DNA

Work Cited:

http://www.pbs.org/wgbh/evolution/library/06/3/l_063_01.html

http://www.biology-online.org/dictionary/Okazaki_fragment

http://www.phschool.com/science/biology_place/biocoach/bioprop/dnabase.html

http://www.phschool.com/science/biology_place/biocoach/dnarep/chemstruc.html

http://www.sciencedaily.com/articles/d/dna.htm

http://www.ncbi.nlm.nih.gov/books/NBK26821/

Okazaki Fragments

Okazaki fragments are short fragments of DNA that have just been synthesized. They are only found on the lagging strand of DNA and are constructed away from the replication fork. These fragments were named after the scientist who discovered them, Reiji Okazaki.

Enzymes Involved in DNA Replication

Here are the enzymes involved in DNA replication and their roles:

Helicase: Separates the strands of DNA

SSB: Prevents reannealing (reattachment of DNA)

Polymerase: Extends DNA chains

Ligase: Links short DNA strands together

Primase: Creates RNA primers

RNAse: Removes RNA

Sliding Clamp: Helps hold polymerase on to the DNA

3' to 5' Direction

DNA replication is semi-conservative, which means that half of the old strand of DNA is always kept in the new strand. This helps reduce the number of errors. DNA Polymerase is the enzyme that constructs new strands of DNA. However, this enzyme can only move in one direction and that is the 3' to 5' direction. Since the two strands of DNA go in different directions (3' to 5', 5' to 3') it causes DNA synthesis to occur in two different ways. One strand, the leading strand (3' to 5') is built continuously. The other strand, lagging strand (5' to 3') is built in Okazaki fragmets moving away from the replication fork. These fragments are then connected by DNA ligase. Despite the different types of synthesis, the overal direction of replication remains the same.

DNA Replication

Base Pairing Rules

DNA Polymerase reads the base on the parent strand and then it adds the complementary base to the new strand. The complementary bases are adenine and thymine, and cytosine and guanine. This means that if the DNA Polymerase reads a thymine base on the parent strand, it will attach a adenine base to the new strand. If it reads a cytosine base it will attach a guanine base. The opposite is also true.

DNA

The Function of DNA

DNA holds the genetic instructions for the growth and development of living organisms. It contains the instructions for construction of proteins and RNA molecules. These proteins help every cell in the organism perform its function. Every cell contains DNA but only part of that DNA is used by the cell. This is because the cell only has to perform a certain function so it does not need to use all of the

DNA.

What is DNA?

The Structure of DNA

DNA has four bases; cytosine, thymine, adenine, and guanine. These bases are attached to a sugar-phosphate backbone which helps the DNA keep it's shape. The bases are connected to one another with the help of hydrogen bonds. Adenine and Thymine are connected by two hydrogen bonds while Guanine and Cytosine are connected by three hydrogen bonds. DNA is in the form of a double helix which resembles a twisted ladder.

DNA stands for deoxyribonucleic acid. It can be found in any living organism and it holds all of the genetic information of that organism.

History of the Double Helix

It is commonly believed that it was Watson and Crick, two young scientists from the University of Cambridge, England, who discovered the unique structure of DNA. This is not the case however. A young female scientist named Rosalind Franklin had been studying the structure of DNA using a technique using a process called x-ray crystallography. This process involved taking an x-ray of the DNA molecule and viewing the shadow made by the DNA. She and her partner, Maurice Wilkins, discovered the double helix structure of DNA using this technique. However, Franklin was not able to receive credit for her discovery because Wilkins showed some of her findings to Watson and Crick who the realized that DNA was composed of two strands of nucleotides which gave it it's double helix shape. The two scientists then published a paper based on Franklin's findings

Parts of a Nucleotide

Base Pairing Rules

How do the bases arrange themselves? There are certain rules known as base pairing rules that state, that adenine will always pair up with thymine and cytosine will always pair up with guanine.

A nucleotide is made up of three parts; sugar, phosphate and a base (adenine, thymine, cytosine, and guanine). The sugar is a 5-carbon sugar deoxyribose, meaning it has 5 carbons. The base is attached to the 1' carbon and the phosphate is attached to the 5' carbon.