Theme B: B2 Cells - B2.3 Cell Specialisation Flashcards
the development progression for humans
gametes –> zygote –> embryo –> foetus –> infant
gametes
the 2 cells that fuse together in sexual reproduction. Gametes are haploid sex cells (sperm in males and eggs in females) that carry half the genetic material of an organism.
zygote
A zygote is the diploid cell formed when two haploid gametes (sperm and egg) fuse during fertilization. It is the first stage of development in a multicellular organism.
cell differentiation
Cell differentiation is the process by which unspecialized cells, such as stem cells, develop into specialized cells with distinct structures and functions. This occurs through the selective expression of certain genes while others are suppressed.
after fertilization
how do cells intitially develop?
(in humans)
the zygote can divide very rapidly, and while the cells initially produced are unspecialised, the cells of the zygote also rapidly differentiate. this process results in the formation of specialised cells driven by the selective expression of certain genes while others remain inactive.
each cell will develop in a very specific manner depending on which genes become active and which signals the cell recieve.
cell signalling
the process by which infomrtaion is transferred from the cell surface to the nucleus. this is essential in controllong gene expression and thus differentiation.
morphogens
what are they? how does it effect the development of cells?
signal molecules that control cell differntiation. they occur in gradients (areas of concentration differences) in different regions of the early embryo.
the concentration of the signal molecules controls the regional development of teh first cells into head and tail structures.
the gradient of the signal molecules results in diffferent genes being expressed in different parts of the embryo. this leads different parts of the embryo to develop different structures.
as embryo develops, other signalling molecules become factors in differentitaion.
stem cells
population of cells within organisms that retain the ability to divide indefinetely and can differentiate along different pathways, resulting in all the cell types an organism posses.
meristematic tissue
Where stem cells are contained in plants. it’s composed of rapidly reproducing cells that can various types if tissue within the root or stem (a.k.a stem cells).
gardeners take advantage of these cells when they take cuttings from stems or roots and use them to grow new plants.
2 unique properties of stem cells
1) self renewal
2) recreate functional tissues
self renewal
when a stem cell divides, there are sveral possible outcomes:
1) both daughter cells remain stem cells
2) a stem cell and a differentiated cell may be formed
3) both cells differentiate
whatever the outcome is, the stem cells are maintained.
this process allows the continual production of a particular tissue whilse also providing for the continuation of stem cells.
stem cell niches
in a stem cell niche, the stem cells are present in high numbers due to regular proliferation.
e.g. bone marrow and hair follicles (in humans)
stem cell niches in humans are also studied in the contral nervous system, intestinal system, and in the muscle fibre bundles.
bone marrow
(as a stem cell niche)
stem cells that produce blood cells are found in the bone marrow alongside self renewing stem cells.
as blood cells are produced, differentiated cells are transported away via a large array of supporting blood vessels.
bone marrow tissue is multipotent.
the soft, spongy tissue that is in the medullary cavities (centers) of bones
hair follicles
as stem cell niches
they exist in the skin, and large numbers of epithelial stem cells are found in the bottom rounded area of a hair follicle. these stemc ells are multipotent.
these stem cells are also involved with hair growth, skin and hair follicle regeneration, and the production of sebaceous (oil-producing) glands associated with hair follicles.
a tube-like structure (pore) that surrounds the root and strand of a hair
what feature to all stem cell niches all have in common?
the presence of signalling factors that bring about both self renewal and differentiation.
types of stem cells
(in order of decreasing potency)
1) totipotent (total - most ‘potent’)
2) pluripotent (plural)
3) multipotent (multiple)
4) unipotent (one - least potent)
totipotent
- capable of continued dividiion and possesses the ability to produce any tissue in the organism.
- very few cells are totiptent.
- only exist in very early stages of embryo development.
- they may form a complete organism.
pluripotent
- arise form totipotent cells and only exist in early embryonic stage
- can mature into almost all the differnet cell types that exist in an organism
- unlike totipotent, they cannot produce a complete organism.
multipotent
- only forms limited number of cell types.
- bone marrow tissue is multipotent
- they occur later in the development of the embryo and present during the remainder of an organism’s life
unipotent
- only forms a single cell type, e.g. sperm cells in mammals
- usually form late in the embryonic stage and exist in the funcioning organism
one problem with using stem cells to treat disease
stem cells cannot be distinguished by appearance. they can only be isolated form other cells based on their behaviour.
therapuetic clones
cell type and size (in decreasing order)
sperm cell:
egg cell
fat cell
red blood cell
white blood cell
skeletal muscle fibre
neuron (nerve cell)
what is cell size determined by
function of a cell determines its size
sperm cell size importance
sperm cells are relatively small because they only carry out the function of transporting genetic material so viable zygote can be formed.
red blood cell adaptations to carry oxygen through the organism
1) contain haemoglobin that combine with and release oxygen
2) biconcave disk shape allowing more surface area for oxygen absorption
3) lack mitcohondria and nucleus
4) flexible and limited size because they need to move through narrow blood capillaries
white blood cell size
- bigger than red blood cell
- main function is defense against infections
