Introduction to DNA ( D eoxyribo n ucleic a cid)

1. Introduction to DNA(Deoxyribonucleic acid)

2. What do you know?

3. Scientists

4. Phoebus Levene • 1920 – Determined the basic structure of nucleotides that make up DNA • 5-carbon sugar, phosphate group, and a nitrogenous base

5. Erwin Chargaff • 1952 - Nitrogenous base composition • % of adenine is equal to % of thymine • % of guanine is equal to % cytosine • Composition of DNA varies from species to species

6. Maurice Wilkins and Rosalind Franklin • 1951 - Worked with a technique called X-ray diffraction • Determined the helical nature of DNA

7. A James Watson and Francis Crick • 1953 – Determined the structure of DNA using Chargaff’s and Franklin’s data

8. What is DNA?

9. DNA (Deoxyribonucleic acid) • Nucleic acid • Consists of monomers called nucleotides • Stores genetic information, determines an organisms traits by synthesizing proteins • Each organisms genome is unique

10. Structure of DNA

11. Structure of DNA • Double helix • Consists of a double strand of nucleotides • Two strands are anti-parallel • 5’ to 3’ • 3’ to 5’

13. Nucleotide • Three parts of a nucleotide • 5 carbon sugar called deoxyribose • Phosphate group • A single nitrogenous base

15. Four Nitrogenous Bases • Purines (double ring) • Adenine (A) • Guanine (G) • Pyrimidines (single ring) • Thymine (T) • Cytosine (C)

16. Chargaff’s Rules • A-T (2 hydrogen bonds) • C-G (3 hydrogen bonds)

17. Sides of molecule - Alternating sugars and phosphates held together by strong covalentbonds • Center – two nitrogenous bases held together by weak hydrogenbonds

18. A DNA Structure • Click on the hyperlink above to watch a short animation about the structure of DNA

19. Genes • The sequence of nucleotides in an organisms genome is unique • Genes consist of sequences of nucleotides

20. Human Genome • 3164.7 million nucleotides • Average gene length is 3000 base pairs • Largest gene is 2.4 million base pairs • Approximately 20,000 – 25,000 genes

21. DNA Replication

22. Why is DNA replication important?

23. Why replicate? • Each new cell created through cell division must receive an exact copy of the original cells DNA • Occurs in the nucleus of cells

24. A DNA Replication • Semi-conservative– new DNA molecules have one original template strand and one new strand • Follows complementarybasepairrules • “Leading strand” – continuously synthesized • “Lagging strand” – synthesized in fragments

25. Origins of Replication

27. A Steps of DNA Replication 1. DNAhelicaseunzips the original DNA molecules by severing hydrogen bonds between nucleotides

28. 2. New nucleotides are added to the template strands using DNA polymeraseenzymes(complementary base pairing)

29. 3. Okazaki fragments are pieced together by DNAligase

30. A DNA Replication C C T A A C G G T A C G A A T