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Molecular Genetics
 1. Frederick Griffith's Experiment - the discovery of transformation
 Using two varieties of streptococcus, he originally searched for a vaccine. One
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variety of bacteria had a capsule (like a cell wall) the other did not have a
capsule.
1. Injection with live encapsulated bacteria -- mice contracted pneumonia and
died
2. Injection with live naked(no capsule) bacteria -- mice lived, immune system
destroyed the bacteria
3. Injection with heat killed encapsulated bacteria -- mice remained healthy
4. Injection with dead encapsulated bacteria and live naked bacteria -- mice
contracted pneumonia and died
*note that neither of this forms caused disease before, but when placed
together something occurred to make the living naked bacteria virulent.
Conclusions:
Living bacteria acquired genetic information from dead bacteria - particularly
the instructions for making capsules, thus transforming the naked bacteria into
encapsulated bacteria.
The Transforming agent was discovered to be DNA. DNA was isolated and added
to live naked bacteria, and they were transformed into the encapsulated kind.
 The Hershey-Chase Experiment - Bacteriophage
 1. Hershey and Chase forced one population of phages to
synthesize DNA using radioactive phosphorous.
2. The radioactive phosphorous "labeled" the DNA.
3. They forced another group of phages to synthesize
protein using radioactive sulfur.
4. The radioactive sulfur "labeled" the protein.
5. Bacteria infected by phages containing radioactive
protein did not show any radioactivity.
 DNA contains phosphorous but not sulfur.
 Proteins contain sulfur but not phosphorous
6. Bacteria infected by phages containing radioactive DNA
became radioactive.
7. This showed that it was the DNA, not the protein that
was the molecule of heredity
 Chargaff analyzed the amounts of the four
nucleotides found in DNA (Adenine, Thymine,
Guanine, Cytosine) and noticed a pattern.
 1. The amount of A, T, G, C varies from species to
species
2. In each species, the amount of A = T, and the
amount of G = C ---- Base Pair Rule
Bases come in two types: pyrimidines (cytosine and
thymine) and purines (guanine and adenine)
 Rosalind Franklin and Wilkins spent time taking X-
ray diffraction pictures of the DNA molecule in an
attempt to determine the shape of the DNA molecule.
 Watson and Crick are credited with finally piecing
together all the information previously gathered on
the molecule of DNA. They established the structure
as a double helix - like a ladder that is twisted. The
two sides of the ladder are held together by hydrogen
bonds.
 Griffith and Transformation- Something transformed
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the bacteria into deadly bacteria.
Hershey and Chase- DNA is the molecule of heredity
Chargaff- A goes with T and C goes with G
Franklin- It’s a double helix
Watson & Crick- Put all the information together.
 DNA = Deoxyribonucleic Acid
 Phosphate
 Sugar = Deoxyribose
 Nitrogenous Bases
 Hydrogen Bonds
1 Nucleotide = 1 phosphate + 1 sugar + 1 nitrogenous base
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A = Adenine bonds to T. Needs 2 Hydrogen Bonds.
G = Guanine bonds to C. Needs 3 Hydrogen Bonds.
T = Thymine Bonds to A. Needs 2 Hydrogen Bonds.
C = Cytosine Bonds to G. Needs 3 Hydrogen Bonds.
 Purines = Larger Molecules A & G
 Pyrimidines = Smaller Molecules C & T
 Need to be a certain size to fit perfectly
between the two vertical backbones
1 purine + 1 pyrimidine = perfect size
- Whenever a cell divides it
makes another copy of itself so one copy can go to each
daughter cell = IT REPLICATES
- Occurs in S phase of interphase
1) DNA separates (unzips) into 2 strands
- Each strand has certain bases that determine what
will be on the new strand.
- The 2 original strands are Complementary
- The strand is unzipped by a molecule called a
helicase
2) When the DNA is split into a 2 prong replication fork
the molecule DNA Polymerase builds the new
complementary strand using the old strand as a
template. (what is a template?)
3)
DNA Polymerase also proofreads the strand to
prevent errors
- Each new double helix is made up of 1 old half and
1 new half = DNA Replication is Semiconservative
- That means it is “half-way” conserved.
 Used in the production of proteins
 Different from DNA
A) The sugar is Ribose instead of Deoxyribose
B) Uracil is used instead of Thymine.
- Uracil bonds to Adenine with 2 hydrogen
bonds. A = U
- There is no thymine in any of the types of
RNA.
 A lot like Replication, only instead of making more
DNA you make mRNA
 m = Messenger. Messenger RNA is a copy of the
instructions needed to make a protein. Proteins are
made by the ribosomes in the cytoplasm of the cell
 mRNA acts as a messenger that takes the instructions
on how to build a protein from the DNA in the nucleus
to the ribosomes in the cytoplasm.
A helicase unzips the DNA
2) RNA Polymerase needs to find
a start codon (3 bases in a row).
This is how it knows where to
start copying = TAC
- The promoter sequence
1)
3)
RNA Polymerase will keep copying until it gets to a
stop codon or termination sequence. ATT, ATC, ACT.
- Transcription starts with one double-strand of DNA
and results in one single-stranded mRNA molecule.
 The information from the DNA is translated into a protein
 Occurs in the ribosomes in the cytoplasm
 Ribosomes are made of pieces of rRNA or =
ribosomal RNA
1) Protein translation Begins when the mRNA brings a
promoter sequence to the ribosome = AUG
2) The ribosome moves down to the next three letter
codon on the mRNA and attaches the correct tRNA
anticodon.
tRNA = Transfer RNA
This process will continue until the ribosome
encounters one of the stop sequences:
- UUA, UAG, UGA
- The protein is now complete
3)
 mRNA
 rRNA
 tRNA
 http://www.youtube.com/watch?v=NJxobgkPEAo
 http://www.youtube.com/watch?v=yJdAxuIA6QM&fe
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