Transcript DNA - California State University, Stanislaus

DNA
• the stuff of life
• genetic blueprint
• essence of being human
• what makes you, you
Humans cells make tens of
thousands of different proteins.
• All of them are linear chains of
amino acids (usually hundreds of
amino acids linked together, single
file).
FACT- all proteins are single
chains of amino acids.
• The order of the amino acids is
different in different proteins.
• The essence of a protein is the
order of the amino acids.
For all living things- there are 20
different amino acids.
Proteins don’t function as linear
single file ‘snakes’:
• Computer graphic of
protein 3D structure
Proteins can form so many functions
because of the great diversity of
structures that can form:
• How many different chains of just
6 amino acids can be formed?
FYI: largest
known protein:
30,000 amino
acids
206 = 64,000,000
Why do 2 chains of amino acids
fold differently:
Of the 20 different amino acids.
Some are:
•
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•
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Large
Small
Positively charged
Negatively charged
Water soluble
Water insoluble
In any
protein,
some of the
amino acids
are critical.
The DNA molecule is a double helix.
Crick and Watson and others knew
that DNA was made of 4 building
blocks (4 bases):
• In all living things:
A, C, G, and T
Crick and Watson discovered
‘base pairing’:
• In all living things:
A=T
G=C
Base Pairing??
DNA is two chains, held together
by base pairs.
DNA
• The order of
the bases is
the genetic
code!
Coincidence?
• The order of the bases is the
essence of DNA.
• The order of the amino acids is
the essence of a protein.
What is a gene?
• A gene is a tiny segment of DNA that
contains the information to make a
product.
What is a gene?
• A gene is a tiny segment of DNA that
contains the information to make a
protein.
Central Dogma
m
• Arrows represent the transmission of genetic
information.
Nucleic Acids
• DNA = deoxyribonucleic acid
• RNA = ribonucleic acid
• Both molecules are found in all living
things.
What is RNA?
Base pairing:
G=C
A=U
• DNA- permanent (All of your DNA is
present in all of your cells, all of the
time)
•
RNA- RNA molecules are small,
transient, carriers of genetic
information.
The DNA unwinds and the
genetic information is copied into
RNA form.
The mRNA and the DNA are base-pairing.
The order of bases in the genetic code is
maintained.
How to make a protein
Translation
=
production
Absolute- The genetic code is a triplet code.
It was suggested in the 1960s that
a ‘bilingual molecule’ must
exist. Why?
• DNA/RNA -----------> protein
• It does exist- It is the tRNA.
Transfer RNA
They are
everywhere!
Where proteins are producedthe Ribosome
•
http://www.cancerquest.org/
http://fig.cox.miami.edu/~cmallery/150/cells/ribosome.jpg
Formation of the protein- joining
of the first two amino acids:
The shift= translocation
The genetic code is
universal (plant, animal,
microorganism).
The genetic code list mRNA codons
and the amino acid each codon
specifies.
• ____AUG
. . . . . 750 nt . . . . UAG ___
How many amino acids are found in the
protein encoded by this mRNA?
• DNA animations
• See http://www.ncc.gmu.edu/dna/index.htm
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Met
Mutation!
• A change in
the genetic
code of a
DNA
molecule is a
mutation.
• Its physical!!
Mutation:
• 1 change in the DNA ==>
• 1 change in the mRNA ==>
• Can produce a change in a particular
protein.
• One amino acid change “may” be fatal.
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Mutations that add nucleotides or
lose nucleotides from a gene are
called frameshift mutations
Human genetic diseases are often
caused by a change of one amino
acid in a particular protein:
• Sickle-cell anemia
The sixth amino acid in
the normal protein is
glutamic acid, while
sickle beta chain has
valine in its place. This
is the sole difference
between the two.
Types of Mutation
• Spontaneous mutation- occurs as a
result of natural processes in cells
• Induced mutation- caused by
mutagens, substances that cause a
much higher rate of mutation
Mutagen
• A mutagen is a natural or
human-made agent which
can alter the structure or
sequence of DNA.
Types of mutagens
Chemical mutagens
• There are over 70,000 man made
chemicals available commercially,
including fertilizers, preservatives,
pesticides herbicides, drugs, etc.
that we may ingest.
• Many natural compounds that may
occur in our air, food and water are
also potential mutagens.
Types of Mutagens
Radiation (X-rays and others)
• Natural sources: cosmic rays from the sun
and outer space, radioactive elements in soil
and terrestrial products (wood, stone) and in
the atmosphere (radon)
• Artificial sources of radiation which contribute
to our radiation exposure. Among these are
medical testing, nuclear testing and power
plants, and various other products (TV's,
smoke detectors, airport X-rays).
DNA repair systems
• Because DNA damage occurs
spontaneously and as a result to
ubiquitous environmental
agents, most organisms possess
some capacity to repair their
DNA.