Download DNA (Deoxyribonucleic Acid)

DNA
(Deoxyribonucleic Acid)
A HISTORY OF DNA
• Discovery of the DNA double helix
A. Frederick Griffith – Discovers that a factor
in diseased bacteria can transform harmless
bacteria into deadly bacteria
(1928)
B. Rosalind Franklin - X-ray photo of DNA.
(1952)
C. Watson and Crick - described the
DNA molecule from Franklin’s X-ray.
(1953)
DNA History
• 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
• Watson & Crick –
created the double
helix model for DNA.
Structure of DNA
• DNA is a long molecule made up of units called
nucleotides.
• Each nucleotide is made up of three parts: a 5carbon sugar called deoxyribose, a phosphate
group, and a nitrogenous base (Nitrogen
Containing).
• The backbone of DNA is formed by sugar and
phosphate groups of the nucleotide.
• The nitrogenous base stick out from the sides
and can be joined together in any order,
meaning that any sequence of bases is possible.
DNA Nucleotide
Phosphate
Group
O
O=P-O
O
5
CH2
O
N
C1
C4
Sugar
(deoxyribose)
C3
C2
Nitrogenous base
(A, G, C, or T)
DNA Double Helix
“Rungs of ladder”
Nitrogenous
Base (A,T,G or C)
“Legs of ladder”
Phosphate &
Sugar Backbone
DNA Double Helix
5
O
3
3
O
P
5
O
C
G
1
P
5
3
2
4
4
2
3
1
P
T
5
A
P
3
O
O
P
5
O
3
5
P
Nitrogenous Bases
• PURINES
1. Adenine (A)
2. Guanine (G)
A or G
• PYRIMIDINES
3. Thymine (T)
4. Cytosine (C)
T or C
Chargaff’s Rules
• Chargaff discovered
how the nitrogenous
bases bond together.
• He discovered that
Adenine always
bonds with Thymine
and that Cytosine
always bonds with
Guanine.
BASE-PAIRINGS
H-bonds
G
C
T
A
Genetic Diversity…
• Different
arrangements of
NUCLEOTIDES in a
nucleic acid (DNA)
provides the key to
DIVERSITY among
living organisms.
The Code of Life…
• The “code” of the chromosome is the
SPECIFIC ORDER that bases occur.
A T C G T A T G C G G…
DNA is wrapped tightly around
histones and coiled tightly to form
chromosomes
DNA Replication
• DNA must be copied
• The DNA molecule produces 2
IDENTICAL new complementary
strands following the rules of
base pairing:
A-T, G-C
•Each strand of the
original DNA serves as
a template for the new
strand
DNA Replication
• During DNA replication, the DNA molecule
separates into two strands, then produces
two new complimentary strands following
the rules of base pairing (Chargaff Rules).
Each strand of double helix of DNA serves
as a template, or model, for the new
strand.
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.
• Complimentary bases are added to the
strands, for example a strand of DNA with
the bases ATTCGAG would have a
complimentary strand of TAAGCTC.
Replication Continued
• Each new DNA molecule has one new
stand and one strand from the original
molecule.
• 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.
A---?
Use the complementary rule to
G---?
create the complementary strand:
C---?
T---?
A---?
G---?
A---?
G---?
C---?
A---?
G---?
T---?
A---T
G---C
Use the complementary rule to create the C---G
T---A
complementary strand:
A---T
G---C
A---T
G---C
C---G
A---T
G---C
T---A
DNA Transcription Overview
• DNA can “unzip”
itself and RNA
nucleotides match
up to the DNA
strand.
• Both DNA & RNA
are formed from
NUCLEOTIDES and
are called NUCLEIC
acids.
Transcription – Step I
A C G T A T C G C G T A
T G C A T A G C G C A T
Template DNA Strands
Transcription – Step II
A C G T A T C G C G T A
U G C A U A G C G C A U
Template DNA is Matched Up with
Complementary mRNA Sequences
Transcription – Step III
A C G U A U C G C G U A
U G C A U A G C G C A U
mRNA leaves nucleus
and goes to ribosomes
DNA Translation Overview
• The cell uses
information from
“messenger” RNA
to produce proteins
tRNA structure
• 3-base code (triplet)
is an “anticodon”
• Attached amino acid
that is carried from
cytoplasm to
ribosomes
• Amino acids make up
the protein
Prokaryotes & DNA
• In prokaryotes, DNA
molecules are located
in the cytoplasm of
the cell.
• Most prokaryotic DNA
is a single circular
molecule that
contains nearly all the
cell’s genetic
information.
Eukaryotes & DNA
• Many eukaryotes
have 1000 times as
much DNA as
prokaryotes.
• DNA is located in the
nucleus in the form of
chromosomes.
• Chromosomes are
DNA wound tightly
around proteins called
histones.
AMAZING DNA FACTS…
• DNA from a single human
cell extends in a single
thread for almost 1-2 meters
long!!!
• It contains information
equal to some 600,000
printed pages of 500 words
each!!!
(a library of about 1,000 books)
DNA Length
• E. Coli have about 4,639,221 base pairs.
It is about 1.6mm in length. This sounds
small until you realize the bacteria is only
1.6µm in diameter.
• Thus DNA must be wrapped tightly to fit
into cells. Imagine fitting 900 feet of rope
into a backpack.