Deoxyribonucleic Acid (DNA) Discoveries • Frederick Griffith (1928) – Did an experiment with bacteria and determined there was something in cells that transferred information. – Could be a gene. Discoveries • Oswald Avery (1944) – Repeated Griffith’s experiment and determined that DNA (nucleic acid) transmitted genetic information from one generation to the next. Discoveries • Alfred Hershey & Martha Chase (1952) – Did an experiment with viruses and determined that viruses contain DNA, also. http://highered.mcgraw- hill.com/sites/0072437316/student_view0/chapter14/animations.html# Structure • DNA (Deoxyribonucleic Acid) – Long molecule made up of units called nucleotides. • Nucleotides –made up of a 5-carbon sugar (deoxyribose), phosphate group, & a nitrogenous base. • 4 different nitrogenous bases – Purines – Adenine & Guanine (A & G) – Pyrimidines – Thymine & Cytosine (T & C) • Backbone made up of Sugar & Phosphates • Can be joined in any order, so any sequence of bases is possible. Composition of DNA • Long molecule made up of units called nucleotides. • Nucleotides are made of 3 parts: 1. *5-carbon sugar (deoxyribose) 2.*phosphate group 3.*nitrogenous base (4 different bases.) A- adenine T- thymime A always binds T G- guanine G always binds C C-cytosine Discoveries • Erwin Chargaff (1930s) – Discovered that percentages of Cytosine (C) & Guanine (G) were almost equal in all samples of DNA – Same was true for Thymine (T) & Adenine (A) Discoveries • Rosalind Franklin (1950) – DNA is a helix – shaped like a coil – Might be two strands with the nitrogen bases pointing towards the center. Discoveries • James Watson & Francis Crick (1970s) – Double helix – 2 strands of DNA wound around each other like a spiral staircase. – Hydrogen bonds form between nitrogenous bases that point toward the center. • Can only form between certain bases – Adenine & Thymine (A-T) – Guanine & Cytosine (G-C) – Called BASE PAIRING Fun Fact The DNA in a single human cell is more than 1 meter in length and is found coiled up inside the nucleus. DNA Replication • The process where a DNA molecule separates into two strands, then produces two new complementary strands following the rules of base pairing. • Each strand of the double helix of DNA serves as a template, or model, for the new strand. • Carried out by the enzyme DNA polymerase – Also proofreads the new strands to make sure each is a perfect copy of the original DNA.
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