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DNA BACKGROUND SECTION 4.1, 4.2

This section explores the fundamentals of DNA, including its double-stranded helical structure composed of nucleotides—nitrogenous bases, deoxyribose sugar, and phosphate groups. DNA encodes the amino acid sequences essential for all living organisms. It details the replication process where enzymes unwind DNA, allowing single strands to act as templates for new DNA synthesis. Historical experiments by J. Hammerling, Griffith, Hershey & Chase, and Avery et al. provide critical insights into DNA as hereditary material and the development of the double helix model by Watson and Crick, informed by Rosalind Franklin's X-ray diffraction imagery.

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DNA BACKGROUND SECTION 4.1, 4.2

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  1. DNA BACKGROUNDSECTION 4.1, 4.2 Homework p. 216 #1-5

  2. DNA BASICS • Double stranded, helical, self • Nucleotides: nitrogenous base, deoxyribose sugar and phosphate group. • DNA codes amino acid sequence of all • . • REPLICATION: enzymes unwind • The single strands act as templates • Two new DNA are the result.

  3. Early research J. Hammerling Expt. Frederick Griffith Discovered process of . Dead, pathogenic cells were able to cause infection in live animals. See animation. Hershey & Chase Used radioactive as DNA tracer on viruses. Bacterial cells contained the tracer. • Algae Acetylbularia. • Only -containing appendages would regenerate. Therefore DNA must be hereditary material. • Avery et al. DNA was the • Principle of dead Pneumococcus • See summary p. 215 text.

  4. Definitions • Deoxyribose sugar: Five C missing OH on 2’C • Phosphate Group: Four O surrounding P • Nitrogenous Base: Alkyline, , with N • Nucleotides:Base, sugar, phosphate • Glycosyl bond. (base to 1’ on sugar) • Ester Bond (Phosphate group to 5’ )

  5. Watson and Crick • Deduced the DNA double Helix model using work by: • Rosalind Franklin revealed the helical structure using • Chargaff’s rule: A=T G=C (complementary) • Two strands: run in opposite directions 5’3’ and 3’5’ • We write the 5’3’ strand only.

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