Growth Flashcards
What are some limits to cellular growth?
- transport
- communication/coordination
- mRNA synthesis: cell only has 1 or 2 copies of gene, limit to how much mrna can be synthesised
What are some methods cells use to make bigger cells?
- vacuoles in plants
- syncytia eg skeletal muscle: cells fuse so multiple nuclei in cell
- polytene chromosomes eg fruit fly salivary glands: replication of chromosomes
- helper cells eg granulosa cells in ovarian cycle
What is a simplified representation of the cell cycle?
G1 -> S -> G2 -> M
G = growth
S = DNA synthesis
M = mitosis and cytokinesis
What is cleavage division in embryos?
embryos divide but stay the same size
What are cyclins?
control cyclin-dependent kinases (cdks) whose abundance controls progression through the cell cycle
What is checked at the checkpoint between G1 and S?
i. cell has enough resources
ii. cell has enough room, external pressure can stop cell division
iii. cell has external signals telling it to divide
iv. no signals saying don’t divide
What is retinoblastoma (Rb)?
it is a protein that inhibits genes needed for S phase
is active and inhibiting when unphosphorylated and inactive when phosphorylated
How is retinoblastoma (Rb) regulated?
cyclins E or D interact with Rb
How is activity of cyclins E and D regulated?
cyclin D inhibited by low ATP levels or a don’t divide signal
cyclin E inhibited by p21 if there is DNA damage or cell-cell contact (crowding)
How are growth factors made and obtained?
cells make growth factors for one another through paracrine signalling
What are the different types of cell division and how do they effect the morphology of a cell colony?
periclinal division: increases radius
anticlinal division: increases circumference
transverse division plane: increases length
What is Hertwig’s rule?
in animals and in absence of over-riding factors: cells orientate their division planes in the direction that will reduce mechanical stress in tissues
How are the gut loops formed?
gut is connected to mesentery, as body grows the gut proliferates much faster than the mesentery causing the gut to loop
How do epithelial cells recognise their own polarity?
cells have certain protein complexes at either end of the cell which have a particular orientation depending on which end of the cell they are present
astral microtubules bind to these proteins which orientates the cell for correct direction of cell division
What is meant by vitruvian and non-vitruvian proportions?
vitruvian proportions refer to the ideallic proportions of an organism
non-vitruvian proportions are those that go against vitruvian proportions
How is the growth of bones regulated?
signals from growth plate cause bone to proliferate, as bone grows the distance between growth plate and bone edge increases causing increasing difficulty to respond to growth signal
What is the growth signal in bones?
FGFR3
What are some consequences of mutation of the bone growth hormone?
growth plates full of chondrocytes, and premature closure of the growth plates
What is the stress receptor in skin?
Piezo1
How does stretching affect skin cell proliferation?
stretching triggers cells paused in early G2 to activate calcium-dependent ERK1/2 phosphorylation that activates cyclin B transcription necessary to drive cells into mitosis
What is the definition of The Trophic Theory?
any cell that is not told to keep itself alive will undergo programmed cell death (apoptosis)
What is the current theory explaining why insertion of multiple foetal spleens after removal of regular spleen grow until mass equals that of a normal spleen?
density of certain molecule secreted by spleens in blood signals how big spleens need to grow
What is the definition of quorum sensing?
organ secretes molecule X, has receptors for X so can detect how much of X has built up
once signal reaches threshold, response
What is an example of an organ that performs quorum sensing?
kidney
What hormone in the kidney signals that the cells have made a big enough aggregate?
Wnt4
Give an example of a molecule that mimics Wnt4
Li+
What is anistropy?
Not being the same everywhere, not growing the same in all directions.
What is Foetal transfusion syndrome?
The placenta is commonly shared in identical twins. If a blood vessel going to one foetus also mistakenly goes to another then one gets more nutrition than the other, therefore growing larger.
How does Growth hormone signalling function?
The pituitary gland produces Growth hormone (endocrine signalling)
Certain tissues such as the liver then produce intermediate growth factors as a response to this which then act on the tissues
How does new growth from growth plate in bones become bone cells?
As the growth plate grows further from the new bone cells, they enlarge and become cartilage cells, they then die and calcify to become bone.
