lecture 16 - the phosphoinositide signalling pathway and Ca2+

Question 1

calcium prevents polysperming by

Answer 1

raising fertilisation envelope

Question 2

calcium phosphate is highly insolube

Answer 2

so calcium is used in processes to keep levels low

Question 3

off mechanisms

Answer 3

Ca-ATPase pump (PMCA, SERCA) :pumps calcium ions out the cell against the concentration gradient
PMCA - on the plasma membrane
SERCA - on the membrane of the ER

Question 4

2nd mechanism

Answer 4

Na/Ca exchanger, exchanges calcium ions for sodium ions driven by inward sodium gradient. sodium potassium sets up the sodium gradient

Question 5

3rd mechanism

Answer 5

mitochondria takes up calcium ions

Question 6

4th mechanism

Answer 6

protein binds to calcium ions. Eg buffers act like a sponge and mop ip the calcium ions, sensors also bind to calcium ions

Question 7

intracellular ion channel in the membrane of the ER is called the

Answer 7

InsP3R, it is a receptor for the second messenger InsP3 when activated calcium comes rushing out eh ER into cytosol

Question 8

ryanodine receptors are also in the membrane of the ER and they release calcium but not activated by InsP3

Question 9

3 types of Ca signal

Answer 9

elementary events - very small, calcium rise occurs in one specific location of the cell
global calcium wave (intracellular) - calcium wave begins in one part of the cell and makes its way across the rest of the cell
global calcium wave (intercellular) - calcium wave doesn’t stop at the boundary of the cell, propagates throughout a monolayer of cells

Question 10

PI pathway

Answer 10

1. chemical signal induces a conformational change in a 7 membrane spanning receptor
2. the III cytoplasmic loop of the receptor activates a G protein
3. G protein stimulates an amplifier, phospholipase C (PLC)
4. PLC acts on PIP2 to give DAG and IP3 which are both second messengers
5. DAG acts with the plane of the lipid bilayer to stimulate its effector protein kinase C (PKC)
6. IP3 diffuses into the cytosol where it acts on ion channels to release calcium stored up in the ER
7. the onset of the calcium signal is augmented by a process of calcium induced calcium release (CICR)
   calcium can act through a protein kinase or it can use specific binding proteins (calmodulin, troponin C) to induce contraction in muscle cels or it can act directly on ion channels to influence excitability

Question 11

fatty acid chains in inner layer of plasma membrane
attached to inositol (6 carbon sugar)
attached to phosphate groups
this is PIP2

Answer 11

PLC-beta clips PIP2 molecule between the CH2 and oxygen
leaving DAG in the membrane which activates protein kinase C
also leaves IP3 which is negatively charge and soluble so it immediately binds to its receptor InsP3R in the ER and causes calcium release from the ER