The biological systems that we see around us are equipped with the millions of chemical reactions happening during the blink of an eye. Biochemistry of covalent bonds, ionic interactions, coordinate bonds, hydrogen bonding, Van der Waals forces, etc. together form the biological structures. Living organisms are of different forms, some are multicellular and some are unicellular.
All of them grow, interact with the environment, and reproduce. While performing all the activities they continuously interact with the different types of environmental conditions, other individuals, and cells. One of the first and foremost chemical structures required for building a cell is the membrane to keep the environment inside the cell under control. In the absence of the membrane is it not possible for a cell to perform all reactions in coordination with all the other processes, the cell is carrying out.
Chemical reactions employ different types bonds
As seen in the previous article, we know that the lesser the energy, more stable a molecule becomes. That’s why the cellular structure like cell wall, cell membranes, and protein filaments that shape the cell, needs to be stronger so that they can stay undamaged for longer periods of time in different environments.
These types of structures are formed from strong chemical bonds like covalent bonds. Breaking these bonds needs a large amount of energy to be supplied from the external environment. So biological entities have adopted covalent bonds to build the structural components. The bond energies of the common biological molecules range from 200-1000 kJ/mol for covalent bonds. This much amount of energy is not easily obtainable in the free environment and ultimately that keeps the biological structures integrated.
We eat a variety of foods with a variety of tastes. The moment we put a piece of food on our tongue we get the taste of it. We can taste the food because of specific chemical reactions that involve sensing the signal and sending it to the Brain. But what if all the molecules were bonded by only covalent bonds?
The sensory receptors will no longer be available for new food signals once they are received. Because covalent bonds are relatively stable and can not be broken easily. So That’s why all such transient reactions like transmitting signals are facilitated by ionic interactions and weak forces. Sensing the signal within milliseconds of stimuli is possible because of ionic interactions. Ionic interactions are relatively less stable than covalent bonds. The conformational changes brought about by the ionic bonds leads to the activation of the signaling cascades.
Atoms with one extra electron are negative ions and with fewer electrons, they are positive ions. The positive and negative ions will have a force of attraction working between them because of which signaling molecules stay physically associated with one another. Force of attraction between the charges stabilizes receptor-ligand or enzyme-substrate interactions which are otherwise unstable. In biological reactions, ionic species involve mostly charged amino acids and phosphate groups.
Secondary and tertiary structures of molecules like DNA and RNA are difficult to be kept in proper shape yet accessible to the enzymes. Hundreds of molecules are engaged with DNA all the time. The DNA is a hereditary molecule that’s why it is very essential to maintain its sequence from getting altered or mutated. Some biological responses to certain stimuli are generated within a few seconds. That’s why enzymes need easy access to the DNA sequence for the transcription.
Stable bonds like covalent bonds and ionic bonds won’t be useful in this case. Here hydrogen bonding serves the purpose. DNA strands are bound together by hydrogen bonds. Bond dissociation energy for hydrogen bonds ranges from 4-50kJ/mol. That’s why they can be easily broken by enzymes making sequence information available. Although hydrogen bonds are prone to breakage because they are so many of them, DNA is a very stable molecule.
Furthermore, the molecular structure of the atom or compounds that we draw in the notebook does not give a complete idea about the dynamic nature of the atoms and molecules. All the time each and every molecule are continuously vibrating. Bonds between atoms stretch and compress all the time. Also, electrons revolving around the nucleus don’t stay at a fixed position. Electrons move so fast that they can get around the earth in a few seconds.
And because of their constantly changing position, transient local positive and negative charges are formed in the molecules. Induction of such charges and force of attraction between them are collectively called Van der Waal’s forces. These forces play a significant role in establishing stable enzyme-substrate interaction which is crucial for enzymatic catalysis and product formation.
One thing we talked initially about is the formation of membranes. Membranes are formed from the long chain of carbon atoms called fatty acids. Fatty acids are highly nonpolar and they can not interact with water and as a result, they are excluded from water. Such a nature of nonpolar molecules is called hydrophobicity.
The particular arrangement of the lipids (a modified form of fatty acids) results in a specialized spherical structure called a membrane enclosing a special mixture of chemicals called cytoplasm. The membrane defines a boundary for the cellular molecules stopping them from mixing with the external environment. Such interaction of hydrophobic molecules with water is very essential in proper protein folding, enzymatic reactions, and many other processes. This is how chemistry in biology has shaped the biological and chemical diversity of the todays world.
Studying how chemical bonds are formed won’t make us understand how molecules behave. For better learning of the biology, thermodynamic behavior of such chemical species must be understood. I hope this article has shed some light on the significance of each mentioned chemical reactions and interactions in biology. I think we are not just the human body, there are greater forces involved in the making of you and me. The more we study about life, the more we will appreciate it.
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