Chemical Constituents of Living Cells

Introduction 

The cell is the basic unit of every living creature on earth. The primary chemical constituents of cells are hydrogen, oxygen, nitrogen, carbon, sulfur and phosphorus. Most of the cell constituents are water molecules. The amount of protein is more in the cell than the DNA. However, the DNA is larger than these protein units. When these components bind together, they form organic biomolecules. The living cells consist of four categories of macromolecules: nucleic acids, proteins, lipids, and polysaccharides. Every living organism on this earth possesses these biomolecules; however, their proportion may vary.

All these molecules possess their specific significance in the body. The structure of cell constituents may vary in shape, size and functional groups.

Classification of Chemical Constituents of Cell

There are basically four classes in which biomolecules are classified. 

The Classification of Chemical Constituents of cells is as follows:

• Nucleic acids
• Proteins
• Lipids
• Polysaccharides

Nucleic Acids

Nucleic acids are the macromolecules that are essential for every living cell. The nucleic acid comprises nucleotides, the monomers. They consist of a pentose sugar, phosphate group and nitrogenous base. They make up the genetic material of the cell. They create, encode  and store information within the cells. Nucleic acid was first discovered in 1869 by Friedrich Miescher. They name it nuclein. The two most common types of nucleic acids are DNA and RNA.

DNA (Deoxyribonucleic acid)

DNA is present in prokaryotic, eukaryotic, and in some viruses’ cells. The structure of DNA is double-helical in the form of a twisted ladder. The DNA is composed of nucleotide monomers. It consists of a deoxyribose sugar, a phosphate group, and four nitrogenous bases. The nitrogenous base consists of two purines (adenine and guanine).

Moreover, it has two pyrimidines (cytosine and thymine). These bases join together by covalent bonding. Adenine binds with thymine with a single bond, whereas cytosine binds with guanine with triple covalent bonding. DNA replication is by the untwisting of one strand. The strand acts as the template for the new DNA strand formation.

RNA (Ribonucleic acid)

RNA is single-stranded ribonucleic acid. It comprises ribose sugar, phosphate groups and nitrogenous bases. As in DNA, they also consist of purines and pyrimidines. However, RNA lacks thymine in its nitrogenous base. Thus, in place of thymine, another base uracil is present—the adenine bonds with uracil and cytosine binds with guanine. There are other three types of RNA: mRNA (messenger RNA), rRNA (ribosomal RNA), and tRNA (transfer RNA). As the name suggests, mRNA carries the genetic codes from the nucleus to ribosomes. tRNA carries the amino acid to the ribosomes, which link to form proteins. rRNA is responsible for the protein synthesis in the cells. RNA creates structures with other molecules such as ribonucleoproteins.

Proteins 

As we all know, proteins are the building blocks for every living cell. They are the polymers of amino acids. Twenty different amino acids synthesize proteins. The body can synthesize some amino acids, therefore called non-essential amino acids. However, the body cannot synthesize certain amino acids; therefore, they should be present in the diet. These are the essential amino acids. The proteins are specific in their action. All enzymes are proteins; however, not all proteins are enzymes.

Some of the essential characteristics of it are as follows:

• They are optically active, colloidal, complex compounds present in the cells
• The amino acids bound by peptide bonds form the polypeptide chain for the formation of proteins
• Proteins are insoluble in water, alcohol or ether However, they are soluble in a salt solution.
• They comprise a large portion of the dry weight of every living organism
• It provides a structural framework and also repairs the damaged parts
• The plant protein is primarily present in their seeds and leaves. The roots contain a significantly less amount of it

Lipids 

Lipids are the derivative of fats and are insoluble in water. The lipids comprise carbon, hydrogen and oxygen. However, the quantity of hydrogen in them is more than oxygen in them. They are soluble in other solvents such as benzene, chloroform, ether, hot alcohol, etc. Lipids in plants are present in their seeds, nuts, and fruits. The animals possess lipids in their cells. They are present as the subcutaneous layer that acts as the insulator and padding over different organs. They are also present in the nervous tissue, bone marrow and liver cells.

Characteristics of Lipids

• They are colorless and have a bland taste
• As already mentioned, they are insoluble in water but soluble in other components such as ether, alcohol and benzene
• The melting point of it varies for different molecules
• They easily crystallize and are bad conductors of heat, due to which they act as the insulator over the skin

Polysaccharides

The polysaccharides comprise numerous monomers of monosaccharides. They are classified as homopolysaccharides and heteropolysaccharides. The homopolysaccharides comprise identical types of monomers, whereas the heteropolysaccharides comprise different types. Cellulose is an example of a homopolysaccharide that comprises glucose monomers. Cellulose is present in plants, but animals lack it.Inulin is a polymer of fructose.Starch is present in plants is a polysaccharide composed of glucose units. Heparin, present in the liver, is an example of heteropolysaccharides. It includes glucosamine, gluconic acid, and sulphuric acid. Chitin, present in the exoskeleton of arthropods, is another example of heteropolysaccharides.It gives protection to the arthropods. Heparin is a polysaccharide ,which prevents clotting of blood.

Conclusion 

Chemical constituents of living cells comprise all organic and inorganic compounds present in them. The primary chemical components of cells are hydrogen, oxygen, nitrogen, carbon-sulfur, and phosphorus. All living organisms possess these compounds. However, their proportion varies. Carbon is the most crucial constituent for living cells. All the four major compounds, i.e. nucleic acids, lipids, polysaccharides, and proteins, consist of carbon. DNA is the largest biomolecule present in almost all living cells. Some virus cells lack DNA and contain only RNA as their nucleic acid.