Restriction enzymes, also known as molecular scissors, are nuclease enzymes found in prokaryotes that cut DNA at specific recognition sites. They were first discovered in the 1960s and are used by bacteria as a defense against bacteriophages by cleaving or modifying viral DNA. There are four main types of restriction enzymes that differ in their recognition sites, cleavage patterns, and enzymatic requirements. Restriction enzymes are widely used in biotechnology and molecular biology applications such as DNA cloning, gene analysis, and production of therapeutic proteins.

1. RESTRICTION ENZYMES
Presented by: JOYDEEP PAL
STUDENT CODE: BWU/BBT/18/036
TOPIC: Restriction Enzymes and their role
SUBJECT: BIOINFORMATICS
REG: NO: 18013000519 of 2018-19
ROLL NO: 18010310021
DATE: 20.05.21

2. NUCLEASE ENZYMES:
• Nuclease enzyme…
• Two types of Nuclease enzyme
are: Exonucleases and
Endonucleases.
• Exonucleases: To remove
nucleotides from the end of a
DNA molecule.
• Endonucleases: Able to break
internal phosphodiester bond.

3. Restriction Enzymes:
• The enzymes are also called “MOLECULAR
SCISSORS”. Found in a wide variety of
prokaryotes.
• First concept of R.E. was postulated in 1960s
by W. Arber and first RE was isolated in 1970s
by Nathans and Smith named HindII.
• Most of bacteria are used Restriction
enzymes as a defense against bacteriophage.
• Restriction enzymes are used for either
cleaving the phage DNA or modification itself.
• Example of R.E: EcoRI, BamHI, HindII etc..
Fig: Viral genome is entering into the
bacterial cell.

4. HOW THE R.E. CLEAVES?
• The sticky ends, have unpaired
DNA nucleotides on either 5'- or 3'-
strand, which are known as
overhangs.
• A straight cut of restriction
enzymes generates blunt ends,
where both strands terminate in a
base pair.
• Sequence of EcoRI: 5’GAATTC 3’ ,
it is PALINDROMIC sequence.
5’ GAATTC 3’
3’ CTTAAG 5’
Fig: The DNA sequences are digested by
the EcoRI and SmaI restriction enzymes.

5. Recognition Site:
• The DNA sequence to which restriction
enzymes can bind.
• The site of the DNA sequence where it is
cleaved by the restriction enzyme.
• The recognition sequences can also be
classified by the number of bases in its
recognition site, usually between 4 and 8
bases.
• Many of them are palindromic. FIG: Recognition site of BamHI
Fig: A palindromic recognition site
reads the same on the reverse strand
as it does on the forward strand when
both are read in the same orientation.

6. TYPES OF RESTRICTION ENZYMES:
 Naturally occurring restriction
endonucleases are categorized into four
groups (Types I, II III, and IIs):
• Type I enzymes cleave DNA at
random sites more than 1kb from a
recognition site; ATP required. Ex:
EcoKI, EcoK12 etc..
• Type II enzymes cleave DNA within a
recognition site, do not require ATP,
most require divalent cation (Mg2++).
Ex: EcoRI, BamHI etc..
• Type III restriction enzymes (e.g.,
EcoP15) recognize two separate non-
palindromic sequences that are
inversely oriented. Ex: EcoP15 etc..
• Type IIs enzymes cleavage occurs on
one side of recognition sequence up to
20bp away. Ex: FauI, HphI etc...

8. RESTRICTION MODIFICATION:
• Restriction-modification (R-M) systems
as defense mechanisms. R-M systems
recognize the methylation status of
incoming foreign DNA, e.g., phage
genomes.
• Methylated sequences are recognized as
self (bacterial genome), while recognition
sequences on the incoming DNA lacking
methylation are recognized as nonself and
are cleaved by the restriction
endonuclease (REase).
• The methylation status at the genomic
recognition sites is maintained by the
cognate methyltransferase (MTase) of the
R-M system.
• The combination of restriction
endonuclease and methylase enzyme
termed as RESTRICTION
MODIFICATION(RM) SYSTEM.
Fig: Bacterial cell is protecting as self
methylated sequence from phage DNA.

9. METHYLATION:
• In bacteria, DNA
methylation is used as a
signal for the regulation of a
specific DNA-protein
interaction.
• Typical sites of methylation
include the N6 position of
Adenine, the N4 position of
Cytosine or the C5 position of
Cytosine residue.
• Dam methylase is responsible
for N-residue of Adenine and
Dcm methylase is responsible
for methylation of Cytosine.

10.  Nomenclature of R.E:
• Since their discovery in the 1970s, many
restriction enzymes have been identified.
• More than 3500 different Type II
restriction enzymes have been
characterized.
• Using a naming system based on
bacterial GENUS, SPECIES and
STRAIN.
• E.C. number of EcoRI enzyme is
3.1.23.13.
• HindII enzyme: Genus: Haemophilus
Species: influenzae; Strain: Rd and
second identified.
Derivation of the EcoRI name
Abbreviation Meaning Description
E Escherichia genus
co coli specific species
R RY13 strain
I
First
identified
order of
identification
in the
bacterium

11.  APPLICATIONS OF RESTRICTION ENZYMES:
• They are used to assist insertion of genes into plasmid vectors during gene
cloning and protein production experiments.
• Restriction enzymes are used to digest genomic DNA for gene analysis by
Southern Blot.
• Allows for the large scale production of human insulin for diabetes using
E.coli, as well as Hepatitis B and HPV vaccine.

12. Acknowledgement:
• I wouldlike to thankour respected facultyKRISHNENDUSIR for guide and support me to
work in this kind of interesting topic.