importance of ions in biology
1) co-transport , digestion
Specific amino acid co-transport proteins (carrier molecules) are found within the cell-surface membrane of the epithelial cells in the ileum
They transport amino acids only when there are sodium ions present
For every sodium ion that is transported into the cell, an amino acid is transported in
This occurs via facilitated diffusion, which requires the movement of molecules down their concentration gradient (from high concentration to low concentration)
Amino acids diffuse across the epithelial cell and then pass into the capillaries via facilitated diffusion
The concentration gradient of sodium ions from the lumen of the ileum into the epithelial cell is maintained by the active transport of sodium ions out of the cell and into the blood via a sodium-potassium pump at the other end of the cell
The glucose carrier proteins in the cell-surface membrane of the small intestine work in a similar way to the amino acid carrier proteins
Sodium ions and glucose molecules are co-transported into the epithelial cells via facilitated diffusion
The glucose molecules diffuse across the epithelial cell and enter the capillary at the other end of the cell by facilitated diffusion
The concentration gradient of sodium ions is maintained by actively transporting sodium ions out of the epithelial cells into the blood
2) muscle contraction
release of calcium ions from the sarcoplasmic reticulum causes tropomyosin to move away from the actin-myosin binding sites
3) action potentials
A stimulus, such as a neurotransmitter or sensory input, can cause the membrane potential to become less negative (depolarization).
Threshold Potential:
If the depolarization reaches a certain threshold, voltage-gated sodium channels open, allowing sodium ions to rush into the cell.
Depolarization:
The influx of positive sodium ions causes the membrane potential to become more positive (depolarization).
Sodium Channels Inactivation:
As the membrane potential reaches a peak, the sodium channels close and become inactive, preventing further sodium influx.
Potassium Channels Activation:
Simultaneously, voltage-gated potassium channels open, allowing potassium ions to flow out of the cell.
Repolarization:
The outflow of positive potassium ions causes the membrane potential to become more negative again (repolarization), returning towards the resting potential.
Hyperpolarization:
Repolarization often overshoots the resting potential, causing a brief period of hyperpolarization (more negative than the resting potential).
Restoration:
The Na+/K+ pump then restores the original ion concentrations, returning the cell to its resting state.
4) respiration
Ions are important in the production of ATP in respiration. NAD and FAD are coenzymes which become reduced in glycolysis, the link reaction and the Krebs cycle. The reduced coenzymes then lose their hydrogen atoms to the electron transfer chain where hydrogen is split into an electron and hydrogen ions. The hydrogen ions are pumped across the inner mitochondrial membrane which creates a concentration gradient across the membrane. They then diffuse through the ATP synthase complex in the membrane. This movement releases energy which is used to phosphorylate ADP into ATP.
Without the movement of hydrogen ions, ATP couldn't be produced so energy would not be available for muscle contractions or reactions.
5) nitrogen cycles
Nitrogen in the air is fixed by nitrogen fixing bacteria. When plants die, the nitrogen is broken down by saprobionts into ammonium ions. These ions are then converted into nitrite ions and nitrate ions by nitrifying bacteria and are absorbed by plants. These plants then convert the nitrates into other nitrogen-containing biological molecules.
If there was no production of ammonium ions, nitrogen would become trapped inside of dead organisms and the plants and animals would run out of the nitrogen that they need to produce amino acids and nucleic acids which are essential for growth.