Stem Cells

Features of stem cells (4)

1. Unspecialized cells

2. Have potential to differentiate to become any one of the specialized cell types in the organism

3. Are able to undergo cell division repeatedly

4. Are a renewing source of undifferentiated cells

What are stem cells a source of?

New cells necessary for growth, development and tissue repair

What happens to stem cells once specialized?

Lose the ability to divide, entering the G0 phase of the cell cycle

What is a stem cell's ability to differentiate into different cell types called?


Potency

The greater the no. of cell types it can differentiate into, the greater its potency

What is meant by the term 'totipotent'


Stem cell can differentiate into any type of cell

Can differentiate into extra-embryonic tissues

Present in fertilized egg, zygote, embryo and 8 or 16 cells from its first few mitotic divisions

What is meant by the term 'pluripotent'?


Stem cells can form all tissue types but not whole organisms (form a range of cells within a tissue)

Present in early embryos, and are the origin of different types of tissues within an organism

What is meant by the term 'multipotent'?

Stem cells that can form a range of cells within a certain type of tissue

Present in tissues of adult organs

How do we know a cell has become differentiated?
(4)

1. Shape

2. Organelles

3. Proteins

4. Deletion of unwanted organelles

Differentiation

The process by which a cell becomes specialized for its job

Where are erythrocytes and neutrophils derived from?


Stem cells in bone marrow

How are erythrocytes' production an example of distinct differentiated cells derived from a stem cell in bone marrow?

Due to the lack of nucleus & organelles, they have a lifespan of 120 days

• Need to be replaced constantly

• Stem cell colonies in the bone marrow produce approx. 3 mil erythrocytes per kilo of body mass per day to keep

How are neutrophils' production an example of distinct differentiated cells derived from a stem cell in bone marrow?


Live for 6 hours & colonies of stem cells in bone marrow produce in the region 1.6 billion per kg per hour

• This figure increases during infection

Where are stem cells found in plants?

In meristematic tissue (meristems) ; wherever growth occurs in plants e.g. tips of roots and shoots (apical meristems)

Where is meristematic tissue located in a plant?

Between phloem and xylem tissues known as vascular cambium

Cells originating from this region differentiate into the different cells present in xylem and phloem tissues (that become xylem vessels and phloem)

• In this way, the vascular tissue grows as the plant grows

• Pluripotent nature of meristematic tissue continues throughout life of the plant

What are some of the potential uses of stem cells in research and medicine?

Repair of damaged tissues, the treatment of neurological conditions, research into developmental biology and drug trials

What are some issues with using stem cells?

Ethical concerns:

• Destruction of embryo raises religious and moral concerns

Rejection