1. Aim: What is DNA composed of?
Modern Genetics DNA
Aim: What is DNA
composed of?

2. What is DNA? A. Deoxyribonucleic acid.
B. A gene is a portion of DNA in a chromosome.
C. Organic compound.
Polymer (chain) of nucleotides.
DNA is the blueprint of life.

3. What is a Nucleotide? A. A nucleotide is made up of 3 parts:
1. Phosphate group (PO4).
2. Deoxyribose molecule (5 carbon sugar).
3. Nitrogenous base
a. There are only 4 bases: A-adenine;
T-thymine; G-guanine; C-cytosine

4. What is a Nucleotide?
b. There are 4 base pair combinations (complimentary pairs): A-T; T-A; C- G; G-C
c. Base pair combinations vary in all humans, making us all look different.

5. Nitrogenous Bases T C A G

6. Nucleotide Nitrogenous Base Phosphate Group Deoxyribose molecule
(5-carbon sugar)

7. Who Figured Out What DNA Looked Like?
James D. Watson & Francis Crick
Watson
Crick

8. Watson-Crick Model
A. DNA is arranged as a double helix (twisted ladder).
B. The sides of the ladder are made up of alternating phosphate & deoxyribose molecules.
C. The rungs or steps of the ladder are nitrogenous base pairs.

9. Watson-Crick Model
D. Double-helix model explains how & why the daughter cells resulting in mitosis are identical copies of the original parent.

10. Double Helix Model

11. DNA Replication
A. Replication is the process which new identical DNA molecules are formed.
1. DNA unzips because the weak hydrogen bonds between base pairs break.
2. The free floating nucleotides fasten to complimentary bases on old DNA strand.
3. Results in 2 DNA helixes each with an old & new strand.

12. Gene Expression
A. Genes control the synthesis of proteins with the help of RNA
B. One Gene-One Polypeptide Hypothesis: 1 gene controls the production of 1 polypeptide (protein).