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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 Think: What does this picture show. • 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 Discovery of DNA structure • Rosalind Franklin took pictures using X-Rays in the 1930’s James Watson Left & Francis Crick right: Nobel prize for DNA structure • James Watson & Francis Crick discovered double helix structure of DNA in 1953 using Fanklin’s pictures. 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 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. 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 Think: how will you recognize the name of a base on a quiz? Four bases of DNA 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? Summary questions 1. 2. 3. 4. Name 2 functions of DNA Who discovered the structure of DNA? What are the 4 base pairs. What is the structure if DNA?