Objectives1. Draw a diagram of DNA label the six parts of

DNA- Circle a nucleotide. OR make DNA Jewelry

2. Distinguish between a Chromosome, Chromatin, DNA and a Gene

3. Discuss the experiments and contributions of the groups of scientists listed below.

4. Griffith, Avery, and Hershey and Chase

Strawberry DNASummary:Students will extract DNA from strawberries.Learning goals/objectives:Students will observe first hand that DNA is in the food that they eat. Students will learn the simple method of DNA extraction and will be able to explain the rationale of each step. Students will be able to explain why DNA extraction is important to scientists.

Prerequisites:Students should know about the basic structure of DNA and its location.

The History of DNA discoveryand current DNA research

Grffith and Transformation A 1928 British scientist, Frederick Griffith

Wondered how certain bacteria cause pneumonia.

Griffith and TransformationA 1928 British scientist, Frederick Griffith Wondered how certain bacteria cause pneumonia.

When injected in mice, they developed Pneumonia

When injected in mice, they remained healthy

Griffith then heat killed the disease causing bacteria and injected it into the mice….. NO sickness!.

When injected in mice, they developed Pneumonia

When injected in mice, they remained healthy

Heat killed disease cells

Transformation: Some factor in the heat killed diseased bacteria was transferred to the harmless form.

Experiment: What happens if kill bacteria and mix material with harmless bactatia? Will it cause a disease?

Yes!

Rough bacteria – a harmless form

were the only live cells given to the mice.

What changed their nature?

Some non-living material must have been responsible for changing the harmless rough into DISEASE CAUSING smooth!

Griffith theorized:

Some molecules from the (heat-killed) smooth disease causing bacteria must have been transferred to the harmless rough edge type, making them “smooth killers”.

Griffith called this phenomenon “Transformation”

Avery treated heat-killed bacteria:

1. with enzymes that destroyed its proteins Still cause disease!

2. then tried enzymes that destroyed its carbohydrates Still cause disease!

3. and so on and so fourth for various other organic molecules in the heat-killed cells…

Transformation was only blocked when destroyed all the DNA molecules left inside the heat-killed bacteria

cells.

DNA must be the molecule responsible for

Transformation!!

1944 about 20 years later….

Oswald Avery: Conducted experiments to determine which organic molecules are causing the transformation

1952 Alfred Hershey and Martha Chase

Studied bacteriophages – viruses that infect bacteria

They tagged the virus protein with radioactive sulfur and the DNA with radioactive phosphate.

They were able to watch the tagged compounds to find out which material was passed on to cause the disease.

Cell contains no radioactive protein

Cell contains radioactive DNA

The Hershey-Chase experiments convinced the scientific community that DNA, not protein, was the material of heredity.

This inspired James Watson and Francis Crick to begin their efforts to discover its structure.

Watson and Crick used an X-Ray of DNA taken by Rosalind Franklin to help them determine DNA structure

History of DNA Discovery: Summary

1920’s-1950’s: various experiments building upon each other determined that DNA is the genetic material for all life on Earth.

-Griffith and “Transformation” of harmless to disease causing

-Avery’s found DNA was responsible when destroyed all other organic compounds

-The Hershey-Chase Experiment Tagged DNA and found it was transferred by the virus

1950’s: The Structure of DNA was determined to be a double helix. - James Watson and Francis Crick constructed various models of how the DNA molecule could be structured.

- Rosalind Franklin’s x-rays of DNA helped Watson and Crick determine that the structure of DNA is the double helix.

DNA Structure and Replication

DNA is the molecule that codes for all proteins of a cell, and transfers hereditary information from one cell to the next.

This is a model of the double helix shape of DNA.

DNA is called a Double helix because not only is it a helix shape, but it is made up of two strands, wound together.

A DNA Strand is a polymer of monomers called nucleotides.

Each nucleotide consists of:

-A phosphate group

-A sugar group

-One of 4 bases: A, C, G, T.

The phosphates and sugars form the outer backbone

The A’s, C’s, G’s, and T’s are the inner “rungs of the ladder”.

The bases of the nucleotides of one strand interact with the bases of the nucleotides of the other strand.

A always pairs with T

G always pairs with C

The bases are held together by hydrogen bonds.

genetics.nbii.gov/ Basic1.html

nuceleosomes

histones

supercoil

DNA

DNA Replication: How more DNA molecules are made in the body.

DNA replicates according to the semi-conservative model.