1. Intro to DNA DNA = Deoxyribonucleic acid
-double polymer of nucleotides
-SS chromosomes contain 1 molecule of DNA (re: double polymer of nuc’s)
-after DNA replication, a DS chromosome contains 2 complete polymers of DNA
-sequence of nucleotides of DNA codes for sequence of amino acids of protein (process referred to as protein synthesis)
-protein synthesis = DNA  RNA  Protein
- The pathway of protein synthesis is also referred to as the Central Dogma of Molecular Biology

2. DNA is a polymer of nucleotides
A nucleotide contains three essential parts:
5 carbon sugar
Deoxyribose in DNA
Ribose in RNA
Nitrogenous base
Adenine, Guanine = purines
Thymine, (Uracil), Cytosine = pyrimidines
Phosphate group

3. Components of nucleotide structure

4. Single polymer of DNA nucleotides

5. Events leading to DNA model proposed by Watson and Crick (1953)
Chargaff’s rules:
the proportion of A’s in DNA = the proportion of T’s
The same holds true for G’s and C’s
Franklin’s X-ray diffraction photos:
Suggested DNA was helical and perhaps contained two separate chains of nucleotides separated by a discrete diameter
Watson/Crick model fit the available data:
Each “backbone” of alternating sugar – phosphate
Each backbone has a polarity in that each is oriented in the opposite direction
Complementary base pairing between purine and pyrimidine:
A binds to T (forming 2 H bonds)
G binds with C (forming 3 H bonds)
Model suggested a mechanism of DNA replication and of protein synthesis

6. DNA structure with double polymer of DNA nucleotides showing antiparallel orientation of complementary nucleotide strands

7. Basics of DNA replication: replication is via semi-conservative model

8. Basics of DNA replication
The DNA helix “unzips” exposing the 2 single-stranded parental templates of nucleotides
New nucleotides are added against each exposed nucleotide in a complementary fashion
Since the enzyme which completes this task “reads” the DNA in only 1 direction, it affects the process of DNA replication

9. The replication process:

10. The replication process:

11. The replication process:

12. Replication process with major enzymes included

13. Replication of lagging strand