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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.
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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
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 Four bases of DNA Think: how will you recognize the name of a base on a quiz?
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 • Name 2 functions of DNA • Who discovered the structure of DNA? • What are the 4 base pairs. • What is the structure if DNA?