b2.3 cell specialisation Flashcards
what is differentiation?
differentiation is the process during development whereby newly formed cells become more specialised and distinct from one another as they mature.
all cells of a multicellular organism share an identical genome - each cell contains the entire set of genetic instructions for that organism. the activation of different genes within a given cell by chemical signals will cause it to differentiate into different cell types.
how do cells differentiate following fertilisation?
following fertilisation, an unspecialised zygote will divide and develop into a mass of specialised cells via differentiation. this process is driven by the release of gene regulating chemicals called morphogens.
- the impact of the morphogen will be determined by its relative concentration
- cells closer to the morphogen source receive higher concentrations of morphogen, resulting in activation of more genes
- cells further away from the morphogen source receive lower concentrations of morphogen, resulting in the expression of fewer genes
what are the properties of stem cells?
stem cells are unspecialised cells that have two key qualities:
self-renewal: they can continually divide and replicate
potency: they have the capacity to differentiate into specific cell types
when a cell differentiates to become specialised, it loses its capacity to form alternative cell types.
what are stem cell niches?
stem cell niches are sites within the body where a pool of adult stem cells are maintained in preparation for future proliferation and differentiation.
what is the stem cell niche of bone marrow?
haemopoietic stem cells are located within the bone marrow and give rise to the different types of blood cells. bone marrow transplants are commonly employed to replace the haemopoietic stem cell niche following chemotherapy for leukemia.
what is the stem cell niche of hair follicles?
the hair follicles contain a range of epidermal stem cells that are involved in cyclic bouts of hair growth, skin innervation, vascularisation and wound repair. these stem cells could potentially be harvested and used to regenerate skin tissue in burns victims.
what is a totipotent stem cell?
can form any cell type and develop into entirely new organisms (zygotes - embryonic)
what is a pluripotent stem cell?
can form any cell type arising from the three germ layers (inner cell mass of blastocyst - embryonic)
what is a multipotent stem cell?
can form a number of closely related cell types (bone marrow - adult)
stem cells can be used therapeutically to treat diseases by replacing damaged cells with healthy ones.
what are the ethical issues concerning the use of stem cells in medicine?
embryonic stem cells have a greater potency but there are ethical issues associated with their use (involves the generation and destruction of an embryo). adult stem cells have less ethical issues and a lower chance of graft rejection (involves the patients own cells), but have lower potency and are therefore limited in their potential use.
the potency of adult stem cells can be increased by triggering the expression of specific genes via nuclear reprogramming, but these induced pluripotent stem cells are both difficult and expensive to create.
how is cell size linked to specialisation?
the size of cells can vary significantly in multicellular organisms inn order to optimise the specific function of a cell.
- red blood cells need to squeeze through narrow capillaries and have a diameter of only 7-8µm
- neurons need to transmit signals throughout the body and can be over 1m in length (but with a width of only 1µm)
- striated muscle fibres consist of fused muscle cells - they can have a width of 20-100µm and a length of up to 12cm
- a human ovum is one of the largest cells with a diameter of 120µm, while the male sperm is extremely small (5µm)
how does the SA:V limit cell size?
cells need to produce chemical energy to survive and this requires the exchange of materials with the environment. the rate of metabolism of a cell is a function of its mass/volume. the rate of material exchange is a function of its surface area.
as a cell grows, volume increases faster than surface area, leading to a decreased SA:V ratio. if metabolic rate exceeds the rate of exchange of vital materials and wastes (low SA:V ratio), the cell will eventually die. hence growing cells tend to divide and remain small in order to maintain a high SA:V ratio suitable for survival.
what are the adaptations of red blood cells?
red blood cells are flattened and biconcave shaped in order to maximise the surface area and minimise volume. this means that oxygen can diffuse into the red blood cell quicker in the lungs and out again at respiring tissues.
what are the adaptations of proximal convoluted tubule cells?
proximal convoluted tubule cells are responsible for reabsorption of vital substances from the glomerular filtrate. they have microvilli and invaginations in the membrane to maximise surface area.
what are the adaptations of type 1 pneumocytes?
type 1 pneumocytes are extremely thin cells that carry out gas exchange. they cover approximately 95% of the alveolar surface area. they are adapted to maximise the rate of gas exchange by providing a short diffusion distance.
what are the adaptations of type 2 pneumocytes?
type 2 pneumocytes are rounded cells that secrete pulmonary surfactant. they cover approximately 5% of the alveolar surface area. pulmonary surfactant reduces surface tension (preventing alveoli from collapsing) and aids gas exchange, by allowing oxygen to dissolve before diffusing into blood.
what are the adaptations of cardiac muscle?
does not tire or fatigue so can contract continuously
fibres form a network through the atria and ventricles
connected via specialised branched connections called intercalated discs, allowing quicker contraction
large number of mitochondria to provide a large quantity of ATP
what are the adaptations of sperm cells?
haploid nucleus, contained within a streamlined head, that can fuse with an ovum nucleus
acrosome containing digestive enzymes to aid entry into the ovum
many mitochondria for the release of energy to aid movement
flagellum made of protein microtubules to aid movement
what are the adaptations of egg cells?
haploid nucleus that can fuse with a sperm nucleus
zona pellucida that can harden to prevent more than one sperm penetrating (polyspermy)
follicle cells which nourish and protect the ova
vesicles containing digestive enzymes that are released inro zona pellucida to prevent polyspermy
cytoplasm rich in nutrients
