Introduction to DNA Structure Ms. Gaynor AP Biology

DNA and Its Structure From 1953

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

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

Nucleoside Structure

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

The Structure of DNA Backbone 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

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

Minor Groove Major Groove

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

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

Why Does a Purine Always Bind with A Pyrimidine?

DNA Double Helix LET’S PRACTICE… Watson & Crick said that… 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’

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

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 5. (3’ end) 5. (5’ end) 3. (2 bonds) 6. T 1. 2. 6. A 3. (3 bonds) 6. C 4. 6. G A and G C and T 5. (5’ end) 5. (3’ end)

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.