STEM CELLS IB topic 2.1

MULTICELLULAR ORGANISMS AND CELL DIFFERENTIATION

One of the functions that many cells retain is the ability to reproduce themselves

In multicellular organisms, this allows the possibility of growth

It also allows for the replacement of damaged or dead cells

Multicellular organisms start out as a single cell

The single cell has the ability to reproduce at a very rapid rate

CELL DIFFERENTIATION

The resulting cells then go through a differentiation process

This produces all the required types of cells necessary for the well-being of the organism A red blood cell carries oxygen around the body A rod cell in the retina of the eye absorbs light &

transmits a nerve impulse to the brain To carry out their functions, each cell types

develops its own specialized structure

CELL DIFFERENTIATION

The number of different cell types is staggering

The development of cells in different ways to perform different functions is call differentiation

This involves each cell type using some of the genes in its nucleus, but not others

When a gene is being used by a cell, we say that the gene is being expressed

In simple terms, the gene is switched on and the information in it is used to make a protein or other gene product

AN EXTREME EXAMPLE

A large family of genes in humans which carry the receptors that detect odorant chemicals (smells)

These genes are only expressed in the cells in the skin inside the nose (called olfactory receptor cells)

Each of these cells expresses just one of the gene and so makes one type of receptor to detect one type of odorant

This is how we can distinguish between so many different smells

Richard Axel & Linda Buck received the Nobel Prize for Medicine in 2004 for their work on this system

LIFE AS AN EMERGENT PROPERTY

Emergent properties are those that arise from the interaction of component parts

The whole is greater than the sum of its parts For example:

Consciousness is a property that emerges from the interaction of nerve cells in the brain

Life itself is an emergent property

LIFE AS AN EMERGENT PROPERTY

“Life is not inherent in any single element constituting the living cell. DNA is not alive, neither are proteins, carbohydrates or lipids. Indeed, for a single short moment, a living cell and a dead cell may, upon analysis, be found to contain precisely the same catalogue of ‘dead’ chemicals in identical concentrations … What distinguishes the living from the dead? Nothing more than actions and interactions. Life emerges from inert matter as a consequence of metabolism, the continuous transfer of energy and information systematically packaged in cells in a way that leads to self-perpetuation. The complexity of dynamic behavior that generates metabolism, growth, and genetic inheritance is what we call life.”

Excerpt from Tending Adam’s Garden: Evolving the Cognitive Immune Self by Irun Cohen

A CELL’S ABILITY TO DIVIDE

Some cells have a greatly, or even completely, diminished ability to reproduce once they’ve become specialized

Nerve cells and muscle cells are examples of this type of cell

Other cells, such as epithelial cells like skin, retain the ability to rapidly reproduce throughout their life

The offspring of these rapidly reproducing cells then differentiate into the same cell type as the parent

WHAT ARE STEM CELLS? HOW CAN THEY BE USED FOR MEDICAL BENEFIT?

STEM CELLS Cells that retain their ability to divide and

differentiate into various cell types At an early stage the whole of a human embryo

consists of stem cells, but gradually the cells in the embryo become committed to differentiating in a particular way

All the cells produced will differentiate in the same way and so they are no longer stem cells

Small numbers of cells seem to remain as stem cells and are still present in the adult body Bone marrow, skin, and liver They give some human tissues considerable powers of

regeneration and repair Stem cells in other tissues (brain, kidney, heart) only

allow limited repair

STEM CELLS – RESEARCH & TREATMENT

There has been great interest in stem cells because of their potential for tissue repair and for treating a variety of degenerative conditions

Promising research has been directed towards growing embryonic stem cells in culture so they could replace differentiated cells lost due to injury and disease

This involves a process called therapeutic use of stem cells

THERAPEUTIC USES OF STEM CELLS

Parkinson’s disease and Alzheimer’s disease are caused by the loss of brain cells Multiple sclerosis and strokes are also caused by

a loss of neurons/other cells in the nervous system

It’s hoped that implanted stem cells could replace many of these lost brain cells Alleviate many of the symptoms

Diabetes (type 1) – cells in the pancreas are not producing insulin It’s hoped that a stem cell transplant in this

organ could have positive effects by creating insulin-secreting cells

Spinal cord injury (Terra Incognita)

STEM CELL BREAK THROUGH IN BREAST RECONSTRUCTION

TYPES OF STEM CELLS

Besides embryonic stem cells, there are tissue specific stem cells

These cells reside in certain tissue types and can only produce new cells of that particular tissue

The greatest success so far in therapeutic use of stem cells involves bone marrow transplants

Hematopoietic stem cells (HS cells) Normally found in bone marrow; divide continually

to produce new cells that differentiate into red and white blood cells

Example: Blood stem cells have been introduced into humans to

replace damaged bone marrow of some leukemia patients

ETHICAL ISSUES & STEM CELL RESEARCH Embryonic stem cells (pluripotent stem cells) This is because these cells come from embryos often

obtained from labs carrying out in-vitro fertilization (IVF) Reproductive technology Woman is injected with FSH; stimulate egg production Several eggs are harvested surgically Eggs are mixed with sperm in culture dishes fertilization Fertilized egg(s) are implanted into woman’s uterus unused healthy embryos can be frozen for later use

Gathering embryonic stem cells involves the death of the embryo

Opponents – taking a human life Proponents – this research could significantly reduce

human suffering, and is, therefore, totally acceptable

EMBRYONIC VS ADULT STEM CELLS

Embryonic Stem Cells Adult Stem Cells

Easier to obtain than adult stem cells

No embryo is destroyed

Almost unlimited growth potential – much greater than adult stem cells

The cells are fully compatible with the tissues of the adult, so no rejection problems occur, whereas embryonic tissue is genetically different from the patient receiving the tissue

Less chance of genetic damage than with adult stem cells

Greater capacity to differentiate into different cell types than adult stem cells

Less chance of malignant tumors developing than with embryonic stem cells