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UNIT 3!

Answer questions 1,2,and 3 on the bottom of
page 204.
Before 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:



Grafted stalk of A.c onto foot of A.m.



A. Mediterranea: disk-shaped cap
A. Crenulata: branched, flowerlike cap.
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.

Nucleus was known to be the site of hereditary
information.


Chromosomes consist of both DNA and proteins.
Which one was responsible for inheritance?



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.
Page 209, #2, 3, 4, 5.