Restriction enzyme: Difference between revisions

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Restriction [[Endonucleases|Endonucleases]] cut [[DNA|DNA]] at a specific sequence, normally 4, 6 or 8 bases long. They recognise specific [[palindromic base sequences|palindromic base sequences]] in [[DNA|DNA]] and are used to selectively cut DNA into defined fragments at sites known as '[[Restriction site|restriction sites]]'. Different restriction nucleases are obtained and purified from different species of bacteria. These [[enzymes|enzymes]] are made in [[bacteria|bacteria]] to degrade viral DNA. Cutting&nbsp;[[DNA]] with restriction enzymes can produce&nbsp;fragments with either [[Blunt_ends|blunt]] or [[‘sticky’_ends|sticky ends]]. Different restriction enzymes recognise different DNA sequences.<br>  
Restriction [[Endonucleases|Endonucleases]]&nbsp;recognise and cut [[DNA|DNA]] at a specific palindromic base sequences, normally 4, 6 or 8 bases long,&nbsp;and are used selectively to cut [[DNA|DNA]] into defined fragments at sites known as '[[Restriction site|restriction sites]]'. Different restriction endonucleases are obtained and purified from different species of [[Bacteria|bacteria]]. These [[Enzymes|enzymes]] are made in [[Bacteria|bacteria]] to degrade viral DNA. Cutting&nbsp;[[DNA]] with restriction enzymes can produce&nbsp;fragments with either [[Blunt ends|blunt]] or [[‘sticky’ ends|sticky ends]]. Different restriction enzymes recognise different DNA sequences. The product of a restriction enzyme can have either [[Sticky ends|sticky ends]] or [[Blunt ends|blunt ends]] as shown below.&nbsp;<br>  


Examples of restriction endonucleases are:  
Examples of restriction endonucleases are:  


*[[EcoRI|''Eco''RI]]- recognines the sequence GAATTC
*[[EcoRI|''Eco''RI]]&nbsp;- recognises the sequence 5'GAATTC'3 - [[Sticky ends|sticky ends]]&nbsp;
*[[BamHI|''Bam''HI]]- recognises the sequence GGATCC
*[[BamHI|''Bam''HI]]&nbsp;- recognises the sequence 5'GGATCC'3 - [[Sticky ends|sticky ends]]&nbsp;<br>
*[[HaeIII|''Hae''III]]- recognises GGCC
*[[HhaI|''HhaI'']] - recognises the sequence 5'GCGC'3 - [[Sticky ends|sticky ends]]
*''[[XhoI|XhoI]]'' - recognises the sequence 5'CTCGAG'3 - [[Sticky ends|sticky ends]]&nbsp;
*''[[HindIII|HindIII]]'' - recognises the sequence 5'AAGCTT'3 - [[Sticky ends|sticky ends]]&nbsp;
*''[[PstI|PstI]]'' - recognises the sequence 5'CTGCAG'3 - [[Sticky ends|sticky ends]]&nbsp;
*''[[Sau3A|Sau3A]]'' - recognises the sequence 5'GATC'3 (produces the same [[‘sticky’ ends|sticky ends]] as [[BamHI|BamHI]] upon cutting)
*[[HaeIII|HaeIII]]&nbsp;- recognises the sequence 5'GGCC'3 - [[Blunt ends|blunt ends]]&nbsp;<br>


Both ''Eco''RI and ''Bam''HI produce fragments with [[‘sticky’_ends|staggered ends]], whilst ''Hae''III produces a DNA fragment with [[blunt ends|blunt ends]] i.e. there is no overhang.
Entire genomes can be digested into defined fragments by Restriction enzymes, this is called a [[Restriction Digest|Restriction Digest]]. The number of fragments formed in a digest is dependent on 2 factors:
 
#The restriction enzyme used; A 4bp recogniser will statistically cut a [[Genome]] in to more fragments than a 6 or 8 bp recogniser because it is more likely for there to be a repeated sequence of less bp.&nbsp;
#The size of the genome; Smaller genomes (10-100 bp, found in viruses) give fewer fragments than larger genomes (&gt;10<sup>6</sup>, found in e.g. humans).&nbsp;<sup></sup><br>
 
Also see&nbsp;[[Restriction endonucleases|Restriction endonucleases]]<ref>Alberts B, Johnson A, Lewis J, Raff M, Roberts K and Walter P. (2008) Molecular Biology of the Cell, Fifth Edition, New York, Garland Science.</ref><br>
 
=== References<br>  ===
 
<references />

Latest revision as of 09:44, 30 October 2018

Restriction Endonucleases recognise and cut DNA at a specific palindromic base sequences, normally 4, 6 or 8 bases long, and are used selectively to cut DNA into defined fragments at sites known as 'restriction sites'. Different restriction endonucleases are obtained and purified from different species of bacteria. These enzymes are made in bacteria to degrade viral DNA. Cutting DNA with restriction enzymes can produce fragments with either blunt or sticky ends. Different restriction enzymes recognise different DNA sequences. The product of a restriction enzyme can have either sticky ends or blunt ends as shown below. 

Examples of restriction endonucleases are:

Entire genomes can be digested into defined fragments by Restriction enzymes, this is called a Restriction Digest. The number of fragments formed in a digest is dependent on 2 factors:

  1. The restriction enzyme used; A 4bp recogniser will statistically cut a Genome in to more fragments than a 6 or 8 bp recogniser because it is more likely for there to be a repeated sequence of less bp. 
  2. The size of the genome; Smaller genomes (10-100 bp, found in viruses) give fewer fragments than larger genomes (>106, found in e.g. humans). 

Also see Restriction endonucleases[1]

References

  1. ↑ Alberts B, Johnson A, Lewis J, Raff M, Roberts K and Walter P. (2008) Molecular Biology of the Cell, Fifth Edition, New York, Garland Science.
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