Transcript structure of DNA

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Chromosomes and DNA
• Chromosomes are
made up of a
chemical called
DNA.
• They contain
genes.
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Genes
• Instructions to build proteins.
– Examples: gene for hitchhiker’s thumb,
widow’s peak, tongue-rolling…
• Humans have over 30,000 genes
encoded in their genome.
3
Why do we study DNA?
We study DNA for
many reasons,
e.g.,
• its central
importance to all
life on Earth,
• medical benefits
such as cures for
diseases,
• better food crops.
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DNA
• DNA is often
called the
blueprint of life.
• In simple terms,
DNA contains the
instructions for
making proteins
within the cell.
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DNA by the Numbers
• Each cell has about 2
m 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.
The earth is 150 billion m
• DNA has a diameter of or 93 million miles from
the sun.
only 0.000000002 m.
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Packaging
7
Packaging
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The Shape of the Molecule
• DNA is a very long
polymer.
• The basic shape is
like a twisted ladder
or zipper.
• This is called a
double helix.
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The Double Helix Molecule
• The DNA
double helix
has two
strands
twisted
together.
http://www.youtube.com/watch?v=4LlB
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One Strand of DNA
nucleotide
• One strand of
DNA is a polymer
of nucleotide.
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Four DNA nucleotides
C
• Thymine T
• Adenine A
• Guanine G
• Cytosine
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13
Two Stranded DNA
• 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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C
N
N
C
N
C
C
C
C
N
N
N
C
C
C
O
• The bases attract each
other because of
hydrogen bonds.
• Hydrogen bonds are weak
but there are millions
and millions of them in a
single molecule of DNA.
• The bonds between
cytosine and guanine are
shown here with dotted
lines
N
Hydrogen Bonds
N
O
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Hydrogen Bonds, cont.
• When making
hydrogen bonds,
cytosine always
pairs up with
guanine
• Adenine always
pairs up with
thymine
• Adenine is bonded
to thymine here
N
O
C
C
O
C C
N
C
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Discovery of DNA
Structure
• Erwin Chargaff showed the amounts
of the four bases on DNA
(A,T,C,G)
• In a body or somatic cell:
A = 30.3%
T = 30.3%
G = 19.5%
C = 19.9%
Adapted from cmassengale
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Chargaff’s Rule:
• Adenine and Thymine
always join together
A
T
• Cytosine and Guanine
always join together
C
G
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Rosalind Franklin
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Watson & Crick’s Model
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EXIT SLIP!
http://www.youtube.com/watch?v=
FUA6_Ucw3i4&feature=related
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• Hip Hip Hooray
• Blame it on the DNA
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Nucleotides
O
O -P O
O
O
O -P O
O
One deoxyribose together
with its phosphate and base
make a nucleotide.
O
O -P O
O
Phosphate
Nitrogenous
base
O
C
C
C
O Deoxyribose
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Two Kinds of Bases in DNA
• 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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Adenine and Guanine are
purines
• 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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Thymine and Cytosine are
pyrimidines
• 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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DNA Replication
• http://www.johnkyrk.com/DNAreplica
tion.html
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