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Calcium Signalling - Term 1 Human Body Notes
Term 1 Human Body Notes
Module
The Human Body (PY4010)
171 Documents
Students shared 171 documents in this course
University
Kingston University
Academic year: 2021/2022
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\azCalcium Signalling
To appreciate some of the properties of the calcium ion (Ca2+) that make it
useful as an intracellular second messenger
The chemistry of calcium ions allows rapid, selective and reversible binding to proteins. This
makes it well suited for high affinity binding to irregular shaped pockets in proteins. Some
properties that allow this are its ionic radius, polarizability, hydration energy and hydrated ions.
Why calcium?
• Ca2+ can bind well with both negatively charged oxygens and uncharged oxygens
• Ca2+ can co-ordinate multiple ligands, typically 7-8 but up to 12. This enables calcium ion
to cross link multiple segments of a protein.
The human body contains calcium, most of which is present as bone minerals in the form of
calcium phosphate. Also, in the blood and in extracellular fluid.
Calcium in the cell is located in stores in the endoplasmic reticulum, or it the cytosol (semi-
fluid substance filling the interior of the cell and embedding the other
organelles and subcellular compartments).
•To understand some of the limitations of Ca2+ ions as second messengers
within the cell cytosol
The diffusion of calcium in the cell cytosol is very slow. This can be due to barriers as the sub-
cellular architecture is very complex.
Also, the cell can contain proteins that will bind to calcium.
So, calcium acts as a LOCAL MESSANGER. This means it will act close to the area that it enters
the cytosol.
•To appreciate the importance and wide spread nature of Ca2+ signalling
pathways in nature
Calcium signalling is very widespread. Eg- fertilization, contraction and exocytosis
•To appreciate the mechanisms by which Ca2+ ions enter and exit the cell
cytosol–
• Across the plasma membrane via ion channels and Calcium exchangers
• From internal Ca stores via ion channels and Ca pumps
The rising phase: voltage gated ion channels, ER/SR channels & triggers
How does Calcium enter the cell?
Voltage gated calcium channels in the plasma membrane sense changes in the electrical
potential of the plasma membrane. The membrane depolarizes in response to a hormone or a
nerve impulse, causing the channel to open and allow calcium ions into the cell cytosol. This
happens RAPIDLY. A calcium influx occurs.
Often targets for calcium are deep inside the cell, which are inaccessible for calcium ions that
enter via the plasma membrane. Internal calcium stores in the endoplasmic reticulum
overcomes this problem. Calcium can be released exactly when needed.
IP3 diffuses very rapidly in the cytosol. Its rate of degradation is slow compared to calcium 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 membrane which causes it to open and release calcium
ions into the cytosol.
Plasma membrane: Voltage gated calcium channels Dihydropyridine receptors (DHPR)
SR membrane: Ligand\Physico mechanical) gated calcium channels: Ryanodine receptors
What else regulates intracellular Ca2+ (calcium buffers and the mitochondria)
Cytosolic calcium buffers- modulate the shape of Ca2+ signals. How the buffers affect the change
in calcium depends on:
- The cytosol
- Affinity for Ca2+ and other metal ions
- Kinetics of Ca2+ binding and release
- Intracellular mobility (whether the buffers are mobile or immobile)
Mitochondria- Regulate cytosolic calcium concentration. When there is an increase in calcium
concentration in the cytosol, the mitochondria start taking up calcium from the cytosol.
How is the rise in intracellular Ca2+ translated into a physiological effect 9calcium
sensors/switches)
Calcium removal from the cytoplasm:
- Sodium, calcium exchanger
- Ca2+ pump which involves energy from ATP
- On the SR/ER membrane, calcium leaves via a Ca2+ pump also involving ATP.
Calcium signalling to effectors, which will detect a change in calcium concentration. These
molecules are called calcium sensors or switches
Eg- Troponin C which is specific to skeletal and cardiac muscle. The effector is tropomyosin.
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Calcium Signalling - Term 1 Human Body Notes
Module: The Human Body (PY4010)
171 Documents
Students shared 171 documents in this course
University: Kingston University
Was this document helpful?
\\azCalcium Signalling
To appreciate some of the properties of the calcium ion (Ca2+) that make it
useful as an intracellular second messenger
The chemistry of calcium ions allows rapid, selective and reversible binding to proteins. This
makes it well suited for high affinity binding to irregular shaped pockets in proteins. Some
properties that allow this are its ionic radius, polarizability, hydration energy and hydrated ions.
Why calcium?
•Ca2+ can bind well with both negatively charged oxygens and uncharged oxygens
•Ca2+ can co-ordinate multiple ligands, typically 7-8 but up to 12. This enables calcium ion
to cross link multiple segments of a protein.
The human body contains calcium, most of which is present as bone minerals in the form of
calcium phosphate. Also, in the blood and in extracellular fluid.
Calcium in the cell is located in stores in the endoplasmic reticulum, or it the cytosol (semi-
fluid substance filling the interior of the cell and embedding the other
organelles and subcellular compartments).
•To understand some of the limitations of Ca2+ ions as second messengers
within the cell cytosol
The diffusion of calcium in the cell cytosol is very slow. This can be due to barriers as the sub-
cellular architecture is very complex.
Also, the cell can contain proteins that will bind to calcium.
So, calcium acts as a LOCAL MESSANGER. This means it will act close to the area that it enters
the cytosol.
•To appreciate the importance and wide spread nature of Ca2+ signalling
pathways in nature
Calcium signalling is very widespread. Eg- fertilization, contraction and exocytosis
•To appreciate the mechanisms by which Ca2+ ions enter and exit the cell
cytosol–
•Across the plasma membrane via ion channels and Calcium exchangers
•From internal Ca stores via ion channels and Ca pumps
The rising phase: voltage gated ion channels, ER/SR channels & triggers
How does Calcium enter the cell?
Voltage gated calcium channels in the plasma membrane sense changes in the electrical
potential of the plasma membrane. The membrane depolarizes in response to a hormone or a
nerve impulse, causing the channel to open and allow calcium ions into the cell cytosol. This
happens RAPIDLY. A calcium influx occurs.
Often targets for calcium are deep inside the cell, which are inaccessible for calcium ions that
enter via the plasma membrane. Internal calcium stores in the endoplasmic reticulum
overcomes this problem. Calcium can be released exactly when needed.
