1. DNA

2. Genetic material of cells…
GENES – units of genetic material that code for a specific trait
DNA belongs to a category of bio-molecules called Nucleic Acids
DNA is a polymer made up of repeating molecules called Nucleotides

3. DNA Nucleotide O O=P-O N CH2 O C1 C4 C3 C2 Phosphate Group
Nitrogenous base
(A, G, C, or T)
CH2 O C1 C4 C3 C2 5
Sugar
(deoxyribose)

4. Watson & Crick proposed…
DNA had specific pairing between the nitrogen bases:
ADENINE – THYMINE
CYTOSINE - GUANINE
DNA was made of 2 long stands of nucleotides arranged in a specific way called Complementary Base Pairing

5. DNA Double Helix Is very much like a twisted ladder… Rungs of ladder
Nitrogenous
Base (A,T,G or C)
Rungs of ladder
Braces of ladder
Phosphate &
Sugar Backbone

6. DNA Double Helix P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A

7. DNA Double Helix
Strands are Antiparallel

8. Nitrogenous Bases PURINES 1. Adenine (A) 2. Guanine (G) PYRIMIDINES
3. Thymine (T)
4. Cytosine (C)
A or G
T or C

9. Chargaff’s Rule Adenine must pair with Thymine
Guanine must pair with Cytosine
Their amounts in a given DNA molecule will be about the same. T A G C

10. BASE-PAIRINGS C G
H-bonds T A

11. Genetic Diversity…
Different arrangements of nucleotide pairs in a nucleic acid (DNA) provides the key to biodiversity among living organisms.

12. The Code of Life… A T C G T A T C A G C G A T C G G A…
The “code” of the chromosome is the specific order that bases occur.
A T C G T A T C A G C G A T C G G A…

13. DNA is wrapped tightly around histones and coiled tightly to form chromosomes

14. DNA Replication A-T, G-C DNA must be copied
The DNA molecule produces 2 IDENTICAL new complementary strands following the rules of base pairing:
A-T, G-C
Each strand of the original DNA serves as a template for the new strand

15. DNA Replication Semiconservative Model: .
1. Watson and Crick, Meselson & Stahl each showed: the two strands of the parental molecule separate, and each functions as a template for synthesis of a new complementary strand. .
DNA Template
New DNA
Parental DNA

16. (which code for a specific AMINO ACID)
DNA controls cell function by serving as a template for PROTEIN structure.
3 Nucleotides = a triplet or CODON
(which code for a specific AMINO ACID)
AMINO ACIDS are the building blocks of proteins.