Transcript DNA extensions

DNA Discovery
How was the molecule found?
Transformation
Frederick Griffith
found that live strains
of bacterium
transformed from
dead strains of
pathogenic
bacterium. The
genetic information of
dead pathogenic
bacteria transformed
onto live non
threatening bacteria
Avery experiment
From 1928-1944 no evidence was found to explain
Griffiths experiment.
In 1944 Oswald Avery started to breakdown the
bacterium used in the Griffith experiment.
First he removed all proteins from the bacteria but
found no change in the results.
When the deoxyribose digesting enzyme was added
to the bacteria, transformation could not be competed.
This proved that DNA was the acting agent to the
specific trait.
Hershey/Chase Experiment
Hershey and Chase just
after WWII used
radioactive isotopes that
were now available to
them to track proteins
and DNA in the
transformation
experiment. Radioactive
isotope 35S was not
present while radioactive
35P was and radioactive
35P was attached to
DNA
DNA vs Protein
Griffith found that specific traits can transform the
characteristics of other cells.
Avery test those results and found that when protein
was removed the outcome was unchanged, but when
the sugar was removed the effects were negated.
Hershey and Chase injected radioactive isotopes into
each aspect of the protein and DNA and found that
DNA was the molecule that moved from one cell to
another, thus DNA became the molecule that
controlled genetic traits within organisms.
The story of Watson and
Crick
Rosalind Franklin carried out an X-ray diffraction
experiment that bombarded the molecule of DNA and
it showed it as a coiled spring.
She gave this information to Watson and Crick and
they made a tinker toy of the structure known as a
double helix.
Watson and Crick won the Noble peace prize, Franklin
got nothing.
Chargaff’s base pairing rule
Chargaff measured various living organisms and
found that in every organism he observed, the amount
of Cytosine=Guanine and the amount of
Thymine=Adenine.
The four nitrogen bases were placed into 2 groups
based upon their structure.
Purines- Adenine and Guanine
Pyrimidines - Cytosine and Thymine
3 Types of replication
Replication types
Conservative- The original strand serves as the
template to create the new strands but the original
reassembles as the new strand assembles with itself.
Semi-Conservative- The original strand serves as a
template but the new strand joins with the original
strand to make the new molecule.
Dispersive- the original strand is still the template but
the new and the old strands disperse between the two
new molecules
Antiparallel
As DNA is replicated the two
new strand move in opposite
directions.
As the original strand opens,
the new strand travels from
the opposite side of the
molecule and moves up the
replication fork.
Meselson-Stahl Experiment
This experiment
showed that
semiconservative
replication was the
typical type of
replication process by
injecting heavy N14
isotopes and lighter
N14 isotopes into
bacteria DNA and
watching as they
settled in a test tube
after centrifugation.
Replication Terms
Leading Strands- part of the newly replicated DNA strand that
is being created toward the replication fork.
Lagging Strand- small fragments of newly replicated DNA that
are being created away from the replication fork.
Okazaki Fragment- the small fragments of lagging strands are
called.
Ligase- enzyme used to connect small fragments after
replication to construct the new molecules.
Primase- enzyme that creates a small segment of RNA
(primer)
Single strand binding protein (SSBP)- after helicase
separates strands, this enzyme keeps DNA separated and
Leading/Lagging strands
Mutations
Although DNA repair is done in every cell and
proofreading is done in every daughter cell, mutations
do occur.
Without mutations evolution would halt and species
may not have the capabilities to continue.
With that said, let’s talk mutations!!
What is a Mutation
A change in the content of the genetic message (the
base sequence of one or more genes).
Some alter the identity of a particular nucleotide, while
others remove or add nucleotides to a gene.
Recombination- is the process of when a genetic
message has a change in its’ original position.
Nitrogen bases are rearranged and the code is
changed.
Types of Mutations
Germ-Line Tissue Mutations- these mutations occur in
the germ-line cells of a gamete and are now part of a
hereditary endowment that will continue for future
generations. These mutations have an enormous
biological importance because they serve as raw
material for the process of natural selection.
Somatic Tissue Mutations- Somatic cells are not
passed on to future generations and can only be
passed to subsequent cells that derive from the
mutated cell. Lung cell passes mutation to daughter
lung cells.
Types of Mutations
Continued
Point Mutations- mutation only occurs in one or a few
base pairs.
Base substitution-base is changed to a new one
Insertion- base pair is inserted into a gene
Deletion- base pair is deleted from a gene
Frame Shift mutation- insertion or deletion causes
the gene message out of register. (commonly
caused by mutagens)
Mutations
Mutagens- environmental conditions that cause the
frame shift mutation. Radiation or chemicals are the
major cause!!!!!!
These frame shifts cause a new amino acid to be
placed within a protein that was not originally there or
an amino acid is deleted from the formation of the
protein.
Either way the protein is now altered and this could
have catastrophic results to the organism.
Transposition vs.
Translocation
Transposition- individual genes may move position
within the structure of DNA
Translocation- when segments of a homologous pair
do not exchange equally during crossing over or
through random exchange. Results in serious genetic
disorders like down syndrome.