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DNA Structure
DNA is a type of nucleic acid.
Nucleic acids are long chains of
nucleotides.
One
Nucleotide
Diagram of a nucleotide
Deoxyribose
DNA=Deoxyribonucleic Acid
DNA is found in
the nucleus of
the cell
Its function is to
store and
transmit genetic
information.
Structure:
Scientists James Watson and
Francis Crick are credited with
discovering the structure of DNA in 1953
Watson
However: Rosalind Franklin played a role
in helping them discover DNA’s structure.
She used x-ray crystallography to take
pictures of DNA.
Unfortunately, she died at age 37
before any recognition was given to
her.
A DNA molecule is made of 2 strands
which wind around each other in the
shape of a double helix. The nitrogen
bases point toward the center of the
molecule.
In other words a molecule of DNA
looks like a twisted ladder with
steps made of Nitrogen Bases.
The four different nitrogen bases in DNA
are: Adenine (A), Guanine (G),
Cytosine (C), and Thymine (T).
A always pairs with T, and
G always pairs with C.
The bases that pair with each other are
called complementary bases.
Two types of Bases:
• Purines (two rings): • Pyrimidines (one ring):
• Ex: Guanine, Adenine • Ex: Thymine, Cytosine
• Drawing:
• Drawing:
A single DNA molecule may contain
thousands of nucleotides (bases).
The order of the nucleotides
(bases) in a DNA sequence is
a code that provides
instructions for making
proteins.
•A segment of DNA that
codes for a specific protein is
called a gene.
• In your cells, DNA wraps up tightly
around proteins called histones to
produce a substance called chromatin.
Chromatin condenses during cell
division (mitosis) to form
chromosomes
What is a gene?
A gene is:
• A segment of DNA that codes for
a specific protein (proteins make
your traits)
So if genes make proteins, what do
proteins do?
• Make up all of your traits:
– Hair type and hair color
(Keratin)
– Skin color (melanin)
– What enzymes you have to break
down the food that you eat (lactase,
peroxidase, amylase)
– How strong you are: muscles (actin
and myosin)
Drawing of DNA
Base Pairs: Adenine,
Guanine, Cytosine,
Thymine
1 Nucleotide
Backbone made of
sugar and phosphate
How can a seemingly simple code with only
4 letters produce millions of different genes?
• The code is read 3 bases at
a time (4x4x4=64) and can
be thousands or millions of
base pairs long.
• (64 x 64 x 64 x 64…….)
end