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What is DNA
DNA is also know as
DeoxyriboNucleic Acid
DNA is the basic “building Block” of life.
But what does that mean? and how does
something soooo small make up ALL that
is you?
Perhaps when you think of DNA, you think of
something out of a sci fi film. Like poor Bryant
here…
Who helped figure out DNA?
• Griffith and Transformation
– Using strains of pneumonia figures out that
DNA can “transform” harmless bacteria into
harmful bacteria
Avery
• discovered that DNA is the nucleic acid
that stores and transmits the genetic
information from one generation of an
organism to the next
Hershey and Chase – 1952
• Used Viruses to infect living organisms
***IMPORTANT NEW STUDIES/
RESEARCH HAVE COME FROM THIS
EXPERIMENT
• Used radioactive markers on the protein
coat vs the DNA
• Conclusion – genetic material of the
bacteriophage (virus) they infected with
bacteria was DNA – not protein.
Watson and Crick/
Rosalind Franklin - 1953
• Franklin studies DNA using x-Ray
diffraction – and gives her pictures to
Watson and Crick
• Watson and Crick Use her pattern and
instantly realize that DNA was a Double
Helix. Every Scientist around the world
was feverishly working out this structure
and without her work might not have
figured it out –
• SHE was NEVER recognized!!!
So let’s Look at the Basic’s
DNA is held in your nucleus. It never leaves (copies get
sent out to do the dirty work but NEVER the DNA itself.)
The subunit of DNA is made of a
Sugar – a Phosphate – and a NITROGENOUS BASE.
5’
3’
Basic’s
There are 4 Nitrogenous
Bases:
A always bonds with T
Adenine (A)
G always bonds with C
Purine
Guanine (G)
Think – “A Tall Girl Called”
Thymine (T)
Cytosine (C)
Pyrimidine
3’
5’
3’
G
C
T
A
C
G
A
T
5’
• Sugar Phosphates are always facing
outward.
• The two complementary strands of DNA
are always oriented in opposite directions
in the double helix, with one strand
oriented 5’ to 3’ and the complementary
strand pointing in the other direction
• The two strands for this reason are said to
be anti parallel!
• Chargaff’s rules - # of A’s = T’s and G=C’s
How is DNA kept in your Cells?
You have roughly 3’ of DNA in each of your
billions of cells.
They need to be tightly coiled like a phone cord
(remember those things) then coiled around
protein.
These are the structures you see as
chromosomes.
Genes, the basic unit of inheritance are
contained in chromosomes and consist of DNA
Chromosomes
Karyotype
When a women has a
child they can do
what is called a
karyotype
This is a picture of the
baby’s DNA before
they are born.
They pair up all the
Chromosomes to see
if there are any
abnormalities.
DNA fingerprints?
Everyone’s DNA is unique to them.
Unless, they are an identical twin.
I’m sure you’ve seen on CSI, they take
DNA evidence.
They do this by doing a DNA Gel
Electrophoresis. (we will be doing one too)
On the following slide you will see a
picture of several twin’s DNA fingerprints.
Twin DNA Fingerprints
How do you make more?
Well we know you are more then the one cell you
started at.
And every cell you have has the same DNA, so
how do you make more DNA?
It’s called DNA Replication.
You’re DNA is in the shape of a Double Helix –
like a twisted ladder. This shape is not really the
best in aiding the replication process.
What to do, what to do …
Replication
First you UNTWIST a section
Then you must UNZIP
This is done by breaking the Hydrogen bonds between
the nitrogenous bases.
Now you find a new “complimentary base”
partner (A with T, G with C)
Once a section has been partnered up it
RETWISTS
Replication
Closer look
at
Replication
This is a SemiCONSERVATIVE
replication because
each new strand has
half of the old strand.
The old strand is
used as a TEMPLATE
or guide of where to
put the new bases
Bidirectional
Replication
• Starts at the replication
origin and creates 2
replication forks that
move away in both
directions.
• DNA Helicase opens the
DNA
• DNA polymerases add to
end of existing nucleotide
elongating it (5’ – 3’
adding onto the 3’ end)
• Since DNA polymerase can not start a
new strand from scratch must add onto a
short primer of RNA (made by RNA
polymerase called primase.
• The continuous strand is called the leading
stand
• The one in smaller pieces (called Okazaki
fragments) is called the lagging strand.
– A DNA polymerase fills in the gaps after the
RNA primer is removed from between the
pieces.
• The sections of DNA are finally joined
together by an enzyme called ligase
Finally
• The ends of eukaryotic chromosomes present a
special problem for DNA replication – therfore
the 5’ – 3’ direction can not copy both ends of
linear eukaryotic chromosomes. The ends of the
chromosomes have special repeating
sequences called telomeres and a specialized
enzymed called telomerase that copies the
telomeres from an RNA template it carries rather
than the usual method. Without telomerase, the
ends of chromosomes would shrink with
repeated rounds of the DNA replication.
• The key to accurate replication dictates
that unpaired bases will attract a free
nucleotide ONLY if the nucleotide has a
proper COMPLEMENTARY BASE!
• As DNA separates at weak hydrogen
bonds, it also recombines at those same
weak hydrogen bonds
But how does DNA control Cell
functions?
Well like any building site – there are a set of
blue prints. You don’t want to hand out the
original, you have to make a copy to give the
plumber, electrician, mason, etc.
So we make a messenger molecule called RNA.
RNA is kind of like DNA in that it is made up of
nucleotides (remember – sugar, phosphate,
base)
RNA
However, RNA’s bases are
Adenine (A)
Guanine (G)
Cytosine (C)
URACIL (U)
Also RNA is single Stranded, that’s how it can fit
out of the nuclear pores.
The process in which we make RNA from DNA is
like replication but the RNA strand leaves, and the
DNA just retwists
Transcription
Transcription
So now you keep the original In the nucleus,
and the copy goes out into the cytoplasm.
The code is an exact copy of the DNA’s code
(with the exception of U’s instead of T’s)
So it looks something like AUGUUUAAAGGGCCCUAGCGCUUAAGGUUAAGGCCUUUGUAUUAAUAG
OK so how does that RNA tell our
cells what to do?
So now the RNA code is in the cytoplasm. A
ribosome bonds to an initiation site.
The ribosome “reads” this code and figures out
what amino acids to put together to make a
protein.
The proteins made are what influences the cells
behavior.
So let’s look at TRANSLATION in detail.
The Ribosome reads the RNA three letters at a time.
This is called the codon.
If you look at the amino acid chart you will see there
are 20 amino acids but 64 different codon
possibilities. That means that several codons code
for the same amino acid. (This is called degeneracy
so if there is a mutation it may not change the amino
acid)
A T-RNA with the anti-codon brings the appropriate
amino acid to the M-RNA and links the amino acids
together.
Codon - Amino Acid Chart
Translation
In the codon chart, you saw the amino acid
sequences. The ribosome knows where to start
reading based on the initiation codon AUG, and
where to end based on three termination
sequences: UAA, UGA, UAG
You saw in that second picture that the ribosome
held two T-RNA. The first one holds the chain of
amino acids, while the second one brings in the
new amino acid.
The following is an animation of the ribosome
traveling down the Messenger RNA
Translation
Here’s an animation of translation I
found online
Many ribosomes can read the RNA
strand at one time.
What’s the big deal making
proteins?
Proteins are what controls the activities
going on in your cells.
Remember, enzymes are protein too.
IMPORTANT :
the sequence of the amino acids
determines the SHAPE of the protein
The SHAPE determines the FUNCTION
of the protein
If the DNA changes (a mutation), the
AMINO ACID could change, which
WOULD change the shape, which WOULD
change the function.
Remember since some codons code for
the same amino acid, substituting one
letter for another MAY change the amino
acid. It is not a guarantee. However, If
you delete or add a letter that would
change the reading frame and would
change almost all the amino acids.
Overview of Transcription and
Translation
Mutations
• In a mutation – nucleotides can be added,
deleted, or substituted.
• For example – PKU – phenylketoneria, you do
not make the proper enzyme to metabolize
phenylalanine (you get a toxic accumulation of
phyenylpyruvic acid.
• Sickle Cell Anemia – red blood cells can not
carry oxygen – one amino acid in hemoglobin
gene wsa changed. The disorder is traced to
the presence of valine (GUA or GUG instead of
glutamic acid (GAA or GAG)
Types of Mutations
• Point mutations – occurs when a single
nucleotide is substituted by another
nucleotide.
• THE CAT ATE THE RAT – original
• THE BAT ATE THE RAT - mutation
• THE CAT ATE THE BAT - mutation
• Frame Shift Mutation – addition or deletion
that involves the loss or addition of a
single nucleotide
• THE CAT ATE THE BAT – original
• THC ATA TET HEB AT – mutation
• THE CAA THT HEB AT – mutation