Download Chapter 12-1 Skeleton Notes

Chapter 12.1
DNA
Genetics Recap
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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
THE DISCOVERY OF DNA – WHO WERE THE SCIENTISTS
Frederick Griffith
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Smooth strain caused pneumonia
Rough strain did nothing
Injected mice with various mixtures of the two strains
1.Living smooth cells injected =
2.Living rough cells injected =
3.Heat killed smooth cells =
4.Heat killed smooth cells & living rough cells =
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Why did the mice die?
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Hypothesized that some factor was transferred from the heat-killed cells into the live cells
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Bacterial transformation occurred 
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Chemical is responsible for causing transformation
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Little did he know that he found DNA
Oswald Avery
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 Destroyed all of the various macromolecules and tested to see if transformation still occurred
 When he destroyed DNA, no transformation; proteins, lipids, and carbs still caused transformation
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How Do Bacteriophages Work?
Hershey and Chase
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Used bacteriophages 
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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
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
When observing the blender 
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Conclusion –
WHAT IS DNA?
DNA’s Responsibilities
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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 Components
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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
DNA is a nucleic acid
– It has monomers called 
Each nucleotide is composed of three basic parts:
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Nitrogenous Bases
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There are four nitrogenous bases categorized into two groups
Purines: (two rings)
• Adenine (A)
• Guanine (G)
Pyrimidines: (one ring)
• Cytosine (C)
• Thymine (T)
DNA’s Structure
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DNA can be considered to be like a ladder
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– They alternate along the sides
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They make up the rungs of the ladder
Erwin Chargaff
 Realized 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
Rosalind Franklin
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Revealed that DNA is in helix form (coil or twisted ladder)
Watson and Crick
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– Used the work of Chargaff and Franklin to create this model
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DNA structure is called a double helix, in which two strands are wound around each other
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DNA and Chromosomes
Chromosomes are tightly wound up DNA strands
• Increased organization allows for the tremendous length of DNA to fit into the nucleus of the cell
Chromosome Structure
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DNA is tightly wound around proteins called histones
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– These form chromatin
• Chromatin tightly wound up makes a chromosome
Prokaryotic Chromosomes
Prokaryotic chromosomes are located floating in the cytoplasm of the cell (not in the nucleus)
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