1. DNA Structure and Replication Adapted from “Biology,” Neil Campbell and Jane Reece, 2002 Northern Virginia Community College John F. Christmas

2. Nucleotides are the the monomers of nucleic acids, composed of three smaller molecular building blocks: 1) a nitrogenous base (a purine or pyrimidine with U substituted for T in RNA), 2) a pentose sugar (either ribose or deoxyribose), and a phosphate group. The phosphate group of one nucleotide is bonded to the sugar of the next. DNA usually exists in a double- stranded form and RNA in a single-stranded form.

3. DNA is only self-replicating macromolecule; Human DNA is 30.9% adenine, 29.4% thymine, 19.9% guanine, and 19.8% cytosine, as determined by Chargaff, A=T and C=G; Hydrogen bonds hold the two strands together; Each strand is complementary and can form a template for a new strand when separated; The order of bases on one strand can be used to add complementary bases.

4. The helix is right-handed, with the strands oriented in opposite directions The bases are joined by H bonds, 2 between A & T, 3 between C and G, and Van Der Waals attractions between adjacent base pairs; The distance from one base to another is 0.34 nm, and the strands are 2 nm wide from one side to the other, with one spiral in the molecule every 10 base pairs (based on x-ray diffraction data).

5. Bases in DNA and hydrogen bonding patterns

9. Summary of DNA Replication

10. Telomeres Eukaryotic DNA has telomeres at the ends, special nucleotide sequences (100-1000), which are noncoding sequences; Become shortened over time because of the 5’ directional manner in which lengthening occurs; In some organisms teloerase catalyzes the lengthening of telomere segments at the 3’ end; in others they just get shorter over time.

11. As DNA molecule unzips, replication proceeds in both directions