DNA Structure and Function

I. Experiments on DNA A. Hershey and Chase: showed DNA, not protein, is the genetic material. 1952 DNA Protein

Used X-ray diffraction to determine the structure of DNA. I. Experiments on DNA B. Rosalind Franklin Used X-ray diffraction to determine the structure of DNA. 1952

II. DNA DNA = Deoxyribonucleic acid Found only in the nucleus of the cell Eukaryotic chromosomes contain DNA wrapped around proteins (proteins called histones). Composed of nucleotides which are the basic building blocks of all nucleic acids

A. Nucleotide: subunit of nucleic acid. II. DNA A. Nucleotide: subunit of nucleic acid. Three parts of a nucleotide: 1. Nitrogen base 2. Phosphate group 3. Simple sugar (ribose or deoxyribose)

II. DNA Four possible bases: A. Purines B. Pyrimidines B. Nitrogen Base Four possible bases: Double Ringed Adenine (A) Guanine (G) A. Purines Single Ringed Thymine (T) Cytosine (C) B. Pyrimidines

II. DNA B. Nitrogen Base

1. Adenine -Thymine (A - T) 2. Guanine - Cytosine (G - C) II. DNA C. Complementary base pairing (Chargaff’s Rule) 1. Adenine -Thymine (A - T) 2. Guanine - Cytosine (G - C) i. Base Pairing: Principle that hydrogen bonds in DNA form only between adenine and thymine and between guanine and cytosine.

D. Shape of DNA: Double Helix II. DNA D. Shape of DNA: Double Helix Discovered by Watson and Crick Sides formed by sugar and phosphate, connected by covalent bonds. Rungs of ladder = nitrogen bases. Double helix is held together by weak hydrogen bonds between the nitrogen bases - 2 bonds for A & T; 3 bonds between G & C

Sugar and phosphate group held together by covalent bonds II. DNA D. Shape of DNA: Double Helix T = Thymine Pyrimidine (1 rings) A = Adenine Purine (2 rings) Sugar and phosphate group held together by covalent bonds G = Guanine Purine (2 rings) C = Cytosine Pyrimidine (1 rings)

D. Shape of DNA: Double Helix II. DNA D. Shape of DNA: Double Helix The two sides of the molecule are anti-parallel to one another (5’ and 3’ ends). Anti-parallel a. 5’ carbon attaches to the phosphate group b. 3’ carbon attaches to the hydroxyl (OH)

a. Watson and Crick developed the double-helix model of DNA. III. Shape of DNA: Double Helix 1953 b. Double Helix: coiled structure of double-stranded DNA in which strands linked by hydrogen bonds form a spiral configuration a. Watson and Crick developed the double-helix model of DNA. Watson and Crick

III. Shape of DNA: Double Helix