• An?ion?is an atom (or sometimes a group of atoms) that has an?electrical charge
  • An ion that has a?+ve charge?is known as a?cation
  • An ion that has a?-ve charge?is known as an?anion

   

• An?inorganic ion?is an ion that?does not contain carbon
• Inorganic ions play an?important role?in many?essential cellular processes
• Inorganic ions?occur in solution?in the?cytoplasm?and?body fluids?of organisms
  • Some occur in?high concentrations?and others in very?low concentrations
  • The concentration of certain ions can fluctuate and can be used in?cell signalling?and?neuronal transmission
  • Each type of inorganic ion has a?specific role, depending on its?properties

   

• Some inorganic ions act as?cofactors
  • Cofactors are?non-protein chemical compounds?that are required for a protein to function

   

• You should know the following inorganic ions, as well as their properties and roles in the body:
  • Hydrogen?ions (H+)
  • Calcium?ions (Ca2+)
  • Iron?ions (Fe2+/Fe3+)
  • Sodium?ions (Na+)
  • Potassium?ions (K+)
  • Ammonium?ions (NH4+)
  • Nitrate?ions (NO3-)
  • Hydrogen carbonate?ions (HCO3-)
  • Chloride?ions (Cl-)
  • Phosphate?ions (PO43-)
  • Hydroxide?ions (OH-)

   

Hydrogen ions

• Hydrogen ions are protons
• The?concentration of H+?in a solution determines the?pH
• There is an?inverse relationship?between the pH value and the hydrogen ion concentration
  • The?more H+?ions present, the?lower the pH?(the more acidic the solution)
  • The?fewer H+?ions present, the?higher the pH?(the more alkaline the solution)

   

• The concentration of H+?is therefore very important for?enzyme-controlled reactions, which are all affected by pH
  • The fluids in the body normally have a pH value of approximately 7.4
  • The?maintenance?of this normal pH is essential for many of the?metabolic processes?that take place within?cells
  • Changes in pH can affect?enzyme structure
  • For example, abnormal levels of hydrogen ions can interact with the?side-chains?of amino acids and change the?secondary?and?tertiary?structures of the proteins that make up enzymes
  • This can cause?denaturation?of enzymes

   

Calcium ions

• Ca2+?is essential in the?movement?of organisms:
  • In?synapses, calcium ions regulate the?transmission?of impulses from neurone to neurone

   

• Ca2+?also stimulates?muscle contraction
  • When an impulse reaches a muscle fibre, Ca2+?is released from the sarcoplasmic reticulum
  • This Ca2+?binds to troponin, removing the tropomyosin from myosin-binding sites on actin
  • This allows actin-myosin cross-bridges to form when the muscle fibre contracts

   

• Ca2+?can also help to?regulate protein channels, which affects the?permeability?of cell membranes
• Many enzymes are?activated?by Ca2+, making these ions key regulators in many biological reactions
• The presence of Ca2+?is also necessary for the?formation of blood clots?(it is known as a?clotting factor?or a cofactor)

Iron ions

• There are actually?two?versions of iron ions (known as?oxidation states)
  • Iron (II) ions, also known as ferrous ions (Fe2+)
  • Iron (III) ions, also known as ferric ions (Fe3+)

   

• Iron ions are essential as they can bind oxygen
  • Haemoglobin?is the large protein in red blood cells that is responsible for?transporting oxygen?around the body
  • Haemoglobin is made up of four polypeptide chains that each contain one?Fe2+
  • This Fe2+?is a key component in haemoglobin as it?binds to oxygen
  • Myoglobin?in muscles functions in a similar way (it is an oxygen-binding protein) but is only made up of?one?polypeptide chain (containing?one?Fe2+)

   

• Iron ions are also essential as they are involved in the?transfer of electrons?during?respiration?and?photosynthesis, so they are key to the biological generation of energy
  • Iron ions are an essential component of?cytochromes?(that are themselves a component of?electron transport chains)
  • Cytochrome c contains an iron ion that is essential to its function
  • During the electron transport process, this iron ion switches between the?Fe3+?and?Fe2+?oxidation states, which allows for electrons to be?accepted?and?donated

   

Sodium ions

• Na+?is required for the?transport?of?glucose?and?amino?acids?across cell-surface membranes (e.g. in the small intestine)
  • Glucose and amino acid molecules can only enter cells (through carrier proteins)?alongside Na+
  • This process is known as?co-transport
  • First, Na+?is?actively transported?out of the epithelial cells that line the villi
  • The Na+?concentration inside the epithelial cells is now?lower?than the Na+?concentration in the?lumen?of the small intestine
  • Na+?now?re-enters?the cells (moving down the?concentration gradient) through?co-transport proteins?on the surface membrane of the epithelial cells, allowing glucose and amino acids to enter at the same time

   

• Na+?is also required for the?transmission of nerve impulses

Potassium ions

• K+?is essential for?nerve transmission
  • Potassium ion voltage-gated channel proteins?in a section of axon membrane?open, allowing the diffusion of potassium ions?out of the axon, down their concentration gradient. This?returns?the potential difference across the axon membrane back to?normal?(about -70mV) – a process known as?repolarisation

   

• K+?allows for the?reabsorption of water?in the kidneys
• Potassium ions also play an important role in guard cells and the?opening? of the stomata

Ammonium ions

• NH4+?is the intermediate ion that forms during the?deamination?of proteins in the liver and kidneys

Nitrate ions

• NO3-?ions are present in the?soil?and are taken up by plants
• NO3-?provides an essential?source of nitrogen?for?protein synthesis
• Proteins are required for growth and repair in plants

Hydrogen carbonate ions

• HCO3-?ions work alongside hydrogen ions in the?transport of carbon dioxide in the blood

Chloride ions

• Cl-?ions are also involved in the transport of carbon dioxide in the blood
• These ions move in and out of red blood cells and help to?maintain pH balance

Phosphate ions

• PO43-?attaches to other molecules to form?phosphate groups, which are an essential component of?DNA, RNA and ATP
• In DNA and RNA, the phosphate groups allow individual?nucleotides?to?join up?(to form polynucleotides)
• In ATP, the bonds between phosphate groups?store energy
  • These phosphate groups can be?easily?attached or detached
  • When the bonds between phosphate groups are broken, they release a?large amount of energy, which can be used for?cellular processes

   

• Phosphates are also found in?phospholipids, which are key components of the phospholipid bilayer of cell membranes

Hydroxide ions

• OH-?ions play a vital role in?bonding?between biochemical molecules
• One oxygen atom is covalently bonded to one hydrogen atom
• The electronegative charge of the oxygen allows for the formation of?hydrogen bonds
• Hydrogen bonds are important in many molecules
  • DNA base pairing
  • Secondary, tertiary and quaternary protein structure
  • Water

   

Inorganic Ions Table