Biomolecules Class 11 Notes: CBSE Biology Chapter 9

Biomolecules

Living organisms produce an organic molecule called a biomolecule that helps in performing important functions and acts as a building block of life. They are composed of carbon, nitrogen, hydrogen, phosphorus, oxygen, and Sulphur. Four types of biomolecules are common, they are proteins, carbohydrates, nucleic acid, and lipids. 

Analysis of Chemical Composition

The living tissues are treated with trichloroacetic acid by grinding them to make a slurry that helps analyse the chemical organic compound and its composition while the tissue should be burned to form ashes in the case of the analysis of the inorganic chemical composition, a sample of tissue should be burnt to obtain ash. 

Primary and Secondary Metabolites:

1. Primary Metabolites:

• Found in animal tissues.

• Include essential compounds like amino acids, sugars, and lipids.

• Play key roles in normal body functions, growth, and development.

2. Secondary Metabolites:

• Found mainly in plants, fungi, and microbes.

• Examples include alkaloids, flavonoids, rubber, essential oils, antibiotics, pigments, and spices.

• Their exact role in producing organisms is often unknown.

• Many are useful to humans for making medicines, perfumes, and other products.

• Some have ecological importance, helping organisms survive in their environment.

Biomacromolecules:

1. Molecular Weight:

• Compounds with molecular weights between 18 to 800 daltons (Da) are found in the acid-soluble pool.

• Compounds with molecular weights above 10,000 Da are found in the acid-insoluble fraction.

2. Types of Biomolecules:

• Micromolecules: Small molecules with molecular weights less than 1,000 Da, found in the acid-soluble pool.

• Macromolecules/Biomacromolecules: Larger molecules are found in the acid-insoluble fraction, including proteins, nucleic acids, and polysaccharides.

3. Lipids Exception:

• Lipids, though small (less than 800 Da), are part of the acid-insoluble fraction because they form structures like cell membranes.

• When tissues are ground, membranes break into vesicles, which are not water-soluble, making them part of the macromolecular fraction.

4. Representation of Living Tissue:

• The acid-soluble pool mainly represents the cytoplasmic composition.

• Macromolecules from the cytoplasm and organelles make up the acid-insoluble fraction.

• Together, these fractions represent the full chemical composition of living tissues.

5. Abundance of Chemicals:

• Water is the most abundant chemical in living organisms.

Proteins

In living organisms, there are essential substances that are important and belong to any class of nitrogenous organic compounds having large molecules that are made up of several long chains of amino acids.

The proteins are composed of amino acids that act as their building blocks. Naturally, around 22 amino acids are found that are made up of hydrogen, carbon, oxygen, and nitrogen. So, one amino acid is composed of the amino group, hydrogen atom, carboxyl group, and distinctive side chain that is bonded with the alpha-carbon.

Image.1. structure of amino acid

Image. 2. Zwitterion

All amino acids are found to rotate along the plane based on the polarised light and are said to be optically active. They consist of chiral carbon except for glycine. A chiral carbon is one having four different constituents in a tetrahedral carbon atom.

Two or more amino acids together constitute a peptide and are linked with the help of the peptide bond that is said to form a dipeptide. A tripeptide is formed when three amino acids are joined together while an oligopeptide chain is formed when 12 to 20 amino acids are joined together. When many amino acids are joined together they result in the formation of polypeptides. The first amino acid in the polypeptide chain is known as the N terminal or amino-terminal and the last amino acid in the polypeptide chain is known as the C terminal or carboxyl-terminal.

Image. 3. Formation of peptide bond

Protein Structure

There are four levels of protein organisation in proteins. They are as follows:

(i) Primary structure: This structure of the protein consists of the amino acids sequence that is joined together by a peptide bond.

(ii) Secondary structure:  This structure is a protein organisation having a higher level that comprises the alpha-helix and the beta-sheets. These both are stabilised due to the presence of hydrogen bonds between the carbonyl and N-H groups in a polypeptide backbone.

(iii) Alpha helix: When a polypeptide chain twists, it will form a rigid, rod-like structure that changes into a helical conformation.

(iv) Beta pleated: The arrangement of two or more polypeptide chain segments that are side by side then results in the formation of a sheet, and every chain segment is known as beta-strand.

(v) Tertiary structures: A three-dimensional structure of protein due to the interaction between the primary structure and its side chains. To make them stabilised, they required hydrophobic interactions, hydrogen bonds, electrostatic interactions, van der Waals forces, and covalent bonds.

Image. 4. Levels of protein organization

(vi) Quaternary structures: They are made up of two or more polypeptide chains that are joined together with the help of hydrophobic interactions, hydrogen bonds, electrostatic interactions, etc. For example, haemoglobin.

(vii) Fibrous and globular proteins

Fibrous proteins are long, rod-shaped molecules that are found to be insoluble in water and are structural and protective while globular proteins are water-soluble and are made up of spherical-shaped molecules.

Nucleic Acids 

Friedrich Miescher was the first to discover nucleic acid from the nuclei of pus cells. The nucleic acids are of two types: deoxyribonucleic acids (DNA) and ribonucleic acids (RNA).

In nucleic acid, the nucleosides are the monomeric unit consisting of three constituents: - a nitrogenous base, a five-carbon sugar, and phosphoric acid.

Image. 5. Structure of nucleotide

The nitrogenous bases are aromatic molecules having a heterocyclic structure. Two types of nucleic acids are found, that are purines and pyrimidines.

Purines are of two types- adenine and guanine while pyrimidines are of three types thymine, cytosine, or uracil.

Image. 6: Structure of purines and pyrimidines

DNA is deoxyribose that constitutes 5- 5-carbon sugar while RNA is ribose. Nucleoside when present with phosphate is known as the nucleotide.

Enzymes

Enzymes are made up of proteins and consist of various structures like proteins that include the primary, secondary, and tertiary structures. The enzyme consists of an active site that helps in binding the substrate molecule. The properties of the enzymes are as follows:

• All enzymes are proteins, but all proteins are not enzymes. 

• For each substrate, the enzymes are specific. 

• Enzymes function as catalysts. 

• During the reaction, the enzymes are not used up. 

• They are of six major types: oxidoreductases, transferases, hydrolases, lyases, ligases, and isomerases. 

• For an enzyme to function, some of them require a cofactor and/or a co-enzyme to function.

• Co-factor: They are the non-protein constituents that when bound to an enzyme will make them catalytically active. 

• Coenzyme: They are the organic compounds that during the reaction will bind to the enzyme transiently. 

• Prosthetic groups: they are the organic substances that are bound to the enzyme very tightly.

Image.7: Enzyme-substrate activity

Factors Affecting the Enzyme Activity 

The enzyme activity can be affected due to various factors that include temperature, pH, and substrate concentration. The optimum temperature needs to be maintained or the high or low temperature will lead to the inactivation of the enzyme activity. The enzyme activity can be altered due to deprotonation or protonation.

The molecules such as the inhibitors are responsible for the inactivation of the enzymes. Competitive inhibitors are the most common type of inhibitors that compete to bind to the active site of the enzyme against the substrates. For example, with the help of Malonate, the inhibition of succinate dehydrogenase can be done. 

5 Important Topics of Biology Class 11 Chapter 9 You Shouldn’t Miss!

Importance of Class 11 Biology Chapter Biomolecules Notes

• Biomolecules Class 11 NCERT Notes PDF provides a strong understanding of basic molecules like carbohydrates, proteins, lipids, and nucleic acids, which are essential for learning more complex biological processes in higher classes.

• Biomolecules is a fundamental chapter for NEET and other competitive exams, making these notes crucial for exam preparation.

• The notes break down complex concepts into simple, easy-to-understand points, helping students grasp the material quickly.

• Well-organised Class 11 Biology Chapter 9 Notes PDF allows for efficient revision, covering key points, important reactions, and structures that are frequently asked in exams.

• Diagrams and examples included in the notes enhance understanding and retention of the subject matter.

• Biomolecules Class 11 Short Notes covers all important topics and subtopics, ensuring that students have a complete understanding of the chapter.

Tips for Learning the Class 11 Biology Chapter 9 Biomolecules

• Start by thoroughly understanding the basic concepts of molecules like carbohydrates, proteins, lipids, and nucleic acids before diving into more complex topics.

• Utilise diagrams, flowcharts, and tables to visualise structures and processes, making it easier to remember and understand the content.

• Simplify complex reactions and processes by breaking them down into smaller, manageable parts to make them easier to learn.

• Use Class 11 Biology Chapter Biomolecules Notes on each topic, highlighting key points, important definitions, and reactions for quick revision.

• Regularly practice drawing and labelling diagrams, as they are crucial for understanding structures and processes and are often tested in exams.

• Consistent revision is key. Go over your notes and practice questions frequently to reinforce your understanding and retention.

• Practice with previous years' exam questions related to the chapter to get familiar with the types of questions asked and improve your answering techniques.

Conclusion

Biomolecules Class 11 Short Notes are key to learning about the building blocks of life. This chapter covers important compounds like carbohydrates, proteins, lipids, and nucleic acids, which are crucial for all living things. These notes help you learn their structures, functions, and roles in the body. By regularly reviewing  Biomolecules Class 11 Notes and practising with diagrams and key points, you will strengthen your grasp of the material. 

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