Flashcards in Cytosolic Control of Calcium Deck (21):
Give approximate values for calcium concentration inside and outside a cell.
What is an advantage of having such a large concentration difference of calcium?
Change in calcium concentration inside the cell will occur rapidly with little movement of calcium.
Describe the function of PMCA
Expels calcium from the cell.
Calcium inside the cell increases and binds to calmodulin (a trigger protein). Ca-calmodulin binds to PMCA which removes calcium.
High affinity and low capacity
Describe the function of NCX
Secondary antiport active transporter.
Electrogenic so works best at a resting membrane potential.
Low affinity and high capacity, can be reversed.
Describe the function of calcium buffers
Limit diffusion - calcium can only travel around 0.1-0.5 micrometers before encountering a binding molecules.
Depends on the concentration of binding molecules and level of saturation
Give an example of a protein which calcium binds to alter it's function.
Describe the function of VOCC
Voltage operated calcium channel. Allows the influx of calcium into a cell.
Give an example of a ligand-gated calcium channel which is a glutamate receptor.
Describe conformation coupling and give an example of a protein which utilises it.
When the conformational change of a protein in the membrane allows it to interact with another.
CICR with VOCC
What is the function of the Gαs subunit in a GPCR?
Stimulates adenylate cyclase which increases production of cAMP so it can modify PKA.
What is the function of the Gαi subunit in a GPCR?
Inhibits adenylate cyclase so production of cAMP is reduced, decreasing PKA activity.
What is the function of the Gαq subunit in GPCR?
Stimulates phospholipase C which causes increased production of IP3 and DAG.
What is the function of the βγ subunit in GPCR?
Regulates opening and closing of channels.
Describe how depolarisation of the membrane allows calcium influx.
VOCC is opened, allowing calcium influx. This activates RyR to increase calcium release from the ER, allowing fast and explosive release of calcium.
NCX reverses after depolarisation, contributing slightly to calcium entry.
What is the major route to refill the ER?
Which organelle has non rapidly releasable intracellular calcium intake?
Describe calcium uptake into the mitochondria.
A uniporter allows calcium uptake and utilises the driving force from respiratory chain protein production. Low affinity and high capacity.
What is the role of calcium uptake into the mitochondria.
Calcium buffering - regulates pattern and extent of calcium signalling.
Stimulates mitochondrial metabolism - matches energy demand and supply.
Role in cell death - apoptosis/altered redox potential.
How are calcium stores refilled?
Recycling cytosolic calcium (e.g. SERCA)
Capacitative calcium entry (e.g. SOC)
Describe the function of SOC
Store operated channel.
Activated by 'depleted' signal from the SR/ER so more calcium will enter the cell and uptake into the ER by SERCA