Download Chapter 9 - Jamestown Public Schools

Chapter 9
DNA: The Genetic Material
Sections 1-3
• Section 1- Identifying the Genetic
Material
• Section 2- The Structure of DNA
• Section 3- The Replication of DNA
A Brief Review
• Chromosomes consist of 2 replicated
strands of DNA tightly coiled around
proteins. The 2 strands (chromatids)
are attached at the centromere.
• Gene is a segment of DNA that codes
for proteins or RNA molecule
• Cell’s DNA is copied during synthesis (S)
• Mutations occur when chromosomes
break, causing the broken piece to
detach or reattach somewhere else
Identifying Genetic Material
• Fredrick Griffith(1928)
studied bacteria. Used
vaccine to kill pneumonia.
(mice)
• Vaccine- substance that is
prepared from dead or
weakened disease-causing
agents.
• Discovered transformation
change in genotype caused
when cells take up foreign
genetic material.
Avery’s Experiments
• Oswald Avery 1944
• The material
responsible for for
transformation is not
affected by proteindestroying enzyme.
• The material was
affected by DNAdestroying enzyme.
• This concluded that
DNA is the material
responsible for
transformation.
• Explained why
harmless R bacterial
changed and became
virulent S bacteria and
killed mouse.
Viral Genes and DNA
• Hershey and Chase used viruses, which were
composed of DNA or RNA surrounded by a
protein coat.
• Bacteriophage- virus that infects bacteria bacteria cell produced more viruses.
• Found that DNA of viruses was injected into
the bacterial cells, the injected DNA
molecule causes bacterial cells to produce
more viral DNA and proteins. This proved
that DNA, not proteins, was the hereditary
material in cells.
The Structure of DNA
• Watson and Crick
pieced together a
model of the
structure of DNA.
• Double helix- 2
strands twisted
around each other
(staircase)
• Each strand was
made of nucleotides.
(subunits of DNA)
Nucleotide
• Each nucleotide is
made of 3 parts.
– A phosphate group
– A five carbon sugar
• deoxyribose
– A nitrogen
containing base
• Adenine ( A)
Guanine (G)
• Thymine (T)
Cytosine (C)
Pairing Between Bases
• The double helix is held together by weak
hydrogen bonds between the pair of bases.
• Base pairing rules- Adenine pairs with Thymine
(A-T) Cytosine pairs with Guanine (C-G)
• The sequence of bases on one strand determines
the sequence of bases on the other strand.
The Replication of DNA
DNA Replication
• DNA copy is made during synthesis. (S)
• Step 1- double helix unwinds (DNA helicases
enzymes break hydrogen bonds)
• Step 2- DNA polymerases enzymes move along
each strand of DNA. Polymerases add
nucleotides to the exposed nitrogen base.
• Step 3- DNA polymerase adds nucleotides to
all of the DNA until entire strand is copied. (2
identical strands are produced)
• DNA polymerase also “proof-read” to reduce
errors. (1 error per 1 billion nucleotide)