CBSE Class 11 Biology Notes- Biomolecules and Its Classes
Biomolecules are the molecules (macromolecules) that are synthesized in living organisms. Proteins, carbohydrates, lipids and nucleic acids are biomolecules found in all living beings. Small molecules like primary and secondary metabolites and natural products are also biomolecules. Carbon and hydrogen along with nitrogen, oxygen, sulphur, and phosphorus are essential constituents of all types of Biomolecules. The various atoms are covalently bonded in these biomolecules.
There are four major classes of biomolecules:
- Nucleic acids
Carbohydrates are long chains of sugars. They are a good source of energy. A carbohydrate is a hydrocarbon molecule that consists of carbon, hydrogen and oxygen atoms, usually with a hydrogen–oxygen atom ratio of 2:1. Carbohydrates are further classified as:
- Monosaccharides: They are simple sugars that are composed of 3-7 carbon atoms. They have a free aldehyde or ketone group; hence they act as reducing agents and are known as reducing sugars. Glucose, fructose and Galactose are monosaccharides.
- Disaccharides: They are made of two monosaccharides units. The bond between two monosaccharide units is called as the glycosidic bonds. Monosaccharides and disaccharides are sweet in taste and crystalline and water-soluble substances. Sucrose, Maltose, Lactose are some disaccharides.
- Polysaccharides: They are polymers of monosaccharides. They are not sweet, but complex carbohydrates. They are insoluble in water and are not in crystalline form. Starch, Cellulose are some polysaccharides.
Lipids are composed of long chains of fatty acids, they are esters of fatty acids. Fatty acids can be unsaturated and saturated hydrocarbons. A lipid is a chemical substance that is insoluble in water but soluble in organic solvents like alcohol, ether etc. Lipids are an important component of living cells. Lipids store a large amount of energy. and are constituent of biological membranes. Lipids have a polar head and non-polar tail. Lipids are part of biological membranes and are of three types based on the type of hydrophilic head present:
Glycolipids are lipids whose head region contains oligosaccharide (1- 15) residues.
Phospholipids contain a positively charged head which is attached to the negatively charged phosphate groups.
Sterols head region contains a steroid ring. Example steroid.
Proteins are polymers of amino acids. They are large molecules that our cells need to function properly. The structure and function of the living organisms depend on proteins. The regulation of the body’s cells, tissues, and organs are dependent on the proteins. Amino acids are linked together by the peptide bond which is formed in between the carboxyl group and amino group of successive amino acids. Proteins are formed from 20 different amino acids.
There are four levels of protein structure depending on the number of amino acids and their sequence.
- Primary structure of protein–This is a linear structure of amino acids that are arranged in a particular sequence (polypeptide chain). They are non-functional proteins.
- The secondary structure of protein – The long chain of the polypeptide is folded and arranged in a helix shape, where the amino acids interact by the formation of hydrogen bonds. This structure is called the pleated sheet. Example: silk
- The tertiary structure of protein–The secondary structure of proteins is stabilized by folding and coiling, by the formation of ionic or hydrophobic bonds or
disulphidebridges, this results in the formation of the tertiary structure of the protein.
- Quaternary structure of protein –The protein structure consists of an assembly of more than one polypeptide of its own, it is said to be the quaternary structure of the protein. Example: Haemoglobin, insulin.
Nucleic acids are organic compounds with heterocyclic rings. They are the polymer of nucleotides. A Nucleotide has three parts; a nitrogenous base, a pentose sugar and a phosphate group. A nucleoside is made of the nitrogenous base attached to a pentose sugar. The nitrogenous bases are adenine, guanine, thiamine, cytosine and uracil. Polymerized nucleotides form DNA/ RNA which are genetic material of every living cell.
FUNCTIONS OF BIOMOLECULES
- Carbohydrates are the instant source of fuel and energy, it aids in proper functioning of our brain, heart and nervous, digestive and immune system. Deficiency of carbohydrates in the diet leads to fatigue, poor mental function.
- Every protein in the body has specific functions, some proteins provide structural support, help in body movement, and also
against germs and infections. defence
- Proteins Lipids are the storage form of energy. Structure of membranes
arecomposed of lipids which formsa barrier and controls the flow of material in and out of the cell. Lipid hormones, like sterols, help in providing communication between cells.
- Nucleic Acids (DNA and RNA), carry genetic information in the cell. They also help in protein synthesis, by the process of translation and transcription.
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Absorption and Assimilation of Proteins
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