Biomolecules Class 11 Biology Notes | Complete Notes and Resources

Life Component

Various chemical substances are the basic constituents of the living organisms. These substances are essential for growth, development and maintenance of life. Such substances are called life components. The life components are:
a) Inorganic life components
b) Organic life components

Inorganic life components

The simple chemical substances are called inorganic life components. They are also essential for living organisms. The inorganic life components are of the following types:
a) Water
b) Mineral nutrients

Water
It is the most abundant inorganic compound in the cells. It makes 60-70% of body weight and 75-90% of the protoplasm. It does not yield energy, but it is vital in the maintenance of life.

It is formed by the combination of two hydrogen atoms and one oxygen, which are connected by a covalent bond. A hydrogen bond is formed among water molecules. The bond angle between hydrogen and oxygen is 104.5°.

Biological functions of water

• Solvent: It is the medium in which soluble materials are dissolved.
• Dispersion medium: It serves as a good dispersion medium for the colloids of cells.
• Temperature stabilizer: It causes elimination of excess heat by evaporation of sweat which gives a cooling effect.
• Maintenance of pH: Water also helps in maintaining the constant pH in cell.
• Surface tension: Due to high surface tension and cohesion, conduction of water through xylem vessels in the plants is possible.

Mineral nutrients
The mineral nutrients are such chemical elements which are essential for growth and development of the organisms. About 27 chemical elements are necessary for the growth and development of the living organism. The mineral nutrients are basically two types:
i. Macro elements or major elements
ii. Micro elements or trace elements

Macro elements
Those chemical elements which are required by the living organisms in a large quantity are called macro elements. Some of them are Ca, N, P, S, Mg, K, Na, Cl etc.

Micro elements
Those chemical elements which are required by the living organism in very small or minute quantity are called micro elements. Some of them are Fe, Zinc, Manganese, Iodine etc.-----

Organic life components

Those complex organic compounds which are essential for growth, development and maintenance of life are called organic life components. They are carbohydrate, protein, lipids, nucleic acid etc.

Biomolecules

Those organic molecules which are essential for growth, development and maintenance of life are called biomolecules or molecules of life or biologically important molecules. Most of the molecules are macro molecules; some of the important biomolecules are Carbohydrate, protein, lipids, nucleic acid etc.

Carbohydrates
They are the complex organic compounds made up of carbon, hydrogen and oxygen. Chemically, Carbohydrates are hydrates of carbon i.e. carbon having hydroxide. Structurally, the carbohydrates are the polyhydroxy aldehyde or polyhydroxy ketone.

Carbohydrates are classified according to the complexity of chemical substances of which they are formed:
a) Monosaccharides
b) Oligosaccharides
c) Polysaccharides

Monosaccharides
Those are simple sugar having empirical formula $C_n(H_2O)_n$ containing 3-7 carbon atoms. They cannot be hydrolyzed into smaller carbohydrates. The common examples of monosaccharides are glucose, fructose and galactose. The sugars containing ketone groups are called ketoses. According to the number of carbon atoms present, they are classified as follows:

• Trioses ($C_3H_6O_3$) $\rightarrow$ glyceraldehyde
• Tetroses ($C_4H_8O_4$) $\rightarrow$ erythrose
• Pentoses ($C_5H_{10}O_5$) $\rightarrow$ ribose
• Hexoses ($C_6H_{12}O_{6}$) $\rightarrow$ glucose
• Heptoses ($C_7H_{14}O_7$) $\rightarrow$ sedoheptulose

Oligosaccharides
The carbohydrates having 2 - 10 molecules of monosaccharide are joined by glycosidic linkage which further can be split on hydrolysis. The common example is disaccharide. The oligosaccharides are of following types:

• Disaccharides e.g. sucrose, maltose
• Trisaccharides e.g. raffinose, rabinose
• Tetrasaccharides e.g. scorodose, stachyrose

Polysaccharides
They are the carbohydrates having more than 10 molecules of simple sugars or polymers made up of monosaccharide. Those monomers are linked together by glucose linkage. The common examples of polysaccharide are starch, cellulose, and glycogen. They are insoluble in water and not sweet in taste.

Functions of Carbohydrates

• About 60% of the total energy is provided by the breakdown of carbohydrates.
• Monosaccharides act as building blocks.
• Carbohydrates are stored in the form of starch and glycogen.
• They help in synthesis of fats and amino acids.
• Monosaccharides like ribose and deoxyribose sugars are the structural components of RNA and DNA.

Amino acids

Amino acids are building blocks of protein. Many or more amino acids are linked to one another to form protein. Each amino acid has an amino group ($-NH_2$) and one carboxyl group ($-COOH$). Where R stands for a variety of chemical combinations. There are 20 types of amino acids which are categorized into two categories:

    H
    |
NH2-C-COOH
    |
    R
Amino Acid

(Based on diagram)

1) Essential amino acids
They are not synthesized in the body. Therefore, they must be included in the diet e.g., leucine, lysine, isoleucine, valine, methionine etc.

2) Non - Essential amino acids
Those are synthesized in the body. They may or may not be present in the diet e.g., Alanine, glycine, glutamine, tyrosine, aspartic acid etc.

Proteins

Proteins are the complex organic compounds made up of carbon, hydrogen, oxygen and nitrogen. Thus they are the nitrogenous organic compounds. The proteins are macromolecules having very high molecular weight. The proteins control and regulate all the activity of the cell. A peptide bond is established between the amino group ($-NH_2$) of one amino acid and the carboxylic group ($-COOH$) of another amino acid with the removal of one molecule of water. When two amino acids are linked together by a peptide bond, a dipeptide molecule is formed.

A) Classification of proteins on the basis of structure

1. Globular proteins: The proteins which are spherical, oval or globular in shape are called globular protein. e.g., globulin, albumin etc.
2. Fibrous proteins: The protein molecules which are elongated and or hair/thread-like structures are called fibrous protein. e.g., collagen, keratin etc.

B) Classification of proteins on the basis of chemical composition

1. Simple proteins: The protein molecules which are made up of polypeptide chains of amino acids only are called simple proteins. e.g., albumin, globulin etc.
2. Conjugated proteins: The protein molecules which are made up of amino acids and non-amino substances are called conjugated protein. They are also called prosthetic groups.
   • Glycoprotein $\rightarrow$ amino acid + glucose
   • Phosphoproteins $\rightarrow$ amino acid + phosphate
   • Lipoprotein $\rightarrow$ amino acid + lipid
   • Nucleoprotein $\rightarrow$ amino acid + nucleic acid
   • Chromoprotein $\rightarrow$ amino acid + coloured pigments
3. Derived proteins: The protein molecules which are formed by the partial hydrolysis of simple and conjugated proteins. e.g., peptones, proteases etc.

C) Classification of protein on the basis of arrangement of polypeptide chain

1. Primary Proteins: The protein molecules which consist of only one polypeptide chain of amino acids are called primary proteins.
2. Secondary Proteins: The protein molecules which consist of two or more polypeptide chains of amino acids linked together by hydrogen bonds are called secondary proteins. e.g., heroin.
3. Tertiary Proteins: The protein molecules which consist of two or more polypeptides of molecules linked together by sulphur bonds are called tertiary proteins. e.g., hemoglobin.
4. Quaternary Proteins: The protein molecules which contain two or more polypeptide chains of amino acids linked together by weak covalent bonds are called quaternary protein. e.g., Phosphorylase.

Functions of Proteins

1. They are building blocks.
2. They provide energy.
3. They act as enzymes or biocatalysts.
4. Some hormones are proteins. e.g., insulin.

Lipids

Lipids are the groups of fat and fat-like substances. These are insoluble in water and soluble in organic solvents like acetone, ether, alcohol etc. Its types:

a) Simple lipids
The lipids which are made up of lipid molecules only are called simple lipids. They are the esters of fatty acid and alcohol. Its types are:

• i. Oils: The oils are the esters of fatty acid and glycerol. The fatty acid is unsaturated type i.e., having one or more double bonds in their substances. The sources of oil are mustard, sunflower etc.
• ii. Fats: The fats are also esters of fatty acids and glycerol. The fatty acid is saturated type, i.e., without any double bond in their structure. They are solid or semi-solid at normal temperature. The sources of fats are ghee, butter etc.
• iii. Waxes: The waxes are the esters of fatty acid and alcohol but not glycerol. They consist of a long chain fatty acid and a long chain alcohol other than glycerol. They act as waterproof materials on the skin of human beings, exoskeleton of insects, cuticle of plants etc.

b) Complex lipids
The complex lipids are the lipids which are made up of lipids and some non-lipid compounds. e.g.,

• Glycolipids $\rightarrow$ lipids + carbohydrates
• Lipoprotein $\rightarrow$ lipids + protein molecules
• Phospholipids $\rightarrow$ lipids + phosphate

c) Derived lipids
The lipids which are derived from either simple or complex lipids by hydrolysis are called derived lipids. e.g., steroids.

Function of lipids:

1. The lipids are an efficient source of energy.
2. It acts as a heat insulator which is deposited in the subcutaneous tissues.
3. Some lipids act as carriers of fat-soluble vitamins A, D, E and K.
4. Vitamin D is synthesized from cholesterol on exposure to direct sunlight.

Nucleic acids

They are made up of a number of nucleotides. The nucleotides are linked together by phosphodiester bonds to form polynucleotides which are the nucleic acids. It is composed of three components:

• Nucleotide = a sugar + a base + a phosphate molecule
• Nucleoside = a sugar + a base

a) Pentose sugar
Two types of nucleic acids are distinguished on the basis of the pentose sugar which they possess. One possesses ribose sugar called RNA and the other contains deoxyribose sugar called DNA.

b) Nitrogenous bases
Two types of nitrogenous bases are found in all nucleic acids, i.e., purines and pyrimidines.

• i) Purines: They have two rings in their structure: Adenine and Guanine.
• ii) Pyrimidine: These have one ring in their structure: uracil, cytosine and thymine.

Types of Nucleic acids:

• Deoxyribonucleic acid (DNA)
• Ribonucleic acid (RNA)

Deoxyribonucleic acid (DNA)
DNA is the genetic material and is capable of self-replication. The purine and pyrimidine bases of DNA carry genetic information, whereas the sugar and phosphate groups perform a structural role. DNA is found mainly in the nucleus but it also occurs in chloroplasts and mitochondria.

A molecule of DNA consists of pentose sugar (deoxyribose), phosphate and nitrogen bases (purines and pyrimidines).

• Purines: Adenine (A), Guanine (G)
• Pyrimidines: Cytosine (C), Thymine (T)

According to the base-pairing rule of Chargaff, pairing is A = T & G $\equiv$ C by hydrogen bonds, and the A+T / G+C ratio is constant. The amount of purine and pyrimidine are always equal. The sugar and phosphate units are structural.

WATSON & CRICK gave the double helix model of DNA structure. According to this model, a double strand of DNA is coiled upon itself like a spiral staircase with the hydrogen-bonded base pairs as the steps. The diameter of the double helix is 20 Å, the bases are 3.4 Å apart along the helix axis and are related by a rotation of 36° after 10 residues. Therefore, the helical structure repeats on each chain i.e., at intervals of 34 Å. In other words, each turn of the helix contains 10 nucleotide residues.

(Reference to Fig DNA and Fig RNA)

Ribonucleic acid (RNA)
RNA is the polymer of ribonucleotides. Its types are: RAMP, RGMP, RCMP, UMP. These nucleotides join together to form single-stranded RNA.

RNA is produced mainly in the nucleus but moves out into the cytoplasm. The prime role of RNA is protein synthesis, but in organisms having only RNA, it acts like genetic material. This fact was proved by Fraenkel-Conrat. Here Thymine is replaced by Uracil (U) and the pentose sugar is ribose. RNA is formed in the nucleus upon DNA, which works as a template. RNA is of different types according to its functions. It is categorized as genetic RNA and non-genetic RNA.

1) Genetic RNA:
The RNA which acts as genetic material as in most plant viruses, viroids, virusoids and some bacteriophages is called genetic RNA. It can be single or double-stranded.

2) Non-Genetic RNA:
When DNA is the genetic material, then RNA is non-genetic and helps in protein synthesis. Non-genetic RNA is of three types:

a) Transfer RNA (10-15%): It is also called the laborer of the cell. T-RNA carries specific amino acids from the cytoplasm to the ribosome.

• b) Messenger RNA (5-10%): It is also called the contractor of the cell. M-RNA carries genetic information contained in DNA to the ribosome for protein synthesis.
• c) Ribosomal RNA (80%): The most stable is R-RNA. It is found in ribosomes.

Enzymes

The term enzyme was coined by Kuhne (1878) and discovered by Buchner (1897). Enzymes are biocatalysts that enhance the rate of biochemical reactions but do not affect the nature of the final product. According to the International Union of Biochemistry (IUB), enzymes are of 6 categories i.e., Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, Ligases.

Function of Enzymes:

1. ATPase helps in the formation of energy in the form of ATP by the process of phosphorylation.
2. Oxidoreductase catalyzes the oxidation reaction.
3. Hydrolases catalyze the hydrolysis reaction by adding water to cleave the bond.
4. Ligases catalyze the joining of two molecules.
5. Transferases help in the transportation of the functional group among acceptor and donor molecules.

Differences between DNA and RNA