When a species reproduces, there is genetic
continuity that is maintained from one
generation to the next.
WHAT is responsible for this continuity?
HOW does this continuity happen?
Genetic material present in ALL organisms
Usually found within the nucleus
Different for each individual within a species
DNA = DeoxyriboNucleic Acid
Polymer made of repeating NUCLEOTIDE
monomers
A molecule made of the following 3 parts:
1. a 5-Carbon sugar group (deoxyribose)
2. a phosphate group
3. a nitrogen base – 4 different possibilities!
(5 Carbon sugar)
Adenine (A)
Guanine (G)
Purines (2 carbon rings)
Cytosine (C)
Thymine (T)
Pyrimidines (1 carbon ring)
It is the arrangement of
these 4 different
nucleotides that allows
DNA to be so unique!
Adenine ALWAYS pairs
with Thymine
(double bond)
Cytosine ALWAYS pairs
with Guanine
(triple bond)
To Help you Remember: AT C-G
2 Scientists credited with
discovering the structure
of DNA in 1953:
James Watson & Francis
Crick (Watson & Crick)
Watson & Crick Model of
structure = DOUBLE
HELIX
They received the Nobel
Prize (Medicine) in 1962
The key to Watson and Crick’s
discovery was an X-ray diffraction
image (known as Photo 51) of DNA
recorded by Rosalind Franklin
Both the image and Franklin’s
interpretation of the image were
shown to Watson without her
permission
Watson, Crick, and Wilkins (the man
who gave Watson the image) received
the Nobel Prize
▪ Franklin had died 4 years earlier
Characteristics:
1. DOUBLE stranded molecule
2. phosphate & sugar portion of
nucleotides form the “backbone”
of each strand
3. Nitrogen base of one strand
forms a HYDROGEN BOND with
the nitrogen base of a second
strand
4. In 3-Dimensional space, it forms
a “twisted ladder” (spiral staircase)
DNA must be able to make a copy of itself in
order for genetic material to be passed on to
the next generation and to preserve genetic
continuity.
DNA Replication
This replication process occurs in 4 basic
steps.
Step 1 – HELICASE (an enzyme) cause the
hydrogen bonds between the nitrogen bases
to break (“Unzips the ladder”)
Step 2 – DNA POLYMERASE (another
enzyme!) is responsible for reading the DNA
template and matching up the
complimentary nucleotide from the free
floating nucleotides present in the nucleus
Step 3 – Base pairs form hydrogen bonds and
the phosphate group of one nucleotide bonds
with the sugar of another to form the
“backbone”
Step 4 – Bonding continues along the strands
until 2 new strands are formed
RESULT = 2 new EXACT copies of the
original DNA molecule!
Pink =
parent
strand
Blue =
daughter
strands
DNA Replication Simulation
0
