DNA – THE CODE OF LIFE

A. Friedrich Miescher – extracted DNA from the nucleus of white blood cells.

I. The discovery of DNA

B. Griffith’s Bacterial Transformation (1928) This is an experiment used disease causing

and harmless bacteria that were injected into mice.

Griffith wanted to find out if the harmless bacteria can become harmful.

Observations: Harmless bacteria can become harmful if they are mixed with dead harmful bacteria. The harmful characteristic was inherited from one generation to the next.

Conclusion: Some chemical component in bacteria act as a transforming factor that cause a heritable change.

Bacterial transformation: When bacteria pick up DNA from the environment or other bacteria to use it for their own benefit.

http://www.youtube.com/watch?v=R_DMK9oDdJw&feature=related

C. The Hershey and Chase Experiment (1952)

This experiment used bacteria and viruses (bacteriophage) that only infect bacteria

They also used radioactive isotopes to label proteins (radioactive sulfur) and DNA (radioactive phosphorous). These radioactive isotopes were moved into two groups of viruses.

They wanted to find out if proteins or DNA are responsible for inheritance.

Virus inserts its DNA into bacteria: http://www.youtube.com/watch?v=9hzUjx_oD8E&feature=related

Conclusion: Bacteriophages inject DNA into the host cell, while proteins remain outside. So DNA must be responsible for determining inheritance.

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120076/bio21.swf::Hershey%20and%20Chase%20Experiment

D. Watson and Crick They were the scientists who proposed a

model to describe the structure of DNA They also predicted how DNA doubles

itself.

II. The Structure of DNA (Review)

Deoxyribonucleic acid (DNA) is a macromolecule that is built up of nucleotide monomers.

The nucleotide contains:DeoxyribosePhosphateNitrogen-containing base (A, T, C, G)

Two long polynucleotide chains face each other by their complementary base pairs.

The two long chains are antiparallel to each other and are held together by hydrogen bonds.

Base pairing rule: A binds with T; C binds with G

Adenine and guanine are called purine bases because they are made up of two rings.

Cytosine and thymine are pyrimidine bases because they are made up of one ring.

III. DNA REPLICATION Replication – the process in which one

DNA molecule produces two identical DNA molecules

This process is semiconservative – one chain of the DNA molecule is parental while the other half is a new chain.

The parental chain is called a template while the new chain is the complementary chain.

The steps of DNA replication:1. DNA unwinds and the hydrogen bonds are

separated – helicase

2. The new chain will be built next to the separated old chain by DNA polymerase enzyme.

3. RNA primase will mark the DNA molecule in a 3’ – 5’ direction so the DNA polymerase enzyme can match up the missing nucleotide and build the leading strand in the 5’ – 3’ direction

4. The replication continues until the entire DNA segment is copied.

5. A different DNA polymerase replaces the RNA primer with DNA nucleotides.

6. The lagging strand is the other side of the DNA molecule that grows away from the replication fork in smaller chunks (discontinuously)

7. First RNA primase marks the beginning of a section, than DNA polymerase begins to synthesize the new section

8. The DNA needs to unwind more before a new lagging strand piece can be built – Okazaki fragments – discontinuous segments of the lagging strand of the DNA molecule.

9. An other DNA polymerase changes the RNA primers to DNA and ligase attaches the separate fragments to each other.

10. The two new DNA molecules are exact copies of the original DNA. If any mistakes occurred in the copying, new enzymes will correct those.

http://www.wiley.com/college/pratt/0471393878/student/animations/dna_replication/index.html -- more detailed http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html -- many things on

DNA replication and the experiments http://www.dnalc.org/resources/3d/03-mechanism-of-replication-basic.html