Chapter 12.1Chapter 12.1DNADNA

Genetics Genetics RecapRecap

• Mendel, through his experiments, concluded that a organism’s traits are a result of the inheritance of genes from that organism’s parents

• Mendel knew that this inheritance was due to some “factor” but was not able to identify what exactly it was– This left room for future scientists to

discover what these mysterious factors were

Frederick GriffithFrederick Griffith• Studied pneumonia and its effects on mice

Smooth strain caused pneumoniaRough strain did nothing

• Injected mice with various mixtures of the two strains

Griffith’s ExperimentGriffith’s Experiment1.Living smooth cells injected =

2.Living rough cells injected =

3.Heat killed smooth cells =

4.Heat killed smooth cells & living rough cells =

– Why did the mice die?

Griffith’s ConclusionsGriffith’s Conclusions• Hypothesized that some factor

was transferred from the heat-killed cells into the live cells

• Bacterial transformation occurred a change in a bacterial trait

• Chemical is responsible for causing transformation Called it the transforming

principle• Little did he know that he found DNA

Oswald AveryOswald Avery• Tried to find out what factor

caused the bacterial transformation

Destroyed all of the various macromolecules and tested to see if transformation still occurredWhen he destroyed DNA, no

transformation; proteins, lipids, and carbs still caused transformation

• Demonstrated that DNA was the transforming principle

Enzymes that Enzymes that destroy the destroy the macromoleculemacromoleculess

The fact that The fact that there is no there is no S S strainstrain means means

that that transformation transformation did not happendid not happen

DNA is the DNA is the transforming transforming

principleprinciple

Hershey and ChaseHershey and Chase• Used bacteriophages

viruses that attack bacteria

Consist of an outer protein coat and an inner core of DNA

How Do Bacteriophages How Do Bacteriophages Work?Work?

• Bacteriophage lands on the plasma membrane of the bacteria

• Injects DNA into the bacteria

• Viral DNA inserts with bacterial DNA gets duplicated when bacteria goes through mitosis

• More viruses will be produced and eventually the bacteria explodes releasing all of the new viruses

http://www.youtube.com/watch?v=YG3d77SRWZI

Hershey and Chase Hershey and Chase ExperimentExperiment

• Wanted to see what was responsible for causing transformation in bacteria– Was it the DNA inside the bacteriophage or the

protein coat surrounding the bacteriophage• Wanted to confirm Avery’s experiment

Labeled the protein coat with a radioactive sulfur isotope and the DNA with a radioactive phosphorous isotope so that they may follow where each part goes after the infection

Hershey and Chase Hershey and Chase ExperimentExperiment

• Mixed solution of bacteriophage and solution of bacteria together and let virus work

• After a time, put mixture into a blender Purpose was to shake viral coats off of the bacteria

• Because the cell is heavier it will go to the bottom of the blender– This part will have the DNA from the virus

Hershey and Chase Hershey and Chase ExperimentExperiment

Hershey and Chase Hershey and Chase ExperimentExperiment

• When observing the blender found that the radioactive phosphorous was in the bottom part of the blender (inside the cells) while the radioactive sulfur was in the top part (empty protein coats)

• Conclusion – DNA causes transformation, NOTNOT protein

DNA’s ResponsibilitiesDNA’s Responsibilities• Genes carry information from one

generation to the next

• Genes determine the heritable characteristics of organisms

• Genes can be replicated or copied exactly

DNA’s ComponentsDNA’s Components• DNA is a nucleic acid

– It has monomers called nucleotides

• Each nucleotide is composed of three basic parts: 5 carbon sugar – deoxyriboseA phosphate groupA nitrogenous base

Nitrogenous BasesNitrogenous Bases• There are four nitrogenous bases

categorized into two groupsPurines: (two rings)

• Adenine (A)• Guanine (G)

Pyrimidines: (one ring)• Cytosine (C)• Thymine (T)

DNA’s StructureDNA’s Structure• DNA can be considered to be like a ladder

The sugar and phosphate groups make up the backbone of the molecule, or the sides of the ladder– They alternate along the sides

The nitrogenous bases stick out of the sides of the sugarsugar– They make up the rungs of the ladder

Erwin ChargaffErwin ChargaffRealized the number of

A’s equals the number of T’s and that the number of G’s equals the number of C’s

• Base pairing rule

A = T G = C Purines Pyrimidines

Rosalind FranklinRosalind FranklinUsed x-ray diffraction

to gather information about DNA structure

– Revealed that DNA is in helix form (coil or twisted ladder)

Watson and CrickWatson and Crick• Made 1st 3-D model of a DNA molecule

– Used the work of Chargaff and Franklin to create this model

• DNA structure is called a double helix, in which two strands are wound around each otherThe two strands are connected by hydrogen

bonds

DNA and ChromosomesDNA and ChromosomesChromosomes are

tightly wound up DNA strands

• Increased organization allows for the tremendous length of DNA to fit into the nucleus of the cell

Chromosome StructureChromosome Structure• DNA is tightly wound around proteins called

histones8 histones + DNA = nucleosome– These form chromatin

• Chromatin tightly wound up makes a chromosome

• http://www.youtube.com/watch?v=yqESR7E4b_8&feature=related

Prokaryotic Prokaryotic ChromosomesChromosomes

• Prokaryotic chromosomes are located floating in the cytoplasm of the cell (not in the nucleus)They are circular in shape (not “X shape” like in

eukaryotes)