It’s the DNA!
The information is in the DNA!
DNA History
• Griffith (1928)– Experimented on mice and observed some harmless strains of bacteria could change into harmful strains. He called this transformation.
DNA History
• Avery (1944) – Discovered that DNA is the nucleic acid that stores and transmits the genetic information from one generation to the next.
The Avery Experiment (1944)
Purified DNA extracted from the smooth pneumonia bacteria could ‘transform’ rough pneumonia bacteria into the smooth form.
The Hershey-Chase experiment (1952)
Viruses called bacteriophages can infect bacterial cells and change the characteristics of the cells.Bacteriophages are only made of two materials… protein and DNA.
DNA Nucleotide
OO=P-O O
Phosphate Group
CH2
O
C1C4
C3 C2
5
Sugar(deoxyribose)
N
Nitrogenous base (A, G, C, or T)
DNA’s StructureDNA contains four nucleotide bases: –adenine (A) –cytosine (C) –guanine (G)–thymine (T)
Nitrogenous Bases
PURINES1. Adenine (A)
2. Guanine (G)
PYRIMIDINES3. Thymine (T)
4. Cytosine (C) T or C
A or G
Chargaff’s Rules (1950)• Chargaff discovered
how the nitrogenous bases bond together.
• He discovered that the amount of Adenine equals the amount of Thymine ,and that the amount of Cytosine equals the amount of Guanine.
Chargaff’s Rule
Adenine pairs with Thymine
Guanine pairs with Cytosine
Their amounts in a given DNA molecule will be about the same.
G CT A
P
P
P
O
O
O
1
23
4
5
5
3
3
5
P
P
PO
O
O
1
2 3
4
5
5
3
5
3
G C
T A
More DNA History
• Watson & Crick created the double helix model of DNA.
DNA Double Helix
How does all this DNA fit into a cell?
• In Eukaryotes, DNA is located in the nucleus in the form of chromosomes.
• Chromosomes are DNA wound tightly around proteins called histones.
Semi-Conservative Replication
One-half of each new molecule of DNA is old (template strand)One-half of new molecule of DNA is new (complementary strand)
DNA Replication
• During DNA replication, the DNA molecule separates into two strands, then produces two new complimentary strands following the rules of base pairing
(Chargaff Rules).
DNA Replication
• Each strand of DNA serves as a template, or model, for the new strand.
How It Occurs
• Complimentary bases are added to the strands, for example a strand of DNA with the bases
ATTCGAG would have a complimentary strand of
• TAAGCTC
How It Occurs
•DNA replication is carried out by a series of enzymes.
