What do you think this is a
model of and why?
Describe the basic
structure (double helix,
sugar/phosphate
backbone, linked by
complementary
nucleotide pairs) of DNA
Describe its function in
genetic inheritance
DNA is often called the
blueprint of life.
DNA contains the
instructions for making
proteins within the
cell.
The main role of DNA in
the cell is the long-term
storage of information
it contains the instructions
to construct other
components of the cell,
such as proteins and RNA
molecules.
The major function of
DNA is to provide the code
for the making of proteins.
We study DNA for many
reasons
all living organisms
contain DNA.
its central importance
to all life on Earth,
medical benefits such
as cures for diseases,
better food crops.
Our genes are on
our chromosomes.
Chromosomes are
made up of DNA.
DNA is located in
the nucleus.
Rosalind Franklin
took diffraction xray photographs of
DNA crystals
She died from
cancer before she
could publish her
findings
In the 1950’s,
Watson & Crick
built the first model
of DNA using
Franklin’s x-rays
Some say they took
credit for work they
stole from Franklin
Their original model
was a single strand.
A DNA nucleotide is
made up of three parts
5 C Sugar-Deoxyribose
Phosphate group
Nitrogenous base
DNA is a very
long polymer.
The basic shape
is like a twisted
ladder or zipper.
This is called a
double helix.
A backbone of
alternating sugar and
phosphate groups
Covalent bonds
between nucleotides
The teeth are
nitrogenous bases.
phosphate
deoxyribose
bases
• DNA has two strands
that fit together
something like a
zipper.
• Each strand is held
together with
hydrogen bonds
between the nitrogen
bases.
DNA has four different bases:
A-Adenine
T-Thymine
G-Guanine
C-Cytosine
Video: Breaking the Code
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
pyrimidines
N
O
C
C
O
C
N
C
N
C
thymine
O
C
C
N
C
N
C
cytosine
Thymine and cytosine each have one ring
of carbon and nitrogen atoms.
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
Complementary base pairs
Hydrogen bonds
C
G
T
A
Cytosine always pairs up
with guanine
Adenine always pairs up
with thymine
The bases attract each other because of hydrogen
bonds. Hydrogen bonds are weak bonds
PURINE
TWO
RINGS
PYRIMIDINE
ONE RING
Purines and
pyrimidines alternate
along the double
helix
Complementary base pairs
adenine + thymine
guanine + cytosine
•The ratio of A to T and C to G equals 1:1
Complementary Base Pairs
A-T + C-G
Apple in the Tree
Car in the Garage
Complimentary base pairs
are lined up in the middle of
the double helix.
The hydrogen bonds that
hold them together will
break during replication and
transcription.
ACGTTCGAGGC TAACGT
ACGTTCGAGGC TAACGT
TGCAAGCTCCGATTGCA
Each cell has about 2 meters
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.
What is the role/function of
DNA?
Where is DNA located?
What are the three molecules
the make up a nucleotide?
What are the four bases?