individual assignment biology

8/11/2019 Individual Assignment Biology

1/3

Individual Assignment: Dideoxy Chain Termination DNA Sequencing

The Dideoxy Chain-termination method for sequencing DNA, or the Sanger Sequencing

Method, is a technique for sequencing a strand of DNA. DNA sequencing is determining the

exact order of nucleotides in a piece of DNA (Campbell, 2005). It was developed by Frederick

Sanger in 1977 (Sanger method, Cold Spring Harbor). It is the type of DNA sequencing most

frequently used today.

The thing that makes the Sanger method possible is specially altered fluorescent dideoxy

nucleotides. Dideoxy nucleotides are regular nucleotides except with a hydrogen group instead

of a hydroxyl (OH) group (Tech council, Sanger DNA). The hydrogen group prevents further

nucleotides from being added, and so the chain of replication is terminated whenever a dideoxy

nucleotide is added, creating many fragments of DNA. (Tech council, Sanger DNA). The

fluorescence allows the different nucleotides to be determined when they are scanned by a laser.

(DNA sequencing, the Welcome Trust).

During the process of the Sanger method, four reaction tubes are set up. Each tube has

DNA polymerase, the DNA to be sequenced, a full supply of normal nucleotides, and one kind

of dideoxy nucleotide (either A, G, T, or C.) (Micklos, 2003). As the DNA polymerase replicates

the DNA, the dideoxy nucleotides cause it to fall off and stop at varying points along it, creating

many different length fragments in each tube. (Sanger method, Cold Spring Harbor). The

fragments are then pieced together to form a coherent stream of DNA information. (Sanger

method, Cold Spring Harbor).

In order to do this, the fragments must be sorted out by length. The fragments are run

through a gel full of very small capillaries, like a maze. The longer fragments get stuck more,


2/3

and take longer to get through the maze, while the shorter ones are faster. This organizes them

from short to longest. They are then scanned by a laser, and recorded as different colored bands.

(DNA Sequencing, the Welcome Trust). These colors stand for each nucleotide, and their order

shows the nucleotide sequence of the DNA molecule.

Sanger won a Nobel Prize for his advancement, and his method has since been used

extensively in the Human Genome Project. His work was and is a major advancement in

understanding the role genes play in our lives and diseases.


3/3

References:

Campbell, Reece. Biology. 7th ed. San Francisco: Pearson Education Inc., 2005. Print.

Council, Tech. "The Sanger DNA Sequencing Methods." Tech Council. N.p., n.d. Web. 04 May

2014.

DNA sequencing - the Sanger method. The Welcome Trust. Web. 4 May 2014.

.

Micklos, David A., Greg A. Freyer, and David A. Crotty. DNA Science. Second ed. Cold Spring

Harbor, New York.: John Inglis, 2003. Print.

Sanger method of DNA sequencing, 3D anim. Cold Spring Harbor Laboratory

Web. 4 May 2014. .

individual assignment biology

Documents