Deoxyribonucleic Acid DNA

Organism Cell Chromosome Gene DNA Nucleotide

I. The Structure of DNA A.DNA Structure 1.Winding Staircase a. DNA is made of chains of nucleotides b. The strands are twisted into the form of a double helix. 2. Nucelotides a. Each Nucleotide in DNA is made up of the sugar deoxyribose, a phosphate group and one of four nitrogenous bases. b. The four nitrogenous bases found in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T) 3. Pairing Between Bases a. The two strands of DNA are complimentary b. Each A on one strand pairs with a T on the opposite strand. c. Each C on one strand pairs with a G on the opposite strand.

B. Discovering DNA’s Structure 1.Erwin Chargoff’s Observations a. Chargoff’s data showed that for each organisms the amount of Adenine equaled the amount of Thymine. b. Likewise the amount of Cytosine equaled the amount of Guanine. 2. Wilkins’ and Franklin’s Photographs – Wilkins’ and Franklin’s X-ray diffraction photographs supported that DNA is a tightly coiled double-helix. 3. Watson and Crick’s DNA Model a. Watson & Crick determined the structure of DNA in 1953 with the help of data gathered by Wilkins,Franklin and Chargoff. b. Watson, Crick and Wilkines won the Nobel Prize in 1962

Erwin ChargoffRosalind Franklin Maurice Wilkins X-ray diffraction image of DNA

James Watson & Francis Crick

II. The Replication of DNA A.DNA Replication 1. Before a cell divides, it copies its DNA by a process called replication. 2.The results of DNA replication is duplication of the cell’s original DNA. 3. Each new double helix is composed of one original and one new DNA strand. B. DNA Replication Enzymes 1. In DNA replication, enzymes work to uncoil the DNA strands 2. Unzip the two strands 3. Add complimentary nucleotides to the exposed strands. C. Checking for Errors 1. DNA polymerase proof-reads DNA during its replication 2. Because of this, very few errors occur.

The End