of same type in a bacterial cell ?

Again it depends if the plasmid is fairly large or small but a large number of plasmid will have a metabolic cost due to its large number of replication events.

 

[gemma786]

Thanks. jansmith and sorry for replying late.
I was just trying to understand how plasmid can be used as a cloning vector.
And as you said plasmids containing a gene for antibiotic resistance can multiply their copies if surrounding medium contains antibiotic but you also said that plasmids can also have regulators now does this means to say that plasmids have operon units like dna ? It would mean that in order clonise a plasmid, we would have to take into consederation those operator units and the products which would lead to activation of those operon units , because we want to make as many copies of plasmid as we can in cloning process along with the desired gene that we have introduced in plasmid , isn't it ?
I am not sure about this . I need help !

 

[iansmith]

In nature, plasmids that are very small will only have one gene, which might be required for their replication, but very large plasmid can contain several genes, including genes that are required for their replication and partitioning into the daughter cells.

For cloning vectors, most plasmids were derived from naturally occurring plasmids but the cloning vector went through major modification and removal of DNA with coding regions. In some case, these modification had major impacts.

Copy number of plasmids are often controlled through the origin of replication. For example, pUC19 or pUC18 are high copy numbers and their source plasmid is pMB1 is a low copy number plasmid. pUC19/18 have a point mutation in their origin of replication which allows for the high copy number but they also lack a rop gene.

 

[LudusRex]

Hello,

Thank you for your questions about plasmids and their role in bacterial cells. Plasmids are small, circular pieces of DNA that exist independently from the bacterial cell's chromosomal DNA. They can be found in both prokaryotic and eukaryotic cells, and their main function is to carry additional genetic information that can provide benefits to the bacterial cell, such as antibiotic resistance or the ability to produce certain proteins.

To answer your first question, the genes coded in plasmid DNA are expressed in a similar manner to chromosomal DNA. Plasmids have their own promoter sequences that allow RNA polymerase to bind and initiate transcription. This means that the genes on plasmids can be transcribed and translated into proteins without the involvement of chromosomal DNA.

Regarding the presence of antibiotics in the environment, plasmids can play a crucial role in the survival of bacterial cells. If a plasmid contains genes for antibiotic resistance, it can be passed on to other bacterial cells through horizontal gene transfer. This allows the bacteria to survive in the presence of antibiotics and can contribute to the development of antibiotic resistance.

The number of plasmids in a bacterial cell can vary depending on the environment and the selective pressures present. In some cases, bacteria may lose plasmids if they no longer provide a benefit to the cell. However, if the plasmid contains important genes, it may be maintained and even replicated to ensure its presence in future generations.

Having a large number of plasmids of the same type in a bacterial cell can have both positive and negative effects. On one hand, it can increase the expression of certain beneficial genes, providing an advantage to the bacterial cell. On the other hand, it can also place a burden on the cell's resources and potentially decrease its overall fitness.

I hope this answers your questions about plasmids and their role in bacterial cells. If you have any further inquiries, please don't hesitate to ask. Thank you.