IB BIO - U1 L4 - CELL DIFFERENTIATION AND STEM CELLS

What are Emergent Properties?

• Multicellular organisms are capable of completing functions that unicellular organisms can’t

• Collective actions of individual cells combining to create new synergistic effects

Levels of organisation

1. Specialised Cell

2. Tissue

3. Organ

4. Organ System

5. Organism

Cellular Differentiation

Process by which a cell becomes specialised to perform a specific function via activation of some genes by chemical signals and not others.

What are specialised cells?

cells designed to carry out a particular role in the body

Gene Packing

Differentiated cells have different regions of DNA packaged as euchromatin and heterochromatin Euchromatin-

Euchromatin:

Expanded form that is accessible for transcription (active gene).

Heterochromatin:

Condensed form that is not accessible for transcription (inactive gene)

Stem Cells

animal cell that can differentiate into many types and continually replicate

Stem Cell Origins

• Embryos

• Umbilical Cord

• Blood Adult Tissues

Types of Stem Cells:

1. Totipotent

2. Pluripotent

3. Multipotent

4. Unipotent

Totipotent Stem Cells

Form any cell type and develop into entirely new organisms (ex- zygote)- embryonic

Pluripotent Stem Cells

Form any cell type arising from 3 germ layers (ex- inner mass of blastocyst)- embryonic.

Multipotent Stem Cells

Only form closely related cell types (ex-bone marrow) adult

Unipotent Stem Cells

Can only regenerate themselves, cannot differentiate.

What are Stem Cell Niches?

Sites within body where pool of adult stem cells are maintained.

Where are Stem Cell Niches located?

1. Bone Marrow

2. Hair follicles

3. Heart

4. Intestines

5. Brain

   1. These are all multipotent (can only differentiate into similar cells/closely related cell types)

Uses of Stem Cells.

• Necessary for embryonic development.

  • undifferentiated cell source from which all other cell types may be derived.

• Viable therapeutic option.

  • when adult tissues become damaged and cannot be regenerated.

Examples of Therapeutic Stem Cells Use

Stem Cell Therapy

• Stargardt’s Disease

  • inherited form of juvenile macular degeneration that causes progressive vision loss to point of blindness

  • Caused by gene mutation that impairs energy transport in retinal photoreceptor cells, cousin them to degenerate

• Treated by replacing dead cells in retina with functioning ones derived from stem cells.

Ethics

• Multipotent

  • Effective for certain conditions, but is limited in its scope of application (lower potency)

• Pluripotent

  • Greatest yield from embryos, but requires destruction of a potential living organisms (greatest potency) This is where ethical consideration comes in

• Umbilical Cord Blood

  • Stored and preserved at cost

  • Raises ethical concerns of availability and access; fairness

Artificial Stem Cell Techniques

• Somatic Cell Nuclear Transfer (SCNT)

• Nuclear Reprogramming

What is a Somatic Cell Nuclear Transfer (SCNT)?

Creation of embryonic clones by fusing a diploid nucleus with an enucleated egg cell (therapeutic cloning)

What is Nuclear Reprogramming?

Induce change in gene expression to transform it into different cell type (transdifferentiation)