Restriction Enzymes
Question 1: Define restriction enzymes and Recognition sites.
Answer:
It is an enzyme that cleaves DNA into pieces at or close to particular molecular recognition sites. A recognition site is a location that a restriction enzyme selects in order to break DNA.
These locations are found on a DNA molecule and contain particular nucleotide sequences (4-8 base pairs)
Question 2: Write the applications of the restriction enzyme.
Answer:
Applications of the restriction enzyme:
- Genetic engineering
- Used in methods for DNA fingerprinting.
- They help in gene cloning, protein expression research, and the insertion of genes into plasmid vectors.
- By specifically identifying single base variations in DNA as single nucleotide polymorphism, they are also useful to distinguish gene alleles.
- DNA mapping.
- Gene sequencing.
Question 3: In which year was the first restriction enzyme identified?
Answer:
In 1970 the first restriction enzyme was identified.
Question 4: Write the difference between Endonuclease and Exonuclease.
Answer:
|
Endonuclease |
Exonuclease |
|---|---|
| A class of enzymes known as endonucleases cleaves the phosphodiester bond found within a polynucleotide chain. | Exonucleases are enzymes that individually cleave DNA sequences from a polynucleotide chain’s 5′ or 3′ end. |
| Endonucleases split the nucleotide sequence down the middle. | Exonucleases cleave the ends of a nucleotide sequence. |
| There is a lag phase before some endonucleases, such as restriction endonucleases, start to work. | There is no delay in the commencement of exonuclease activity |
| The endonuclease slices a piece of DNA in the middle, forming oligonucleotides. | DNA sequences are broken down by exonucleases into single nucleotides or nucleosides. |
Restriction Enzymes
Restriction enzyme is a bacterial protein that cleaves DNA at particular locations, these sites are called restricted sites. The restriction enzymes guard against bacteriophages in living bacteria. They identify the bacteriophage and cleave it at its restriction sites, destroying its DNA. Important genetic engineering tools include restriction enzymes. They may be separated from bacteria and applied in research facilities. The recognition sequences, or short and distinct nucleotide sequences, are recognized by restriction enzymes in DNA. When a DNA sequence is recognized by the restriction enzyme, it hydrolyzes the bond between neighboring nucleotides and cleaves the DNA molecule. The bacteria use the enzyme methylases to add the methyl group at the adenine or cytosine bases within the recognition sequence, preventing the DNA sequences from disintegrating.
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