Chapter 3- Sec 1
What is DNA?
Life Science
DNA
 What
does DNA stand for?
 Deoxyribonucleic Acid !!!
 De/oxy/ribo/nucleic Acid
 Deoxyribonucleic
Acid, or DNA,
is a code that contains information
that an organism needs to grow
and function.
Discovering DNA

In 1952, Rosalind Franklin discovered
that DNA is two chains of molecules in
a spiral form.
– Used X-Rays

In 1953, James Watson and Francis
Crick created an accurate model of
DNA.
– Model was similar to a ladder

The structure of DNA is similar to a
twisted ladder.
Crick
Thieves?
Watson
The structure of DNA is a
similar to a twisted ladder
(double helix)…
DNA Structure

The structure of the “Ladder”…
 The
sides of the ladder are made
up of Deoxyribose (sugar) and
Phosphate.
 The
rungs (or steps) of the ladder
are made up of nitrogen bases
(ATCG).
 The
steps of the ladder are made
of pairs of smaller molecules
called Nitrogen Bases.
bases “fit together” in the
combination:
 These
– Adenine fits with Thymine
– Cytosine fits with Guanine
 Connected
by a Hydrogen bond
Joined nucleotides
7
PO4
A molecule of DNA
is formed by millions
of nucleotides joined
together in a long
chain
PO4
PO4
PO4
sugar-phosphate
backbone
+ bases
What does ATCG stand
for???
DNA Replication
 When
a cell divides, the DNA
“code” is copied (or duplicated)
and passed to the new cells.
 The
DNA duplicates itself by
unwinding and separating the
bases forming 2 strands.

http://www.hhmi.org/biointeractive/med
ia/DNAi_replication_vo1-lg.mov
 DNA
makes up chromosomes
–Each chromosome is composed
of a long strand of DNA
wrapped around.
 Human
Body cells have 46
chromosomes or 23 pairs.
<stop here>
How many chromosomes
are in other living things?

Toucan – 104

Goldfish – 94

Dogs – 78 chromosomes

Horse- 64

Banana- 22 chromosomes

Jack Jumper Ant- only 2 chromosomes!