1. Why is replication of DNA important?
DNA Replication
Why is replication of DNA important?

2. Recall - What is DNA?
DNA molecules are large (polymer) made up of thousands of repeating units called nucleotides (monomer)
Nucleotide: -Phosphate group -5-carbon deoxyribose sugar -Nitrogenous base

3. Why & How
Why? Cell Division
Before a cell divides it must make two copies of DNA, so that each daughter cell receives the same amount of DNA.
How? Semi-conservative
Because DNA is double stranded it aids in its own replication by serving as a template for the new strand.

5. DNA Replication DNA Replication - Steps
DNA - can make EXACT copies of itself in a process called replication.
Replication occurs during Interphase of the cell cycle, in preparation for Mitosis or Meiosis
DNA Replication - Steps
1. Enzyme breaks hydrogen bonds between bases so the DNA helix unwinds - two strands separate (unzip)
2 Free nucleotides from the cytoplasm enter the nucleus, where they bond to complementary bases on the DNA strands.
3. Proofreading – fix errors made
Result - two identical DNA molecules that are EXACT copies of the original.

6. Strong Phosphodiester Bonds
DNA is Antiparallel
Side of ladder are made of alternating phosphate and deoxyribose molecules.
Rung of ladder made up of pairs of nitrogen bases attracted by hydrogen bonds.
Strong Phosphodiester Bonds
Weak
H Bonds

7. Extension – 5 carbon sugar is numbered 1 5
This is where the 3’ and 5’ comes from

8. Complimentary Information
the two strands of a DNA molecule are complementary.
Information is contained in the linear sequence of the bases in the polynucleotide chain
DNA for all organisms has same structure, but difference sequences = different information

9. DNA Replication: Basic Concept
As the DNA unzips, free nucleotides are attracted to their compliments but they need an enzyme to form the phosphodiester bonds that connect them as a strand
Enzyme only works in one direction (from 5’  to 3’) Can only add to the 3’ end
Antiparallel - one goes 5’ to 3’; the other goes 3’ to 5’.
New synthesis has to go in opposite directions.
The discontinuous side is called the Lagging strand and forms in fragments called Okazaki Fragments

10. Watch: DNA Replication Made Easy https://www. youtube. com/watch

11. Semiconservative Model
Meselson and Stahl: the two strands of the parental molecule separate, and each functions as a template for synthesis of a new complementary strand.

12. The most beautiful experiment in Biology
Write up the lab
Purpose
Hypothesis
Reasons
Procedure
Results
Conclusion
Turn It In