1. Characteristic of Life!!
DNA is found in all living things and has the same structure!

2. Nucleic Acids
Examples - DNA and RNA
Slide 2.35

3. DNA Location and Function
Location – Nucleus (Eukaryotes)
Function – contains the genetic instructions for the development and function of living things.
Slide 3.37

4. Monomer = Nucleotides
DNA is made up of two long chains of nucleotides. Each nucleotide has three parts.
phosphate group
deoxyribose sugar
nitrogen-containing base (A,T,C,G)
There are four different nucleotides
Each contain a different nitrogen base.
phosphate group
deoxyribose (sugar)
nitrogen-containing
base

5. Structure = Double helix
Double = two strands connected
Helix = twisted
Looks like a “twisted ladder”.
Main Parts
Backbone
Phosphate and 5 carbon sugar
Nitrogen bases

6. Four Nitrogen Bases
Adenine, Thymine, Cytosine, and Guanine
Can be either a single or double carbon ring
Pyrimidine = Single Carbon Ring
Purine = Double Carbon Ring

8. DNA Discovery James Watson & Francis Crick
Determined the three-dimensional structure of DNA.
Identified the double helix structure with a sugar-phosphate backbone on the outside and bases on the inside.

9. Other Contributors
Rosalind Franklin’s x-ray images suggested that DNA was a double helix of even width.
Erwin Chargaff found that nucleotides can be found in even ratios.
Chargaff’s Rules
Adenine to Thymine
Cytosine to Guanine

10. Nucleotide Paring Rules (Complementary Base Pairing)
The base-pairing rules dictate how nucleotides always pair up in DNA.
Since a pyrimidine base (single ring) pairs with a purine base (double ring), the helix has an even width.
Adenine pairs with Thymine
Cytosine pairs with Guanine C G T A

11. Nucleotide Bonding Backbone is connected by covalent bonds.
Nitrogen bases are connected by hydrogen bonds.
hydrogen bond
covalent bond

12. DNA Replication – The process of copying a strand of DNA
Why do cells need to make a copy of their DNA?
Occurs in the nucleus during interphase (Synthesis)
Is a “semi-conservative” process
The original (parent) DNA strand is used as a “Template” to make the new DNA strand
Results in 2 strands of DNA that are half old and half new (2 semi conservative DNA molecules)

13. DNA Replication: Semi-conservative
DNA helicase uncoils and unzips DNA
New nucleotides line up next to both old (parent) chains of the DNA

14. DNA Replication – cont’d
DNA polymerase binds the new nucleotides together and “proofreads” the new strands for errors.
Results in 2 semi-conservative strands of DNA

15. DNA Replication
Final Result – 2 Semi-Conservative Strands of DNA

16. DNA: the Genetic Code is carried in Triplets
Genetic code = Order of nitrogenous bases
Gene: a DNA segment that carries the information for building a protein.

17. Reading DNA DNA is read in sets of three nucleotides called a triplet!
1 DNA triplet codes for 1 amino acid in a protein