Download DNA PPT

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We study DNA for
many reasons:
  its central
importance to all
life on Earth,
  medical benefits
such as cures for
diseases,
  better food crops.
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Rosalind Franklin’s photo
Watson and Crick
with their famous
model
 Our genes are on
our chromosomes.
 Chromosomes are
made up of a
chemical called
DNA.
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DNA Structure
  DNA consists of two molecules that are
arranged into a ladder-like structure called a
Double Helix.
  A molecule of DNA is made up of millions of
tiny subunits called Nucleotides.
  Each nucleotide consists of:
1.  Phosphate group
2.  Pentose sugar
3.  Nitrogenous base
  The backbone of the
molecule is alternating
phosphates and
deoxyribose sugar
  The teeth are
nitrogenous bases.
phosphate
deoxyribose
bases
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Nucleotides
Phosphate
Nitrogenous
Base
Pentose
Sugar
Nucleotides
  The phosphate and sugar form the backbone of the DNA
molecule, whereas the bases form the “rungs”.
  There are four types of nitrogenous bases.
Nucleotides
A
Adenine C
Cytosine T
Thymine G
Guanine Nucleotides
  Each base will only bond with one other specific base.
  Adenine (A)
  Thymine (T)
  Cytosine (C)
  Guanine (G)
Form a base pair. Form a base pair. 5
O
3
3
P
5
O
O
C
G
1
P
5
3
2
4
4
P
5
P
2
3
1
O
T
A
3
O
3
5
O
5
P
P
DNA Structure
 Because of this complementary
base pairing, the order of the bases
in one strand determines the order
of the bases in the other strand.
A
C
T
C
A
G
T
T
G
A
G
T
C
A
Two Kinds of Bases in DNA
N C
C
N
C
N C
N
N C
C
C
N C
C
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N
N
N
C
C
C
N
C
C
C
C
C
N
C
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N
N
N
C
C
N
C
N
C
C
N
C
C
C
C
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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C
N
N
N
C
C
C
C
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
  The bases attract each
C
N
C
C
C
N
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  When making
hydrogen bonds,
cytosine always pairs
up with guanine
  Adenine always pairs
up with thymine
  Adenine is bonded to
thymine here
N
C
C
C C
N
C
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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 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.
  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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DNA Structure
  To crack the genetic code found in DNA we
need to look at the sequence of bases.
  The bases are arranged in triplets called
codons.
AGG-CTC-AAG-TCC-TAG
TCC-GAG-TTC-AGG-ATC
DNA Structure
  A gene is a section of DNA that codes for a protein.
  Each unique gene has a unique sequence of bases.
  This unique sequence of bases will code for the production
of a unique protein.
  It is these proteins and combination of proteins that give us
a unique phenotype.
  Advantages of Double-Stranded Nature of DNA
  Forms a stable structure
  Hydrophobic (water repelling) bases stack on top of one
another, away from solvent
  Negatively charged phosphate backbone is on the
outside accessible to solvent
  Each strand of DNA molecule serves as the template:
  For a new strand of DNA (replication)
  For an RNA molecule (transcription)
Nucleic Acids
  DNA and RNA are nucleic acids
  Comprised of:
  A 5-carbon sugar (deoxyribose or ribose)
  Nucleotides
  DNA has two strands bonded together
  RNA has one strand ONLY
  C, H, N, O, P atoms
Nucleotide Structure
  Three different
components
  Phosphate group
  Nitrogen containing base
(A,T,G,C,U)
  Five-carbon sugar
(ribose or deoxyribose)
DNA
Gene
Protein
Trait
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