The Role Of Metal Ions In Biochemistry
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Published: Wed, 03 May 2017
Metal ions are essential for living processes. Intra and inter cellular communications rest largely on the concentration gradients of potassium, sodium, calcium ions like calcium play a significant role in blood clotting and muscle contraction, magnesium ions help in photosynthesis. Electron transfer processes are mainly based on iron proteins, transport of oxygen requires iron and copper proteins, and zinc plays an important role in regulation of DNA transcription. Metal ions have been used in bimolecular and biological processes up to a great extent that we can’t even imagine a life without metals. Through the process of evolution, metal ions have been co-opted into numerous roles in biology. Metal ions are required for so many biochemical reactions.
BASIC UNDERSTANDING OF THESE INORGANIC ELEMENTS
Metal ions were abundant in the primordial soup. It is believed that many years ago, the ocean was between 80°C and 100°C with a pH possibly as low as 6.Although the concentrations of most of these ions in the ocean are not known, the higher temperature and lower pH relative to the current ocean would have solvated a variety of ions and leached metal ions from the mineral-rich ocean beds. The more reactive metal ions may in fact have helped to drive the evolution from the RNA world to the modern protein world, where the polymer backbone is more stable to the potential side reactions induced by the metal cofactors.
MINERALS VITAL TO THE BODY
POTASSIUM-major cation (K+) is found in intracellular fluids. Excess excreted in urine, present in most of the foods. It helps in generation and conduction of action potentials in neutrons and muscle fibres.
SODIUM-it is the most abundant cation (Na+) in extracellular fluids. Some are found in bones. Normal intake of NaCl supplies more than the required amounts. It strongly affects distribution of water through osmosis. It is the part of bicarbonate buffer system. It functions in nerve and muscle action potential conduction.
MAGNESIUM- it is the important cation (Mg2+) in intracellular fluids. It is excreted in urine and feces. It is required for normal functioning of muscle and nerve tissue, it also participates in bone formation.
ZINC-it is the important component of certain enzymes. It is widespread in many foods. Zinc ions (Zn2+) are component of carbonic anyhdrase, Important in carbon dioxide metabolism, necessary for normal growth and wound healing, normal taste sensations and appetite. As a component of peptidases, it is involved in protein digestion.
CALCIUM-it is the most abundant mineral in the body, appears in combination with phosphates. Blood (Ca2+) level is controlled by parathyroid hormone. It helps in formation of bones and teeth, blood clotting, normal muscle and nerve activity, chromosome movement during cell division, glycogen metabolism, and release of hormone.
ROLE OF METAL CATIONS IN CHEMICHAL REGULATION OF HEART RATE-
Differences between intracellular and extracellular concentrations of several cat ions (e.g Na+ and K+) are crucial for the production of action potentials in all nerve and muscle fibers. It is not suprising that ionic imbalances can quickly compromise the pumping effectiveness of the heart. In particular the relative concentrations of three cations K+, Ca+ and Na+ have a large effect on cardiac function. Elevated blood vessels of K+ decrease heart rate and contractility. Excess Na+ blocks Ca2+ inflow during cardiac action potentials, thereby decreasing the force of contraction, whereas excess K+ blocks generation of action potentials. A moderate increase in interstitial Ca2+ level speeds heart rate and strengthens the
ROLE OF METAL IONS AS ENZYME ACTIVATORS
Certain enzymes need a metal ion for full activity .Removal of metal ion often results in partial or total loss of enzyme activity .The activity may be restored by replacing the original metal ion. Some such metal ions are K+,Cu+,Fe2+,Mg2+,Mn2+,Ca2+,Cu2+,Zn2+,Fe3+ etc, Common metal ions which play a role in enzyme action are mentioned below:-
1. Magnesium ions help the enzymes that catalyze the synthesis of oligosaccharides and proteins.
2. Molybdenum ions help in catalyzation of fixation of nitrogen.
3. Iron and copper ions are required in oxido-reduction reactions.
Certain mechanisms as to how the metal ions bring about activation are given below:-
DIRECT PARTICIPATION IN CATALYSIS-certain metal ions may directly participate in the oxidation reduction reactions by undergoing a valence change and thus function in electron transport system.
FORMATION OF METALLOSUBSTRATE- a metal ion combines with the substrate to form metallosubstrate, it further forms enzyme metal substrate complex, this complex further decomposes to produce product.
FORMATION OF METALLOENZYME-a metal ion may first combine with an enzyme to form a metalloenzyme, which then combines with the substrate forming an enzyme-metal substrate complex.
CONFIRMATIONAL CHANGE IN THE ENZYME-metal ions may also bring change in the enzyme molecule, converting it into an active form.
ROLE OF CALCIUM IONS IN BLOOD CLOTTING-
Clotting involves several substances known as clotting factors. These factors include calcium ions and some inactive enzymes that are synthesized by liver cells and are released into the blood stream. The extrinsic pathway begin with a substance called tissue factor released by damaged blood vessels and surrounding tissues. In the presence of other plasma proteins and calcium ions, activation of a protein. The intrinsic pathway begins with a substance, released by blood platelets. Again in the presence of calcium ions(Ca++), this pathway leads to the activation of factor. This it is due to presence of calcium ions tissue factor begins a sequence of reactions that ultimately activates clotting.
ACTIVE TRANSPORT SYSTEM IN CELLS-
There are many active transport systems in cells .Two of them are sodium potassium exchange pump and calcium pump.
1. SODIUM-POTTASIUM EXCHANGE PUMP-sodium pump is present in plasma membrane. This pump transfers Na+ and K+ ions against their concentration gradient. This process uses energy from ATP with the help of an enzyme. For each molecule of ATP used, three Na+ ions are pumped out and two K+ ions are pumped in simultaneously. This enables the cell to maintain much higher concentration of Na+ outside the cell, making the outside of the cell membrane positively charged with respect to inside. This creates and maintains the resting potential of the cell membrane. Sodium and potassium ions help the pump in controlling water contents of the cells.
ROLE OF MAGNESIUM ION IN RIBOSOMES-
Mg++ ions help in binding of the subunits together to form a ribosome when required. These ions are required for maintenance of pairing, stacking and stability of nucleotide bases.
ROLE OF METAL IONS IN VARIOUS GENERAL BIOLOGICAL ACTIVITIES-
1. Magnesium ions present in chlorophyll of green cells of plants traps the radiant energy of sunlight to synthesize carbohydrates.
2. Sodium and potassium ions maintain the membrane potential, an electrical property of plasma membrane. This electrical property plays a role in muscle contraction and nerve impulse transmission in animals.
3. Calcium and magnesium ions also assist in muscle contraction.
4. Potassium ions control movement of stomata and various movements in plants.
ROLE OF METAL IONS IN RNA BIOCHEMISTRY
With these physical properties, we can address the question of the role metal ions play in RNA biochemistry. Since each residue contains an anionic phosphodiester group, the principles of charge neutralization and electrostatic condensation dictate that cations must be closely associated with the polyanionic RNA molecule .In principle, these can be any cationic species, but in general, the condensation layer consists of the abundant surrounding monovalent and divalent ions. Mg (II) and K+ are believed to dominate in this role. Charge neutralization becomes particularly important during the process of RNA folding, as the negatively charged backbones from two or more regions of the primary sequence most come close together in space. Without cations to screen these charges, the repulsive forces generated in the close-packed structure would overwhelm the energetically favorable interactions that dictate the proper three-dimensional structure. Since there is a formal charge of -1 for every residue, RNAs carry around a sufficient number of metal ions in a condensation layer to neutralize the charge. Studies measuring the number of Mg (II) ions bound to different RNAs have borne out this expectation. The majority of these metal ions bind the RNA. Each individual counter ion is very weakly bound and in rapid exchange with more freely diffusing ions. Furthermore, they cannot be localized by most biophysical techniques because of the diversity of binding environments at any given instant. Among the metal ions that bind RNA, a subset interacts specifically. Metal ions generally bind to these sites more tightly than to the nonspecific ones. They are better localized because of discrete interactions and they cannot be as easily substituted by other ions. For that reason, these sites dictate the metal preferences of the RNA molecule as a whole. These specific sites can be further subdivided based on the role of the metal ion in the biochemistry. Metal ions can serve in structural roles, or as catalytic cofactors. Metal ion interactions may significantly affect RNA folding pathways, and controls should always be included to determine whether the conditions used resulted in the stabilization of an alternate conformation of the RNA.
INORGANIC NUTRITION IN PLANTS
In plants nutrients are classified into two parts:-
Micronutrients and Macronutrients
Micronutrients are generally present in plant tissues in large amounts. The micronutrients include potassium, calcium and magnesium.
Macronutrients are needed in very small amounts. These include iron, manganese, copper, molybdenum, zinc, boron, chlorine and nickel.
FUNCTION OF MICRONUTRIENTS:-
1. CALCIUM: – Plant absorbs calcium from the soil in the form of calcium ions. Ions are mostly present in cell vacuoles and bound in cell walls to polysaccharides. Calcium ions play following important role in plants:-
1. It controls cell permeability.
2. It is important in the formation of cell membrane.
3. It is responsible to reduce toxicity by forming calcium salts of organic acids.
4. It helps in translocation of carbohydrates and amino acids.
5. It encourages root development.
POTTASIUM:-It is absorbed as potassium ion. Potassium ions have the following physiological roles:-
1. Potassium ions are needed for growth and development.
2. A high amount of potassium ions are required in the process of protein synthesis.
3. Ions activate several enzymes.
4. They are required in maintaining cellular organization, permeability and hydration.
5. These ions help in regulating the movement of stomata.
6. Ions are needed in photosynthesis, respiration, translocation and chlorophyll formation.
MAGNESIUM:- It is absorbed by plants in the form of divalent Mg2+.it activates the enzymes of respiration,photosynthesis,respiration and are involved in the synthesis of RNA and DNA.it helps to maintain the ribosome structure. It also act as an activator of several enzymes.
FUNCTION OF MACRONUTRIENTS:-
1. IRON: – plants obtain iron in the form of Ferric ions (Fe3+).it is required ion large amounts in comparison to other macronutrients. It is reversibly oxidized from Fe2+ ions to Fe3+ during electron transfer
1. Inhibits chloroplasts formation
2. Mark cholorsis in younger leaves.
3 .iron ions are present in various proteins involved in electron transport during respiration and photosynthesis.
2. COPPER:-it is absorbed as cupric ions. Main functions of these ions are involved in:-
1. It is associated with certain enzymes’ involved in redox reactions and it is reversibly oxidized from Cu+ to Cu2+.
2. Copper ions are involved in various proteins involved in oxidation reduction reactions.
3. ZINC:-plants obtain zinc as Zn2+ ions. Main functions are:-
1. Ions help in activating various enzymes, zinc ions are essential for functioning of various enzymes.
2. Zinc ions participate in chlorophyll formation.
3. It is needed in synthesis of auxin (growth hormone)
4. MOLYBDENUM: – plants obtain it in the form of molybdate ion. It is the component of several enzymes, including nitrogenase and nitrate, which are necessary for nitrogen metabolisms.
5.MANGANESE:- it is absorbed in the form of manganous ion(Mn2+).main functions in which ions are involved are:-
1. They are involved in photo oxidation of water and evolution of molecular oxygen in photosynthesis.
2. Plays a structural role in choloroplasts membrane system.
3. They activate enzymes involved in photosynthesis, respiration and nitrogen metabolism.
4. Test defined function of manganese ions is in the spilling of water to liberate oxygen during photosynthesis.
MECHANISM OF MUSCLE CONTRACTION:-
In the resting muscle fibre, the outside of sarcollema is positively charged with respect to inside.The potential difference across a membrane is called resting potential.A membrane with a resting potential is said to be polarized.It is maintained by Na+ and K+ ions. Sodium ions predominate on the outside of the sarcolemma and K+ ions predominate on the inside.sodium ions are pumped out and K+ ions enter inside by active transport.
The process of moving ions against their concentrations is called sodium potassium exchange pump. The Na+ and K+ ion helps the pump conduction in muscle contraction,
KEY ROLE OF CALCIUM IONS IN MUSCLE CONTRACTION
Calcium ions bind to troponin causing a change in its shape and position. This in turn alters the shape and the position of myosin,to which tropomin binds.This shift exposes the active sites on a molecule.Myosin cross bridges and then able to bind to the active sites. It is in the presence of calcium and magnesium ions, myosin and ATP breaks into ADP releasing energy. All muscle fibers use Ca2+ as their main regulatory and signaling molecule. In short muscle contraction is regulated by calcium ions, which will change thin filament into an activated state by binding to troponin.
KEY ROLE OF Ca2+ ION IN MUSCLE RELAXATION
The sodium calcium exchanger is a passive system that allows for ion exchanges along an electrochemichal gradient.the pump operates to extrude one calcium ion from the cytosol by exchanging it for one sodium ion on a one to one molar ratio.When the cell membrane is depolarized,these pump may become uncoupled and allow for calcium influx.
This exchange pump does not use the energy directly to affect these ions.
Relaxation of the cell is accomplished by pumping calcium out of the cell.or into sites within the cell.ion pump translocates the calcium ion against large gradients.
ROLE OF IRON IONS IN HAEMOGLOBIN (AN OXYGEN CARRIER):-
The property of iron to form complexes is also important in haemoglobin.Haemoglobin in the blood is responsible for carrying oxygen around the body during respiration.Haemoglobin contains four large polypeptide groups and four iron ions surrounded by ligands known as haem groups, a group essential for the protein to be able to carry out its function. At high oxygen concentrations, haemoglobin binds to oxygen molecules. In this process oxygen bonds onto the iron ion in the haem group as an extra ligand.At low concentrations the reverse process occurs.
In these proteins, chemical properties of metal surrounding the region, plays a key role in modulating the overall activity. Metal ions in metalloproteins are well located inside a polypeptide chain which provides the ligands and tunes the hydrophobic or hydrophilic character of region around them e.g. in carboxypeptidase a large pocket near the zinc ion accommodates the side chain of the terminal residue of the peptide substrate, thus zinc ions help both in binding the substrate and polarizing the peptide bond.
ROLE OF CALCIUM IONS IN NEUROCHEMISTRY-
In the field of neurochemistry, calcium ions are involved in the release of neurotransmitters from nerve cells, and an instructive connection can be made with the release and initiation of transcription. Calcium ions bind to the effector protein that trigger enzymatic and cellular responses. Ca2+ is the major component of the signaling pathways that regulate epithelial cell secretion which include both discharge of proteins and regulation of transepithelial secretion of salts and water, and carbohydrate metabolism in the liver
ROLE OF METAL IONS IN DNA SYNTHESIS:-
The various stages of DNA replication require metal ions.DNA replication is a vey complex process in which a variety of enzymes are involved. The enzyme copies one strand of DNA by incorporating complementary bases from nucleoside triphosphates which are attached with the growing chain with the loss of pyrophosphate. The enzymes contain tightly bound zinc. There is the evidence that zinc ions bind the enzyme to DNA to fulfill its function the enzyme also must be activated by a divalent magnesium and manganese ion. These metal ions serve to bind the nucleoside triphosphate substrates to the enzyme. Metal ions participate in enzymatic reactions. Enzyme bound metal ions modify the structure of the substrate molecule. Thus the metal ions seem to facilitate the rearrangement in the structure of the substrate that is necessary to place in into the double helix.
RESULT AND DISCUSSION:-
I have discussed about the role of metal ions in various biochemical processes occurring both in plants and human beings like respiration, muscle contraction, explanation of micro and macro nutrients, RNA and DNA synthesis, in neurochemistry. I have individually explained the role of zinc, iron, magnesium, coppers ions in detail which help in biochemical processes. Metal ions are used in various intercellular and intracellular processes. Metal ions helped greatly in the revolution of DNA and RNA.
As we have seen that metal ions are involved in various day to day processes occurring both in plants and human beings. They are absorbed in the form of metal ions as nutrients which are essential for growth and development. Thus life without metal ions cannot be imagined .
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