Transcript Chapter 6 - TeacherWeb

Chapter 6
Genes and Gene Technology
Genes need to do 2 things
1) Supply instructions for cell processes
and for building cell structures
2) Must be able to be copied so that each
cell contains an identical set of genes.
Nucleotides – the subunits of DNA
• DNA is made of only four
subunits
• Each subunit is identical
except for the base.
sugar + phosphate + base
• Possible bases are
1) adenine
2) thymine
3) guanine
4) cytosine
Adenine
Guanine
Thymine
Cytosine
Chargaff’s Rule
In 1950, he found that the amount of adenine in
DNA always equaled the amount of thymine and
that the amount of guanine always equaled the
amount of cytosine.
# adenine = # thymine
# guanine = # cytosine
Watson and Crick
* Discovered the
structure of DNA
* Concluded that it resembles
a twisted ladder called a
double helix
DNA
Double Helix
DNA Structure
• The two sides of the
ladder are made of
alternating sugar and
phosphate molecules.
• The rungs of the ladder
are composed of a pair of
nucleotide bases.
– Adenine always pairs with
Thymine
– Guanine always pairs with
Cytosine
Making Copies of DNA
• Because adenine always bonds with
thymine and guanine always bonds with
cytosine, one side of a DNA molecule is
complementary to the other side.
• ACCGT will always bind with TGGCA
• In order to copy itself the DNA must first
partially unwind.
Exceptions to Mendel’s Rules
•
In higher level organisms, like
humans, Heredity is much more
complicated and harder to predict
than Mendel’s peas.
1)
2)
3)
4)
Incomplete Dominance
Codominance
One gene influencing many traits
Many genes influencing a single trait
The importance of environment
• Many things in your
environment also influence
how you grow and develop.
• Diet, exercise, exposure to
dangerous chemicals or
radiation.
• Genetic Predisposition – a
higher than normal probability
that a particular trait will
appear. Expression of the
gene is influenced by the
environment. Something in the
environment turns the gene on
(the ?)
DNA unites all organisms
• DNA functions in the
same way for all
organisms from
bacteria to mosquitoes
to whales to humans.
All life as we know it is
governed by DNA.
• At the same time it is
what causes each of us
to be unique.
How DNA Works
• The order of the
bases on the DNA
determines the order
of amino acids on the
proteins which are
assembled based
upon the instructions
coded in the genes.
Each group of 3 bases codes for one amino acid
Why Proteins
Proteins exist in an
almost limitless
variety.
The human body contains
about 50,000 different proteins.
Proteins are the reason for the
multitude of different shapes,
sizes, colors, and textures
found in living things, such as
antlers, claws, hair, and skin.
How the Protein is Made
1) A copy of the section of the DNA containing the
gene for a particular protein is made.
2) Copier enzymes copy this by utilizing the
complementary code.
3) A mRNA (messenger RNA) than carries this
genetic info from the nucleus out into the
cytoplasm.
How the Protein is Made continued
4) The copied DNA is fed through
the ribosome (acting like a
factory) reading three bases at
a time & constructing the
protein.
5) Transfer molecules (tRNA)
carry around a specific amino
acid in the cytoplasm. As the
DNA copy is fed through the
ribosome, the appropriate
tRNA links up with the bases
on the DNA. This causes the
tRNA to drop off the amino
acid it is carrying, such that a
chain of amino acids is formed
in concert.
Changes in Genes
Mutation – a substitution, deletion, or an
insertion of an extra base into the code.
Caused by random errors and mutagens.
Most mistakes are corrected by repair
enzymes but sometimes the code is not
corrected.
3 possible outcomes of mutations
1) An improvement
2) No change
3) Harmful change
If the mutation occurs in the sex cells
then it can be passed on from
generation to generation
How can DNA be damaged
Mutagen – physical or chemical agent that
can cause a mutation.
high energy radiation
asbestos
cigarette smoke
Sickle Cell Anemia
One 3 base sequence
(GAA) that codes for the
amino acid glutamic acid
if changed to (GTA) ends
up coding for valine
instead resulting in a
human blood cell being
sickle shaped instead of
the normal biconcave resulting in substantial
reduction in oxygen
carrying capacity.
Genetic Counseling
Carriers?
Why counsel?
What is a Pedigree
diagram?
Sickle Cell Pedigree Chart
Designer Genetics
Selective genetics – organisms
with desirable
characteristics are mated to
produce a new breed or a
super organism.
Genetic Engineering – manipulation of individual
genes to improve an organism or to repair a
problem.
Ethical, Beneficial or Not?
Cloning?
Genetic Engineering of Foods?
Gene Therapy for Diseases?
Genetic Choice for babies?
Creating super animals?
Creating super humans?