After discovering DNA was the carrier of genetic info, it became apparent that control over its mechanisms would be essential

We have ways of isolating DNA, determining the order of its nucleotides, and can even insert of piece of DNA from one organism to another

To get at DNA, we have to remove the two membranes that protect it◦ Cell membrane and nuclear envelope

These are made of phospholipid bilayers Detergents are used to dissolve the lipids to

expose the genetic material Next, a protease is used to dissolve

unwanted proteins Sodium acetate further precipitates the

remaining protein

Next, the sample is centrifuged, and the protein can be removed

DNA can be precipitated by the addition of cold ethanol◦ This both precipitates the DNA and washes the

salt Finally, the solution is centrifuged, and the

pellet of DNA is removed

The DNA extracted is often very long◦ Too long to be useful in many cases

Restriction enzymes are used to cut the DNA However, it is not a random cut site, rather a

very specific sequence There are many different enzymes (~1000),

many with their own unique sequence they attach to

They do not cleave the DNA straight down, instead the cut the bond between adjacent nucleotides

The uneven cutting creates what is known as “sticky ends”

They are “sticky” because they are single stranded◦ DNA is normally doubled stranded, and naturally

anneals (reforms hydrogen bonds) into double There is a random number of cut sites on

every strand of DNA But, in the end, the sample is cut into

smaller pieces

These smaller segments can be run through a gel

The gel is a semi-solid, porous medium that DNA can move through

Electrodes are set at either end to make one positive, the other negative

DNA is slightly negative, and will be attracted to the positive end

The smaller samples can move through the gel faster, and will make it farther down

Each band represents a strand of DNA, of a specific length

The bands furthest down are the smallest Gels are normally run to compare a sample

of DNA to a known sample, cut with the same enzymes

If the bands line up, it is likely that the samples are the same

This is very useful in DNA fingerprinting