Section Objectives: Structure of DNA How the structure of DNA enables it to reproduce itself accurately.

What is DNA? Although the environment influences how an organism develops, the genetic information held in the molecules of DNA ultimately determines an organism’s traits. DNA determines the structure of proteins.

What is DNA? All actions, such as eating, running, and even thinking, depend on proteins called enzymes. Enzymes control the chemical reactions needed for life. DNA —is the complete instructions for manufacturing all the proteins for an organism.

DNA as the genetic material In 1952 Alfred Hershey and Martha Chase – believed proteins coded for life so the performed an experiment using radioactively labeled viruses that infect bacteria. Hershey and Chase labeled the virus DNA with a radioactive isotope and the virus protein with a different isotope. By following the infection of bacterial cells by the labeled viruses, they demonstrated that DNA, rather than protein, entered the cells and caused the bacteria to produce new viruses.

The structure of nucleotides DNA is a polymer made of repeating subunits called nucleotides. Nucleotides have three parts: a simple sugar, a phosphate group, and a nitrogenous base. Phosphate group Nitrogenous base Sugar (deoxyribose)

The structure of nucleotides The simple sugar in DNA, called deoxyribose (dee ahk sih RI bos), gives DNA its name—deoxyribonucleic acid. The phosphate group is composed of one atom of phosphorus surrounded by four oxygen atoms. A nitrogenous base is a carbon ring structure that contains one or more atoms of nitrogen.

The structure of nucleotides In DNA, there are four possible nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Purines – Double ringed Pyrimidines – single ringed Adenine (A) Guanine (G) Cytosine (C) Thymine (T)

The structure of nucleotides A = T C = G 2 H- bonds 3 H-bonds

The structure of DNA In 1953, Watson and Crick proposed the structure of DNA DNA is shaped like a long zipper that is twisted into a coil like a spring. its shape is called double helix.

DNA Replication of DNA Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes. - DNA replication Replication Without DNA replication, new cells would have only half the DNA of their parents. Replication

Replication of DNA Click this image to view movie

Copying DNA New DNA molecule Original DNA Strand Free Nucleotides New DNA molecule New DNA Strand Original DNA Strand Original DNA DNA is copied during interphase prior to mitosis and meiosis.

Question 1 What importance did the experiment performed by Alfred Hershey and Martha Chase have in determining what genetic material was? Answer Many scientists believed protein was the genetic material. However, an experiment using radioactively labeled viruses allowed Hershey and Chase to provide convincing evidence that DNA is the genetic material.

Question 2 A. simple sugars B. phosphate groups C. nitrogenous bases Which of the following is NOT a component of DNA? A. simple sugars B. phosphate groups C. nitrogenous bases D. proteins The answer is D.

Question 3 A. adenine – thymine B. thymine – guanine Which of the following correctly comprises a complimentary base pair? A. adenine – thymine B. thymine – guanine C. guanine – adenine D. cytosine – thymine The answer is A.