Molecules and their Interaction Relevant to Biology

Intermolecular interactions are forces of attraction or repulsion between molecules and unbonded atoms. All parts of chemistry, biochemistry, and biophysics rely on molecular interactions, including protein folding, drug design, pathogen detection, material science, sensors, gecko feet, nanotechnology, separations, and the origins of life.

Molecular Interactions

Noncovalent interactions, intermolecular contacts, non-bonding interactions, noncovalent forces and intermolecular forces are other names for molecular interactions.

Non-Bonding Interactions

Molecular Interactions occur between molecules or atoms that are not bonded to one another. Cohesive (attraction between like molecules), adhesive (attraction between unlike molecules), and repulsive forces comprise molecular interactions. When (a) ice melts, (b) water boils, (c) carbon dioxide sublimes, (d) proteins unfurl, (e) RNA unfolds, (f) DNA strands separate, and (g) membranes disintegrate, molecular interactions alter (but bonds stay intact). The enthalpy of a particular molecular interaction between two unbonded atoms is between 1 and 10 kcal/mole (4 and 42 kJ/mole), which is on the order of RT and much less than a covalent bond at the highest limit.

Bonding Interactions

Atoms are held together within molecules via bonds. Molecules are groups of atoms that bind so firmly that they do not dissociate or lose their structure while interacting with their surroundings. At normal temperature, bonding between two nitrogen atoms is possible (N₂ ). During chemical processes, bonds break and form. In the chemical process known as fire, cellulose molecules are broken while carbon dioxide and water bonds are formed. At room temperature, bond enthalpies are on the order of 100 kcal/mole (400 kJ/mole), which is far more than RT; bonds do not break at room temperature.

Boiling Points

Ideally, when a molecule moves from the liquid to gas phase (as occurs during boiling), all molecular connections are broken. The ONLY situations in which there are no molecular interactions are ideal gases. Variations in boiling temperatures provide reliable qualitative indicators of the strength of molecular interactions in the liquid phase. Liquids with a high boiling point exhibit strong molecular interactions. H₂ O’s boiling point is hundreds of degrees higher than that of N₂  due to stronger molecular interactions in H₂ O(liq) than in N₂  (liq). The intermolecular forces in H₂ O(liq) are stronger than those in N₂ (liq).

Types of Intermolecular Forces

Intermolecular force is an attractive force between the positive (or proton) components of one molecule and the negative (or electron) components of another molecule. This force influences the physical and chemical characteristics of a material. The boiling point of a material is related to its intermolecular forces; the greater the forces, the higher the boiling point.

Intermolecular forces are determined by the subsequent interactions:

1. Dipole-Dipole Interactions

Dipole-dipole interactions among polar molecules are attractive forces. Due to variations in the electronegativity of the atoms involved in a covalent connection, polar molecules have permanent dipoles. The partly positive component of one molecule attracts the partially negative portion of another.

Example: Dipole-dipole interactions occur in HCl molecules. Comparatively more electronegative than hydrogen, chlorine obtains a partial negative charge as a result (whereas hydrogen acquires a partial positive charge). The dipole-dipole interaction then occurs between the molecules of HCl.

2. Ion-Dipole Interactions

These interactions are comparable to dipole-dipole interactions, except that they include ions and polar molecules. When NaCl and water are combined in a beaker, the polar H2O molecules are attracted to the salt and chloride ions. This interaction’s intensity is dependent on:

• The size of the dipole moment
• The size and charge of an ion
• The size and charge of a polar molecule

3.  Ion Induced Dipole Interactions

In this form of interaction, an ion placed near a nonpolar molecule polarises it. Upon acquiring a charge, the non-polar molecules act as induced dipoles. Ion-induced dipole interaction describes this interaction between an ion and an induced dipole.

4. Dipole Induced Dipole Interaction

These interactions resemble dipole interactions caused by ions. Nevertheless, the presence of a polar molecule nearby transforms non-polar molecules into induced dipoles.

5. Dispersion Forces or London Forces

This force works over a small distance and is the weakest. This force results from the motion of electrons, which generates transient positively and negatively charged areas.

Important Biological Compounds

• Amino acid

A monomer of a protein

• Carbohydrate

A biological macromolecule with a carbon-to-hydrogen-to-oxygen ratio of 1:2:1; carbohydrates serve as cellular energy sources and structural support

• Cellulose

A polysaccharide that gives structural support to the cell walls of plants

• Chitin

A kind of carbohydrate that forms the outer skeleton of arthropods, such as insects and crustaceans, and the cell walls of the fungus

• Denaturation

The deformation of a protein is caused by changes in temperature, ph, or chemical exposure.

• DNA

A double-stranded polymer of nucleotides that contains the genetic information of the organism. DNA is a disaccharide.

• Enzyme

A catalyst in a biological reaction is frequently a complex or conjugated protein fat a lipid molecule comprised of three fatty acids and glycerol (triglyceride) that is normally solid at room temperature

• Glycogen

A storage carbohydrate in animals

• Hormone

A chemical signalling substance, often a protein or steroid, produced by an endocrine gland or set of endocrine cells; controls or regulates various physiological processes.

• Lipids

A category of macromolecules that are nonpolar and water-insoluble.

• Macromolecule

A big molecule is often generated through the polymerization of smaller monomers.

• Monosaccharide

A single unit of carbohydrates, or monomer

• Nucleic acid

A large biological molecule that holds a cell’s genetic information and instructions for the cell.

• Nucleotide

A nucleic acid monomer containing a pentose sugar, phosphate group, and nitrogenous base

• Oil

A fat that is liquid at ambient temperature and is unsaturated

• Phospholipid

A significant component of cellular membranes; consists of two fatty acids and a phosphate group connected to a glycerol backbone.

• Polypeptide

A lengthy chain of amino acids held together by peptide bonds

• Polysaccharide

A lengthy chain of monosaccharides may be branched or unbranched.

• Protein

A biological macromolecule comprised of several amino acid chains

• RNA

A polymer of nucleotides with a single strand that is involved in protein production.

• Saturated fatty acid 

The maximum number of hydrogen atoms is bonded to the carbon skeleton.

• Starch

A plant storage carbohydrate

• Steroid

A kind of lipid composed of four fused hydrocarbon rings.

• Trans-fat

An unsaturated fat with the hydrogen atoms on opposite sides of the double bond, rather than on the same side.

• Triglyceride

A fat molecule is composed of three fatty acids and one glycerol molecule.

• Unsaturated fatty acid

A long chain of hydrocarbons has at least one double bond.

The significance of atomic interactions

Molecular interactions are crucial to molecular biologists for the following reasons:

1. They can help us predict the biological processes in which an uncharacterized protein is involved:

• “Guilt by association” may be assumed if a protein of unknown function connects with one of known functions
• Proteins participating in the same process should cluster in network maps

2. They can help us characterise protein complexes and pathways; interaction networks may be used as a preliminary “map” to add depth to biological processes and routes, and they can aid in the discovery of novel pathways, complexes, and functional modules inside the cell.

Conclusion

Therefore we can finally conclude that by comparing the boiling temperatures of various compounds, we may compare the intermolecular forces of these substances. This is because the heat received by the material at its boiling point is utilised to break these intermolecular interactions and transform the liquid into vapour. Also, atomic interactions assist us to understand the function and behaviour of proteins.