17 - Proteolysis Based Signalling - Williamson

Question 1

what are the simple molecules involved in the reversible, low energy signalling pathways we have seen?

Answer 1

phosphates, Ca release, cGMP/cAMP, GTP binding

Question 2

give an example covered of irreversible signalling, state briefly how we get activation of this signalling pathway

Answer 2

• auxin signalling

- signal turned on following degradation of inhibitor using Ub / proteasome

Question 3

name 3 more pathways whose pathways invovle protein degradation. state broadly what these pathways are invovled in

Answer 3

• Notch, Wnt, Hedgehog

- cell differentiation and development hence why irreversible

Question 4

what is notch and name its ligands

Answer 4

notch is a R

L= Delta, Jagged, Serrate (first observed in Dropsophila and have funny wing shapes)

Question 5

what is the function of notch signalling? give an example of this and draw a diagram

Answer 5

• notch signalling causes lateral inhibition
• differentiated cells (expressing notch) will prevent neighbouring cells differentiating into the same cell type (when the neighbouring cells express Notch ligand - eg delta)
• this is apparent in early embryo development when we have one cell developing into neuron which prevents surrounding cells also developing into neurons

Question 6

draw a diagram showing processing of the notch receptor and state the functions of notch signalling

Answer 6

• Notch has extracellular domain, TM and intracellular domain
• Notch controls;
  maintenance and self-renewal of Stem cells
  cell cycle progression
  differentiation
• can also function as both an oncogene and tumour suppressor in different cells

Question 7

how does cleavage of the intracellular part of notch occur?

how was this protein first identified?

Answer 7

protease named Presenilin
firs identified in Alzheimer’s patients, cleaved AB into amyloid precursor protein
- could having a drug effective against Notch signalling be effective in Alzheimer’s ?

Question 8

give the overall way that Drosophila controls its body plan;

a) Front and back ends
b) function of gap genes
c) function of pair rule genes
d) how to make segment boundaries

Answer 8

a) diffusion of inhibitor/activator proteins from both ends making diffusion gradients along the body. bicoid determines anterior/front end
b) gap genes inhibited or activated AND expressed in bands down body. eg Kruppel activated by bicoid but inhibited by Hunchback therefore in the middle of the embryo
c) pair rule genes are expressed in these bands. but different levels at each end, auto regulated to make them sharper. eg Eve2 needs bicoid and hunchback for activation but repressed by giant on one side and Kruppel on the other
d) segment polarity genes build on these divisions to make sharply defined segment boundaries eg hedgehog, wingless

Question 9

what are the functions of homeobox genes?

Answer 9

target features to different segments

Question 10

name the 3 Drosophila proteins that can reinforce eachother and draw a diagram of this

Answer 10

• Wnt, hedgehog and engrailed can all reinforce each other to form segment boundaries
• hedgehog maintains wingless transcription and wingless maintains hedgehog transcription. paracrine signalling

Question 11

draw a diagram highlighting Wnt signalling

Answer 11

343 - 17 word

Question 12

what is the human name for Wnt?

Answer 12

wingless

Question 13

how does Wnt travel from cell to cell?

Answer 13

secreted attached to extracellular vesicles therefore does not diffuse far

Question 14

what is the B catenin equivalent in Drosophila? describe its structure

Answer 14

called Armadillo

many a helices -linear recognition protein

Question 15

in Drosophila, what is another protein (in addition to Wnt) involved in the segment pair determination system? why is it called this name? give the alternative names for this protein in humans.

Answer 15

Hedgehog, called this because mutation of the gene in larvae -> spiky
humans; Sonic, Desert and Indian

Question 16

give the functions of hedgehog in flies, worms and other animals

Answer 16

• flies and worms, key for segmented body plan

- other animals; key for spinal cord development, fingers, teeth

Question 17

what are some of the defects in hedgehog?

Answer 17

can cause eye abnormalities eg cyclopia

Question 18

describe the structure of the hedgehog protein, ie where it is attached and explain how it reaches its target

Answer 18

hedgehog attached to cholesterol at one end and is palmitolyated at the other - therefore attaching it to the membrane
- secreted potentially attached to vesicles giving rise to short range signal

Question 19

draw a diagram showing how hedgehog signalling works

Answer 19

343 - 17 word

Question 20

what happens In the presence of hedgehog protein?

Answer 20

hedgehog R patched is continually internalised and degraded.

Question 21

how does this hedehog signalling act as a good switch of protein expression

Answer 21

• the Ci protein acts as a v good switch because actively turns ON/OFF genes
• intact Ci enters nucleus, activates transcription
• degradation of Ci leaves a fragment which enters the nucleus and is a transcriptional repressor

Question 22

what is the function of NFkB signalling?

Answer 22

normally in inflammation and innate immune response. also important in memory
- also found in development eg dorsal/ventral patterning

Question 23

draw a diagram outlining NFkB signalling

Answer 23

343 - 17 word