Growth Flashcards
What is:
- anisotropy
- proportionality
- adaptability
- discontinuous scaling
- anisotropy - direction-dependent nature of growth. different parts of a structure grow at different rates or in different directions.
- proportionality - different parts of an organism or system grow in relation to each other to maintain overall balance and function.
- adaptability - refers to an organism or system’s ability to adjust its growth in response to environmental changes or internal needs.
- discontinuous scaling - refers to non-linear changes in size or shape as a system or organism grows. In some cases, growth may occur in sudden spurts rather than a steady, continuous manner.
What are the limits to cellular growth and what is the result of cells being too big?
- transport
- communication/coordination (time delay)
- mRNA synthesis - maximum rate of transcription
What are the 4 “tricks” to make big cells?
- vacuoles
- syncytia (skeletal cell stretched out, lots of nuclei so lots of cytoplasm)
- polytene chromosomes (lots of nuclei)
- helper cells - large oocyte has surrounding normal cells that delivers nutrient
What 2 factors are balanced during cell proliferation?
division and growth
Outline the cell cycle
G1 - growth
S - DNA synthesis
G2 - growth and preparation of mitosis, checks for errors
M - mitosis cell division
cyclins work by controlling cyclin-dependent-kinases:
1. what is a kinase?
2. how does it regulate cell cycle
- phosphorylates other molecules
- each cdc only binds to specific cyclins. when it meets the right cyclin it will turn on and off proteins to push cells onto next cycle. always in cell but needs to meet specific cyclin to trigger response
- creates feedback loop when one is active it creates condition to activate next one and inactive the one before
Which stage are there checkpoints and what do they check?
G2 check for DNA damage
What causes the difference between well fed and less well fed cells?
well fed = more surface area facing outside to get nutrient
How are crystallising cells formed
- side branches have higher SA so grows longer
What is hertwig’s rule?
(In the absence of over-riding factors) Cells orientate their division planes in the direction that will reduce mechanical stress in tissues. e.g. stretching ear piercing
How does crowding cells orientate?
- avoiding to make crowd worse
- crowded = more patterned and oriented
- sparse = ignores orientation
How does Piezo1 link stretch or crowding to division decisions?
Piezo 1 transducing stress to calcium to mitosis, and Piezo 1 being in the membrane in tense cells and cytoplasm in crowded ones.
- opens calcium channel when experiencing stress and tension, calcium comes in = mitosis
How does developing bird guts make loops
- mesentery = thin membrane
- gut tissue grows faster than mesentery but they remain attached
- curve accommodates the faster growth of gut tissue relative to mesentery
Explain how planar cell polarity is achieved on cell sheets
- Within epithelium, there’s a different polarity (apical-basal vs. planar)
- The south end is inactive.
- The north end is active due to lack of inhibition.
- Cell A signals to cell B which side is active, determining its north-south orientation. This, in turn, informs cell C of its directional activity.
Give an example of how inhibition lines up and controls epithelium growth using polarity and direction
forming of neural tube (starting as a valley)
What is the foetal transfusion syndrome
- risk of having an identical twin
- two individuals - surrounding the same placenta
- one twin can get more blood, more nutrients than the other
- leads to different birth sizes (cardiovascular tissue)
In terms of sizing of an organism, what is the relative difference in animals vs plants
animals have clear maximum size for a species, plants and fungi do not
What is sexual dimorphism
Within a species, the two sexes can show marked differences in adult size
What is a vitruvian man? Give examples of cases where vitruvian proportion is not shown
perfectly proportioned man by Leonardo da Vinci. e.g. gigantism or dwarfism
In the case of gigantism, how did pituitary tumours affect growth?
pituitary gland secretes growth hormone which tells muscles to grow. overproduction or mutations in GH receptors
What are GH signals often translated into ?
local signals of IGF 1 and 2
Why are our 2 legs the same length? What happens when you restrict growth in one and what does it tell us?
- Contralateral leg grows normally (-> lop-side bunny), no communication between the legs (didn’t wait for eachother)
- Release the inhibition -> inhibited leg catches up (faster growth than the other).
The ability of the growth plate of the long bone to respond to GH declines with the number of cell divisions it has made. the more it has grown, the less able it is to grow with every division, concentration will divide and growth is diluted
- growth plates are at the end of the bone and has several zones (proliferation with stem cell to maintain own number and create daughter cells that enlarge and turn into cartillage)
- cartillage die but matrix picks up calcium. bone cells come in and displaces the dead cells
- chain reaction asking different cell types to replace each layer allowing proliferation and growth
- the bigger the bone is, the less efficient the signalling loops, slower it will grow
- because small bone = growth plate closer to the edge
- large bone = further away
Achondroplasia = limbs are smaller but head and trunk are normal. How does FGF signalling work?
FGF signalling via FGFR3 usually inhibits both proliferation and differentiation of chondrocytes (it’s complicated). Activating mutations in FGFR3 cause growth plates full of chondrocytes, and premature closure of the growth plates
- growth plates gets shut down earlier on
- FGF tells signals its active when it isn’t due to mutation
2 key points with Achondroplasia
- some parts of body keeps growing anyways
- amount of skin and tendon and muscle is correct for peculiar shortened limbs so tissue is not independent from eachother.
3 Example of skin being in right proportion
- pregnancy
- male central obesity
- cultural practices
In a plate, researcher grew cells. some corners were sharp and some were gentle. what is the difference in frequency of division?
stress is higher in sharp corners than gentle corners (spread out). high frequency where corners were sharp as they divide in an attempt to relieve the mechanical stress
mechanical stress drives ___ of channels to increase ___
channels, division
spleen in mouse: spleen extracted from mice and added lost of foetal spleens to see how big they would grow, result: each of the 9 grew to 1/9th of the size so total mass = mass of one normal spleen. what is the explanation
tissues release specific hormones called “chalones” which circulate and tissues detects chalone concentration coming back from the blood. too little = not enough tissue, correct amount of chalone = stops growing tissue.
What is quorum sensing?
minimum number of cells needed to make something. once they reach a size they flip gene expression and differentiates
How do cells know they’ve reached the right size for quorum sensing?
- cells have receptors for a factor that they themselves excrete
- so they detect the factor from themselves and also their neighbours
- local concentration of those secretions will rise due to : 1) more cells making it 2) crowd of cells reducing ability to diffuse away
- once enough of a signal, cell will make its response as it knows its in a big enough group
Explain quorum sensing in the case of the kidney
- these signals pushes mesenchyal cells and aggregates
- when a big enough aggregate is formed, they switch their gene expression to pick up epithelial cells
- as they make this, they switch on gene coding for Wnt4, they diffuse slowly
What happens if Wnt4 is eliminated in nephron development forming aggregates?
no nephron. end up with large mass of mesenchyme because they are still waiting for signal to differentiate
What happens to neurons in chicken embryo when one of the wings was removed vs graft wing attached onto diff chicken embryo
- fewer motor neurons when target field reduced
- more motor neurons when 2 wings on one side
Time course of neuronal development.
1. 2 stages ___ and ____
2. cells make far _____neuron than it needs so lots of cells go through ____
3. T.D neurotrophic “independent” during ____ and dependent in ____
- mitosis & elective cell death
- too much & cell death
- mitosis & elective cell death
What is T.D target derived?
they dont know how much they need but they continue dividing until maximus is reached, no target derived signals
How does cell death depend on T.D neurotrophins?
competing for limited amount of T.D neurotrophins, so the ones that gets less will die and will keep happening until there’s enough neurotrophins to keep cell alive
What Is the trophic theory?
generalised: beyond very early embryos, every cell depends its survival on survival factor secreted by different cells. keeps populations balanced (except in cancerous cells).
