19.3 DNA is the Hereditary Material

Intro DNA is the only molecule that is

capable of replicating itself DNA provides for the continuity of life

and accounts for the biodiversity of all life forms

Finding the Material of Heredity

In 1943 Joachim Hammerling found that the nucleus in the cell was the likely “holder” of hereditary information

He used a large single-celled green algae Acetabulaira which grows up to 5 cm

Experiment 1 When he cut the algae in distinct

pieces, only the rhizoid (foot) was capable of growing a new stalk and cap – it held the nucleus

Experiment 2 Regardless of what stem was put on

the foot, it was the identity of the foot that would cause the specific cap to grow (they “matched”)

To Do for 20 minutes

Work with a partner or on your own and do the investigation on page 644 and 645. Hand in one page per group

Frederick Griffith, Avery, McCarty and MacLeod did work that questioned the assumption that protein was the heritable material

Alfred D. Hershey and Martha Chase

Hershey and Chase used a virus or a bacteriophage T2 which affects its bacterial host

The phage is composed of 2 parts1) Protein coat2) DNA

The virus survives and duplicates by attaching to the bacteria and injecting its hereditary into it

The bacteria begins to make the new viruses inside it and it eventually bursts with thousands of viruses coming out

http://www.youtube.com/watch?v=41aqxcxsX2w&feature=related

Hershey and Chase proved that DNA was the hereditary material by using tagged viral proteins with a radioisotope of sulphur and phosphorus

Both of the radioisotopes give off radiation as they decay

Sulphur is found in the protein coat while phosphorus is found in the DNA

What molecule would you expect to be found inside the bacteria?

The radioactive phosphorus was found within the bacteria

The radioactive sulphur was found outside of the bacteria

DNA was accepted as the hereditary material

Check out the diagram on page 647

The Race to Reveal Structure

James Watson and Francis Crick discovered the structure of DNA with the help of a picture (X-ray diffraction) taken by Rosalind Franklin

The Definitions

Nucleotide – molecule having a five-carbon sugar with a nitrogenous base attached to its 1’ carbon and a phosphate group attached to its 5’ carbon

Nitrogenous base – an alkaline cyclic molecule containing nitrogen

Deoxyribose sugar – a sugar molecule containing five carbons that lost the –OH (hydroxyl group) on its 2’ position

Phosphate group – a group of four oxygen atoms surrounding a central phosphorus atom found in the backbone of DNA

Make-Up of DNA – a double helix

DNA is made up of 3 things1) Phosphate group – makes up the

“edges” of the ladder – same for each2) Deoxyribose sugar (made up of 6

carbons, 5 within a ring) – same for each

3) Nitrogen base – there are 4 and all contain nitrogen – causes the difference

ADENINE, GUANINE, CYTOSINE, THYMINENote: the amount of adenine always

equals the amount of thymine and the amount of guanine always equals the amount of cytosine

To Do:

Read page 650 as a class on Politics and Science

Page 657 #1-10, 17-20, 22-24