Restriction the 3′ direction of the G

Restriction enzymes are used in science laboratories to cut DNA. These enzymes can make pieces with sticky ends that fit together like puzzle pieces.

They can also create blunt ends which are flat and can fit up against any other DNA sequence.

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Restriction Enzymes

Blunt ends? Sticky ends? What in the world are those? What kinds of ends are we even talking about here?In this case, we’re talking about the results of restriction enzymes. Restriction enzymes are proteins that cut DNA at specific sequences. These handy proteins are useful tools for genetic engineering.

The ends in this case refer to the ends of the DNA strands. Depending on where and how the restriction enzyme cuts, it will produce either sticky ends or blunt ends. Sticky ends get their name because they have overlaps that allow the two ends to base-pair and join together with another DNA strand. Blunt ends have no overlap.

Where Do Sticky Ends Come From?

What do we mean when we say that sticky ends have overlaps? To answer this question, we first need to understand how a restriction enzyme cuts DNA. Restriction enzymes recognize a specific DNA sequence, normally between four and eight base pairs long.

The enzyme EcoRI, for example, recognizes a sequence that is six bases long:5′ G A A T T C 3’3′ C T T A A G 5’EcoRI cuts this sequence on both strands between the G and the A. So, each of the two strands of DNA is cut, and looks like this:5′ G / A A T T C 3’3′ C T T A A / G 5’The A A T T C sequence to the 3′ direction of the G is called an overhang. It is a short sequence of DNA that is not base paired with other DNA.These sticky ends are helpful for research scientists. If two pieces of DNA are cut with the same restriction enzyme, they would both have the same sticky ends with the same overlaps.

When these two pieces of DNA are combined, they have complementary sticky ends, meaning they could base-pair together. Using sticky ends helps scientists ensure the DNA sequences they are working with can be joined together easily. They fit together perfectly, like pieces of a puzzle.

The restriction enzyme EcoRI makes sticky ends when it cuts DNA. If both sequences are cut with EcoRI, they can be joined together.

Where Do Blunt Ends Come From?

Blunt ends are also made by restriction enzymes, but they don’t have any overlap. Instead the restriction enzyme cuts both strands of DNA evenly, so there’s no overhang.The restriction enzyme SmaI recognizes the sequence:5′ C C C G G G 3’3′ G G G C C C 5’It cuts both strands between the C and G, so it looks like this:5′ C C C / G G G 3’3′ G G G / C C C 5’You can see that both strands are even.

These are the blunt ends.Blunt ends aren’t as helpful as sticky ends for scientists, because there is no guarantee the strands will line up as desired. They cannot line up specifically the same way DNA with sticky ends can. However, because there is no base-pairing required, blunt ends are useful when sticky ends can’t be lined up perfectly between two pieces of DNA.

Lesson Summary

Restriction enzymes are used to cut DNA at specific sequences. The cut can leave sticky ends, meaning there is an overhang of bases. These bases are useful because it allows scientists to specifically match up pieces of DNA. EcoRI is a restriction enzyme that makes sticky ends.Restriction enzymes can also make blunt ends. Blunt ends have no overhang.

They cannot match up as specifically as DNA with sticky ends; however, they can be useful when sticky ends can’t be used. SmaI is a restriction enzyme that makes blunt ends.


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