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 causes:

1. Age: The cell clock “tells” the cell that it has reached it last division

2. Differentiation: usually once a cell is differentiated it stops dividing (becomes a specific type of cell, i.e. a brain cell)

3. 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. Create an enucleated cell (the nucleus

is removed with a thin glass tube from an unfertilized egg cell) to act as the “host cell”

2. Take the nucleus from the fertilized cell to be cloned

3. Insert the nucleus in the enucleated cell

Animation: http://

www.youtube.com/watch?v=q0B9Bn1WW_4

To do: Complete “Cell Clock” Article

Assignment Page 100 question 1, 2, 3, 4