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DNA
DNA is a molecule that contains genetic
information for heritable traits and directs the
structures and functions of the cell. DNA is the
“stuff of life”; it is the blueprint for what you look
like and to an extent – you we are. The DNA is the
material that is passed down from parent to
offspring.
The nucleus is the control centre of the cell. It
contains the genetic material (DNA) of the cell.
DNA has a library of four letters! The different
sequences and arrangements of these four letters
produces the genetic code – which is responsible
for your traits. DNA can be stretched out to a
distance of 3 000 000 km. 97% of the letters are
junk!
A gene is a section of DNA. A gene may contain
thousands of the “four letters”, and the unique
arrangement of these letters, directs the cell to
carry out specific functions (ie. Produce blue eyes).
On one strand of DNA there may be 1000’s of
genes. In the human there are 30, 000 genes.
DNA is coiled up and compacted into chromosomes
(see diagram). So chromosomes are strands of
DNA that look like an X. (Humans have 46
chromosomes; 23 from each parent).
BLM 1-15.
Why do cells divide?
- growth
- repair
- replace
There are 2 types of cell division
1) Mitosis - A cell divides into 2 identical copies
(like binary fission)
- each daughter cell has the same number of
chromosomes as the original parent. See
diagram
The life span of cells in the human body:
Brain cells
30-50 years
Red Blood cells
120 days
Stomach lining
2 days
Skin cells
20 days
2)Meiosis
A form of cell division that leads to the formation
of sex cells (gametes). Human sperm cells contain
23 chromosomes, and human egg cells contain 23
chromosomes. When the two gametes unite, a
zygote is formed with 46 chromosomes. The final
result of meiosis is that the gametes have only half
the original number of chromosomes as the parent
cell.
Unlike mitosis, meiosis results in genetic variation –
what chromosomes do you get from each parent
creates 8.4 million possible chromosome
combinations! Therefore sexual reproduction and
the process of meiosis increases the variation
within a species!
Genetics and technology (a form of biotechnology)
Genetic engineering involves moving pieces of DNA
from one species to another.
Example – a gene from the firefly that produces
bioluminescence can be moved into a tobacco plant
causing the tobacco plant to grow. Another
example is moving the human gene for insulin into
bacteria, which has allowed the bacteria to
produce insulin as a waste product.
Concerns with genetic engineering:
- create a genetic “monster” that might
spread to the environment which might
compete with and displace native species,
interbreed with and change the genetics of
a native species, or grow out of control in
the absence of natural predators.
- It is not morally acceptable to change
organisms in such fundamental ways. These
ethical considerations supersede all others
such as economic considerations
- Has become valuable for studying the
genetic bases of disease. By manipulating
DNA researchers can learn which genes are
important to disease and how they have
their effects.
Read page 53.
Biotechnology is currently used in medicine – the
production of proteins, such as insulin and
hormones and vaccines, by genetically engineered
organisms can be much less costly than producing
these proteins chemically in a lab.
Biotechnology is currently used in food production
– we have inserted genes for rapid growth and
disease resistance, and even antifreeze genes into
fish, and are currently harvesting these fish
(aquaculture). 25% of the fish consumed are
produced in fish farms.
Some crops such as corn and tomatoes, are
resistant to diseases and drought, and are tastier
and more nutritious. (One concern is that we are
creating monocultures – all the same species with
little variety).
2) Page 56 #1-8
3) Page 57 #1-14