Molecular Bio
Name ________________________________
DNA – Discovering the Molecule of Inheritance.
WHAT SCIENTISTS KNEW:
1. DNA Components:
a. Through testing on extracted DNA samples, scientists understood the
basic ingredients of DNA but NOT the structure.
b. Made of ________ different kinds of nucleotides.
2. Protein Components
a. Large complex molecule made of ___________ different amino acids (much
variability)
DNA Nucleotides
 Scientists at this point understood the chemical components of the DNA
molecule (But not the __________________________!)
 3 Basic Parts
 5-carbon sugar (deoxyribose)
 Phosphate group
 ______________________ Base (4 kinds)
 Adenine
 Guanine
 Cytosine
 Thymine
Now what????
BIG DEBATE!!!!!!!
Is it proteins or DNA that
So, lets bring on the scientists!
Molecular Bio
Name ________________________________
Frederick Griffith
 1928
 British Medical Officer
 Discovers that genetic information can be transferred from heat-killed
bacteria cells to live ones.
 Pneumococcus (which infects mice),
 S (smooth)  ________________
 R (rough) strain  ______________________
 Experiment
 S strain were killed by heat, and their remains were added to R strain
bacteria.
 formerly harmless R strain now _____________________________________
 CONCLUSIONS?
This phenomenon, called transformation, provides the first evidence
that the genetic material is a heat-stable chemical. Are proteins????
Molecular Bio
Name ________________________________
Oswald Avery
 1944
 Used a ______________________________________________________________ kind of
experiment.
 Using different enzymes and detergents Avery and
colleagues were able to deduce what was
responsible for the “transformation”
 Oswald Avery, and his colleagues Maclyn McCarty and Colin
MacLeod, identify Griffith's transforming agent as
_________________
 Why were other scientists skeptical about __________________
Being the transforming agent?
Alfred Hershey and Martha Chase
 1952 - Studies viruses,
 Bacteriophage – infects _____________________
 Viruses composed of
 ___________________________________
 ___________________________________
 Viruses
 Injects ____________________________ into host cell
 host cell create many more virus particles.
What they did
 Used radioisotope labels P32 and S35
 Phosphorus(P32) is a component of __________________
 Sulfur (S35) is a components of ____________.
HMMM…….What could we do with this????
Molecular Bio
Name ________________________________
Protein coat (proteins contain Sulphur (S))
DNA core (DNA contains Phosphorous (P))
RED = Radioactivity
USE RED TO INDICATE RADIOACTIVITY
Molecular Bio
Name ________________________________
So now what do we know??????
What don’t we know???????
When you do a puzzle, what strategies do you use?
DNA STRUCTURE
 Scientists realized that the DNA molecule needed to do 3 things
 Carry information generation to generation
 Code had to be translatable into proteins
 Easily copied during cell division
Erwin Chargaff
 1949
 Discovery:
 amount of ____________________ equals the amount of thymine
 amount of _____________________ equals the amount of cytosine
 CHARGAFF’S LAW!
NOW WHAT????
Rosalind Franklin (1920-1958)
 Early 1950’s
 King’s College, London, England
 Using X-ray photography and crystalized DNA, took pictures of the molecule.
 Hinted that the DNA molecule is ___________________________________________________.
Molecular Bio
Name ________________________________
James Watson and Francis Crick
 Working on developing model of DNA molecule
- Figured out the “_________________”
 1953, shown one of Franklin’s X-ray picture indicating shape of molecule
“twisted ladder”
 Published paper in 1953 of DNA being a double helix with two strands being
wound around each other
Double Helix
 Each DNA strand has a ____________________________
backbone
 Nitrogenous bases face inward towards each
other
Nitrogenous Bases
 Purines
 Adenine and Guanine
 Pyrimadines
 Thymine and Cytosine
Gives us __________ different kinds of nucleotides!
Base Pairing
 Chargaff’s rule,
 A bonds to T
 G bonds to C.
 Weak _____________________________ connect the two bases.
Hmmm……I wonder why we use weak hydrogen bonds???
Molecular Bio
Name ________________________________
COMPARING DNA AND RNA
Note the 3 main differences
- RNA single stranded
- Ribose instead of deoxyribose
- Nitrogenous base uracil replaces thymine in RNA
Molecular Bio
Name ________________________________
DNA consists of lots of smaller monomer units called
NUCLEOTIDES!
Each nucleotide consists of 3 parts
-
5 carbon Sugar
Phosphate Group
Nitrogenous Base
o Adenine
o Thymine
o Cytosine
o Guanine
NUCLEOTIDE
The DNA CODE
Remember, the code for proteins is found in the sequence of nitrogenous bases…..in
other words, if your cell wanted to build an enzyme as complex as ATP synthase
(remember the light bulb looking protein in the mitochondria and thylakoid?), it
would do this by first reading a long sequence of A’s, T’s, C’s and G’s.
Human Genome Project - The Human Genome Project was an international
scientific research project with a primary goal to determine the sequence of
chemical base pairs which make up DNA.
Identified the approximately 20,000-25,000 genes of the human genome from both
a physical and functional standpoint.