Biomolecules
Habish Ribin Haneef
Biomolecules are the primary building blocks of every living organism. They are chemical compounds found in living organisms. These chemical compounds perform essential functions in living organisms that are necessary for life. The biomolecules include chemicals composed of carbon, oxygen, hydrogen, sulfur, nitrogen, and phosphorus. In the battle for survival, these non-living molecules are the actual foot soldiers. The biomolecules range from small molecules like primary and secondary metabolites and hormones to large macromolecules such as proteins, nucleic acids, carbohydrates, lipids, etc. Anyways, the four major types of biomolecules are carbohydrates, proteins, nucleic acids, and lipids. The major types of biomolecules are basically polymers of simple elements. For example, amino acids are the building blocks for proteins. Phosphate, sugar, and nitrogen form the basis for nucleic acids. Glycerol and fatty acids form the basis for lipids and simple sugar for carbohydrates. Now, let’s have a look at each of these biomolecules in detail.
Carbohydrates:
The term ‘carbohydrate’ is derived from a french word ‘hydrate de carbone’ which means hydrate of carbon. Carbohydrates are biomolecules consisting of carbon, hydrogen, and oxygen atoms. They are macronutrients which include sugars, fibers, and starches. Our body uses carbohydrates as one of the important sources of energy. Carbohydrates are mainly found in grains, fruits, vegetables, milk, and other dairy products. Food items containing carbohydrates are very imperative for a healthy life. The digestive system converts food containing carbohydrates into glucose or blood sugar during the process of digestion. This sugar is utilized by our body as a source of energy for cells, organs, and tissues. The additional amount of sugar or energy is stored in our muscles and liver for further requirements. Some examples of carbohydrates include glucose, galactose, maltose, fructose, sucrose, lactose, starch, cellulose, and chitin. Carbohydrates are classified into two- simple carbohydrates and complex carbohydrates.
Simple carbohydrates consist of one or two sugar molecules. They are found in milk products, beer, fruits, refined sugars, candies, etc. Simple carbohydrates are also called “empty calories” because they do not contain fiber, vitamins, and minerals. In these types of carbohydrates, the molecules are digested and converted quickly thereby increasing the blood sugar levels. Simple carbohydrates are again classified into three- Monosaccharides, disaccharides, and oligosaccharides.
Monosaccharides are simple sugars consisting of one sugar unit that cannot be further broken down into simple sugars. Examples of monosaccharides include glucose, galactose, fructose, mannose, etc. Depending on the number of carbon atoms, monosaccharides are again classified into five-trioses (three carbon atoms per molecule), tetroses (four carbon atoms per molecule), pentoses (five carbon atoms per molecule), hexoses (six carbon atoms per molecule), and heptoses (seven carbon atoms per molecule). The structural organisation of galactose and glucose are shown below,
Disaccharides are sugars formed when two monosaccharides join via glycosidic linkage. Examples of disaccharides include sucrose, lactose, maltose, etc. Sucrose is a combination of glucose and fructose. Lactose is the combination of galactose and glucose. Maltose is the combination of glucose and glucose.
The structure of these sugars is shown below,
Oligosaccharides are carbohydrates formed by the condensation of 2-9 monomers. Hence, trioses, pentoses, and hexoses are all oligosaccharides.
Complex carbohydrates are found in lentils, beans, peanuts, potatoes, peas, corn, cereals, whole-grain bread, etc. They are known as starchy foods as they have two or more sugar molecules. In the case of complex carbohydrates, molecules are digested and converted slowly compared to simple carbohydrates.
Polysaccharides are complex carbohydrates that are formed by the polymerization of a large number of monomers. Starch, glycogen, cellulose, etc. are some examples of polysaccharides.
Proteins:
A protein is a large, complex molecule that performs a variety of critical functions in our bodies. In cells, the proteins perform most of the functions. Proteins are required for the structure, function, and regulation of the body’s tissues and organs. Proteins are composed of hundreds or thousands of smaller units known as amino acids. The amino acids are attached to one another in long chains. Each protein’s 3-dimensional structure and specific function are determined by its sequence of amino acids. Amino acids are coded by combinations of three DNA building blocks, determined by the sequence of genes. Examples of proteins include antibodies, enzymes, messengers, structural components, and transport/storage proteins.
The antibodies play a major role in blocking the entry of foreign particles like bacteria and viruses into the body and hence protecting the body.
Example: Immunoglobulin G (IgG)
The enzymes perform almost all of the thousand chemical reactions that take place in cells. They also read the genetic information stored in DNA and assist in the formation of new molecules.
Example: Phenylalanine hydroxylase
The messenger proteins send signals to coordinate biological processes between different cells, tissues, and organs.
Example: Growth hormone
The structural component, as the name indicates provides structure and support for the cells. They also help the body to move.
Example: Actin
The transport/storage proteins bind and carry atoms and small molecules within the cells and throughout the body.
Example: Ferritin
Nucleic Acids:
Nucleic acid is the genetic material in the cell that constitutes all the hereditary information from parents to progeny. They are long-chain polymeric molecules. Nucleic acids are primarily involved in the transfer of genetic information, as well as the synthesis of proteins through processes called translation and transcription. The monomeric unit of nucleic acids is called nucleotide. The nucleotide is made up of a nitrogenous base, pentose sugar, and phosphate. There are two types of nucleic acids- Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA).
Deoxyribonucleic acid (DNA) has a double-strand helical structure in which the strands are complementary to each other. Most DNA is located in the cell nucleus called nuclear DNA. But, a small amount of DNA is also found in the mitochondria called mitochondrial DNA. DNA is chemically composed of pentose sugar, phosphoric acid, and some cyclic bases having nitrogen. Adenine (A), guanine (G), cytosine(C), and thymine (T) are the cyclic bases having nitrogen in them. These cyclic bases and their arrangement in the DNA molecules play a very important role in the storage of information from one generation to the next. The sugar moiety seen in DNA molecules is β-D-2-deoxyribose.
Ribonucleic acid (RNA) has a double helix structure that results from a single strand that sometimes folds back. Similar to DNA, RNA molecule is also composed of phosphoric acid, pentose sugar, and some cyclic bases having nitrogen. The cyclic bases in RNA are adenine (A), guanine (G), cytosine(C), and uracil (U). The sugar moiety seen in RNA molecules is β-D-ribose. RNA molecules are of three types- messenger RNA (m-RNA), ribosomal RNA (r-RNA), and transfer RNA (t-RNA). The m-RNA carries instructions for making proteins. The m-RNA instructions are destroyed when the cell no longer needs to make that protein. The r-RNA is a non-coding RNA and it helps to form ribosomes, which are the protein-synthesizing organelle of the cell. When encoded, r-RNA can either be small or large. These small and large r-RNAs combine with the ribosomal proteins and serve as ribosomal subunits for protein synthesis. The t-RNA has a crucial role in the process of protein synthesis. The t-RNA helps to decode a messenger RNA sequence into a protein.
Lipids
The fatty, waxy, oily compounds that are soluble in organic solvents and are insoluble in polar solvents (like water) are called lipids. They are organic compounds containing hydrogen, carbon, and oxygen atoms which form the framework for the structure and function of living cells. Lipids are found in food items such as oil, butter, whole milk, cheese, fried foods, some red meats etc. The lipids are synthesized in the liver of the human body.
The structure of lipids is shown below,
Lipids are classified into two- Non-saponifiable lipids and saponifiable lipids.
A non-saponifiable lipid is composed of fat-soluble A and E vitamins and cholesterol. These lipids are also called complex lipids. These types of lipids cannot be disintegrated into smaller molecules through hydrolysis. Cholesterol, prostaglandins, etc. are some non-saponifiable lipids.
A saponifiable lipid is part of the ester functional group. These lipids undergo hydrolysis in the presence of a base, acid, or enzymes like waxes, triglycerides, sphingolipids, and phospholipids. Saponifiable lipids are further classified into two- polar lipids, and non-polar lipids.
Polar lipids comprise sphingolipids and glycerophospholipids. Polar lipids can form a barrier with an external water environment and are utilized in the membranes.
On the other hand, non-polar lipids are utilized as fuel to store energy. Triglyceride is an example of non-polar lipid.
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Check your knowledge
Answer. The four major types of biomolecules are carbohydrates, proteins, nucleic acids, and lipids.
Answer. Disaccharides are sugars formed when two monosaccharides join via glycosidic linkage. Examples of disaccharides include sucrose, lactose, maltose, etc.
Answer. Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA)