Introduction to DNA Structure

1. Introduction to DNA Structure Ms. Gaynor AP Biology

2. DNA and Its Structure • From 1953

3. What is the Double Helix? • Shape of DNA • Looks like a twisted ladder • 2coils are twisted around each other • Double means 2 • Helix means coil

4. The Structure of DNA • Made out of nucleotides • Includes a phosphate group, nitrogenous base and 5-carbon pentose sugar Nucleotide Structure 1 “link” in a DNA chain

5. Nucleoside Structure

6. A Polynucleotide • MANY nucleotides (“links”) bonded together Nucleotide Structure DNA has a overall negative charge b/c of the PO4-3 (phosphate group)

7. The Structure of DNA • Backbone= alternating P’s and sugar • Held together by COVALENT bonds (strong) • Inside of DNA molecule = nitrogen base pairs • Held together by HYDROGEN bonds (weaker) Backbone

8. Phosphodiester Bond • The covalent that holds together the backbone • Found between P & deoxyribose sugar • STRONG!!!

9. Minor Groove Major Groove

10. DNA is antiparallel • Antiparallel means that the 1st strand runs in a 5’ 3’direction and the 2nd 3’ 5’ direction • THEY RUN IN OPPOSITE or ANTIPARALLEL DIRECTIONS • P end is 5’ end (think: “fa” sound) • -OH on deoxyribose sugar is 3’ end • 5’ and 3’ refers to the carbon # on the pentose sugar that P or OH is attached to

11. DNA Bonding • Purines (small word, big base) • Adenine • Guanine • Pyrimidines • (big word, small base) • Cytosine • Thymine • Chargaff’s rules • A=T, C=G • Hydrogen Bondsattractions between the stacked pairs; WEAK bonds

12. Why Does a Purine Always Bind with A Pyrimidine?

13. DNA Double Helix • http://www.sumanasinc.com/webcontent/animations/content/DNA_structure.html • Watson & Crick said that… • strands are complementary; nucleotides line up on template according to base pair rules (Chargaff’s rules) • A to T and C to G • LET’S PRACTICE… Template: 5’AATCGCTATAC3’ Complementary strand: 3’ TTAGCGATATG5’

14. REVIEW… • ______ discovered the double helix structure of DNA and won a Nobel prize for this work in 1962 • ______ made photo 51, which helped discover the correct helical shape of DNA • ______ worked with pneumococcus bacteria and mice to conclude an inheritance molecule is present in cells • ______ worked with fruit flies and discovered genes are linked (connected to) chromosomes (chunks of DNA) • ______ worked with bacteriophages and discovered that DNA not protein is the inheritance molecule in cells • ______ worked with pneumococcus bacteria and test tubes to discover DNA not RNA or protein is a transforming agent • ______ worked with x-ray crystallography and created pictures of DNA; won a Nobel prize in 1962 for this work • ______ discovered DNA in any species contains equal amounts of adenine and thymine and equal amounts of guanine and cytosine; credited with forming the “base pair rules” • ______ worked with garden pea plants and was the first scientist to study inheritance patterns

15. 5. (3’ end) 5. (5’ end) 3. (2 bonds) 6. T 1. 2. 6. A • Label the DNA strands shown below. • Label a deoxyribose sugar molecules • a phosphate molecules (PO43-) • Hydrogen bonds • Label the phosphodiester bonds • The 5’ and 3’ ends • Label the bases that are not already labeled • Purines • Pyrimidines 3. (3 bonds) 6. C 4. 6. G A and G C and T 5. (5’ end) 5. (3’ end)

16. A nucleotide is made of three parts: a ________ group, a five carbon __________________, and a nitrogen containing _____________________. Nucleotides are monomers for _______ and ________. • In a single strand of DNA, the phosphate group binds to the _______ of the next group to form the _____________ of the molecule. What bond holds together the sugars and phosphates in DNA? _______________ • The _______ _______ form the middle of the DNA molecule (rungs or steps of the ladder) and are held together by _________________ bonds. • Purines have _____ rings of carbon, and pyrimidines have ______ ring. • Purines include ___________ base and ____________ base. • Pyrimidines include __________ base and ____________ base. • In DNA, thymine is complementary to ________________ ; cytosine is complementary to _____________. • Thymine and _____________________ are _____ hydrogen bonds together. • Cytosine and _____________________ are _____ hydrogen bonds together.