Download Chapter 12-1 - DNA

Chapter 12.1
DNA
• 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
Genetics
Recap
Frederick Griffith
• Studied pneumonia and its effects on mice
Smooth strain caused pneumonia
Rough strain did nothing
• Injected mice with various mixtures of the
two strains
Griffith’s Experiment
1.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 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 Avery
• Tried to find out what
factor caused the
bacterial transformation
 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
• Demonstrated that DNA
was the transforming
principle
The fact that
there is no S
strain means
that
transformation
did not happen
DNA is the
transforming
principle
Enzymes that
destroy the
macromolecules
Hershey and Chase
• Used bacteriophages
viruses that attack
bacteria
 Consist of an outer
protein coat and an
inner core of DNA
How Do Bacteriophages
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
Experiment
• 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
Experiment
• 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
Experiment
Hershey and Chase
Experiment
• 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,
NOT protein
DNA’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 Components
• DNA is a nucleic acid
– It has monomers called  nucleotides
• Each nucleotide is composed of three
basic parts:
 5 carbon sugar – deoxyribose
A phosphate group
A nitrogenous base
Nitrogenous Bases
• 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
• 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 sugar
– 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
A=T
Purines
G=C
Pyrimidines
Rosalind Franklin
Used x-ray diffraction
to gather information
about DNA structure
– Revealed that DNA is
in helix form (coil or
twisted ladder)
Watson 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
other
The two strands are connected by hydrogen
bonds
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
• DNA is tightly wound around proteins
called histones
8 histones + DNA = nucleosome
– These form chromatin
• Chromatin tightly wound up makes a
chromosome
•
http://www.youtube.com/watch?v=yqESR7E4b_8&feature=related
Prokaryotic Chromosomes
• 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)