Growth 4 - Proportion

Question 1

What is the effect of mechanical stress on cell divisions?

Answer 1

it causes cell division

Question 2

Describe a mouse experiment to look at organ size

Answer 2

• remove spleen from mouse
• add multiple foetal spleens back in
• the result was the total was of all of the spleens was equal to the mass of one normal spleen
• if you do this with a thymus all of them will grow to the normal size
• contradictory

Question 3

What is the chalone theory?

Answer 3

• cells release calones and other cells detect their concentration
• not enough the organ will continue to grow
• correct amount - organs wills top dividing
• This has not been proven - they either dont exist or are in very low concentrations

Question 4

What is quorum sensing?

Answer 4

cell-cell communication about density

Question 5

Explain a model fro quorum sensing

Answer 5

• cells secrete a signal
• the cell responds to its own signals and the signals from neighbouring cells
• will respond at a certain level of signal
• if signal falls, response will stay on until a much lower concentration, and will then switch off

Question 6

Give an example of evidence foe quorum sensing

Answer 6

• nephrons in the kidney form from mesenchymal cells
• these cells aggregate and when the aggregate is large enough they change their gene expression to become epithelial cells
• in the aggregate there is strong Wnt4 expression

Question 7

What will the nephrons be if no Wnt4 produced?

Answer 7

• no nephrons form
• large mass of cells form
• Wnt4 encourages its ow synthesis

Question 8

What will the nephrons be if Li+ is added to the aggregates?

Answer 8

• Li+ minics Wnt
• small aggregates
• nephrons made but too small
• Wnt blocks the enzyme GSK3beta which blocks the TF
• anything else that blocks GSK3beta mimics Wnt4

Question 9

Explain an experiment on a chick embryo to look at motor neurone in wing formation

Answer 9

• wing bud removed - less motor neurones than before
• extra wing bud added - more motor neurones than before

Question 10

How does the embryo know how many motor neuron’s it will need in different locations?

Answer 10

• the cell produces much more motor neurone than it will need (neurotrophin independent)
• motor neurone then undergo elective cell death
• does this by the cell sending their axons out and if they don’t find a muscle there will be no neurotrophins and they will die
• axons compete for muscle fibre - if there is multiple there will only be enough neurotrophin to keep one alive

Question 11

Name 6 neurtrophins

Answer 11

• NGF - nerve growth factor
• BDNF - brain derived neurotrophic factor
• NT-3
• GDNF - glial derived NF
• CNTF - ciliary derived TF
• HGF - Hepatocyte growth factor

Question 12

What is the trophic theory?

Answer 12

• cells constantly need a signal so they can survive
• this signal inhibits cell death
• can be between or within tissues

Question 13

What is a pro to the trophic theory?

Answer 13

• if there is a mutation that makes legs larger for example, then the effect will be in both legs as survival factors will be picked up in both legs
• the larger legs will also have sufficient nerves ect