Class 11 Biology


Nature of Bond Linking Monomers in a Polymer

Glycosidic Bond

Certain type of functional group which joins a sugar molecule to another group is called glycosidic bond. Another group may or may not be another carbohydrate.

glycosidic bond

Peptide Bond

A chemical bond formed between two molecules; when the carboxyl group of one molecule reacts with the amine group of another molecule; is called peptide bond (amide bond). A molecule of water is released during this reaction. This is a dehydration synthesis reaction and usually occurs between two amino acids. This is also known as a condensation reaction. The resulting CO – NH bond is called a peptide bond. The resulting molecule is called an amide. The four atom functional group – C (=O)NH – is called an amide group or a peptide group.

peptide bond

Phospho-diester Bond

A group of strong covalent bonds between a phosphate group and two other molecules over two ester bonds is called a phosphor-diester bond. Phosphodiester bonds make the backbone of the strands of DNA and hence are central to all life on Earth. In DNA and RNA, the phosphodiester bond is the linkage between the 3’ carbon atom of one sugar molecule and the 5’ carbon atom of another.

phospho-diester bond

Dynamic State of Body Constituents


All the biomolecules are constantly being changed into some other biomolecules and also made from some other biomolecules. The turnover of biomolecules takes place continuously. All these reactions are together called metabolism.


When a complex biomolecule is synthesized from simple biomolecules through a biological process, the process is called anabolism. Energy is utilised during anabolism.


When a complex biomolecule is disintegrated to produce simple biomolecules through a biological process, the process is called catabolism. Energy is released during catabolism.

Metabolic Pathway

Metabolites are converted into each other in a series of linked reactions. Such a series of linked reactions is called metabolic pathway. Every chemical reaction in the metabolic pathways is a catalysed reaction. The metabolic pathways are either linear or circular. These pathways crisscross each other; which means there are traffic junctions. But the interlinked metabolic traffic is very smooth and no single mishap has been reported for healthy conditions.

The Living State

All living organisms exist in a steady state; characterized by concentrations of each of the biomolecules. The steady state is a non-equilibrium state. It can be said that the living process is a constant effort to prevent falling into equilibrium. Without metabolism, there cannot be a living state.