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DNA
The Language of Life
How Did We Find It??
• Fredrick Griffith conducted an experiment
with mice
• Heated (dead) fatal strain doesn’t kill it
• Fatal strain kills mice
•Mix of heated (dead) fatal strain and
healthy non-fatal strain kills it
• Non fatal strain doesn’t kill it
• Why?
So How Did We Discover It Was DNA?
Frederick Griffith, Biologist
Oswald Avery, Biologist
Optimus Prime, Autobot
Is this guy serious??
I know! It…..it……
TRANSFORMS!!
Don’t worry, I got this.
So How Did We Discover It Was DNA?
PROCESS OF
ELIMINATION!
Avery used protein –
destroying enzymes
with Griffith’s
experiment, and
nothing changed.
He switched to DNA
– destroying
enzymes, and the
bacteria didn’t
become fatal.
DNA DID IT!
This lead them to
believe that DNA was
the source of the cell’s
genetic material, and
the cause of traits that
are “heritable”, which
means they can be
passed down from
generation to
generation.
Hershey And Chase Solidify Avery’s Findings
Don’t Worry, Avery
We’ve Got Your Back.
Hershey and Chase tagged the DNA in a virus with a radioactive
isotope, and traced it into the cell. They also tagged the protein
that makes up the virus, just to make sure it was the DNA that
was passing on genetic information, not the protein.
Watson And Crick Show Us What It Looks Like
Using the results of their
own research, and data
from the research they, um,
“borrowed” from Rosalind
Franklin, they showed how
DNA comes together and
forms a double-helix
structure.
She was NOT happy about that.
WHAT IS DNA MADE OF?
• DNA stands for
Deoxyribonucleic Acid
• It is made of nucleotides.
• The nucleotide has 3
components: a ring-shaped
sugar called “deoxyribose”, a
phosphate group, and a
nitrogenous base.
MEET THE NITROGENOUS BASES
THE PURINES
• Double-ring structure
• Adenine and Guanine
THE PYRIMIDINES
• Single-ring structure
• Thymine and Cytosine
• Purines will ONLY bond with
pyrimidines, and vice-versa. This is
called “Chargaff’s Rule”.
• Adenine only bonds to Thymine
• Cytosine only bonds to Guanine
REMEMBER!
In DNA, Adenine
only bonds to
Thymine, and
Cytosine only bonds
to Guanine!!
These are called
“Complimentary
Base Pairs”.
These
Complimentary
Base Pairs join
together via
hydrogen bonds
to form the
double-helix
shape that we
all know and
love.
SEMICONSERVATIVE
REPLICATION
DNA has two
sides, and each end
is either a 3’
(prime) or a 5’.
The sides run
ANTIPARALLEL,
or opposite. One
end starts at 3’, the
complimentary
strand starts at 5’.
HOW DO WE MAKE MORE??
When DNA replicates, DNA Helicase “unzips” it, breaking it at the base pairs.
DNA Polymerase works its way down the open ends, adding new base pairs, until
there are 2 new strands of DNA made.
V
HOW DO WE MAKE MORE??
DNA Polymerase can only write in the 3’ to 5’ direction. This works great for the
LEAD strand (top) but not for the LAGGING strand (bottom)
DNA Polymerase writes the LAGGING strand in small sections called OKAZAKI
FRAGMENTS.
HOW DO WE MAKE MORE??
DNA Ligase acts
as “glue” , adding
phosphates to the
nucleotides, giving
them a structured
backbone.