Biology Class Eleven  


Analysis Of Chemical Composition: For this, a living tissue is taken. The tissue is ground in trichloroacetic acid (Cl3CCOOH); by using pestle and mortar. The slurry is then filtered through a cloth. The filtrate contains acid-soluble pool and the retentate contains acid-insoluble fraction. Organic compounds are found in the acid-soluble pool, while inorganic substances are found in acid-insoluble fraction.

Biomolecules: All the carbon compounds which are obtained from living tissues are called biomolecules.


Amino acids are organic compounds which contain an amino group and an acidic group as substituents on the same carbon, i.e. α-carbon. Due to this, they are called α-amino acids. The amino acids are substituted methanes. There are four substituent groups which occupy the four valency positions. These groups are; hydrogen, carboxyl group, amino group and a variable group; called R group. The nature of the R-group governs a particular type of amino acids.

However, there are only 21 types of amino acids which occur in proteins. The R-group in these proteinaceous amino acids could be of various types. The amino, carboxyl and the R functional groups decide the chemical and physical properties of an amino acid.

Amino acid with a hydrogen is called glycine, one with a methyl group is called alanine, one with hydroxyl methyl group is called serine, etc. Based on the number of amino and carboxyl group, the amino acids can be acidic, basic or neutral. A particular feature of amino acid is the ionizable nature of –NH2 and –COOH groups. Hence, structure of amino acids changes in solutions of different pH.


Lipids are usually insoluble in water. Lipids can be simple fatty acids and some lipids have phosphorous and phosphorylated organic compounds in them. Lipids; containing phosphorus; are called phospholipids. A fatty acid has a carboxyl group attached to an R group. The R group can be a methyl or ethyl or higher number of CH2 group (1 carbon to 19 carbons).

Fatty acids could be saturated or unsaturated. Many lipids have both glycerol and fatty acids. In this case, the fatty acids are found esterified with glycerol. They can be monoglycerides, diglycerides and triglycerides. On the basis of melting points, they can be termed as fats and oils. Oils have lower melting points while fats have higher melting points.

There are a number of carbon compounds; with heterocylic rings; found in living organisms. Some of them are nitrogenous bases, e.g. adenine, guanine, cytosine, uracil and thymin. When a nitrogenous base is attached to a sugar, it is called a nucleoside, e.g. adenosine, guanosine, thymidine, uridine and cytidine. If a phosphate group is also found esterified to the sugar then they are called nucleotides, e.g. adenylic acid, thymidylic acid, guanylic acid, uridylic acid and cytidylic acid.

Primary Metabolites: Metabolites which have identifiable functions are called primary metabolites. They play known key roles in normal physiological processes. All the primary metbaolites are found in animal cells.

Secondary Metabolites: There are certain metabolites about which we do not have enough information to suggest their role in physiological processes. Such metabolites are called secondary metabolites. Secondary metabolites are not found in animal cells.

Class eleven biology - proteins and their function

Mircomolecules: Biomolecules with molecular eights less than one thousand Dalton are called micromolecules or simple as biomolecules.

Biomacromolecules: Biomolecules with molecular weights more than one thousand Dalton are called biomacromolecules. These are found in the acid-insoluble fraction.


Protein is a polymer of amino acids. Based on similar or different monomers repeating in a protein, it is classified as homopolymer and heteropolymer. When same monomer is repeated in the protein, it is called homopolymer. When different monomers are present in the protein, it is called heteropolymer.

Essential Amino Acids: Some amino acids are essential for our health. But our body does not make them and they need to be supplemented through diet. Such amino acids are called essential amino acids. Collagen is the most abundant protein in the animal world. Ribulose biphosphate Carboxylase-Oxygenae (RUBISCO) is the most abundant protein in the whole biosphere.

Class eleven biology - biomolecules

The long chains of sugars are called polysachharides. If a polysaccharide is made up of similar monosaccharides, it is called homopolymer, e.g. cellulose. If a polysaccharide is made up of different monosachharides, it is called heteropolymer.

The right end of a polysaccharide chain is called the reducing end and the left end is called the non-reducing end.

Starch forms helical secondary structures. Starch can hold I2 (iodine) molecules in helical portion. Cellulose does not contain complex helices and hence cannot hold I2 .

In a polysaccharide chain, the right end is called the reducing end and the left end is called the non-reducing end. Starch forms helical secondary structures. In fact, starch can hold I2 molecules in the helical portion.


A nucleic acid is composed of nucleotide. There are three chemically distinct components in a nucleotide. One of them is a heterocyclic compound, the second is a monosaccharide and the third is phosphoric acid or phosphate.

The heterocyclic compounds; present in nucleic acids are the nitrogenous bases, viz. adenine, guanine, uracil, cytosil and thymine. Adenine and Guanine are substituted purines, while uracil, cytosil and thymine are substituted pyrimidines.

Based on the presence of purine or pyrimidine, the heterocyclic ring is called purine and pyrimidine. Polynucleotides contain either ribose sugar or 2’ deoxyribose sugar. If ribose sugar is present then the nucleic acid is called ribonucleic acid (RNA). If deoxyribose sugar is present then the nucleic acid is called deoxyribose nucleic acid (DNA).


Primary Structure: The sequence of amino acids is called the primary structure of a protein. The left end is represented by the first amino acid, while the right end is represented by the last amino acid. The first amino acid is also called N-terminal amino acid. The last amino acid is called C-terminal amino acid.

Secondary Structure: The protein is not a linear chain of amino acids rather the chain would bend at some places and even form helices. Regularly repeating local structures gives secondary structure to protein.

Tertiary Structure: The overall shape of a protein molecule; and the spatial relationship of the secondary structures to one another; is called tertiary structure of protein. In other words, the various folds which give three dimensional appearances to protein form its tertiary structure.

Quaternary Structure: The manner in which the individual folded polypeptides are arranged with respect to each other is called quaternary structure of protein.

Biomolecules - class eleven Biology - Nature of Bond Linking monomers in a Polymer
Biomolecules - class eleven Biology - Enzymes
Biomolecules - class eleven Biology - NCERT Solution

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