Biology IB HL - 1.1 Cell Introduction Part 2

Organs are then formed from the functional grouping of multiple tissues

Organs that interact may form organ systems capable of carrying out specific body functions

Organ systems collectively carry out the life functions of the complete organism

Differentiation is the process during development whereby newly formed cells become more specialised and distinct from one another as they mature

share an identical genome i.e each cell contains the entire set of genetic instructions for that organism

The activation of different instructions (genes) within a given cell by chemical signals will cause it to differentiate

DNA is packaged with proteins to form chromatin

packaged in an expanded form called euchromatin that is accessible to transcriptional machinery

Inactive genes are typically packaged in a more condensed form called heterochromatin (saves spaces, not transcribed)

NO

differentiated cells will have different regions of DNA packaged as eurochromatn and heterochromatin according to their specific function

When a cell differentiates and becomes specialised, it loses its capacity to form alternative cell types

unspecialised cells

Self Renewal – They can continuously divide and replicate

| 2. Potency – They have the capacity to differentiate into specialised cell types

totipotent

pluripotent

multipotent

unipotent

– Can form any cell type, as well as extra-embryonic (placental) tissue (e.g. zygote)

Can form any cell type (e.g. embryonic stem cells)

– Can differentiate into a number of closely related cell types (e.g. haematopoeitic adult stem cells)

Can not differentiate, but are capable of self renewal (e.g. progenitor cells, muscle stem cells)

Stem cells are necessary for embryonic development as they are an undifferentiated cell source from which all other cell types may be derived

Cell types that are not capable of self-renewal (e.g. amitotic nerve tissues) are considered to be non-stem cells

As these tissues cannot be regenerated or replaced, stem cells have become a viable therapeutic option when these tissues become damaged

the use of biochemical solutions

surgical implantation

impression of host immune system

careful monitoring of new cells

to trigger the differentiation of stem cells into the desired cell type

Surgical implantation of cells into the patient’s own tissue

to prevent rejection of cells (if stem cells are from foreign source)

Careful monitoring of new cells to ensure they do not become cancerous

stargardt's disease

parkinson's disease

leukemia

paraplegia

diabetes

burn victims

An inherited form of juvenile macular degeneration

causes progressive vision loss to the point of blindness

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

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

A degenerative disorder of the central nervous system caused by the death of dopamine-secreting cells in the midbrain

Dopamine is a neurotransmitter responsible for transmitting signals involved in the production of smooth, purposeful movements

Consequently, individuals with Parkinson’s disease typically exhibit tremors, rigidity, slowness of movement and postural instability

Treated by replacing dead nerve cells with living, dopamine-producing ones

Bone marrow transplants for cancer patients who are immunocompromised as a result of chemotherapy

Repair damage caused by spinal injuries to enable paralysed victims to regain movement

Replace non-functioning islet cells with those capable of producing insulin in type I diabetics

Graft new skin cells to replace damaged tissue

Embryos (may be specially created by therapeutic cloning)

Umbilical cord blood or placenta of a new-born baby

Certain adult tissues like the bone marrow (cells are not pluripotent)

Using multipotent adult tissue may be effective for certain conditions, but is limited in its scope of application

Stem cells derived from umbilical cord blood need to be stored and preserved at cost, raising issues of availability and access

The greatest yield of pluripotent stem cells comes from embryos, but requires the destruction of a potential living organism

Stem cells can be artificially generated via NUCLEAR TRANSFER or NUCLEAR REPROGRAMMING, with distinct benefits and disadvantages

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

More embryos are created by this process than needed, raising ethical concerns about the exigency of excess embryos

Induce a change in the gene expression profile of a cell in order to transform it into a different cell type (transdifferentiation)

Involves the use of oncogenic retroviruses and transgenes, increasing the risk of health consequences (i.e. cancer)

stem cells produced which are indistinguishable from embryo-derived cells

Stem cells autologous to adult donor