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In: Biology

What is the part of the crispr mechanism that are the steps prior to the cas9...

What is the part of the crispr mechanism that are the steps prior to the cas9 crispr DNA cuts? Give an idea of how many proteins this other part takes. (In the bacterial immune/defense system)

Solutions

Expert Solution

CRISPR is a unique technology that enables to edit parts of the genome by removing, adding or altering sections of the DNA sequence.

The CRISPR-Cas9 system consists of two key molecules which introduce a change in mutation of DNA.

  • An enzyme called Cas9 and this act as ‘molecular scissors’ in which DNA can be added or removed by cutting the two strands of DNA at a specific location in the genome.
  • a piece of RNA called guide RNA (gRNA), which consists of a small piece of pre-designed RNA sequence located within a longer RNA scaffold. The scaffold helps to binds DNA and the pre-designed sequence ‘guides’ Cas9 which is on the right part of genome. This will ensure that the Cas9 enzyme cuts at the right point within genome.
  • The guide RNA has RNA bases that iscomplementary to the target DNA sequence in the genome and it will bind only the target sequence. Cas9 follows the guide RNA towards DNA sequence in the same location and makes a cut across both strands of the DNA.
  • At last stage the cell recognises that the DNA is damaged and tries to repair it.

Cas9 (CRISPR associated protein 9) is a protein that plays a vital role in the immunological defense of certain bacteria against DNA viruses and plasmids and which finds major application in genetic engineering applications. Its main function is to cut DNA and therefore it can alter a cell's genome. CRISPR activity is essential for the immune response, as the presence of a set of CRISPR-associated (cas) genes, that is adjacent to the CRISPR, which code for proteins. Since the genome is modified in the process of spacer acquisition, offspring inherit the protection.

CRISPR-Cas mediated defense process can be divided broadly into three stages. The first stage, adaptation, whcih leads to insertion of new spacers within the CRISPR locus. In the second stage, expression, the cas genes is ready which lead to transcribing the CRISPR into a long precursor CRISPR RNA (pre-crRNA). The pre-crRNA is processed towards the mature crRNA by Cas proteins and accessory factors. In the third and last stage, interference,by the combined action of crRNA and Cas proteins ensures target site of nucleic acid that is recognized and destroyed.


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