Transcript Document

I. Scientist
1. Frederick Griffith
2. Oswald Avery
3. Alfred Hershey
4. Martha Chase
5. Erwin Chargaff
6. Rosalind Franklin
7. Maurice Wilkins
8. James Watson
9. Francis Crick
I. Frederick Griffith’s Experiment
1928
a. S (smooth bacteria-pneumonia) bacteria
Kills Mouse
b. R (rough bacteria-pneumonia) bacteria
DOES NOT KILL MOUSE
c. Heat-Killed S bacteria
DOES NOT KILL MOUSE
d. Heat-Killed S bacteria and Live R bacteria
KILL MOUSE
e. Results
• Live, disease causing bacteria (S strain) from
dead mouse
– WHY?
• Transformation – one type of bacteria (the harmless form)
has been changed permanently into another (the diseasecausing form)
• Thus Griffith concluded that the transforming factor had
to be a gene
f. Vaccine
A substance that is prepared
from a KILLED or WEAKENED
disease-causing agents,
including certain bacteria
II. Oswald Avery Experiment
1944
a. Repeated Griffith’s Experiment
i. Observing bacterial transformation, Avery
and his team discovered that the nucleic
acid DNA stores and transmits genetic
information from one generation of
bacteria to the next.
III. Alfred Hershey and Martha Chase’s
Experiment 1952
a. Hershey and Chase’s experiment convinced
many scientist that DNA was the genetic
material found in genes
i.
Not just in viruses and bacteria, in all living cells
b. Bacteriophage – is a virus that infects
bacteria
i. Remember this is NOT a bacteria it is a VIRUS
IV. Erwin Chargaff Observations
a. Showed that the amount of Adenine
ALWAYS equals the amount of
Thymine
i. A = T
T=A
OR
b. Showed that the amount of Guanine
ALWAYS equals the amount of Cytosine
i. C = G
OR
G=C
1. So if there is 50
micrograms of adenine in
a strand of DNA, there
would also be 50
micrograms of
___________________.
Thymine
V. Rosalind Franklin’s & Maurice Wilkins
Photographs, Early 1950’s
a. Wilkins and Franklin
developed high-quality
x-ray diffraction of
strands of DNA
b. The photograph
suggested that the DNA
molecule resembled a
TIGHTLY COILED HELIX
VI. James Watson and Francis Crick
Early 1950’s – published 1953
a. Discovered the structure of DNA
b. Watson and Crick built a model of
DNA with the configuration of a
Double Helix (Spiral Staircase)
of two strands of nucleotides twisting
around a central axis
https://www.youtube.com/watch?v=1vm3od_UmFg
II. Structure of DNA
a. DNA – Deoxyribonucleic
Acid
i. Five-carbon sugar found on
DNA is called deoxyribose
b. Nucleotides
i. Watson and Crick determined that a DNA
molecule is made up of a chain of nitrogen
bases called Nucleotides
ii. 3 parts of DNA nucleotide
1. 1 - phosphate group
2. 1 - 5-carbon sugar – deoxyribose
3. 1 – nitrogen base (A, T, C, G)
iii. Label the illustration
Phosphate
Nitrogen base
Five-Carbon
Sugar
1.The phosphate and five-carbon sugar
group are always the same for each
nucleotide
2.The nitrogenous base may be any one of
the 4 bases
a.Adenine
b.Guanine
c.Cytosine
d.Thymine
c. Purines
i. Adenine and
Guanine are purines
1. Nitrogen bases
are made of two
rings of carbon
and nitrogen
2. How do we remember that?
a. Aggies - AGs are pure = purines
d. Pyrimidine
i. Thymine and
Cytosine are
pyrimidines
1. Nitrogen bases are
made up of a single
ring of carbon and
nitrogen
2. How do we remember that?
a. pYrimidine = cYtosine
and thYmine
i. Hint –
for the Y’s
e. Pairing and Structure
i. Watson and Crick, with the help of Chargaff’s
work, realized that purines are always paired
with pyrimidines
1. Adenine ALWAYS pairs with Thymine and Guanine
ALWAYS pairs with Cytosine this is called
Complementary Base Pairs
2. Complementary base pair – the sequence of bases
on one strand determines the sequence of bases on
the other strand
a. Adenine (purine) = Thymine (pyrimidine)
i.
AT
or
TA
b. Guanine (purine) = Cytosine (pyrimidine)
i.
i. T
___
A
GC
or
CG
c. Example:
C
G
T
A
C
___
___
___
A ___
T
G ___
C
G
A G C A T G C A A C A T G T C G
A G T C A G T A A C C G G T A A C
G G T C
ii. Sides of DNA (backbone)
1. Phosphate and five-carbon
sugar (deoxyribose)
iii. Middle
1.Nitrogen Bases (A, T, C, G)
2. Hydrogen bond holding the helix
together
iv. Bonds
1. Adenine forms two hydrogen bonds with
Thymine
2. Guanine forms three hydrogen bonds with
Cytosine
a. The bonds help keep the DNA strands (2) together
v. Label the DNA illustration
Adenine – Blue
Thymine – Yellow
Guanine – Pink
Cytosine – Green
Phosphate – purple
5-Carbon Sugar – Orange
2 Hydrogen Bond – red
3 Hydrogen Bond - brown
EOC TEST PREP QUESTION:
# 1. Which pattern show how bases pair in
complementary strands of DNA?
a. A-C and T-G
c. A-G and T-C
b. A–T and C-G
d. A-A and C-C
# 2. If the sequence of nucleotides on one
strand of DNA molecule is GCCATTG, the
sequence of the complementary strand is
a. GGGTAAG
b. CCCTAAC
c. CGGTAAC
d. GCCATTC
III.The Replication of DNA
a. Roles of enzymes in DNA Replication
i. The complementary strands of the double helix
serve as a TEMPLATE for building new DNA.
ii. The process of making a copy of DNA
is called REPLICATION.
1. Remember that DNA replication
occurs in the SYNTHESIS (S)
phase of the cell cycle, before a
cell DIVIDES.
b. Steps of Replication
i. Step 1:
1. The double helix UNWINDS because of enzymes called
DNA HELICASES.
a. ASE = enzyme
2. DNA helicase breaks open the DOUBLE HELIX that link
the complementary bases between 2 strands.
3. PROTEINS keep the strands separated.
4. The areas where the double helix separates are called
REPLICATION FORKS because of the Y-SHAPE.
ii. Step 2:
At the replication fork, ENZYMES known
as DNA POLYMERASES move along each
of the DNA strands and add
NUCLEOTIDES to the exposed nitrogen
bases, according to the BASE-PAIRING
rules.
iii. Step 3 :
1. Once all of the DNA has been copied,
the POLYMERASES are signaled to
DETACH.
2. This process produces TWO DNA
molecules (each strand is made up of one
OLD and one NEW) that are IDENTICAL to
each other.
c. Checking for ERRORS
iv. Sometimes ERRORS occur and the
wrong NUCLEOTIDE is added to the new
strand.
v. An important feature of DNA
replication is that DNA polymerases have
a “PROOFREADING ROLE”
1. DNA Polymerase can only add nucleotides to a growing
strand only if the PREVIOUS NUCLEOTIDE is
CORRECTLY PAIRED to its complementary base.
2. In the event of a mismatched
NUCLEOTIDE, the DNA polymerase can
BACKTRACK and remove the incorrect
nucleotide and replaces it with the
CORRECT one.
a. This proofreading reduces error in
DNA replication to about ONE error per
ONE BILLION nucleotides.
d. The Rate of Replication
i.
Replication DOES NOT begin at one
end and end at the other.
1.
Prokaryotic DNA (ex: Bacteria)
a. Their circular DNA has TWO replication
forks that begins at a single point.
2. Eukaryotic DNA
(Ex: animals and plants)
a. Their linear DNA has MANY
replication forks
b. If replication in eukaryotic DNA
started at a single point it
would take 33 days for a single
strand to replicate.
c. Each human chromosome is
replicated in about 100
SECTIONS that are 100,000
NUCLEOTIDES long, each section
with its own STARTING POINT.
d. An entire human chromosome
can be replicated in about 8 hours.
EOC PREP QUESTIONS
# 3. How many DNA molecules exist after one
molecule of DNA has been replicated?
A. 1
B. 2
C. 4
D. 8
EOC PREP QUESTIONS
# 4. Multiple replication forks along the DNA
a. correct replication errors
b. reduce DNA replication time
c. ensure that the new and old DNA strands are
complementary
d. signal DNA polymerase to stop