MOLECULAR GENETICS UNIT 3!

Reflect on your Learning... Answer questions 1,2,and 3 on the

bottom of page 204.

History of DNABefore the 20th Century:

It was believed that proteins were the hereditary material (because they are so prevalent in the cell)

Friedrich Miescher 1869 Used pus cells to investigate the material

inside the nucleus Called this substance nuclein. did not

behave like proteins. Did not know this was the hereditary material.

Hammerling 1930s Used Acetabularia, a one-celled green

algae to investigate WHERE hereditary information was stored in the cell.

Reaches 5 cm in length: great to work with. Three distinct parts:

Foot (contains the nucleus) Stalk cap

The hereditary information must be in the foot (and possibly the nucleus)

He furthered his experiments: Two species of Acetabularia:

A. Mediterranea: disk-shaped cap A. Crenulata: branched, flowerlike cap.

Grafted stalk of A.c onto foot of A.m. Subsequent cap was an intermediate between

the two species: because substances that determined cap type were still in the stalk.

Excised the cap and found that the new cap formed was A. m: substances in the transplant were used up under the control of the new nucleus.

Concluded that YES, the hereditary material is in the nucleus.

The Transforming Principle Nucleus was known to be the site of

hereditary information. Chromosomes consist of both DNA and

proteins. Which one was responsible for inheritance?

Alfred D. Hershey and Martha Chase

Not until 1952 that DNA accepted as hereditary material.

Conducted experiments using a virus, bacteriophage T2: __________________. (Bacteriophages are commonly called phages)

Two components DNA Protein coat.

How viruses work: Attach to membrane Inject hereditary information (PROTEIN

COATS REMAIN OUTSIDE OF THE CELL) DNA of phage takes over cell mechanics Cell makes components (proteins and

nucleic acids) of the virus Cell assembles components into new

viruses New viruses burst out of the cell,

resulting in host cell’s death New viruses can then infect other cells.

Key aspects: Proteins contain sulfur but no phosphorous DNA contains phosphorus and no sulfur

Hershey and Chase tracked the location of DNA and proteins throughout infection. Tagged some viral proteins with an isotope of sulfur,

35S Tagged some viral DNA with an isotope of

phosphorus, 32P. Both 35S and 32P are radioisotopes: emit

radiation as they decay: can be tracked. Both types of tagged T2s were allowed to infect

bacterial cells. Cells put in blender and centrifuged to isolate

bacteria parts (pellet) and viral parts (liquid)

Results? Bacterial cells infected by 35S – containing

viruses did NOT contain any radioactivity. Bacterial cells infected by 32P – containing

viruses DID contain radioactivity. THEREFORE, PHOSPHORUS-RICH DNA

WAS INJECTED INTO THE BACTERIAL CELL. This must be the genetic information.

Seatwork/HomeworkPage 209, #2, 3, 4, 5.