Inorganic Ions

Ions can be found in living organisms floating in solution in the cytoplasm or in body fluids. They are fundamental for several vital processes: each ion performs a specific function. Ions can be present in high or low concentrations, and fluctuation of this concentration might be helpful for cell signalling and transmission of information in the brain. However, big changes to the concentration of ions can be dangerous and have unwanted impacts.

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Table of contents

    What are inorganic ions?

    An ion is an atom (or group of atoms) with an electric charge. An ion with a positive charge is known as a cation, whilst an ion with a negative charge is known as an anion. Ions are typically paired with an ion with an opposite charge. Organic ions contain carbon, whilst inorganic ions don’t.

    Examples of inorganic ions

    There are many inorganic ions in the body. Some of the most important ones with their functions are listed below:

    • Hydrogen ions and pH.

    • Iron ions as a component of haemoglobin.

    • Sodium ions in the co-transport of glucose and amino acids.

    • Phosphate ions as components of DNA and of ATP.

    Hydrogen ions and pH

    pH is a measure of the concentration of H+ in a solution. We measure it on a scale from 1 to 14. The higher the pH (the more basic it is), the lower the concentration of hydrogen ions and vice versa. Therefore, we say that the value of pH has an inverse relationship with the hydrogen ion concentration.

    Why is maintaining pH important in living organisms?

    Maintenance of the pH of fluids in the body at approximately 7.4 is vital to ensure the metabolic processes in a cell take place in optimum conditions. If the pH is not close to 7.4, enzymes can be damaged, causing them to be denatured and ineffective. This happens because the excess hydrogen ions interact with the side chains of amino acids, changing the enzyme’s tertiary structure.

    Iron ions in haemoglobin

    Iron ions are positively charged ions that can either come as Fe2+ or Fe3+ due to their two oxidation states. Approximately 70% of the iron ions in our body are in an oxygen-binding protein called haemoglobin within red blood cells, in the form Fe2+. Four polypeptide chains, each with one Fe2+ ion present in the centre, make up haemoglobin . Haemoglobin is essential for transporting oxygen around the body. The remainder of the iron is present in a different oxygen-binding protein called myoglobin, or in other proteins such as ferritin.

    Inorganic Ions, Haemoglobin representation, StudySmarterFig. 1 - Structure of haemoglobin

    Sodium ions: co-transport of glucose and amino acids

    The body requires sodium (Na+) ions for a number of different roles, including fluid balance and nerve impulses’ conduction. The function we must learn about in detail is how sodium ions enable glucose and amino acids to be transported across cell membranes via co-transport.

    Carrier proteins along the cell-surface membrane of the small intestine will only allow glucose and amino acid molecules through if they are alongside Na+. Na+ is actively transported out of the epithelial cells that line the villi to begin the process. Remember that villi are tiny projections that line the inside of the small intestine. They absorb substances into the bloodstream. This causes the concentration of sodium ions inside the epithelial cells to be lower than inside the lumen of the small intestine - a concentration gradient has been formed. Na+ will then move down its concentration gradient and re-enter cells through the carrier proteins on the surface membrane of epithelial cells. This will allow glucose and amino acids to enter alongside Na+ at the same time.

    Inorganic Ions, Sodium Glucose co-transport, StudySmarterFig. 2 - Sodium Glucose co-transport

    Phosphate ions: components of DNA and ATP

    We write phosphate ions as PO43-. They join with other molecules to form phosphate groups. We can find these phosphate groups in DNA, RNA, and ATP. Phosphate groups allow ATP to be an ideal source of energy for cellular processes because energy is stored in the bonds between phosphate groups. So, when we break these phosphate groups, a large amount of energy is released. Also, phosphate groups in DNA and RNA enable individual nucleotides to join, forming polynucleotides.

    Inorganic Ions - Key takeaways

    • Ions are atoms (or groups of atoms) with an electric charge. An ion that doesn’t contain carbon is called an inorganic ion. This is the difference between organic and inorganic ions.

    • Hydrogen ions and pH: the concentration of hydrogen ions determines pH. Maintaining pH is key for enzyme-controlled reactions.

    • Iron ions as a component of haemoglobin: haemoglobin contains four polypeptide chains, each with an iron ion (Fe2+) in the centre. Iron binds oxygen, allowing haemoglobin to transport oxygen around the body.

    • Glucose and amino acids cannot move into a cell through carrier proteins without being transported alongside sodium ions (Na+).

    • Phosphate ions (PO43-) attached to other molecules form phosphate groups. Energy in ATP is stored between bonds between phosphate groups. In DNA and RNA, the phosphate groups also allow nucleotides to join together to form polynucleotides.

    Frequently Asked Questions about Inorganic Ions

    What are inorganic ions?

    Inorganic ions are atoms (or groups of atoms) with an electric charge that do not contain carbon.

    How do inorganic ions enter cells?

    Inorganic ions can move down a concentration gradient which is a passive process (does not use energy). They can move through protein channels in the membrane during co-transport (e.g. sodium). Inorganic ions can also move against a concentration gradient by active transport, which uses energy.

    Are ions the same as inorganic ions?

    Inorganic ions are a type of ion. Remember that an ion just refers to an atom (or group of atoms) with an electric charge. Inorganic ions are just ions that do not contain carbon.

    How are inorganic ions transported?

    They are transported by specialised carrier proteins found in the lipid bilayer.

    How are inorganic ions used in living organisms?

    Different ions have a range of different functions. The ones we need to know in detail are that hydrogen ions determine pH, iron irons make up haemoglobin, sodium ions help transport glucose and amino acids across the cell-surface membrane, and phosphate ions are a vital component of ATP and DNA.

    Test your knowledge with multiple choice flashcards

    What is pH a measure of?

    What kind of relationship does the value of pH have with the hydrogen ion concentration?

    What are the two different types of iron ion? 


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