Biomolecules Class 11 Biology Revision Notes

Class 11 Notes

Please see Biomolecules Class 11 Biology Revision Notes provided below. These revision notes have been prepared as per the latest syllabus and books for Class 11 Biology issues by CBSE, NCERT, and KVS. Students should revise these notes for Chapter 9 Biomolecules daily and also prior to examinations for understanding all topics and to get better marks in exams. We have provided Class 11 Biology Notes for all chapters on our website.

Chapter 9 Biomolecules Class 11 Biology Revision Notes

1. Trichloroacetic acid (Cl3CCOOH) 
• Used to analyse chemical composition of living tissue
• Acid-soluble pool →
✔ Compounds found have molecular weights ranging from 18 to around 800 daltons (Da) approximately. @ Micro molecules
• Retentate or the acid-insoluble fraction →
✔ Only four types of organic compounds i.e., proteins, nucleic acids,
polysaccharides and lipids. @ Macro molecules except Lipid
✔ Except lipids, all have molecular weights 10000 daltons and above.

2. All the carbon compounds present in living tissues → ‘Biomolecules’.
3. Amino acids →
• Organic compounds
• Have an amino group and an acidic group on the same carbon
✔ i.e., the alpha-carbon. Hence, they are called α-amino acids.
✔ They are substituted methanes.
• There are four substituent groups
✔ Hydrogen,
✔ Carboxyl group,
✔ Amino group and
✔ A variable group designated as R group.
• Based on the nature of R group there are many amino acids.
• In proteins → only of twenty types of amino acids .
• The R group
✔ a hydrogen → Glycine
✔ a methyl group → Alanine
✔ a hydroxy methyl → Serine
• The chemical and physical properties of amino acids determined by →
✔ Amino group, carboxyl group and the R functional groups.
• Based on number of amino and carboxyl groups,
✔ Acidic (e.g., glutamic acid),
✔ Basic (lysine) and
✔ Neutral (valine) amino acids.
✔ Aromatic amino acids (tyrosine, phenylalanine, tryptophan).
✔ A particular property of amino acids is the ionizable nature of –NH2 and –COOH groups. @ Isoelectric pH & Zwittor ion
Ø In solutions of different pHs, the structure of amino acids changes.

4. Lipids
• Generally water insoluble.
• A fatty acid has a carboxyl group attached to an R group.
• The R group → Generally 1 carbon to 19 carbons
✔ Palmitic acid has 16 carbons
✔ Arachidonic acid has 20 carbon atoms
• Fatty acids
✔ saturated (without double bond)
✔ unsaturated (with one or more C=C double bonds).
✔ Most simple lipid is glycerol which is trihydroxy propane.
• Many lipids have both glycerol and fatty acids.
• Oils have lower melting point (e.g., gingely oil)
• Some lipids have phosphorous and a phosphorylated organic
compound → Phospholipids → Found in cell membrane.
✔ Example – Lecithin
✔ Neural tissues have lipids with more complex structures.

5. Nitrogen Base →
• Heterocyclic rings
• Nitrogen bases – adenine, guanine, cytosine, uracil, and thymine.
• Nitrogen base + sugar → Nucleosides.
✔ Adenosine, guanosine, thymidine, uridine and cytidine are nucleosides.
 Nucleotide = Nucleoside + Phosphate.
✔ Adenylic acid, thymidylic acid, guanylic acid, uridylic acid and cytidylic acid
• Nucleic acids like DNA and RNA consist of nucleotides only.
• DNA and RNA function as genetic material.

• Primary metabolites → Have identifiable functions and play roles in normal physiological processes.
✔ Proteins, amino acids, nucleotides, carbohydrates, lipids etc.
• Secondary metabolites → Not clear understanding about the role or functions of all the ‘secondary metabolites’ in host organisms.
✔ Many useful to ‘human welfare’
✔ Some secondary metabolites have ecological importance.
✔ e.g., rubber, drugs, spices, scents, pigments, alkaloids, flavonoids, rubber, essential oils, antibiotics, coloured pigments, scents, gums, spices.

• Polypeptides.
• Linear chains of amino acids linked by peptide bonds
• Polymer of amino acids.
• 20 types of amino acids (e.g., alanine, cysteine, proline, tryptophan, lysine, etc.),
• Heteropolymer and not a homopolymer.

8. Dietary proteins are the source of essential amino acids. Therefore, amino acids can be essential or non-essential.
• We get essential amino acids through our diet/food.
• Proteins carry out many functions in living organisms, some transport nutrients across cell membrane, some fight infectious organisms, some are hormones, some are enzymes, etc.

9. Collagen is the most abundant protein in animal world

10. Ribulose bisphosphate Carboxylase-Oxygenase (RuBisCO) is the most abundant protein in the whole of the biosphere.

• Long chains of sugars.
• Threads containing different monosaccharides as building blocks.
✔ For example, cellulose (Polymer of beta-D-glucose)
12. Cellulose is a homopolymer.
13. Starch is → A store house of energy in plant tissues.
14. Glycogen is → A store house of energy in animal tissue
15. Inulin is a polymer of fructose. 
16. In Glycogen → The right end is called the reducing end and the left end is called the non-reducing end.
17. Starch forms helical secondary structures. Starch can hold I2 molecules in the helical portion. The starch-I2 is blue in colour.
18. Cellulose does not contain complex helices and hence cannot hold I2 .
19. Plant cell walls, Cotton fibre, Paper pulp are made of cellulose.
20. Complex polysaccharides → Have as building blocks, amino-sugars and chemically modified sugars (e.g., glucosamine, N-acetyl galactosamine, etc.).
• Exoskeletons of arthropods, (chitin)
• These complex polysaccharides are mostly homopolymers.

• Polynucleotides.
• Building block → nucleotide.
• A nucleotide = One is a heterocyclic compound, the second is a monosaccharide and the third a phosphoric acid or phosphate.
• Heterocyclic compounds in nucleic acids are the nitrogenous bases
✔ adenine, guanine, uracil, cytosine, and thymine.
✔ Adenine and Guanine are substituted purines while the rest are substituted pyrimidines..
• The sugar found in polynucleotides → either ribose or 2’ deoxyribose.
✔ A nucleic acid containing deoxyribose → DNA
✔ A nucleic acid containing ribose → RNA

• Biologists describe the protein structure at four levels.
• The sequence of amino acids → Primary structure of a protein.
• The first amino acid is also called as N-terminal amino acid.
• The last amino acid is called the C-terminal amino acid.
• A protein thread is folded in the form of a helix → Secondary structure
• In proteins, only right handed helices are observed.
• In addition, the long protein chain is also folded upon itself → Tertiary structure
• This gives us a 3-dimensional view of a protein.
• Tertiary structure is absolutely necessary for the many biological activities of proteins.
• Some proteins are an assembly of more than one polypeptide or subunits. → quaternary structure of a protein.
✔ Adult human haemoglobin consists of 4 subunits.

• In a protein, amino acids are linked → by peptide bond
✔ formed when the carboxyl (-COOH) group of one amino acid reacts with the amino (-NH2 ) group of the next amino acid
• In a polysaccharide monosaccharides are linked → by glycosidic bond.
✔ formed between two carbon atoms of two adjacent monosaccharides.
• In a nucleic acid nucleotides are linked → by Phosphodiester bond
✔ a phosphate moiety links the 3’-carbon of one sugar of one nucleotide to the 5’-carbon of the sugar of the succeeding nucleotide.

24. Nucleic acids exhibit a wide variety of secondary structures.
• Secondary structures exhibited by DNA is the famous Watson-Crick model. 
✔ DNA is a double helix.
✔ The two strands are antiparallel i.e., run in the opposite direction.
✔ The backbone is formed by the sugar-phosphate-sugar chain.
✔ A and G of one strand pairs with T and C, on the other strand.
✔ 2 H – bonds between A and T and 3 H – bonds between G and C.
✔ Each strand appears like a helical staircase.
✔ Each step of ascent is represented by a pair of bases.
✔ At each step of ascent, the strand turns 36°.
✔ One full turn of the helical strand would involve ten steps or ten base pairs.
✔ The pitch would be 34Å. The rise per base pair would be 3.4Å.
✔ This form of DNA with the above mentioned features is called B-DNA.

25. Biomolecules have a turn over.
• Constantly being changed into some other biomolecules and also made from some other biomolecules.
• Breaking and making is through chemical reactions → metabolism.
• In other words, metabolites are converted into each other in a series of linked reactions called metabolic pathways.
• These metabolic reactions is that every chemical reaction is a catalysed reaction.
• Proteins with catalytic power are named enzymes.

26. Metabolic pathways can lead to
• More complex structure from a simpler structure (biosynthetic or anabolic pathways)
• Simpler structure from a complex structure (catabolic pathways)
• Anabolic pathways, as expected, consume energy.
• catabolic pathways lead to the release of energy.
• Energy currency in living systems is the bond energy in a chemical called adenosine triphosphate (ATP).

27. These biomolecules are in a metabolic flux.

28. Any chemical or physical process moves spontaneously to equilibrium. The steady state is a non-equilibrium state.
29. The living state is a non-equilibrium steady-state to be able to perform work;living process is a constant effort to prevent falling into equilibrium. This is achieved by energy input.
30. Metabolism provides a mechanism for the production of energy. Hence the living state and metabolism are synonymous.
31. Without metabolism there cannot be a living state.
• Almost all enzymes are proteins.
• Ribozymes → catalytic RNA.
• An active site of an enzyme is a crevice or pocket into which the substrate fits.
• Enzymes get damaged at high temperatures (say above 40°C).
• Thermal stability seen in enzymes isolated from thermophilic organisms.
33. Rate of a physical or chemical process refers to the amount of product formed per unit time.
34. There are thousands of types of enzymes each catalysing a unique chemical or metabolic reaction.
35. Enzymes eventually bring down activation energy barrier making the transition of ‘S’ to ‘P’ more easy.
36. Each enzyme (E) has a substrate (S) binding site in its molecule so that a highly reactive enzyme-substrate complex (ES) is produced.
37. This complex is short-lived and dissociates into its product(s) P and the unchanged enzyme with an intermediate formation of the enzyme-product complex (EP).
38. The catalytic cycle of an enzyme action has following steps:
• 1. First, the substrate binds to the active site of the enzyme, fitting into the active site.
• 2. The binding of the substrate induces the enzyme to alter its shape, fitting more tightly around the substrate.
• 3. The active site of the enzyme, now in close proximity of the substrate breaks the chemical bonds of the substrate and the new enzyme- product complex is formed.
• 4. The enzyme releases the products of the reaction and the free enzyme is ready to bind to another molecule of the substrate and run through the catalytic cycle once again.

39. Factors Affecting Enzyme Activity
• The activity of an enzyme can be affected by a change in the conditions which can alter the tertiary structure of the protein.
• These include temperature, pH, change in substrate concentration or binding of specific chemicals that regulate its activity.
• Enzymes generally function in a narrow range of temperature and pH
• Each enzyme shows its highest activity at a particular temperature and pH called the optimum temperature and optimum pH.
• Activity declines both below and above the optimum value.
• Low temperature preserves the enzyme in a temporarily inactive state
• high temperature destroys enzymatic activity because proteins are denatured by heat.

40. Concentration of Substrate
• With the increase in substrate concentration, the velocity of the enzymatic reaction rises at first. → ultimately reaches a maximum velocity (Vmax) which is not exceeded by any further rise in concentration of the substrate. → This is because the enzyme molecules get saturated of these molecules (no free enzyme molecules to bind with the additional substrate molecules)

41. The activity of an enzyme is also sensitive to the presence of specific chemicals that bind to the enzyme. When the binding of the chemical shuts off enzyme activity, the process is called inhibition and the chemical is called an inhibitor.
42. When the inhibitor closely resembles the substrate in its molecular structure and inhibits the activity of the enzyme, it is known as competitive inhibitor.
• e.g., inhibition of succinic dehydrogenase by malonate which closely resembles the substrate succinate in structure. Such competitive inhibitors are often used in the control of bacterial pathogens.
43. Classification and Nomenclature of Enzymes
• Most of these enzymes have been classified into different groups based on the type of reactions they catalyse.
• Enzymes are divided into 6 classes each with 4-13 subclasses and named accordingly by a four-digit number.
✔ Oxidoreductases/dehydrogenases: Enzymes which catalyse oxidationreduction between two substrates
✔ Transferases: Enzymes catalysing a transfer of a group
✔ Hydrolases: Enzymes catalysing hydrolysis of ester, ether, peptide, glycosidic, C-C, C-halide or P-N bonds.
✔ Lyases: Enzymes that catalyse removal of groups from substrates by mechanisms other than hydrolysis leaving double bonds.
✔ Isomerases: Includes all enzymes catalysing inter-conversion of optical, geometric or positional isomers.
✔ Ligases: Enzymes catalysing the linking together of 2 compounds, e.g.,enzymes which catalyse joining of C-O, C-S, C-N, P-O etc. bonds.

44. Co-factors →
• Non-protein constituents
• bound to the enzyme to make the enzyme catalytically active.
• In these instances, the protein portion of the enzymes is called the apoenzyme.
• Three kinds of cofactors may be identified:
✔ prosthetic groups,
✔ co-enzymes and
✔ metal ions.
• Prosthetic groups are organic compounds → tightly bound to the apoenzyme.
• Co-enzymes are also organic compounds → their association with the apoenzyme is only transient, usually occurring during the course of catalysis.
✔ The essential chemical components of many coenzymes are vitamins, e.g.,coenzyme nicotinamide adenine dinucleotide (NAD) and NADP contain the vitamin niacin.
• A number of enzymes require metal ions for their activity
✔ e.g., zinc is a cofactor for the proteolytic enzyme carboxypeptidase.
• Catalytic activity is lost when the co-factor is removed from the enzyme which testifies that they play a crucial role in the catalytic activity of the enzyme.