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The History &
Structure of the DNA
Molecule
CHAPTER 10
PART 1
The History of the DNA
Molecule
The Impossibility of Information
The DNA molecule is one of the
greatest scientific discoveries of all time.
First described by James Watson and
Francis Crick in 1953, DNA is the
famous storehouse of genetics that
establishes each organism's physical
characteristics.
DNA History
Griffith – Experimented on mice and
observed some harmless strains of
bacteria could change into harmful strains.
He called this transformation.
Avery – Discovered that DNA is the
nucleic acid that stores and transmits the
genetic information from one generation to
the next.
More DNA History
Hershey-Chase –
Concluded that the
genetic material in
bacteria was DNA not
proteins
http://highered.mcgrawhill.com/olc/dl/120076/bio21.swf
Watson & Crick –
created the double
helix model for DNA.
Nucleotides
1. DNA is made up of subunits
which scientists called
nucleotides.
A nucleotide is a
chemical compound that
consists of 3 portions: a
nitrogenous base, a
sugar, and one or more
phosphate groups.
DNA's structure.
1.
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)
PURINES - nitrogenous bases that
have a double ring of carbon and
nitrogen atoms
PYRIMIDINES - nitrogenous bases
that have a single ring of carbon and
nitrogen atoms
Base Pairing Rules
Chargaff’s Rules
In DNA, Cytosine
on one strand
always pairs with
Guanine on the
opposite strand.
Adenine always
pairs with thymine
DNA
Replication
How DNA Replication Occurs
DNA replication is the process by which
DNA is copied in a cell before a cell
divides by mitosis, meiosis, or binary
fission.
How It Occurs
DNA replication is carried out by a series
of enzymes.
The enzymes unzip the DNA molecule
creating two strands that serve as
templates. (helicase enzyme moves along
DNA molecule breaking the hydrogen
bonds)
The Y- shaped region the results when the
two strands separate is called a replication
fork
Complimentary bases are added to the
strands by enzymes called DNA
Polymerase that are found floating freely
inside the nucleus, for example a strand of
DNA with the bases ATTCGAG would
have a complimentary strand of
TAAGCTC
Each new DNA molecule has one new
stand and one strand from the original
molecule. (this is called semi-conservative
replication)
The enzyme DNA polymerase, the
principal enzyme, “proofreads” the new
DNA strands, helping to maximize the
odds that each molecule is a perfect copy
of the original.
DNA polymerase Finish replicating the
DNA and fall off
http://www.youtube.com/watch?v=zdDkiRw1PdU&feature=related
DNA REPLICATION
http://www.youtube.com/watch?v=8kK2zwj
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