Growth

Question 1

Anisotrophy

Answer 1

Growing and changing shape.

Question 2

Porportionality

Answer 2

Organisms have porportions (ie vetruivian man)

Question 3

Adaptability

Answer 3

Adpating where/how organisms grow to their envrionment (ie vines)

Question 4

Discontinous scaling

Answer 4

Ie. humans- our organs scaled to our bodies but cells the same size as every other organsims

Question 5

Discontinous scaling

Answer 5

Ie. humans- our organs scaled to our bodies but cells the same size as every other organsims

Question 6

Limits on cell size

Answer 6

mRNA synthesis is rate limiting on cell size. Also transport and communication issues.

Question 7

Tricks to make cells bigger

Answer 7

• 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)

Question 8

Cell cycle order

Answer 8

1. mitosis
2. G1(first growth)
3. S-phase (synthesis)
4. G2 (second growth)

Question 9

What is cleavage division and why is abnormal?

Answer 9

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)

Question 10

What are cyclin and CDK’s?

Answer 10

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

Question 11

How do cyclins and CDK’s control cell cycle

Answer 11

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.

Question 12

Explain the G1-S checkpoint

Answer 12

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

Question 13

Example of dysfunction of the checkpoints

Answer 13

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

Question 14

Paracrine signalling and potential consequences

Answer 14

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.

Question 15

Cell cycle and cancer cells

Answer 15

They 1. ignore stop signals
2. misinterpret growth signals
3. Damage crowding sensors

Question 16

What are sources of anisotrophic growth?

Answer 16

1. Diffusion limited growth (eg. Bacillus subtilis, the outermost cells will get the most nutrients bc the nutrients dont have to diffuse as far)
2. Direct cell division (eg A. Thaliana replicates vertically and then one horizantal divison) (important in non-motile organisms ie plants n fungi)
3. Crowding cells (cells will grow where its the least crowded)
4. Patterned substrates (cells will grow in a groove)

Question 17

Hertwigs rule and its significance

Answer 17

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

Question 18

Planar cell polarity mechanisms

Answer 18

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

Question 19

How does the gut grow?

Example of unequal growth as a mechinism of morphogenesis

Answer 19

Gut looping from gut growing faster than the mesentery and creates looping (like flimsy tube attached to a stretched out peice of rubber)

Question 20

What controls body size?

Answer 20

-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

Question 21

Vitruvian porportions vs non vitruvian

Answer 21

Pituitary hormones and laron syndrome have vitruvian porportions ; achondroplasia do not have vitruvian porportions

Question 22

Significane of (non)vitruvian porportions

Answer 22

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

Question 23

GH mechanism and its mutations

Answer 23

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

Question 24

Explain rabbit leg experiement

Answer 24

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

Question 25

Explain bone growth and growth plate

Answer 25

IGFI comes from the liver, PTHrp comes from sheath of bone, and tells cells to proliferate. Bone cells are telling (secrete CNP) the proliferating cells to mature (ie calcify and die leaving behind space for bone cells to fill). Maturation of cells stimulates secretion of Indian hedgehod which stimulates sheath of bone to secrete PTHrP= feedback loop

Question 26

Significance of long feedback loop in providing feedback

Answer 26

when bone=small, distance from bone to growth plate is small so it grows fast bc strong signals
When bone = large, distance from bone to growth plate is big so doesnt grow fast because weak signals
So its a self correcting negative feedback loop!

Question 27

Achondroplasia, why is it non-vitruvian?

Answer 27

FGF signalling (via FGFR3) stops chondrocytes from differentiating/proliferating. Mutation in FGFR3 = loads of choanocytes = growth plates close early.

Achondroplasia= super short limbs and normal trunk

Question 28

Are tissues independent of one another?

Answer 28

No. Achrondroplasia demonstrates this, bc the amt of skin/tendon/muscle is still correct for shortened limb so tissues are not independent of one another. However, shows that body parts are slightly independent bc the trunk grew anyways even tho the limbs didnt.

Question 29

What is mechanosensation?

Answer 29

Mechanism skin uses, apply force to the skin and it grows that way (pregnancy, obesity, tumors etc). Its how the skin is always porportionate to limb growth no matter what. Mechanosensation is scale free.

Question 30

Evidence for mechanosensation

Answer 30

-Cells grew in corners when put in a metal square grid and sprayed with cell-deterent spray - grew bc corners are a point of stress
- stretched cells grow rapidly. Piezo1 stretchs cells and triggers them out of G2 (triggers CdkERK1/2 phosphorylation that activates cyclin B that activates mitosis)
-

Question 31

Growth without mechanical stress

Answer 31

Potentially KHLAOE? Fetal spleen grew to the total mass of the removed adult spleen. But fetal thymus EACH grew to mass of removed adult thymus. So dont know!

Question 32

Quorum sensing

Answer 32

Bacteria divide until they have reached a quota (through autocrine signalling)

Question 33

What affect does Wnt4 have on the Kindeys?

Answer 33

If you take Wnt4 away the mesenchymal aggregate continues to grow (doesnt know its size), if you replace it with Li then it doesnt grow at all (thinks its already big). Strong Wnt4 expression tells mesenchymal cells to stop growing.
- Evidence for quourm sensing

Question 34

Whats the trophic theory and elective cell death?

Answer 34

Elective cell death means that cells are predensitined to die unless they have signals telling them not to. This is bc embryonic cells over proliferate and any unneeded cells are marked for death. Trophic theory explains why the amt of neurons will match the size of the limbs.

Question 35

What dictates limb size/tissues size?

Answer 35

Size is due to cell signalling- only bone is directly affected by genes