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 Walter
Sutton discovered
chromosomes were made of
DNA and Protein
 However,
scientists were NOT
sure which one (protein or
DNA) was the actual genetic
material of the cell
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

Frederick Griffith in
1928 showed the
DNA was the cell’s
genetic material
In 1944, Oswald
Avery demonstrated
that DNA is the
material responsible
for transformation.
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 In
1952, Alfred Hershey and
Martha Chase, proved that the
DNA of a virus is injected into
the bacterial cells. That then
causes the bacterial cells to
produce more viral DNA and
proteins.
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

DNA is often called
the blueprint of life.
In simple terms, DNA
contains the
instructions for
making proteins
within the cell that
make up you.
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We study DNA for
many reasons:



Important to all
life on Earth
Medical benefits
such as cures for
diseases
Better food crops
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



Gene – segment of DNA that is
located in a chromosome and
that codes for a specific
hereditary trait.
Basic unit of heredity.
Each cell in the human body
contains about 25,000 to
35,000 genes, which carry
information that determines
your traits.
Our genes are on our
chromosomes.
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



Chromosomes are made up
of a chemical called DNA and
proteins.
Chromosomes come in pairs,
and there are hundreds,
sometimes thousands, of
genes in one chromosome.
There are 46 chromosomes in
each human cell.
Draw and explain Figure 2
Chromosome structure on p.119
on the left side of your notebook.
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


Deoxyribonucleic
acid
Stores hereditary
information
Found in all cells
Organic Comound
made up of C, H, O,
N and P

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Watson & Crick in
the 1950’s built
the 1st model of
DNA
With the help of
Chargraff’s
observations and
Wilkins and
Franklin’s
photographs (x-ray
diffraction)
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



DNA is a very long polymer.
The basic shape is like two
strands twisted around
each other, like a winding
staircase.
This is called a double
helix.
Read the first paragraph on
p. 194; then summarize
what you read in your
notes.
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 The
DNA
double helix
has two
strands
twisted
together.
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
Each DNA strand is
made of linked
nucleotides.

Nucleotides are the
subunits of DNA

Each nucleotide is made
up of 3 parts:
1. phosphate group
2. 5 carbon sugar
(deoxyribose)
3. nitrogen base
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

The backbone of
the molecule is
alternating
phosphates and
deoxyribose
sugar
The teeth are
nitrogenous
bases.
phosphate
deoxyribose
bases
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O
O -P O
O
O
O -P
O
One deoxyribose together
with its phosphate and base
O
make a nucleotide.
O
O -P O
O
Phosphate
Nitrogenous
base
O
C
C
C
O Deoxyribose
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

One strand of DNA is
a polymer of
nucleotides.
nucleotide
One strand of DNA
has many millions of
nucleotides.
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DNA has four different bases:




Cytosine
Thymine
Adenine
Guanine
C
T
A
G
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 Pyrimidines
are
single ring bases.
 Purines
are
double ring
bases.
N
N C
O C
C
N C
N
N C
C
C
N
N C
N C
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
Thymine and cytosine each have one ring
of carbon and nitrogen atoms.
N
O
C
C
O
C C
N
C
thymine
N
O
C
C
N
C
N
C
cytosine
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
Adenine and guanine each have two rings
of carbon and nitrogen atoms.
N
C
Adenine
N
C
C
N
O
N
C
N
N
C
N
C
C
C
N
Guanine
C
N
N
C
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

Remember, DNA
has two strands
that fit together
something like a
zipper.
The teeth are the
nitrogenous bases
but why do they
stick together?
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
The bonds between
cytosine and guanine are
shown here with dotted
lines
N
C
N
N
C
C
N
C
C
C
C
N
N
N
C
Hydrogen bonds are weak
but there are millions and
millions of them in a
single molecule of DNA.
C

The bases attract each
other because of hydrogen
bonds.
O

O
N
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


When making
hydrogen bonds,
cytosine always pairs
up with guanine
Adenine always pairs
up with thymine
N
C
O C
O
C C
N
C
Adenine is bonded to
thymine here
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•
Adenine and Thymine always
join together
A
•
T
Cytosine and Guanine always
join together
C
G
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



Each cell has about 2m
of DNA.
The average human has
75 trillion cells.
The average human has
enough DNA to go from
the earth to the sun
more than 400 times.
DNA has a diameter of
only 0.000000002 m.
The earth is 150 billion m
or 93 million miles from
the sun.
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What:
The process of making
a copy of DNA.
When:
DNA replication occurs
during the synthesis (S)
phase of the cell cycle,
before a cell divides.
How Long:
One chromosome can be
replicated in about 8
hours.
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

Double helix
unwinds
DNA helicases
open the double
helix by breaking
the hydrogen
bonds that link the
complementary
nitrogen bases.
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
The areas where the
double helix
separates are called
replication forks
because of their Y
shape. Once the 2
strands are separated,
additional proteins
attach to each strand,
holding them apart.
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

At the replication fork,
enzymes known as
DNA polymerases add
nucleotides to the
exposed nitrogen
bases, according to
the base-pairing rules.
As it moves along, two
new double helixes
are formed.
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

Process continues
until all of the DNA
has been copied
and the
polymerases are
signaled to detach.
Results in two
identical DNA
strands.
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



Errors sometimes occur and
the wrong nucleotide is
added to the new strand.
An important feature of
DNA replication is that DNA
polymerases have a
“proofreading” role.
It can backtrack to remove
the incorrect nucleotide.
Reduces errors in DNA
replication to about one
error per 1 billion
nucleotides.
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1. RNA has a sugar ribose
DNA has a sugar deoxyribose
2. RNA contains the nitrogen base uracil (U) so..
A pairs with U and C pairs with G
DNA has thymine (T)
3. RNA molecule is single-stranded
DNA is double-stranded
Just like DNA…RNA is made up of the subunits called
nucleotides.
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.
 Messenger
RNA (mRNA) carries
genetic information to the
ribosomes
 Ribosomal RNA (rRNA), along with
protein, makes up the ribosomes
 Transfer RNA (tRNA) transfers
amino acids to the ribosomes where
proteins are synthesized
More recently discovered RNA:
Interference RNA (RNAi)
inhibit gene expression
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