DNA - Deoxyribose nucleic acid Composed of nucleotides store and transmit genetic information replicate undergo changes (mutate)

DNA (Deoxyribonucleic Acid) Found in almost all living cells –in the nucleus of eukaryotes (3 Feet/Cell) 2 primary functions Control protein (enzyme) production-These enzymes then control chemical reactions in cells. Duplicate itself for new cells that are created

Nucleotide Deoxyribose sugar Phosphate group Nitrogenous base A, T, C, G

Nitrogenous Bases 4 Bases Purine – Double ring Adenine (A), Thymine (T), Cytosine (C), Guanine (G) Purine – Double ring A and G Pyrimidine – single ring T and C

Frederick Griffith: Transformation 1928 Discovered that bacteria could give other bacteria heritable traits, even after they were dead.

Avery, McCarty & MacLeod: Griffiths Refined (1944) Refined Griffith's Experiment Exposed R-strain Streptococcus to purified S-strain protein, and purified S-strain DNA Only the bacteria exposed to the S-strain DNA were transformed

Hershey & Chase: The "Blender" Experiment (1952) Worked with bacteriophages Conclusively demonstrated that DNA was the molecule of heredity Tagged phage DNA and protein with radioactive atoms and tracked the transmission of that radioactivity to infected bacteria Nobel Prize: Hershey (1969)

Chargaff’s Rule Amount of guanine equals amount of cytosine Amount of adenine equals thyamine Chargaff’s rule: C=G A=T

Watson & Crick, Franklin & Wilkins (1953)

Two competing teams to determine the structure of DNA Watson and Crick used X-ray diffraction data developed by Rosalind Franklin to develop their "double helix" model of DNA Nobel Prize: Watson, Crick & Wilkins (1962)

James Watson and Francis Crick DNA is a Double Helix James Watson and Francis Crick **Similar to ladder that is twisted** Sugar and phosphate form the backbone Bases lie between the backbone Nucleotides A, G, T, C Held together by H-bonds between the bases A-T – 2 H bonds G-C – 3 H bonds

Orientation of DNA The nucleotides form a chain Phosphate end is the 5' end The opposite end (sugar) is the 3' end Q: Since DNA is complementary, what end matches with the 5’ end?

Bases on one strand are covalently bonded to each other ("phosphodiester bonds") Bases on opposite strands are hydrogen bonded to each other ("base pairs"). Adenine = Thymine (2 H bonds) Cytosine = Guanine (3 H bonds)

Forms of DNA Chromatin –Partially unwound (Normal Situations) Chromosome – tightly wound DNA (Cell division)

Chromosome Structure DNA wraps around histones Chromatin Fibers DNA wraps around histones histones form nucleosome Histones Nucleosomes

Plasmids small, circular, double-stranded DNA molecule Different from chromosomal DNA naturally exist in bacterial cells Often provide bacteria with genetic advantages antibiotic resistance Hundreds to thousands of base pairs each daughter cell receives a copy of plasmid Bacteria can also transfer plasmids to one another through conjugation