Download C - Valhalla High School

DNA
(Deoxyribonucleic Acid)
Mr. Coleman
Biology
DNA
• DNA is often
called the
blueprint of life.
• In simple terms,
DNA contains the
instructions for
making proteins
within the cell.
Genetic material of cells…
• GENES – units of genetic material that
CODES FOR A SPECIFIC TRAIT
• Called NUCLEIC ACIDS
• DNA is made up of repeating molecules
called NUCLEOTIDES
A HISTORY OF DNA
• Discovery of the DNA double helix
A. Frederick Griffith – Discovers that a factor
in diseased bacteria can transform harmless
bacteria into deadly bacteria
(1928)
B. Rosalind Franklin - X-ray photo of DNA.
(1952)
C. Watson and Crick - described the
DNA molecule from Franklin’s X-ray.
(1953)
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.
Chromosomes and DNA
• Our genes are on
our
chromosomes.
• Chromosomes
are made up of a
chemical called
DNA.
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.
The Double Helix Molecule
• The DNA double
helix has two
strands twisted
together.
• (In the rest of this
unit we will look at
the structure of one
strand.)
Nucleotides
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
One Strand of DNA
• One strand of DNA
is a polymer of
nucleotides.
• One strand of DNA
has many millions
of nucleotides.
nucleotide
One Strand of DNA
• The backbone
of the molecule
is alternating
phosphate and
deoxyribose.
• The teeth are
nitrogenous
bases.
phosphate
deoxyribose
bases
Nitrogenous Bases
• PURINES
1. Adenine (A)
2. Guanine (G)
A or G
• PYRIMIDINES
3. Thymine (T)
4. Cytosine (C)
T or C
Two Kinds of Bases in DNA
• Pyrimidines are
single ring bases.
N C
O C
N
C
N C
• Purines are double
ring bases.
N
N C
C
C
N
N C
N C
Thymine and Cytosine are
pyrimidines
• Thymine and cytosine each have one
ring of carbon and nitrogen atoms.
N
O
N
O
C
C C
N
N
C
C
thymine
O
C
C
C
N
C
cytosine
Adenine and Guanine are
purines
• Adenine and guanine each have two
rings of carbon and nitrogen atoms.
O
N
N
C
N
C
N
C
C
C
C
N
N
N
C
Adenine
N
C
N
C
Guanine
N
C
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?
N
N
C
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.
C
N
Hydrogen Bonds
N
C
N
C
C
C
N
O
Hydrogen Bonds, cont.
• When making
hydrogen bonds,
cytosine always
pairs up with
guanine,
• And adenine always
pairs up with
thymine.
O
N
O
C
C
C C
N
C
BASE-PAIRINGS
H-bonds
G
C
T
A
Chargaff’s Rule
• Adenine must pair with Thymine
• Guanine must pair with Cytosine
• Their amounts in a given DNA molecule will be
about the same.
T
A
G
C
Important:
• Adenine and Thymine always
join together
A
T
• Cytosine and Guanine always
join together
C
G
Watson & Crick proposed…
•DNA had specific pairing between the
nitrogen bases:
ADENINE – THYMINE
CYTOSINE - GUANINE
•DNA was made of 2 long stands of
nucleotides arranged in a specific
way called the “Complementary Rule”
DNA Double Helix
5
O
3
3
O
P
5
O
C
G
1
P
5
3
2
4
4
2
3
1
P
T
5
A
P
3
O
O
P
5
O
3
5
P
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
The earth is 150 billion m
sun more than 400
or 93 million miles from
times.
the sun.
• DNA has a diameter of
only 0.000000002 m.
Genetic Diversity…
• Different
arrangements of
NUCLEOTIDES in a
nucleic acid (DNA)
provides the key to
DIVERSITY among
living organisms.
The Code of Life…
• The “code” of the chromosome is the
SPECIFIC ORDER that bases occur.
A T C G T A T G C G G…