Inorganic ions

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Summary

  • Inorganic ions are crucial components of cells
  • Inorganic ions have an electrical charge, owing to loss or gain of electrons.
  • A positively charged ion is called a cation, whereas a negatively charged ion is called anion.
  • Sodium, potassium and calcium ions are all important for creating membrane potentials across cell membranes. They regulate cellular homeostasis and are important in modulating important body processes such as nerve signalling, muscle contractions and water balance.
  • Other important ions include iron, phosphate, chloride and hydrogen ions, which regulate a variety of processes and help to maintain cellular and extracellular environments.

Inorganic compounds are chemical compounds that generally do not have bonds between carbons and hydrogens (C-H). More simply, they are compounds that are not organic compounds, which are generally molecules containing carbons. Inorganic ions are an important class of inorganic compound, which have important and varied roles in the cells.

Ions are particles (atoms or groups of atoms) that have an electrical charge due to gaining or losing electrons. Positively charged ions are called cations, negatively charged ions are called anions. Sometimes in relation to health and the human body, inorganic ions are referred to as electrolytes.

Inorganic ions exist in the cytoplasm and in the extracellular environment of cells, some exist in high concentrations and others exist in low concentrations. This depends on the properties of the specific ion and also the roles it has in the cells, tissues, and entire organism. Examples of different ions and some of their roles are discussed below.

Sodium ions (Na+)

A single atom of sodium (Na) becomes a sodium ion (Na+) when it loses the lone outer electron that exists in its outer orbital. This stabilises the atom (atoms are stable when their outer orbital is full). Sodium ions are important in co-transport, where they help glucose and amino acids cross cell membranes due to the presence of a Na+ concentration gradient. Sodium ions are also key in the generation of nerve impulses, as sodium ions move across the nerve cell membrane, which is important in signal transduction in the central nervous system. Other roles for sodium ions include regulating heart activity, blood volume, and salt balance in the human body. Reflecting this important role is the fact that most of the ions in blood plasma (extracellularly) are sodium ions.

Potassium ions (K+)

Potassium ions are the most common cation in animal cells (with sodium ions being the most common in the extra cellular environment). The differences in charges inside an outside the cell causes a membrane potential, a type of electric potential allowing the cells to carry out neurotransmission, contract muscles and pump the heart.

Hydrogen ions (H+)

Hydrogen ions (H+, also known as protons) are important in regulating the pH of an environment. In fact, pH is calculated based on the concentration of hydrogen ions in a solution, the more hydrogen ions there are, the more acidic the solution is. (pH = -log10[H+]). H+ ions have a huge impact on metabolic processes, because enzyme reactions and other biochemical reactions are hugely influenced by the pH of their environment. Maintaining the correct pH of bodily fluids and cells is also crucially important, a slightly acidic blood pH (even just pH 6.95) would be fatal!)

Iron (Fe2+ or Fe3+)

Iron ions are part of various biological molecules, including cytochromes and haemoglobin. Haemoglobin is the main protein involved in oxygen transport in red blood cells. Haemoglobin is made up of four protein subunits which bind to iron (Fe2+/Fe3+) in the centre of the protein. The Fe2+ ion can bind oxygen, forming an Fe3+ ion until the oxygen is released.

Calcium (Ca2+)

Calcium ions are also important in signalling pathways, where they often act as a second messenger (molecules that the cell releases in response to signalling cues), and can move into the cell cytoplasm with calcium channels. Calcium also has important roles in muscle contraction. Calcium ions are important components of bones and teeth, where they are a part of the compound calcium phosphate (calcium ions combined with phosphate ions).

Phosphate ions (PO43-)

Phosphate ions are negatively charged ions that are crucial components of nucleic acids (DNA and RNA) and in the production of ATP, a crucial molecule for energy production and storage in the cell. Phosphate ions are crucial for cell membranes, as they make phospholipids which make up the majority of membranes. Phosphate groups are also commonly added to proteins (as a post-translational modification) to regulate their function.

Chloride ions (Cl-)

Chloride ions are cations that are present in all body fluids, and important in regulating fluid balance (and cell volume), nerve signalling and maintaining cellular homeostasis. Chloride channels also exist in cells to regulate the movement of chloride ions across the cell membrane, maintaining a balance of ions inside and outside of the cell,

Magnesium ions (Mg2+)

Magnesium ions are present in all cell types, and is required for the activation of many enzymes, including ATP. Therefore, magnesium ions play diverse functional roles in cells. In plants, magnesium is required for the synthesis of chlorophyll, and is therefore necessary to drive photosynthesis. Magnesium ions require transport proteins to get in and out of the cell, as they cannot pass through the cell membrane.

Nitrate ions (NO3-)

Nitrate ions are essential in the synthesis of proteins. These ions are required by plants to synthesise proteins from the carbohydrates they make during photosynthesis.

Further reading and references:

[1]. https://www.bbc.com/bitesize/guides/ztc6w6f/revision/1 (Image sodium ions)

[2]. https://www.biotopics.co.uk/A15/Inorganic_ions.html

[3]. https://www.sciencedirect.com/book/9780444537829/biological-inorganic-chemistry