CBSE Class 11 Biology Revision Notes Chapter 9

CBSE Class 11 Biology Revision Notes Chapter 9 – Biomolecules

The chapter on Biomolecules in Class 11 Biology is a significant one. The chapter deals with several important topics such as introducing biomolecules, lipids, proteins, polysaccharides, nucleic acids, metabolism and its living state, enzymes, regulation of enzymes, and many more. The importance of the chapter lies in the fact that it is a crucial part of the syllabus for NEET (biology). The NEET aspirants should especially put extra focus on the chapter.  

Extramarks offers Revision Notes for Chapter 9 Biomolecules which summarises all the key topics covered in this chapter in a simple and easy-to-understand language. Students can access these notes to prepare for this chapter more effectively and save a lot of their time and energy.

Revision Notes for Class 11 Biology Chapter 9 – Biomolecules

Chapter 9 is focused on learning about the different chemicals and elements that make up living organisms. Although there is a wide diversity of living organisms on our planet, there are many similarities to be found in terms of chemical compositions of these living organisms. A closer look at the chemical composition of living organisms reveals that the most abundant elements in their bodies include carbon, hydrogen, oxygen and a few others.

Biomolecules

The biomolecule is produced by living organisms which helps them perform essential functions, and it also acts as the central pillar of life. Biomolecules encompass carbon, nitrogen, hydrogen, oxygen, sulphur, and phosphorus. Four common biomolecules are proteins, carbohydrates, nucleic acid, and lipids.

Analysis of chemical composition

Trichloroacetic acids are used to treat living tissues. It is done by crushing them and making a slurry that is helpful in the assessment of the organic chemical compound and its composition. In the inorganic chemical composition analysis, the tissue is supposed to be burnt to obtain ashes.

Proteins

Proteins are substances found in living organisms that are very significant. They have large molecules that belong to any class of nitrogenous organic compounds. Their large molecules are composed of several long chains of amino acids.

Proteins constitute amino acids which act as their lifeline or building blocks. Around 22 amino acids are composed of hydrogen, oxygen, carbon, and nitrogen. Therefore, one amino acid comprises the amino group, hydrogen atom, carboxyl group, and different side chains that bond with the alpha-carbon.

Structure of the amino acid: When the amino acids get dissolved in the water, they exist in solutions in the form of zwitterion or dipolar ions. They work as either proton donors or as proton acceptors.

Zwitterion: All the amino acids are optically active, and they keep rotating along the plane, which is based on the polarised light. They constitute chiral carbon, the exception being glycine. Chiral carbons are composed of four different ingredients in a tetrahedral carbon atom.

A peptide is the formation of two or more amino acids bonding together. They are linked with the peptide bond, which then forms a dipeptide. When three amino acids join together, a tripeptide is created. An oligopeptide chain results from 12 to 20 amino acids joining hands together. Polypeptides are formed when numerous amino acids are joined together. The Amino-terminal, also known as the N terminal, is the first amino acid in a polypeptide. The carboxyl-terminal or C terminal is the last amino acid in a polypeptide chain.

Protein structure

There are several stages of the organisation of proteins. They are as given below:

1. Primary structure: The amino acid sequence is joined by a peptide bond in the primary structure.
2. Secondary structure: The secondary structure is a higher level consisting of the alpha-helix and the beta-sheets. Due to the hydrogen bonds between the carbonyl and the N-H groups, these two exist in a stable form in a polypeptide backbone.
3. Alpha helix: A polypeptide chain will form a firm, rod-like structure when twisted. The structure can change into a helical conformation.
4. Beta pleated: A sheet is formed when two or more polypeptide chain segments are arranged together side by side. Every chain segment is called a beta-strand.
5. Tertiary structure: It is a three-dimensional protein structure and is formed due to the interaction between the primary structures and the side chains. Hydrophobic interactions, hydrogen bonds, electrostatic interactions, van der Waals forces, and covalent bonds help them become stable.
6. Quaternary structures: Quaternary structures are joined together by the hydrophobic interactions, hydrogen bonds, and electrostatic interactions, and they are composed of two or more polypeptide chains.
7. Fibrous and globular proteins: Fibrous proteins are not soluble in water and are long in structure. They are rod-shaped molecules that are very protective. The globular proteins are soluble in water and are made of spherically shaped molecules.

Nucleic acids

Friedrich Muescher first discovered nucleic acid from the nuclei of pus cells. They are of two kinds: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The monomeric unit of the nucleotides in nucleic acid consists of three ingredients: a nitrogenous base, a five-carbon sugar, and phosphoric acid.

Since the nitrogenous bases have a heterocyclic structure, they are aromatic. Two types of nucleic acids are found, basically, the purines and the pyrimidines. Purines are further categorised into two kinds: adenine and guanine. The pyrimidines are of three types: thymine, cytosine, and uracil. 

Structure of Double-Stranded DNA

DNA consists of a five-carbon sugar and is deoxyribose. RNA is ribose. The nucleotide is formed when the nucleoside adds up with phosphate.

There are two different types of DNA. They are as follows:

B DNA

Some characteristics of the B DNA are given below:

• Two strands of the long polynucleotide are found coiled up around the axis. 
• The two strands are arranged so that they both lie in an antiparallel way to each other.
• Nucleoside adenine base pairs itself with thymine, and guanine base pairs up with cytosine.
• Two hydrogen bonds are formed between adenine and thymine, and in between guanine and cytosine, three hydrogen bonds are formed.

Z DNA

Some characteristics of the Z DNA are given below:

• Z DNA is thinner than B DNA from a structural viewpoint.
• The purine and pyrimidine bases are arranged in an alternative manner.
• The Z DNA has a high concentration of salt, which makes its structure stable.

Denaturation of DNA

Denaturation of DNA is when the two strands of the DNA get separated when they are exposed to varying pH, temperature, etc. The original condition of the structure of DNA can be retained by removing the denaturants such as temperature and pH. This process is then known as renaturation or annealing.

RNA

RNA has a single-stranded structure. It is called ribonucleic acid and is found in various forms inside the cell. The forms of RNA are as follows:

1. Messenger RNA: The prime function of messenger RNA is to convey the genetic information from the parent DNA to the DNA of the next generation. It does so in the form of Codons. Three nucleotides form a codon, and it helps in coding amino acids or proteins.
2. Transfer RNA: The prime function of transfer RNA is to synthesise proteins. They are located within the cytoplasm of a living cell and assist in the interaction between nucleic acid and protein.
3. Ribosomal RNA: Ribosomal RNA contains ribosomes. In the case of both the eukaryotes and the prokaryotes, ribosomes are essential for the synthesis of proteins.

Carbohydrates

Carbohydrates are made of carbon, hydrogen, and oxygen. The polyhydroxy aldehydes or polyhydroxy ketones fall under this category. 

Glucose, a monosaccharide, is the simplest carbohydrate known. The disaccharides are composed of two monosaccharides joined together. The oligosaccharides are composed of around 2 to 10 units of monosaccharides. A polysaccharide is formed when hundreds and thousands of monosaccharides are joined together.

Aldoses are the monosaccharides that constitute the aldehyde group, and ketoses are the monosaccharides that consist of the ketone group. Trioses are the most simple monosaccharides.

Some common saccharides

We all know that the energy in plants is stored in the form of starch. It is a branched structure and is composed of numerous units of glucose. Starch is made of two distinct polymers, amylose and amylopectin. Amylose is the unbranched polymer, and amylopectin is the branched polymer in the glucose units.

The energy is stored in the form of glycogen found in the liver and muscle in case of animals. It is also composed of two distinct polymers, amylose and amylopectin, that has a highly branched polymer structure. In the glucose units, the unbranched polymer is cellulose. In-plant cells, it is a structural polysaccharide. Polysaccharide in the plant cells provides strength and rigidness to the cell, and it is also the organic molecule present in abundance.

Chitin is a linear polysaccharide found in the exoskeleton of insects and crustaceans. It is composed of N-acetyl-D-glucosamine residues.

Reducing and Non-Reducing Sugar

Reducing sugars such as all the monosaccharides helps reduce ferric or cupric ions. Non-reducing sugars like sucrose do not assist in the reduction of ferric or cupric ions.

Lipids

Lipids are compounds that are not soluble in water or are poorly soluble. However, lipids are soluble in non-polar solvents such as chloroform, ether, or benzene.

Biological Functions of Lipids

The biological functions of lipids are given below:

• The essential function of lipids is to store the energy to be utilised later when required.
• In the structure of the membranes, lipids are the major constituent.
• One of the most vital functions of lipids is to protect plants, bacteria, insects, and vertebrates.

Fatty Acids

Fatty acids are the simplest form of lipids, and they are composed of long chains of hydrocarbons with one carboxyl group. The alkyl chain present in it may or may not be saturated. In the case of unsaturated fatty acids, both the polar and nonpolar ends can exist. The essential fatty acids are not synthesised in the body but should be obtained from our diet. The fatty acids that are not important are synthesised in the body. Triacylglycerol is also known as triglycerides in both nonpolar and hydrophobic nature. They are made of esters of fatty acids and glycerol. 

Enzymes

Enzymes are composed of proteins and contain various structures of the proteins, such as the primary, secondary, and tertiary structures. It should be noted that all the enzymes are proteins, but all the proteins are not enzymes. There are specific enzymes for each substrate. Enzymes act as catalysts, and they consist of an active site. An enzyme may require a cofactor and a co-enzyme to function correctly.

The cofactor is called the non-protein constituents that make an enzyme catalytically active when they bind with it. The co-enzyme is the organic compound that binds to an enzyme transiently during the ongoing reaction. Enzymes are of six major types: oxidoreductases, transferases, hydrolases, lyases, ligases, and isomerases.

Factors Affecting the Enzyme Activity

Factors such as temperature, pH, and substrate concentration can affect enzyme activity. It is essential to maintain the required temperature. Otherwise, inactivation of the enzyme activity may take place. Protonation or deprotonation can also alter the enzyme activity. 

The inhibitors are responsible for the inactivation. The most common type of inhibitors is the competitive inhibitors which continuously compete to secure the active site of the enzymes against the substrates. For example, the inhibition of succinate dehydrogenase can be done with the assistance of Malonate.

Class 11 Biology Chapter 9 Revision Notes

Biomolecules can become a challenging chapter as there are a lot of terms and concepts to memorise. The CBSE Class 11 Biology Chapter 9 notes by Extramarks will help students cover all these concepts and memorise them faster. Students can access these notes at any time from the Extramarks’ website.

Class 11 Biology Biomolecules Notes

Revision Notes by Extramarks are prepared by subject matter experts that take care of providing quality content that covers all the important concepts that students need from an exam point of view. These notes will come in very handy for students for their revisions and last-minute preparations.

Ch 9 Bio Class 11 Notes

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Chapter 9 Class 11 Biology Notes

The Revision Notes cover all the essential topics covered in the chapter including biomolecules, lipids, proteins, polysaccharides, nucleic acids, metabolism and its living state, enzymes, regulation of enzymes, and more.