Question

The restriction endonuclease is having a defence mechanism in the bacterial system against foreign DNA such as viruses. But how it is able to protect its own DNA? Not yet answered Marked out of 100 Flag question Select one:

a. By methylation of bacterial DNA by restriction enzyme
b. By methylation of foreign DNA by restriction enzyme
c. By phosphorylation of foreign DNA by restriction enzyme
d. By phosphorylation of bacterial DNA by restriction enzyme

Answer 1

Bacteria use a defense mechanism where DNA methylase methylates their own DNA, making it immune to the cleavage by restriction endonucleases, which, in turn, cleave unmethylated foreign DNA including that from viruses.

Step-by-step explanation:

The restriction endonuclease has a defense mechanism in the bacterial system against foreign DNA such as viruses, by differentiating between its own DNA and that of the invaders. Bacterial DNA is protected through methylation by DNA methylase, which modifies nucleotides at specific sequences in the bacterium's genome.

These sequences are short and palindromic, and are recognized by the restriction endonucleases that will not cleave methylated DNA. Therefore, since bacterial DNA is methylated, it is not cleaved by its own restriction endonucleases. In contrast, when foreign DNA, such as that from viruses, is not methylated, the restriction endonucleases cleave this DNA at these specific sequences. This process leads to the destruction of the intruder DNA while keeping the host bacterial DNA intact.

Essentially, the correct answer to the question of how restriction endonuclease is able to protect its own DNA is By methylation of bacterial DNA by restriction enzyme.

Answer 2

Bacterial DNA is protected from the action of restriction endonucleases through the methylation of specific DNA sequences, which prevents the enzyme from cleaving the host DNA while allowing it to target and degrade unmethylated foreign DNA. Option a is the correct answer.

Step-by-step explanation:

The student is inquiring about how bacteria can protect its own DNA from being degraded by restriction endonucleases, which are enzymes used to defend against foreign DNA such as that from viruses. The correct answer to the student's question is: a. By methylation of bacterial DNA by restriction enzyme.

The bacterial cells utilize a restriction modification system, which includes DNA methylase enzymes that add methyl groups to specific DNA sequences within the bacterial genome. These sequences are typically short and palindromic. Since the restriction enzymes recognize these sequences and only cleave DNA that is not methylated, the bacterial DNA is protected because the methylation prevents the restriction enzymes from cutting the host DNA.

Methylation serves as a protective marker to differentiate between self and non-self DNA. Foreign DNA that lacks this methylation will be targeted and cleaved by the restriction endonucleases, thereby inhibiting the spread of invading viruses and protecting the bacterial cell from potential threats.

This mechanism of action allows the restriction enzymes to function as molecular scissors, selectively cutting the non-methylated or 'foreign' DNA at specific recognition sites, which usually are palindromic sequences. This system is very effective in ensuring the survival of bacteria in a world full of genetic invaders like bacteriophages.