16 
May I have the next slide (3), please? 
Slide 3 
CLEAVAGE OF DNA BYRI 
RESTRICTION ENDONUCLEASE 
I 
▼ 
Just to show you, this is a molecule of DNA, and I focus only on a 
short sequence, six nucleotides out of the 5,000; and a particular enzyme, 
which as I said has been described by Herbert Boyer, was found to cut the 
DNA at the positions indicated by the arrows. So it cuts one strand be- 
tween G and A, and a second strand here between the A and G, to produce 
a linear structure which has the short, cohesive or sticky ends, this end 
being able to pair or react with this end. It is possible to go from this 
state to that state very simply. 
May I have the next slide (4), please? 
To illustrate how the use of that enzyme has made it possible to join 
DNA molecules from different sources, here we have the DNA molecules indi- 
cated as such. Again, the position where this enzyme breaks, indicated by 
the arrow, is to produce two DNA molecules having the short, cohesive or 
sticky tails. 
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