Restriction enzyme: Difference between revisions

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Restriction [[Endonucleases|Endonucleases]]&nbsp;recognise and cut [[DNA|DNA]] at a specific plaindromic base sequences, normally 4, 6 or 8 bases long,&nbsp;and are used to selectively cut DNA into defined fragments at sites known as '[[Restriction site|restriction sites]]'. Different restriction endonucleases 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. The product of a restriction enzyme can have either sticky ends or blunt ends as shown below.&nbsp;<br>  
Restriction [[Endonucleases|Endonucleases]]&nbsp;recognise and cut [[DNA|DNA]] at a specific plaindromic base sequences, normally 4, 6 or 8 bases long,&nbsp;and are used to selectively cut 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:  
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*''<u>PstI</u>'' - recognises the sequence 5'CTGCAG'3 - [[Sticky ends|sticky ends]]&nbsp;  
*''<u>PstI</u>'' - recognises the sequence 5'CTGCAG'3 - [[Sticky ends|sticky ends]]&nbsp;  
*<u>''Sau3A''</u> - recognises the sequence 5'GATC'3 (produces the same [[‘sticky’ ends|sticky ends]] as [[BamHI|BamHI]] upon cutting)  
*<u>''Sau3A''</u> - 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;
*[[HaeIII|HaeIII]]&nbsp;- recognises the sequence 5'GGCC'3 - [[Blunt ends|blunt ends]]&nbsp;<br>


<br>
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 dependant on 2 factors:


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 dependant on 2 factors:
#The restriciton 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>


1. The restriciton enzyme used; A 4bp recogniser will statistically cut a genome in to more fragments than a 6 or 8bp recogniser because it is more likely for there to be a repeated sequence of less bp.&nbsp;
Also see&nbsp;[[Restriction endonucleases|Restriction endonucleases]]&nbsp;<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>


2. The size of the genome; Smaller genomes (10-100bp, found in viruses) give fewer fragments than larger genomes (&gt;10^6, found in e.g humans).&nbsp;<sup></sup>  
=== References<br> ===


<br>  
<references />
 
Also see&nbsp;[[Restriction endonucleases|Restriction endonucleases]]
 
<br>
 
References&nbsp;
 
1.&nbsp;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.

Revision as of 07:09, 22 October 2014

Restriction Endonucleases recognise and cut DNA at a specific plaindromic base sequences, normally 4, 6 or 8 bases long, and are used to selectively 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 dependant on 2 factors:

  1. The restriciton 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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