1. Unit 5: Genetics
Learning Goal 3: Describe the structure of DNA, its discovery, and its importance in DNA replication.

2. History of Discovering DNA
Fredrick Griffith (1928)
Discovers that a factor in
heat-killed, disease-causing
bacteria can “transform”
harmless bacteria into ones
that can cause disease.
Oswald Avery (1944)
Avery’s team determined that genes are
composed of DNA.

3. History of Discovering DNA
Erwin Chargaff (1949)
Discovers that DNA composition is species specific.
Finds that the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine in DNA for every species.

4. History of Discovering DNA
Alfred Hershey and Martha Chase (1952)
Concluded that the genetic
material of the bacteriophage
was DNA not protein.
Rosalind Franklin (1952)
Studied DNA molecules using
X-ray diffraction.
James Watson and Francis Crick
(1953)
Developed the double-helix model of
the structure of DNA.

5. History of Discovering DNA
Sidney Brenner (1960)
Show the existence of messenger RNA.
Brenner and Crick (1961)
Establish that groups of three nucleotide bases, or codons, are used to specify individual amino acids.
Walter Gilbert, Allan Maxam, and Fredrick Sanger (1977)
Develops methods to read the DNA sequence.

6. History of Discovering DNA
Human Genome Project (2003)
identify all the approximately 20,000-25,000 genes in human DNA,
determine the sequences of the 3 billion chemical base pairs that make up human DNA,
store this information in databases,
improve tools for data analysis,
transfer related technologies to the private sector, and
address the ethical, legal, and social issues (ELSI) that may arise from the project.

7. DNA (Deoxyribonucleic Acid)
Shape of DNA is a double helix
Two strands of DNA twisted like a spiral staircase.

8. DNA Each strand is made of many nucleotides.
Nucleotide consists of a:
Sugar
Phosphate
Nitrogen base
Adenine
Thymine
Guanine
Cytosine
Hydrogen bonds between the nitrogen bases held the two strands together.
Base pairing
Hydrogen bonds will only form between certain nitrogen bases.
Adenine---Thymine
Cytosine---Guanine

9. DNA Replication

10. DNA Replication The DNA molecule is unzipped by a series of enzymes.
Hydrogen bonds are broken.
DNA polymerase joins individual nucleotides to produce a DNA molecule.
DNA polymerase also “proofreads” each new DNA molecule to maximize the odds that each molecule is a perfect copy of the original DNA.
The DNA polymerase will continue down the DNA molecule until it has made a complete copy of the DNA molecule.