Textbook Reference: pg. 38-45

Mitosis produces cells with exact copies of the same chromosomes…therefore the same genes

But cells will produce different proteins and therefore differ in structure and function

E.g. Bone cells, nerve cells, muscle cells, skin cells….

Every new organism (animal or plant) begins as a single cell, the fusion of their parents genes (sperm + egg = zygote)

This cell divides into two identical cells by the processes of mitosis and cytokinesis.

Two daughter cells then divide and the process continues.

Blastocyst

Every cell contains the same chromosomes and the same genes.

How then do organisms produce very different types of cells?

Not every gene in a cell gets expressed or “switched on”.

Therefore, not every protein gets produced!

What decides how/which genes are expressed?

1. Cytoplasm in the Cell – amount of cytoplasm and number of other organelles affects how the cell will develop

2. Environmental Conditions of the Cell – temperature, nutrients, contaminants….

3. Neighbouring Cells – diffusion across the cell membranes from one cell to another when cells are close to each other (chemical communication between cells)

Both plants and animals have cells which can become ANY type of cell

Plants – meristematic cells

Animals – embryonic stem cells

Animals - Stem cells Unspecialized cells – the first few cells within

an embryo are totipotent - able to eventually become any type of cell

As an embryo develops (after 1 week), cells become less versatile and can only produce some kinds of cell (tissue). They are pluripotent.

After birth, people have only adult stem cells (or unipotent)– these can only produce very specific types of cell. E.g. Skin cells can only produce more skin cells.

Embryonic stem cells – can be cultured (grown) to produce many types of tissue

Holds great promise for treating many diseases including life-threatening ones. Many would say that this fact alone should mean “full speed ahead” with research.

Requires the destruction of an embryo - usually grown from eggs fertilized with sperm “in vitro” (outside the womb)

Some say this is destroying a human life (a person)

Some say that personhood does not come until much later (brain cells?, blood?)

Adult stem cells – can be cultured (grown) to produce the type of tissue they came from

No ethical issue Requires the addition of “growth

factors” (nutrients)

Embryos can only be used which are no longer wanted for reproductive purposes.

Illegal to “create” embryos solely for stem cell research

Embryos must be less than 14 days old (after conception) to be used to harvest stem cells

Donors must provide consent to the use of embryos

Cannot buy/sell embryos

Very recent research (last 5 years) Taking normal tissue cells (e.g. skin)

that are unipotent and “forcing” them to become pluripotent (by the addition of genes)

A kind of “cellular reprogramming” This removes the ethical issue (no

destruction of embryos/blastocysts)

http://singularityhub.com/2009/06/08/growing-organs-in-the-lab/

Human skin grown in the lab from stem cells

http://www.youtube.com/watch?v=4nqw1yjyKEs&safety_mode=true&persist_safety_mode=1&safe=active