Exley cell signalling 5

Question 1

What is InsP6 also known as?

Answer 1

Phytic Acid

Question 2

What was the original role of InsP6?

What other role in plants has recently been discovered?

Answer 2

1) A phosphate store for seeds

2) Activation of K+ channels in guard cells

Question 3

What are guard cells?

Answer 3

Cells found on the underside of plant leaves, which pair up to form the stomata.
They control the stomata size and therefore regulate gas exchange in the leaf

Question 4

Levels of Insp6 in guard cells increase rapidly in response to hormonal - abscisic acid stimulation. What is Abscisic acid?

Answer 4

A plant hormone originally discovered for it’s ability to regulate leaf detachment. It is also a key regulator in guard cell shape and thus gas exchange in the LEAF.

Question 5

What is found when submicromolar concentrations of InsP6 are applied to the leaf?

Answer 5

It inhibited the inward rectifying K+ channel that is an intrinsic part of the response of these cells to abscisic acid.

Question 6

Extracellular InsP6 probably originates from ___ the cell.

Intracellular InsP6 probably originates from ___ the cell.

Answer 6

Extracellular InsP6 probably originates from outside the cell (dietary).
Intracellular InsP6 probably originates from inside the cell.

Question 7

What are the roles of IP6 in animal cells? (4)

Answer 7

• mRNA export from nucleus
• inibits clathrin cage assembly - important in formation of endocytic vesicles
• Inhibits serine and threonine protein phosphatases which may regulate L type Ca2+ channels in pancreatic islet cells
• Stimulate endocytosis by activation f protein kinase C and inhibition of synaptogamin

Question 8

Recently, IP6 was shown to be bound within the core of an enzyme (an _________) involved with editing of RNA.

Answer 8

adenosine deaminase

Question 9

IP6 is a _____ regulator of the interactions of _____ with plasma membrane and nuclear signalling proteins

Answer 9

Negative regulator of the interactions of arrestin

Question 10

What are arrestins?

Answer 10

proteins with roles in desensitizing G protein-coupled receptors. Bind activated and phosphorylated receptors, rendering them refractory to extracellular stimuli.

Question 11

What is the intracellular local store inactive arrestin?

Answer 11

Arrestin-2-oligomer

Question 12

What combination of factors regulates the dissociation of arrestin oligomers and the movement of monomeric arrestin to activated receptors?

Answer 12

The combination of arrestin-2 containing a low and high affinity site for IP6 along with the changing level of free IP6 within the cell.

Question 13

Where can Arrestin-2-monomers be transported to?

Answer 13

An activated receptor to become activated arrestin-2

OR the nucleus (where nuclear binding partners might be enhanced)

Question 14

How many anions can the ligand IP6 have?

Answer 14

5

Question 15

What is the fully deprotonated form of IP6? (physiological PH)

Answer 15

H2(IP6)10-

Question 16

What is the fully protonated form of IP6? (acidic PH)

Answer 16

H6(IP6)6-

Question 17

___ will out compete ___ for binding IP6 at any pH

Answer 17

Al(III) will out compete Mg(II) for binding IP6 at any pH