TeenHelp - B3 diabetes coursework

Quote:

Originally Posted by wishful-thinking (Post 817986)

yes please......??

I don't know if there's a specific question you have in mind so I'll briefly explain restriction enzymes, DNA ligase and "sticky ends".

Restriction enzymes cuts the double-strand DNA at certain nucleotide sequences. They are found naturally in bacteria to combat invading pathogens and can be used experimentally to examine protein expression, gene cloning and certain blotting methods (i.e. Southern blotting). Once they have cut the DNA strand, DNA ligase catalyzes the DNA strand, such as through complimentary base pairing (i.e. sticky ends).

For a more in-depth view, there are different types of restriction enzymes and they differ in terms of the reactions they catalyze, dependence of ATP, whether they cleave far or near the recognition nucleotide sequence, etc... . Type I requires ATP, Mg2+ ions and SAM-e, although it is inaccurate because it produces randomized 5' as the recognition site is asymmetrical. It cleaves far away from the actual recognition nucleotide sequence. This inaccuracy can be beneficial from an evolutionary perspective, such as the Red Queen's Hypothesis. Interestingly, it can also demonstrate methyltransferase activity depending on the abundance of SAM-e.

Type II uses Mg2+ but neither ATP nor SAM-e, making it less expensive to use and the most abundant restriction enzyme type. Their recognition sites are quite easy to spot since they are palindromic, meaning the base pair sequence reads the same whether from 3' or 5'. In other words, their sticky ends are mirror-images. Since they are the most abundant, there are sub-categories but I think that will go into too much detail for what you'd need.

Type III can function without ATP, although the reaction is sped up when present. Additionally, SAM-e often is present. Unlike Type I and Type II, Type III restriction enzymes only modify single-strand DNA through methyltransferase at the N-6 position and produce 5' over-hangs.

Restriction enzymes can be studied in bacteria, such as EcoRI, EcoRII and EcoRV found in E. coli, or they can be created synthetically. They can even be found in plants, such as Xbal in X. badrii.