Growth

Question 1

What are some limits to cellular growth?

Answer 1

1. transport
2. communication/coordination
3. mRNA synthesis: cell only has 1 or 2 copies of gene, limit to how much mrna can be synthesised

Question 2

What are some methods cells use to make bigger cells?

Answer 2

1. vacuoles in plants
2. syncytia eg skeletal muscle: cells fuse so multiple nuclei in cell
3. polytene chromosomes eg fruit fly salivary glands: replication of chromosomes
4. helper cells eg granulosa cells in ovarian cycle

Question 3

What is a simplified representation of the cell cycle?

Answer 3

G1 -> S -> G2 -> M

G = growth
S = DNA synthesis
M = mitosis and cytokinesis

Question 4

What is cleavage division in embryos?

Answer 4

embryos divide but stay the same size

Question 5

What are cyclins?

Answer 5

control cyclin-dependent kinases (cdks) whose abundance controls progression through the cell cycle

Question 6

What is checked at the checkpoint between G1 and S?

Answer 6

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

Question 7

What is retinoblastoma (Rb)?

Answer 7

it is a protein that inhibits genes needed for S phase
is active and inhibiting when unphosphorylated and inactive when phosphorylated

Question 8

How is retinoblastoma (Rb) regulated?

Answer 8

cyclins E or D interact with Rb

Question 9

How is activity of cyclins E and D regulated?

Answer 9

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)

Question 10

How are growth factors made and obtained?

Answer 10

cells make growth factors for one another through paracrine signalling

Question 11

What are the different types of cell division and how do they effect the morphology of a cell colony?

Answer 11

periclinal division: increases radius
anticlinal division: increases circumference
transverse division plane: increases length

Question 12

What is Hertwig’s rule?

Answer 12

in animals and in absence of over-riding factors: cells orientate their division planes in the direction that will reduce mechanical stress in tissues

Question 13

How are the gut loops formed?

Answer 13

gut is connected to mesentery, as body grows the gut proliferates much faster than the mesentery causing the gut to loop

Question 14

How do epithelial cells recognise their own polarity?

Answer 14

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

Question 15

What is meant by vitruvian and non-vitruvian proportions?

Answer 15

vitruvian proportions refer to the ideallic proportions of an organism
non-vitruvian proportions are those that go against vitruvian proportions

Question 16

How is the growth of bones regulated?

Answer 16

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

Question 17

What is the growth signal in bones?

Answer 17

FGFR3

Question 18

What are some consequences of mutation of the bone growth hormone?

Answer 18

growth plates full of chondrocytes, and premature closure of the growth plates

Question 19

What is the stress receptor in skin?

Answer 19

Piezo1

Question 20

How does stretching affect skin cell proliferation?

Answer 20

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

Question 21

What is the definition of The Trophic Theory?

Answer 21

any cell that is not told to keep itself alive will undergo programmed cell death (apoptosis)

Question 22

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?

Answer 22

density of certain molecule secreted by spleens in blood signals how big spleens need to grow

Question 23

What is the definition of quorum sensing?

Answer 23

organ secretes molecule X, has receptors for X so can detect how much of X has built up
once signal reaches threshold, response

Question 24

What is an example of an organ that performs quorum sensing?

Answer 24

kidney

Question 25

What hormone in the kidney signals that the cells have made a big enough aggregate?

Answer 25

Wnt4

Question 26

Give an example of a molecule that mimics Wnt4

Answer 26

Li+

Question 27

What is anistropy?

Answer 27

Not being the same everywhere, not growing the same in all directions.

Question 28

What is Foetal transfusion syndrome?

Answer 28

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.

Question 29

How does Growth hormone signalling function?

Answer 29

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

Question 30

How does new growth from growth plate in bones become bone cells?

Answer 30

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.