lecture 19

Question 1

what is the hierarchical organisation of intracellular Ca2+ signalling?

Answer 1

-stimulation of cell with intermediate level of order to see the stages

Question 2

what does an intermediate amount of hormone generate?

Answer 2

-intermediate amount of IP3 receptor (enough to enable cluster of 10 IP3 receptors to behave as CICR channels)
-not enough ip3 to diffuse to enable each receptor and cause CICR (as intermediate leave of stimulant)
-elementary calcium signalling

Question 3

what does increasing stimulation generate?

Answer 3

-more IP3
-more IP3 receptors acting as CICR channels
-more Ca2+ released

Question 4

what are the two types of elementary event?

Answer 4

puff (when IP3 is the receptor)
spark (when RyR is the receptor)

Question 5

when does an abortive wave occur?

Answer 5

between cusp of intermediate and high stimulation

Question 6

how does a fundamental event occur?

Answer 6

-low stimulation
-little IP3 in cell and little receptors
-Ca2+ release detected from one receptor

Question 7

what are the two types of fundamental event?

Answer 7

calcium blip = receptor is IP3
calcium quark = receptor is RyR

Question 8

what are elementary release events?

Answer 8

physiological signals

Question 9

how does muscle contraction and relaxation occur?

Answer 9

-smooth muscle cell produces elementary wave- near calcium activated potassium channel in the membrane
-highly localised sparks cause channel activation if within vicinity
-K+ leaves cell down conc grad = more negative cell = hyper polarisation = muscle relaxation

Question 10

what is contraction triggered by?

Answer 10

global calcium wave

Question 11

what is relaxation triggered by?

Answer 11

elementary signal

Question 12

what causes the cilia to start beating?

Answer 12

calcium propagation

Question 13

how does the calcium signal move between cells?

Answer 13

-cells connected by gap junctions
-cytosol of one is continuous with cytosol of neighbouring cells
-IP3 produced in stimulating cell could move through gap junction/ calcium moves via CICR
-both IP3 and Ca2+ needed to move throughout junction - no propagating calcium wave if not

Question 14

what is an example of where Ca2+ is decoded into a physiological response?

Answer 14

glycogen breakdown in the liver

Question 15

how is the Ca2+ signal decoded into a physiological response?

Answer 15

-Ca2+ binds to its sensing protein (calmodulin)
-Ca2+ calmodulin activates an enzyme called Ca2+ calmodulin dependent kinase 2
-this phosphorylates enzyme phosphorylase kinase (using ATP for source of phosphate)
-phosphorylase kinase phosphorylates its substrate phosphorylase (source is ATP)
-activates phosphorylase enzyme which converts glycogen to glucose

Question 16

what enzyme converts glycogen to glucose?

Answer 16

phosphorylase

Question 17

if you increase frequency of spikes do you get more glucose?

Answer 17

yes- different frequencies of spikes are decoded into different amounts of enzyme activity