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This presentation introduces the structure of DNA. Deoxyribonucleic acid is a molecule composed of two polynucleotide chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning, growth, and reproduction of all known organisms and many viruses. DNA and ribonucleic acid are nucleic acids.
2.
Chromosomes and DNA
• Chromosomes are
made up of a
chemical called
DNA.
• They contain
genes.
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3.
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.
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4.
Why do we study DNA?
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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5.
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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6.
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
only 0.000000002 m. the sun.
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9.
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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10.
The Double Helix Molecule
• The DNA
double helix
has two
strands
twisted
together.
http://www.youtube.com/watch? 10
11.
One Strand of DNA
nucleotide
• One strand of
DNA is a polymer
of nucleotide.
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12.
Four DNA nucleotides
• Cytosine C
• Thymine T
• Adenine A
• Guanine G
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14.
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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15.
Hydrogen Bonds
• The bases attract each
N
other because of
hydrogen bonds.
C
N
N
• Hydrogen bonds are weak
but there are millions
C
C
and millions of them in a
C
N
O
single molecule of DNA.
N
• The bonds between
C
N
cytosine and guanine are C N
shown here with dotted
C C O
lines 15
C N
16.
Hydrogen Bonds, cont.
O
• When making N C
hydrogen bonds,
cytosine always pairs O C C C
up with guanine N
N C
• Adenine always pairs C
up with thymine N
C N
• Adenine is bonded to
thymine here C
C C
N N
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18.
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 18
19.
Chargaff’s Rule:
• Adenine and Thymine
always join together
A T
• Cytosine and Guanine
always join together
C G C
A
G
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21.
Watson & Crick’s Model
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22.
EXIT SLIP!
http://www.youtube.com/watch?
22
v=FUA6_Ucw3i4&feature=related
23.
• Hip Hip Hooray
• Blame it on the DNA
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24.
O Nucleotides
O -P O
O
One deoxyribose together
O with its phosphate and base
O -P O make a nucleotide.
O O
O -P O
O Nitrogenous
O base
Phosphate
C
C
C
C C
O Deoxyribose 24
25.
Two Kinds of Bases in DNA
N
• Pyrimidines are N C
O C C
single ring bases.
N C
• Purines are N C
N
double ring C C
N
bases. N C
N C
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26.
Adenine and Guanine are
purines
• Adenine and guanine each have two
rings of carbon and nitrogen atoms.
N O
N C N C
C C N C C
N N
N C N C
C
Adenine N C Guanine N 26
27.
Thymine and Cytosine are
pyrimidines
• Thymine and cytosine each have one ring of
carbon and nitrogen atoms.
O N
N N C
C
O C C
O C C C
N C
N C
thymine cytosine
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28.
DNA Replication
• http://www.johnkyrk.com/
DNAreplication.html
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