Biomolecules

Biomolecules

May 24, 2023, 16:45 IST

Biomolecules are the building blocks of the system of living beings. These are organic compounds which are composed of carbon, hydrogen, oxygen and nitrogen in abundance. The elements in the human body are similar to those present in the earth’s crust.

Introduction

Biomolecules are crucial organic molecules involved in the growth and development of living organisms. Carbohydrates, proteins, lipids, nucleic acids and enzymes are some of the essential biomolecules.

Carbohydrates

Carbohydrates are the main source of sugars and the most abundant biomolecule in the body. They are produced in green plants by the process of photosynthesis in the presence of carbon dioxide, sunlight and chlorophyll.

nCO2+nH2O+energyCnH2nOn+nO2 where the value of ‘n’ is between 3 to 7.

Carbohydrates are those compounds which yield aldehydes and ketones on hydrolysis. They are also called saccharides, meaning sugar. Glucose, fructose, lactose, maltose, starch, cellulose and glycogen are some common carbohydrates.

Classification of carbohydrates

According to functional groups:

1. Aldoses- The functional group in the molecule is aldehyde. Eg. glucose, galactose, ribose.
2. Ketoses- The functional group in the molecule is ketone. Eg. fructose.
3. Reducing sugars- The functional group in the molecule is hemiacetal or hemiketal. Eg. maltose, lactose.
4. Non- reducing sugars- No hemiacetal group is present, hence they cannot act as reducing agents. Eg. Sucrose, raffinose.

According to sugar units:

1. Monosaccharides- The simplest type of carbohydrate with one sugar unit and cannot be broken down into smaller units. Eg. glucose, fructose, galactose.
2. Oligosaccharides- They are made up of two or more monosaccharide units. Eg. Raffinose, stachyose.
3. Polysaccharides- They are long chain monosaccharides that are linked by glycosidic bonds. Eg. Cellulose, glycogen, starch.

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Lipids

Lipids or fats are esters of fatty acids and glycerol and glycerides of fatty acids. They release high amounts of energy on oxidation. Lipids are nonpolar in nature and hence dissolve in nonpolar solvents like acetone, toluene and benzene. Lipids are not soluble in water. Wax, sterols, oils, butter, cheese,glycolipids, phospholipids, and certain vitamins are examples of lipids.

Classification of Lipids

1. Simple lipids- These are esters of fatty acids and alcohols. They are soluble in nonpolar solvents. Eg. Fats, oils, waxes etc.
2. Complex lipids- They have other functional groups besides fatty acids and glycerol. They are found in plasma membranes of cells and body tissues. Eg. Lecithin.
3. Derived lipids- They are formed on hydrolysis of simple and complex lipids. Eg. Fat soluble vitamins, cholesterol etc.

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Proteins

Proteins are polymeric compounds of amino acids that are linked together through covalent polypeptide bonds. Amino acids are the basic structural and functional unit of proteins. Proteins may be made up of essential or non-essential amino acids.

Classification of Proteins

Since proteins are large polymers, their structure is complex and classified into four levels:

1. Primary Structure- It is a simple chain of amino acids in a specific order.
2. Secondary Structure- The interlinking of polypeptide chains through hydrogen bonds results in the formation of right handed helices.
3. Tertiary Structure- When the lengthy polypeptide chains coil in the form of a hollow sphere, they form a tertiary protein structure.
4. Quaternary Structure- The overlapping of several tertiary proteins forms a quaternary structure.\

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Nucleic Acids

Nucleic acids are the crucial information relaying polynucleotide sequences in living beings. They consist of several nucleotide units where each monomer has a nitrogenous base attached to a phosphate group and a sugar molecule. Two types of nitrogenous bases are present namely purines (adenine and guanine) and pyrimidines (cytosine, thymine and uracil). Adenine forms two hydrogen bonds with thymine whereas guanine forms three hydrogen bonds with cytosine. The sugar may be of deoxyribose or ribose type depending on the nucleic acid.

Classification of Nucleic Acids

Two major types of nucleic acids are found in living systems:

1. Deoxyribonucleic Acid- DNA strand is double stranded and coiled to form a double helix structure. A single DNA molecule has a deoxyribose sugar, nitrogenous base and a phosphate sugar. Glycosidic bonds join the sugar and the base. The strands have four nitrogenous bases namely adenine, guanine, cytosine and thymine. These bases are joined together by hydrogen bonds. Adenine has two hydrogen bonds with thymine whereas cytosine has three hydrogen bonds with guanine. The strands are antiparallel. One strand runs from five prime to three prime whereas the other strand runs three prime to five prime. Each turn of DNA has ten base pairs and the length is 4nm. A major groove is formed when sugar and phosphate groups are close to each other. A minor groove is formed when sugar and phosphate groups are far apart from each other.
2. Ribonucleic acid- RNA is a single stranded nucleic acid which has a nitrogenous base attached to a phosphate group and a sugar unit. Adenine, guanine, cytosine and uracil are the bases present in a nucleotide. Adenine binds to uracil whereas guanine binds to cytosine via hydrogen bonds. The sugar unit is ribose sugar. It is shorter than a typical DNA strand and less susceptible to ultraviolet damage. RNA has a single helix and is of three types namely mRNA (messenger RNA), tRNA (transfer RNA) and rRNA (ribosomal RNA).

Biomolecules: FAQs

Q1. Define the term ‘biomolecules’.

Ans. The complex organic compounds required for the growth and metabolism of living beings are called biomolecules.

Q2. What are the major types of biomolecules?

Ans. The major types of biomolecules are carbohydrates, lipids, proteins, nucleic acids and enzymes.

Q3. What are the forms of nucleic acids?

Ans. Nucleic acids are found in two primary forms namely DNA and RNA. Deoxyribonucleic acid carries the genetic information in organisms whereas RNA is mainly involved in synthesis of proteins.

Q4. What is the function of biomolecules?

Ans. Biomolecules are important for the growth and development of organisms. Carbohydrates are used as a source of energy and lipids provide insulation and structural integrity to cell membranes. Proteins form hormones and enzymes besides repair and growth of cells. Nucleic acids are the building blocks of the genetic makeup in living organisms.