The Structure of the DNA
Molecule
Middle School
Science
Dr. Romano
DNA stands for:
D: Deoxyribose
N: Nucleic
A: Acid
DNA is too small
to see, but under a
microscope it looks
like a twisted up
ladder!
Every living
thing has DNA
That means that
you have something
in common with a
zebra, a tree, a
mushroom and a
beetle!!
DNA is made up of steps and rails of a ladder.
This is a rail
This is a step
Green can only go with Red
Purple can only go with Yellow
Deciphering DNA's structure.
1. DNA is made up of subunits which
scientists called nucleotides
1. Each nucleotide is made up of
-a sugar
- a phosphate
- a Nitrogen base
DNA Subunits
• Are called nucleotides:
DNA Subunits
There are 4 different bases in a DNA molecule:
a.
b.
c.
d.
adenine (a purine)
cytosine (a pyrimidine)
guanine (a purine)
thymine (a pyrimidine)
DNA Molecule
• The DNA molecule is one of the
greatest scientific discoveries of all time
• It was described by James Watson and
Francis Crick in 1953
• Watson and Crick used the photo of
DNA from Rosalind Franklin
• DNA is what makes up our genes which
decides each organism's physical
characteristics.
Watson and Crick
Rosalind Franklin and Photo 51
DNA is like a fingerprint because
everyone’s is a little different!
You can tell people apart
by their fingerprints………
and their DNA!
How would the police look at DNA to
figure out who committed a crime?
DNA Molecule
Within cells, DNA is
organized into
structures called
chromosomes.
These chromosomes
are duplicated before
cells divide, in a
process called DNA
replication.
Summary of DNA Structure
•
•
•
•
DNA is a double helix
DNA has a base-pair rule: A –T, C—G
The N bases are on the inside of the ladder
The sugar and phosphate groups are on the
outside rungs of the ladder
Our DNA has different sizes of pieces so it
makes a different pattern when it’s all cut up.
Suspect #1 DNA sample
Suspect #2 DNA sample
In DNA profiling, the lengths of sections of DNA are compared
between people. This is a technique used for identifying a criminal
Suspect #1
Suspect #2
Genetic fingerprinting is used
in forensic science, to match
suspects to samples of blood,
hair, saliva or semen.
This is what it really looks like!!!
DNA Replication
Steps of DNA Replication
• The two strands of the DNA molecule
“unzip”
• Each strand becomes a “template” or model
to make a new matching strand
• A always bonds with T and C always bonds
with G
• Two new identical DNA strands form!