Structure of DNA and the history of its discovery

Function of DNA DNA is the genetic material of the cell The structure of DNA must allow: the storage and transmission of genetic information exact replication to occur.

Genes code for proteins Genetic information must tell cells how to make proteins. Sections of the DNA called genes code for one protein Proteins form structures and control chemistry of cell. Think: Proteins are made in the cytoplasm but DNA remains in nucleus. How do you think that works?

Transformation The transfer of genetic material Discover by Griffith Experiment injected mice with disease causing & non-disease causing bacteria Found combination of dead disease bacteria with live non-disease still killed the mice Later Avery discovered DNA to be the agent Think: What does this picture show.

Discovery of DNA structure Rosalind Franklin took pictures using X-Rays in the 1930’s James Watson & Francis Crick discovered double helix structure of DNA in 1953 using Fanklin’s pictures. James Watson Left & Francis Crick right: Nobel prize for DNA structure 5

DNA Structure DNA is a polymer. The monomer of DNA is called a nucleotide. Nucleotides linked together to form the sides of the DNA molecule. DNA molecule has shape of a double helix. The sides are anti-parallel. deoxyribonucleic acid 6

Deoxyribose, a pentose sugar, has each carbon numbered. What’s in a name? One 5 carbon sugar called deoxyribose. “Deoxy” = one less oxygen. “ribo” = than ribose. Deoxyribonucleic acid “nucleic” = found in nucleus. “acid” = acidic Deoxyribose, a pentose sugar, has each carbon numbered. 7

Nucleotide Structure Phosphate group attached to the #5 carbon of the sugar. One nitrogenous base attached to the #1 carbon in the sugar. Purines -2 rings Adenine Guanine Pyrimidines -1 ring Cytosine Thymine Four bases of DNA Think: how will you recognize the name of a base on a quiz? 8

Complementary base pairing rules Nitrogenous bases form rungs of the helix. Adenine (2 rings) is bonded with Thymine (1 ring) using 2 hydrogen bonds. (A-T) Guanine (2 rings) is bonded with Cytosine (1 ring) using 3 hydrogen bonds. (G-C) Think: how will you remember which bases pair with each other? 9

Summary questions Name 2 functions of DNA Who discovered the structure of DNA? What are the 4 base pairs. What is the structure if DNA?