Growth Flashcards
Anisotrophy
Growing and changing shape.
Porportionality
Organisms have porportions (ie vetruivian man)
Adaptability
Adpating where/how organisms grow to their envrionment (ie vines)
Discontinous scaling
Ie. humans- our organs scaled to our bodies but cells the same size as every other organsims
Discontinous scaling
Ie. humans- our organs scaled to our bodies but cells the same size as every other organsims
Limits on cell size
mRNA synthesis is rate limiting on cell size. Also transport and communication issues.
Tricks to make cells bigger
- Plant cells have a vaccuole
- Syncytia: lots of nuclei (eg skeletal muscle)
- Polytene chromosome: replicate chromosomes paralelly and get fat thick ones (eg drosophilia fruit fly)
- helper cells: surround and make big (granulosa cells in haploid oocyte)
Cell cycle order
- mitosis
- G1(first growth)
- S-phase (synthesis)
- G2 (second growth)
What is cleavage division and why is abnormal?
Cleavage division occurs in the absense of growth. Cell division usually grows, then divides then grows then divides but this isnt always the cause. (ie tadople embryos and Tim Hunt)
What are cyclin and CDK’s?
Tim Hunt used sea urchin embryos bc they showed cleavage division. Measured proteins at various time points and discovered cyclins! Which are proteins that activate CDK’s which trigger the next stage of cell cycle
How do cyclins and CDK’s control cell cycle
Checkpoints at each stage signal for cyclin degredation, only pass checkpoints unless requirements are met. Eg DNA damage would be stopped at checkpoint so cyclins degraded to stop cycle from proceeding.
Explain the G1-S checkpoint
Must have 1. Enough resources (low ATP inhibits Cdk4/6)
2. Enough room (if not p21 activated and inhibits Cdk2)
3. External signalling of divison (GF stops GSK3b from inhibiting Cdk3/4)
4. Absense of division inhibitory signals (TGFb activates Smad3/4 inhibits Cdk3/4 and Cdk2)
If Cdk3/4 and Cdk2 are active Rb is phosphorylated (unactive) and stops inhibiting expression of genes needed for S phase
Example of dysfunction of the checkpoints
Neoplasia: Retinoblastoma; happens when there is no Rb so cell cycle is unhinged and creates eye tumor and blindness. Only happens in the eye tho which means there must be other pathways for other body parts
Paracrine signalling and potential consequences
Cells signal each other in pos feedback loop. (eg one cell makes GF for another one which makes GF for previous cell) Sometimes autocrine signalling occurs which leads to tumors.
Cell cycle and cancer cells
They 1. ignore stop signals
2. misinterpret growth signals
3. Damage crowding sensors
What are sources of anisotrophic growth?
- Diffusion limited growth (eg. Bacillus subtilis, the outermost cells will get the most nutrients bc the nutrients dont have to diffuse as far)
- Direct cell division (eg A. Thaliana replicates vertically and then one horizantal divison) (important in non-motile organisms ie plants n fungi)
- Crowding cells (cells will grow where its the least crowded)
- Patterned substrates (cells will grow in a groove)
Hertwigs rule and its significance
Cells predominantly orientate their divison plane in direction of reducing mechanical stress (eg earings, pregnancy). Hertwigs rule allows tissue level events to drive cell level ones
Planar cell polarity mechanisms
sense of direction within a sheet of cells. (eg apical basal polarity) Done by having different proteins at either end that tell cell its orientation. (eg mitosis microtubules) (eg. neural tube closed by cells pushing towards each other and follic acid)
Follic acid needed for neural tube formation or else spina bifida occurs
How does the gut grow?
Example of unequal growth as a mechinism of morphogenesis
Gut looping from gut growing faster than the mesentery and creates looping (like flimsy tube attached to a stretched out peice of rubber)
What controls body size?
-Enviromental controls (access to nutrients eg foetal transfusion syndrome)
-Endogenous controls (genetic or temperature controls (aligators) like sexual dimorphism)
Avg hieght increased over years because of improved nutrition, increased vaccination, clean drinking water, hygeine
Vitruvian porportions vs non vitruvian
Pituitary hormones and laron syndrome have vitruvian porportions ; achondroplasia do not have vitruvian porportions
Significane of (non)vitruvian porportions
Vitruvian: shows that there is a global growth control system (ie GH, IGFI etc)
Non-vitruvian: shows that different body parts have individual mechanisms of interpreting the global signals
GH mechanism and its mutations
GH secreted by pituitary, stimulates local tissues to secrete IGFI/II. Mutated GHR results in v small porportionate person and pituitary tumor (too much GH) makes v large porportionate person
Explain rabbit leg experiement
If you stop 1 leg from growing, the other grows full size. - means limbs dont talk about their size
Release inhibition from the leg and it grows faster than the other one does - means growth plate responds less to GH as it grows away from signals
Max size is set by amount of GH and sensitivity of the cells
