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DNA
Deoxyribose Nucleic Acid
DNA
•
DNA is a double helix.
•
A bonds to T: C bonds to G
•
In man, the DNA molecule ,
if fully extended, would
have a total length of 1.7
metres. If you unwrap all
the DNA you have in all your
cells, you could reach the
moon ...6000 times!
What is the structure of a gene?
• Genes once thought to be made of
protein
• Chromosomes contain both DNA &
protein (histones)
• Cell structures are built of protein,
cell function controlled by enzymes
(protein)
• Nucleus once thought to contain a
“master molecule” for each of cell’s
protein.
Identifying the Genetic Material
Three “classic” experiments show its
DNA
Griffith: Found “transforming factor” in a type
of pneumonia-causing bacteria.
Avery: Found TF was deactivated by DNAdigesting &not protein-digesting enzymes.
Hershey & Chase: Labeling experiments with
viruses that infect bacteria.
Why the historical
perspective?
• Classic experiments are straightforward, low-tech, elegant and
understandable.
• Provide an opportunity to apply the
logic of scientific, using “what if”
scenarios
• To learn “How we know what we
know”
• Knowledge builds on previous
knowledge
Griffith (1928)
• A type of bacterial pneumonia has two
forms: “smooth” (S) causes pneumonia,
but “rough” does not.
• When S-type bacteria are heat-treated, they
die and no longer can cause pneumonia.
• But, if inject live R along with heat-killed
S, the mouse gets pneumonia.
Griffith (1928)
• Live S bacteria found in the treated mice
• So something in the heat-killed S bacteria
“transformed” the live but harmless R
bacteria into pneumonia-causing S bacteria
• What was this “transforming factor”
Oswald Avery (1944)
• Fascinated with Griffin’s work
• Injected protein-digesting enzymes to some
extracts• Cells were transformed
• Then added an enzyme that breaks apart
DNA and heredity material was blocked.
• Proof that it was the DNA not proteins
Hershey & Chase (1950)
Side by side experiments are
performed with separate
bacteriophage (virus) cultures in
which either the protein capsule
is labeled with radioactive sulfur
or the DNA core is labeled with
radioactive phosphorus.
DNA
•DNA
•DNA
•DNA
•DNA
STRUCTURE
REPLICATION
TRANSCRIPTION
TRANSLATION
Components of DNA
• NUCLEOTIDE
– Phosphate group
– 5-Carbon sugar
– nucleic acid (1 of the
nucleic acids)
•
•
•
•
guanine
cytosine
adenine
thymine
COMPONENTS
DNA REPLICATION
•TAKES PLACE IN THE NUCLEUS
•END PRODUCT IS TWO IDENTICAL STRANDS
•DURING CELL DIVISION- ONE STRAND
FOR EACH CELL
DNA Replication
• DNA is opened by
enzymes (unzips)
• Complementary
nucleotides bond
with the old
strands
• 2 strands created:
½ is the old strand;
½ is the new
strand.
DNA TRANSCRIPTION
DNA- GIVES CODE TO mRNA
DNA TRANSLATION
tRNA translates mRNA into proteins
SUMMARY
Comparison of DNA and RNA
• RNA is single
stranded
• RNA has uracil
instead of
thymine
• A-U
• DNA is double
stranded
• DNA has
thymine instead
of uracil
• A-T
Understanding DNA
• Inheritance/ Genetic Counseling
• Cell function/protein synthesis
• Embryonic development/gene
regulation
• Evolution/ phylogenetic
relationships
• Medicine/genetic diseases
• Genetic engineering/ recombinant
DNA