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In general chemistry, we come across the term matter, which is defined as anything that takes up space and volume and has a mass. From this, we can define what an atom is. The smallest unit of matter that cannot be broken down is called an atom. The atom also contains electrically charged particles such as the proton, neutron and electron, which have a positive charge, no charge and negative charge, respectively, smaller than an atom’s size. Although these charged particles are present inside the atom, why are these particles not the smallest unit of matter? This is because these subatomic particles cannot be present by themselves even if we manage to isolate them. They are highly unstable. Therefore, the atom is the smallest unit of matter that can be present around us because it is the smallest and most stable unit of matter.
When similar atoms are combined, they form what is called an element. Similarly, when two or more elements of different types are combined, they form a compound. A simple compound is made up of only two elements.
When one combines simple compounds, we can form a complex molecule. Thus, a complex molecule can be defined as the combination of simple compounds held together with chemical forces such as ionic or covalent bonds. One such instance of a complex molecule is that of the glucose molecule.
Simple Compound
A simple compound can be defined as the union of only two elements. An ionic or covalent bond can connect them.
An example of a simple compound is NaCl, commonly known as salt and chemically called Sodium Chlorine.
Na is the symbol for sodium, and Cl is the symbol of chlorine.
Thus, NaCl consists of two elements, Na and Cl and one atom each of Na and Cl.
The atoms of the two elements are joined with an ionic bond (a bond formed due to the electrical attraction between two opposite polarity ions, i.e. proton and electron).
Consider another example of CO₂.
This simple compound comprises two elements, i.e., carbon, represented by the symbol C and Oxygen, represented by the symbol O.
Here, one atom of carbon is present, and two atoms of oxygen are present.
The bonds connecting C and O are two double or polar covalent bonds.
More examples of simple compounds are N₂O, SO₄, H₂O, etc.
Complex Molecule
In organic chemistry, a complex molecule can be defined as the combination of functional groups attached to the central atom, generally carbon. Susceptible chemical bonds link these elements, such as the London dispersion force or van der Waals force.
Consider an example of the metal complex molecule Hexa-ammine cobalt ( III ) chloride, [Co(NH₃)₆]Cl₃.
It is a chloride salt of the “Werner complex”.
Here, NH₃ is the ligand.
Metal ammine complex is the cation which is present along with ammonia ligands and linked to the cobalt(III) ion.
As one can observe that in this complex molecule, many elements are present in different amounts, such as Cobalt (Co), Hydrogen (H), Nitrogen (N), and Chlorine (Cl) with 1,18,6 and 3 atoms each, respectively.
In this complex molecule, sigma and pi types of bonds are present.
Another such example is a complex organic molecule, the glucose molecule.
Glucose is a sugar molecule.
It comes under the monosaccharide classification of sugar.
The chemical formula of glucose is C₆H₁₂O₆.
This organic complex molecule can be found in plants and algae as a product of photosynthesis.
As we can observe, glucose has 6 atoms of carbon represented by the symbol C, 12 atoms of Hydrogen (H) and 6 atoms of oxygen (6).
This molecule is considered a complex molecule because of its interconvertible structure and the bonding structure present in them chemically.
Prototype Reaction of a Complex Molecule (Glucose)
Let us take the example of a glucose molecule to understand the synthesis of a complex molecule. Gluconeogenesis is the process through which glucose is synthesised. This phenomenon of gluconeogenesis occurs in plants and begins with a pyruvate molecule.
At first, the Pyruvate molecule is converted to an Oxaloacetate molecule via the addition of Pyruvate carboxylase.
Oxaloacetate, when combined with PEP Carboxykinase, forms Phosphoenolpyruvate.
2-Phosphoglycerate is formed from Phosphoenolpyruvate as a redox reaction
2-Phosphoglycerate converts to 3-Phosphoglycerate.
From 3-Phosphoglycerate, 1,3-Bisphosphoglycerate is formed.
1,3-Bisphosphoglycerate converts to Glyceraldehyde-3-Phosphate.
Glyceraldehyde-3-Phosphate can be converted to Fructose-1,6-bisphosphate.
Fructose-1,6-bisphosphate is converted to Fructose-6-Phosphate.
Fructose-6-Phosphate changes into Glucose-6-Phosphate.
Finally, Glucose-6-Phosphate changes into glucose. This process is due to the non-linear activation of Glucose-6-Phosphate. This means that a certain amount of minimum energy with the help of which a molecule can change into another form in which the Phosphate molecules are lost.
Conclusion
We can conclude that combining two elements can form a simple molecule. Simple compounds combined can form a complex molecule. A complex molecule can be a metal complex molecule or an organic molecule. To synthesise a complex molecule such as glucose, gluconeogenesis takes place in plants that form glucose from a molecule of pyruvate. As learnt, the pyruvate molecule is converted into various other molecules, which are very tedious to finally end up with a glucose molecule that is performed inside plants and algae due to photosynthesis. Plants require glucose as energy to produce starch and other materials required for it. At the end of the gluconeogenesis process, an important concept of non-linear activation of glucose is also observed.
