calcium signalling

Question 1

why is Ca2+ an important second messenger

Answer 1

-calcium allows rapid selective and reversible binding to proteins
- this make It well suited for high affinity binding to irregular shaped pocket in proteins
- Ca2+ can bind well with negatively charged oxygens and uncharged oxygens
- Ca2+ can also co ordinate multiple ligands 7-8 usually this allows calcium ion to cross link multiple segments of the protein

Question 2

what is the distribution of Ca2+ in the human body

Answer 2

human body contains 1.2-1.4kg of calcium in the body which is in bones minerals

1.5g of calcium in the blood

Question 3

How does Ca2+ enter/exit the cell

Answer 3

• voltage gated calcium channels sense changes in the electrical potential in the plasma membrane
• the membrane depolarises in response to a hormone or a nerve impulse causing the channel to open and allow Ca2+ ions into the cell cytosol - ca2+ influx occurs
• IP3 diffuses rapidly into the cell cytosol, its rate of degradation is slow compared to Ca2+ so it can move very quickly without being destroyed, IP3 acts as a global messenger
• IP3 is generated by the action of phospholipase C on the plasma membrane
• IP3 activates a receptor on the endoplasmic reticulum which causes it to open and release ca2+ into the cell cytosol

Question 4

What else regulates intracellular Ca2+ (calcium buffers and the
mitochondria)

Answer 4

cytosolic calcium buffers modulate the shape of ca2+ signals
the change is due to
- the cytosol
- affinity for ca2+ and other metals ions
- kinetics for ca2+ binding and release
-intracellular mobility

mitochondria
- regulate cytosolic caclium concentration
- when there is a increase in calcium concentration in the cytosol then mitochondria starts taking up calcium from the cytosol

Question 5

How is the rise in intracellular Ca2+ translated into a physiological
effect (calcium sensors/switches)

Answer 5

calcium removal from the cytoplasm
- sodium calcium exchanger
-ca2+ pump which involves energy from ATP
- on the SR/ER membrane, calcium leaves using ca2+ pump also involving ATP

ca2+ sensors and switches
- troponin C- skeletal and cardiac muscle - binds to 2 calcium ions - effector is tropomyosin
- calmodulin - calcium modulated protein , binds to 4 calcium ions
- effector is ca2+ calmodulin dependent protein kinases