DNA: the Genetic DNA: the Genetic MaterialMaterial

Chapter 9.1Chapter 9.1Identifying the Genetic Identifying the Genetic

MaterialMaterial

Chapter 9 ObjectivesChapter 9 Objectives

Describe the three components of a nucleotide.

Develop a model of the structure of a DNA molecule.

Evaluate the contributions of Chargaff, Franklin, and Wilkins in helping Watson and Crick determine the double-helical structure of DNA.

Relate the role of the base-pairing rules to the structure of DNA.

What is Genetics?What is Genetics? GeneticsGenetics – Study of heredity. – Study of heredity. HeredityHeredity – Transmission of genetic – Transmission of genetic

traits from parent to offspring.traits from parent to offspring. TraitTrait – Attribute in an organism – Attribute in an organism

controlled by genes.controlled by genes. I could do this all day people … mwuah I could do this all day people … mwuah

ha ha ha ha!ha ha ha ha! GeneGene – A section of a chromosome that – A section of a chromosome that

codes for a protein or RNA molecule.codes for a protein or RNA molecule. ChromosomeChromosome – Structure made of DNA – Structure made of DNA

& Protein on which genes are located.& Protein on which genes are located.

AAAHH HHAAAA!AAAHH HHAAAA! ChromosomeChromosome – Structure made of DNA & – Structure made of DNA &

Protein on which genes are located.Protein on which genes are located. I know that for the most part you’re I know that for the most part you’re

thinking to yourself, “Uuuhhhh, so what!” thinking to yourself, “Uuuhhhh, so what!” Well almost 100 years ago this was a Well almost 100 years ago this was a

ginormous issue.ginormous issue. Biologists knew that chromosomes carried Biologists knew that chromosomes carried

genetic material, but there was something genetic material, but there was something that they didn’t know which became a that they didn’t know which became a rush against time & other Biologist to rush against time & other Biologist to discover.discover.

I know you’re all at the edge of your I know you’re all at the edge of your seat!seat!

The question was, what part of a The question was, what part of a chromosome actually contained the chromosome actually contained the genetic material? Is it the DNA or is it genetic material? Is it the DNA or is it protein?protein?

Biologists couldn’t exactly do genetic Biologists couldn’t exactly do genetic testing until they knew which one of testing until they knew which one of these was actually carrying the genes.these was actually carrying the genes.

For years Biologists worked on finding For years Biologists worked on finding the answer. A couple good the answer. A couple good experiments and a couple of accidents experiments and a couple of accidents later an answer was found.later an answer was found.

Frederick Griffith’s Frederick Griffith’s ExperimentsExperiments Griffith was a bacteriologist who was Griffith was a bacteriologist who was

looking for a vaccine against a bacterium looking for a vaccine against a bacterium called called Streptococcus pneumoniaeStreptococcus pneumoniae..

S. pneumoniaeS. pneumoniae is the bacteria that causes is the bacteria that causes pneumonia.pneumonia.

VaccineVaccine – A substance prepared from – A substance prepared from killed or weakened pathogens & killed or weakened pathogens & introduced to a body to produce immunity.introduced to a body to produce immunity.

Griffith’s 1928 ExperimentsGriffith’s 1928 Experiments Griffith worked with two types of Griffith worked with two types of S. S.

pneumoniae.pneumoniae.

A.A. A strand of A strand of S. pneumoniaeS. pneumoniae that that was encased in a capsule made of was encased in a capsule made of polysaccharides. The capsule protects the polysaccharides. The capsule protects the bacterium from the body’s immune bacterium from the body’s immune system. This helps the bacterium to system. This helps the bacterium to become a become a virulentvirulent or able to cause the or able to cause the disease. These bacteria look smooth so disease. These bacteria look smooth so they were called the “S” type.they were called the “S” type.

Griffith’s 1928 Experiments Griffith’s 1928 Experiments cont.cont.

B. The other type of B. The other type of S. S. pneumoniaepneumoniae that Griffith used did not that Griffith used did not have a capsule, therefore it did not have a capsule, therefore it did not cause the disease. These bacterium cause the disease. These bacterium appeared rough so they were given the appeared rough so they were given the name “R” type.name “R” type.

Griffith did 4 experiments which Griffith did 4 experiments which accidentally strengthened the argument accidentally strengthened the argument that DNA was the genetic carrier.that DNA was the genetic carrier.

Four Blind MiceFour Blind Mice

1. Griffith first injected mice with the S 1. Griffith first injected mice with the S bacteria. The S type bacteria was a bacteria. The S type bacteria was a virulent so it caused the disease and killed virulent so it caused the disease and killed the mouse.the mouse.

2. Griffith then injected the R bacteria that 2. Griffith then injected the R bacteria that did not kill the mouse. The lack of the did not kill the mouse. The lack of the capsule caused the mouse’s immune to kill capsule caused the mouse’s immune to kill the bacteria.the bacteria.

Four Blind Mice Cont.Four Blind Mice Cont.

3. Griffith then heated up the S bacteria 3. Griffith then heated up the S bacteria so that the DNA would die but the capsule so that the DNA would die but the capsule would remain. Why do you think he did would remain. Why do you think he did this? this?

The “heat-killed” bacteria did not kill the The “heat-killed” bacteria did not kill the mouse. What does that mean about the mouse. What does that mean about the capsule?capsule?

Four Blind Mice Cont.Four Blind Mice Cont.

4. Just as a gag Griffith took the “heat-4. Just as a gag Griffith took the “heat-killed” S bacteria and the normal R type killed” S bacteria and the normal R type mixed them together and injected that into mixed them together and injected that into the mouse.the mouse.

What happened?What happened? The mouse died! What? Why?The mouse died! What? Why? When Griffith looked at the blood of the When Griffith looked at the blood of the

dead mouse he noticed that the living R dead mouse he noticed that the living R type had acquired capsules. The harmless type had acquired capsules. The harmless R type had transformed into harmful S R type had transformed into harmful S types.types.

Griffith’s DiscoveryGriffith’s Discovery

Griffith discovered what is now called Griffith discovered what is now called transformation.transformation.

TransformationTransformation - is a change in - is a change in shape or identity when bacteria take shape or identity when bacteria take in foreign genetic material. in foreign genetic material.

This “gag” was the first real step in This “gag” was the first real step in proving that DNA was the real proving that DNA was the real genetic carrier. genetic carrier.

Next we find out how it happened!Next we find out how it happened!

Griffith’s Discovery of Griffith’s Discovery of TransformationTransformation

Want more Proof?Want more Proof?

In 1944 a Biologist named Oswald In 1944 a Biologist named Oswald Avery performed an experiment very Avery performed an experiment very similar to that of Griffith.similar to that of Griffith.

Avery used DNA and protein Avery used DNA and protein destroying enzymes in his stock of destroying enzymes in his stock of S. S. pneumoniaepneumoniae..

If DNA were the instructions for If DNA were the instructions for making the capsule what would making the capsule what would happen to the bacteria if a DNA happen to the bacteria if a DNA destroying enzyme was introduced?destroying enzyme was introduced?

Hershey and ChaseHershey and Chase In 1952 Alfred Hershey In 1952 Alfred Hershey

and Martha Chase and Martha Chase performed an experiment performed an experiment that put a final nail in that put a final nail in protein’s coffin.protein’s coffin.

H & C used a virus called H & C used a virus called a T2 Bacteriophage (T2 a T2 Bacteriophage (T2 phage) which injects it’s phage) which injects it’s hereditary material into a hereditary material into a bacteria.bacteria.

A T2 phage is made of a A T2 phage is made of a protein sheath that protein sheath that protects its DNA…that’s protects its DNA…that’s it.it.

Fun with Radioactive Fun with Radioactive MaterialMaterial

Step 1: They first grew T2 with Step 1: They first grew T2 with E. coliE. coli in a medium that contained in a medium that contained radioactive Sulfur (radioactive Sulfur (3535S). Sulfur S). Sulfur attaches to proteins. They also attaches to proteins. They also prepared T2 with prepared T2 with E. coliE. coli in a medium in a medium that contained radioactive Phosphorus that contained radioactive Phosphorus ((3232P). Phosphorus attaches to DNA. P). Phosphorus attaches to DNA.

Step 2: The Step 2: The 3535S and S and 3232P were allowed P were allowed to infect the to infect the E. coli.E. coli.

Fun with Radioactive Material Fun with Radioactive Material Cont.Cont.

Step 3: The Step 3: The 3535S and S and 3232P with the P with the E. coli E. coli were thrown into a centrifuge to strip them were thrown into a centrifuge to strip them apart from each other. The lighter apart from each other. The lighter material at the top of the test tube was material at the top of the test tube was the virus, the heavier material was the the virus, the heavier material was the bacteria.bacteria.

H & C Finally!H & C Finally!

H & C noticed that the radioactive H & C noticed that the radioactive DNA material was with the bacterial DNA material was with the bacterial material and the radioactive protein material and the radioactive protein material was only found with the material was only found with the viral material in the top part of the viral material in the top part of the test tube.test tube.

What does that mean?What does that mean?