1. DNA
The Secret Code

2. Genes Genes, which are sections of DNA, are known to:
Carry information from one generation to the next.
Put that information to work by determining the heritable characteristics of organisms.
Be easily copied, because all of a cell’s genetic information is replicated (copied) every time a cell divides.

3. How do we know that all of our genetic information comes from DNA?
Thanks to many scientists and many experiments over the last ≈ 80 years.
Griffith
Hershey and Chase
Franklin
Watson and Crick

4. DNA Nucleic Acid: Deoxyribonucleic Acid (polymer)
Made up of units (monomers) called nucleotides.
Three components:
5-carbon sugar: Deoxyribose
A phosphate group
A nitrogenous base
DNA
Nucleotide

5. DNA Structure Called a double helix
Twisted Ladder
Backbone (sides) : carbon sugar and phosphate groups
Rungs: nitrogenous bases

6. Nitrogenous bases Our alphabet has 26 letters
Can create many different words  many different sentences  billions of different books of information.
DNA’s alphabet has 4 letters
A, T, C, and G
Create 3 letter words  Amino acids  proteins  billions of different organisms

7. Nitrogenous bases Purines: Pyrimidines: Adenine Guanine Thymine
Cytosine

8. DNA Replication Replication: The process of making a copy of DNA
The “parent” molecule has two complementary strands of DNA.
Each is base paired by hydrogen bonding with its specific partner:
A with T and G with C

9. DNA Unzips
The first step in replication is the separation of the two strands.
An enzyme called DNA helicase unzips DNA

10. New nucleotides added
Each parental strand now serves as a template that determines the order of the bases along a new complementary strand.
an enzyme called DNA polymerase adds the bases

11. Gaps are closed (zipped closed)
The nucleotides are connected to form the sugar-phosphate backbones of the new strands. DNA ligase
Each “daughter” DNA molecule consists of one parental strand and one new strand….semi-conservative

12. Reviewing DNA Replication
Replication #3 and more