Stem Cells (BN)

Self renewal

stem cells can continually divide and replicate

Potency

stem cells have the capacity to differentiate into specific cell types

stem cell supplies are typically limited

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

Totipotent

Can form any cell type and develop into entirely new organisms

Pluripotent

Can form any cell type arising from the three germ layers

Multipotent

Can only form a number of closely related cell types

embryonic stem cells

Totipotent stem cells (e.g. zygotes) and pluripotent stem cells (inner cell mass of blastocyst)

adult stem cells

multipotent stem cells (e.g. bone marrow)

Embryonic and adult stem cells

can be used therapeutically to treat diseases by replacing damaged cells with healthy ones

Embryonic stem cells have a greater potency

can treat more conditions) but there are ethical issues associated with their use (involves the generation and destruction on an embryo)

Adult stem cells have less ethical issues and a lower chance of graft rejection

(involves use of patient’s own cells), but have lower potency and are therefore limited in their potential use

Stem cell niches

sites within the body where a pool of adult stem cells are maintained in preparation for future proliferation and differentiation

Locations of stem cell niches

bone marrow, hair follicles, heart, intestines and brain

Bone Marrow

Haemopoietic stem cells are located within the bone marrow and give rise to the different types of blood cells (e.g. erythrocytes, leucocytes and thrombocytes)

Hair Follicles

contain a range of epidermal stem cells that are involved in cyclic bouts of hair growth, skin innervation, vascularisation and wound repair

Differentiation

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

genome

each cell contains the entire set of genetic instructions for that organism

Differential Gene Expression

early zygote

unspecialised zygote will divide and develop into a mass of specialised cells

morphogens

release of gene regulating chemicals (transcription factors)

cells closer to the morphogen source

receive higher concentrations of morphogen, resulting in the activation of more genes

Cells further away from the morphogen source

receive lower concentrations of morphogen, resulting in the expression of fewer genes

morphogen gradients

control the differential expression of genes within an early-stage embryo

Morphogen Gradients

rate of metabolism

is a function of its mass / volume (larger cells need more energy to sustain essential functions)

rate of material exchange

function of its surface area (large membrane surface equates to more material movement)

cell will die

metabolic rate exceeds the rate of exchange of vital materials and wastes (low SA:Vol ratio)

ratio suitable for survival

growing cells tend to divide and remain small in order to maintain a high SA:Vol

SA:Vol Ratio

size of cells

vary significantly in multicellular organisms in order to optimise the specific function of a cell