Transcript Cell Clock, Cloning and Cancer

Cell Clock
and Cloning
Biology 12
Review of Mitosis:
 Mitosis
occurs in all
body cells (aka
somatic cells) except
egg and sperm
 Mitosis
maintains the
correct # and type of
chromosomes and
results in two
daughter cells which
are identical to the
parent cell.
Review of Mitosis Cont’d:
 Chromatin
is the hereditary material in the
nucleus. It is replicated, and then shortens
and coils into two connected (by the
centromere) chromatids which are copies
of one chromosome.
 The
chromosome number is different in
different organisms.
Ex. Humans 46 (23 pairs)
Bull Frog 26 (13 pairs)
 The
chromosomes come in pairs because
one originally came from the “mother”
and one from the “father.”
So…

If cells can divide, why do we age, why do
we die?


Thoughts?
The truth is scientists are not sure but the
theory of a “cell clock” is the most current
explanation!

The life of a cell can be from minutes to
decades. There is a biological clock which
regulates the number of times a cell can divide.
Stopping cell division:
 Main
1.
2.
3.
causes:
Age: The cell clock “tells” the cell that it
has reached it last division
Differentiation: usually once a cell is
differentiated it stops dividing (becomes a
specific type of cell, i.e. a brain cell)
Cell to cell contact – most normal cells will
grow until they come in contact with
another cell.
Cell Clock
Experiment
 Page
90
Cell Clock Experiment:


Research indicates that a
biological clock regulates the
number of times a cell will
divide. The cells stop because
of their age/number of divisions
As eukaryotic cells divide, the
protective ends of their
chromosomes, the telomeres,
gradually shorten with each
cell division. When a critical
telomere length is reached, the
cells are no longer able to
divide
Interesting…
 Cells
seem to stop dividing at the same
stage in the cell cycle, just before DNA
replication takes place (Interphase.)
Once replication occurs the cell seems
committed to cell division.
 The
only cells which divide continuously
are sperm producing cells and the
cancer cells.
What is cloning?
 Type
of asexual reproduction (mitosis
is asexual as well)

So that means that offspring are
identical to parent cell (produced
from a single cell)
Cloning in Nature:

Many examples of cloning
exist in nature.



Identical twins
Single celled organisms like
yeast germs and protozoa
make cells exactly like
themselves (asexual
reproduction).
Plants also can make other
plants asexually. The process
is called vegetative
propagation. This process is
where a stem or root that is
planted makes an exact
replica of itself.
Artificial Cloning:

Have you heard of Dolly the
sheep?



Dolly was born on July 5,1996
Dolly was the first clone
produced from a cell taken
from an adult mammal.
She was created using
somatic cell nuclear transfer,
where the cell nucleus from an
adult cell is transferred into an
unfertilised oocyte
(developing egg cell) that has
had its nucleus removed.
Artificial Animal Cloning:
1.
2.
3.
Create an enucleated cell (the nucleus
is removed with a thin glass tube from an
unfertilized egg cell) to act as the “host
cell”
Take the nucleus from the fertilized cell
to be cloned
Insert the nucleus in the enucleated cell
Animation:
 http://www.youtube.com/watch?v=q0B9
Bn1WW_4
To do:
 Complete
“Cell Clock” Article Assignment
 Page 100 question 1, 2, 3, 4