DNA
& Replication
Notes
DNA
A.k.a. Deoxyribonucleic Acid
Molecule present in all living cells
Contains information that determines the
traits that an organism inherits and
needs to live
Rosalind Franklin
 Took one of the first
photos of DNA using
X-Ray Diffraction
Watson & Crick
 Two scientists who
discovered the
structure of DNA as
a double helix
Won a Nobel Prize for
it
Maurice Wilkins also
won nobel prize for
DNA structure
DNA Structure
DNA Structure
 Double Helix
Twisted ladder
 Made up of
nucleotides
Nitrogenous base,
phosphate, and sugar
DNA Structure
 Sides of ladder =
alternating
phosphates and
sugars
 Rungs of ladder =
nitrogenous bases
3D Model
DNA Picture
DNA Structure -Bases
 There are 4
nitrogenous bases
 Adenine (A)
 Thymine (T)
 Guanine (G)
 Cytosine (C)
Nitrogenous Bases
 Certain bases match
together
 Guanine and Cytosine
(C - G) pair together
“Good Couples”
 Adenine and Thymine
(A - T) pair together
“Always Together”
DNA Replication
DNA molecules are very long, nucleus of
human cell has more than 1 meter of DNA.
DNA Replication
Each side of the DNA strand has all of the
information needed to reconstruct the
other half of the strand through the
process of base pairing.
 Due to this process (base pairing), the
strands are said to be complementary.
DNA replication happens at hundreds of
places along the strand- makes the
process very fast!
Replication proceeds in both
directions until each chromosome is
completely copied.
Sites where separation and
replication happen are called
replication forks.
New Strand
Original strand
Nitrogen Bases
Replication Fork
Replication Fork
DNA Polymerase
Duplicating DNA
Replication- the copying process
in which a cell duplicates its DNA,
before it divides into 2 cells with
complete sets of DNA molecules.
Step 1 --> Pull old DNA Apart
DNA molecule separates into two
strands
DNA polymerase is the principle
enzyme involved in DNA replication.
It pulls apart the old DNA strand so
that each side can be copied
Step 2 --> Base Pairing
Bases are added to each side
following the rules of base pairing.
Each strand of the double helix DNA
serves as a template, or model, for
the new strand.
Step 3 =RESULT
Result is two DNA molecules
identical to each other and the
original molecule.
Each DNA molecule from
replication has one original
strand and one new strand.
Replication Example
Replication Example
Replication Example
Real Chromosome Pictures!
Real Chromosome Pictures!
DNA Replication Video
http://www.dnalc.org/resources/3d/DNA
ReplicationBasic_w_FX.html