Restriction enzymes are proteins that cut DNA at specific recognition sequences. They are classified into three types based on their composition and target site. Type I enzymes recognize asymmetric sites and require cofactors. Type II enzymes recognize palindromic sites and require magnesium. Type III enzymes recognize two non-palindromic sites and require cofactors. Restriction enzymes are widely used in gene cloning, DNA manipulation, and other applications that involve modifying DNA.

1. Government PG college Jhalawar (Raj.)
PRESENTED BY
SANIYAALI

2. WHAT IS AN ENZYME?
• Enzymes are proteins and certain class of
RNA (ribozymes) which enhance the rate
of a thermodynamically feasible reaction
and are not permanently altered in the
process.

3. MOLECULAR SCISSORS
Restriction enzymes are
molecular scissors

4. RESTRICTION ENZYMES
• A restriction enzyme (or restriction
endonuclease) is an enzyme that
cuts double-stranded or single
stranded DNA at specific
recognition nucleotide sequences
known as restriction sites.

5. HISTORY OF RESTRICTION
ENZYME
• First restriction enzyme was isoltaed in 1970 by
Hindll.
• He also done the the subsequent discovery and
characterization of numerous restriction
endonucleases.
• From then Over 3000 restriction enzymes have
been studied in detail, and more than 600 of these
are available commercially and are routinely used
for DNA modification and manipulation in
laboratories

6. HOW RESTRICTION ENZYMES WORKS?
• Restriction enzymes recognize a specific
sequence of nucleotides, and produce a
double-stranded cut in the DNA. these
cuts are of two types:
• BLUNT ENDS.
• STICKY ENDS.

7. blunt end
sticky end

8. BLUNT ENDS
• These blunt ended fragments can be
joined to any other DNA fragment with
blunt ends.
• Enzymes useful for certain types of DNA
cloning experiments

9. “STICKY ENDS” ARE USEFUL
DNA fragments with
complimentary sticky ends
can be combined to create
new molecules which
allows the creation and
manipulation of DNA
sequences from different
sources.

10. • While recognition sequences vary
widely , with lengths between 4 and 8
nucleotides, many of them are
palindromic.

11. PALINDROMES IN DNA SEQUENCES
Genetic palindromes
are similar to verbal
palindromes. A
palindromic sequence
in DNA is one in which
the 5’ to 3’ base pair
sequence is identical on
both strands (the 5’ and
3’ ends refers to the
chemical structure of
the DNA).

12. NOMENCLATURE OF RESTRICTION
ENZYME
• Each enzyme is named after the bacterium from
which it was isolated using a naming system based
on bacterial genus, species and strain.
For e.g EcoRI
Derivation of the EcoRI name
Abbreviation Meaning Description
E Escherichia genus
co coli species
R RY13 strain
I First identified
order of identification
in the bacterium

13. TYPES OF RESTRICTION ENZYMES
• Restriction endonucleases are
categorized into three general groups.
• Type I
• Type II
• Type III

14. CONTINUE…
• These types are categorization based on:
Their composition.
Enzyme co-factor requirement.
the nature of their target sequence.
position of their DNA cleavage site
relative to the target sequence.

15. TYPE I INTRODUCTION
• Type I restriction enzymes were the first to be
identified and are characteristic of two
different strains (K-12 and B) of E. coli.
• The recognition site is asymmetrical and is
composed of two portions – one containing
3-4 nucleotides, and another containing 4-5
nucleotides – separated by a spacer of about
6-8 nucleotides.

16. COFACTORS OF TYPE I
• Several enzyme cofactors include:
S-Adenosyl methionine.
Hydrolyzed adenosine triphosphate
(ATP).
Magnesium (Mg2+).

17. SUBUNITS OF TYPE I
• Type I restriction enzymes possess three subunits:
o HsdR: is required for restriction.
o HsdM: necessary for adding methyl
groups to host DNA
(methyltransferase activity).
o HsdS: important for specificity of cut site
recognition in addition to its
methyltransferase activity.

18. TYPE II
• These are the most commonly available and used
restriction enzymes
• They are composed of only one subunit.
• Their recognition sites are usually undivided and palindromic
and 4-8 nucleotides in length, they recognize and cleave DNA
at the same site.
• They do not use ATP or AdoMet for their activity –
they usually require only Mg2+ as a cofactor.

19. CUTS OF TYPE II
• Type II restriction enzymes can generate two
different types of cuts depending on whether
they cut both strands at the centre of the
recognition sequence:
• The former cut will generate “blunt ends” with
no nucleotide overhangs.
• The latter, generates “sticky” or “cohesive”
ends

20. SUBGROUPS OF TYPE II
• These subgroups are defined using a letter
suffix.
 Type IIB restriction enzymes.
 Type IIE restriction endonucleases.
 Type IIM restriction endonucleases.
 Type IIT restriction enzymes

21. TYPE III
• Type III restriction enzymes ) recognize two separate
non-palindromic sequences that are inversely oriented.
• They cut DNA about 20-30 base pairs after the
recognition site.
• These enzymes contain more than one subunit.
• And require AdoMet and ATP cofactors for their roles
in DNA methylation and restriction

22. APPLICATION OF RESTRICTION
ENZYMES
• They are used in gene cloning and protein expression
experiments.
• Restriction enzymes are used in biotechnology to cut
DNA into smaller strands in order to study fragment
length differences among individuals (Restriction
Fragment Length Polymorphism – RFLP).
• Each of these methods depends on the use of agarose
gel electrophoresis for separation of the DNA
fragments.