Biomolecules Notes
Study Notes
Topics
5π 1. Chapter Overview
Overview
Biomolecules are carbon-based compounds present in living systems and are essential for structure, energy, growth, heredity and regulation. In NCERT Class 12 Chemistry, the focus is mainly on carbohydrates, proteins, enzymes, vitamins, nucleic acids and hormones. Carbohydrates act as energy sources and structural materials; proteins form body tissues and catalyse reactions as enzymes; vitamins are required in small amounts for normal metabolism; nucleic acids store and transfer genetic information; and hormones act as chemical messengers. For NEET, the chapter is highly memory-based but also concept-driven, especially in classification, structures, deficiency diseases, enzyme activity and DNA-RNA comparison.
- 1NCERT questions often test classification, examples and deficiency diseases directly.
- 2Carbohydrates are classified as monosaccharides, oligosaccharides and polysaccharides.
- 3Glucose exists mainly in cyclic pyranose form, not as open-chain aldehyde.
- 4Proteins have primary, secondary, tertiary and quaternary structures.
- 5Enzyme activity depends on temperature, pH, substrate concentration and inhibitors.
- 6DNA has complementary base pairing: adenine pairs with thymine, guanine pairs with cytosine.
- 7Hormones differ chemically: some are steroids, some proteins or peptides, and some amino acid derivatives.
Chapter Order Trick
Remember the chapter flow as C-P-V-N-H: Carbohydrates give energy, Proteins build and catalyse, Vitamins assist, Nucleic acids store information, Hormones regulate.
Biomolecule Function Shortcut
Energy = carbohydrates, Body-building = proteins, Control = hormones, Code = nucleic acids, Co-factors = vitamins.
Daily Meal Example
Rice provides starch, pulses provide proteins, fruits provide vitamins, and all cells use DNA/RNA and hormones for growth and regulation.
Exam-Oriented Example
A question asking 'Which vitamin deficiency causes scurvy?' is answered by Vitamin C, while 'Which biomolecule stores hereditary information?' is DNA.
Treating All Biomolecules as Polymers
Carbohydrates, proteins and nucleic acids can be polymeric, but vitamins and most hormones are not polymers.
Confusing Biology and Chemistry Focus
In Chemistry NCERT, emphasis is on structure, classification and chemical nature rather than detailed physiology.
Ignoring Examples
NEET frequently asks direct examples such as sucrose, maltose, insulin, thyroxine, vitamin deficiency and DNA base pairs.
Many simple sugars such as glucose and fructose follow this empirical formula, though it is not a universal definition of carbohydrates.
Variables
n=Number of carbon atoms in the monosaccharide
A peptide bond forms by condensation between the carboxyl group of one amino acid and amino group of another.
Variables
HβO=Water molecule eliminated during peptide bond formation
π 2. Carbohydrates
Overview
Carbohydrates are optically active polyhydroxy aldehydes or ketones, or compounds that produce such units on hydrolysis. They are classified by hydrolysis into monosaccharides, oligosaccharides and polysaccharides, and by functional group into aldoses and ketoses. Glucose is an aldohexose and fructose is a ketohexose. Disaccharides like sucrose, maltose and lactose contain two monosaccharide units joined by glycosidic linkage. Polysaccharides such as starch, cellulose and glycogen are large carbohydrate polymers. Important NEET concepts include reducing and non-reducing sugars, cyclic structures, glycosidic bonds, hydrolysis, oxidation reactions and biological roles such as energy storage, cell wall formation and dietary fibre.
- 1Glucose is an aldohexose with molecular formula CβHββOβ.
- 2Fructose is a ketohexose and is found in fruits and honey.
- 3Sucrose on hydrolysis gives glucose and fructose and is non-reducing.
- 4Maltose gives two glucose units and is a reducing sugar.
- 5Lactose gives glucose and galactose and is a reducing sugar.
- 6Starch contains amylose and amylopectin; glycogen is animal starch.
- 7Cellulose has beta-glycosidic linkages and humans cannot digest it.
Reducing Sugar Trick
Remember: SuCrose is Sealed, so it is non-reducing. Maltose and Lactose have a free end, so they are reducing.
Storage vs Structure
S-G are Storage: Starch in plants, Glycogen in animals. Cellulose is Cell wall.
Aldose and Ketose
GLU-cose has an aldehyde group like GLUe at the end; FRUctose has ketone inside the chain.
Glucose in Blood
Blood glucose is an immediate energy source for cells and is regulated by hormones such as insulin and glucagon.
Cellulose in Diet
Vegetables contain cellulose, which humans cannot digest but which acts as roughage and supports bowel movement.
Sucrose in Daily Life
Common table sugar is sucrose; on hydrolysis it gives glucose and fructose.
Calling All Sugars Reducing
Sucrose is a sugar but non-reducing because both anomeric carbons are involved in glycosidic bonding.
Forgetting Cyclic Glucose
Glucose is often drawn open-chain for convenience, but it mainly exists in cyclic hemiacetal forms.
Confusing Starch and Cellulose
Both are glucose polymers, but starch is digestible storage material while cellulose is structural and indigestible to humans.
Using CβHββOβ as Definition
This formula is useful for many monosaccharides but is not the exact definition of carbohydrates.
Many carbohydrates appear as hydrates of carbon, but this is not a strict definition because some carbohydrates do not fit exactly and some non-carbohydrates do.
Variables
x=Number of carbon atoms
y=Number of water-like HβO units
Glucose is the most common monosaccharide and an aldohexose.
Variables
Cβ=Six carbon atoms
HββOβ=Hydrogen and oxygen in 2:1 ratio
𧬠3. Proteins & Enzymes
Overview
Proteins are natural polymers of alpha-amino acids joined by peptide bonds. Amino acids contain both amino and carboxyl groups and often exist as zwitterions. The sequence of amino acids gives the primary structure, while hydrogen bonding forms secondary structures such as alpha-helix and beta-pleated sheet. Further folding produces tertiary structure, and association of multiple chains gives quaternary structure. Proteins may be fibrous or globular and perform structural, transport, protective, hormonal and catalytic functions. Enzymes are highly specific biological catalysts, mostly proteins, that lower activation energy. NEET frequently tests peptide bond formation, protein denaturation, enzyme specificity, optimum pH and temperature, and factors affecting enzyme activity.
- 1All proteins contain C, H, O, N and often S.
- 2Essential amino acids must be obtained from diet.
- 3Fibrous proteins are usually insoluble and structural; globular proteins are generally soluble and functional.
- 4Hydrogen bonds stabilize secondary structure.
- 5Tertiary structure is stabilized by hydrogen bonds, disulfide bonds, ionic interactions and hydrophobic interactions.
- 6Enzymes lower activation energy but do not change equilibrium constant.
- 7Substrate concentration increases rate only up to saturation.
Protein Structure Order
Remember P-S-T-Q: Primary Sequence, Secondary Turns, Tertiary 3D, Quaternary multiple subunits.
Enzyme Graph Trick
Temperature graph is a hill; substrate graph is a plateau. Hill means denaturation after optimum, plateau means active-site saturation.
Fibrous vs Globular
Fibrous = Fibre = Framework; Globular = Globe = works in solution.
Cooking Egg
When an egg is boiled, albumin protein denatures and coagulates, showing loss of native structure.
Digestive Enzymes
Amylase digests starch, proteases digest proteins and lipases digest fats, showing enzyme specificity.
Insulin
Insulin is a protein hormone that helps regulate blood glucose level.
Assuming Denaturation Breaks Peptide Bonds
Denaturation usually disrupts secondary and tertiary structures, not the primary peptide-bond sequence.
Saying Enzymes Change Equilibrium
Enzymes lower activation energy and speed up attainment of equilibrium but do not change equilibrium constant.
Ignoring Zwitterion Nature
Amino acids have both acidic and basic groups and can exist as dipolar ions.
Confusing Substrate Specificity with Product Quantity
Specificity means an enzyme recognizes a particular substrate or reaction, not that it produces only one molecule.
All standard alpha-amino acids have amino and carboxyl groups attached to the same alpha carbon, with R as side chain.
Variables
R=Side chain that determines amino acid identity
CH=Alpha carbon attached to amino, carboxyl, hydrogen and R group
Condensation reaction between carboxyl group of one amino acid and amino group of another forms a dipeptide.
Variables
R, R'=Side chains of two amino acids
-CO-NH-=Peptide linkage
π 4. Vitamins
Overview
Vitamins are organic compounds required in small amounts for normal growth, metabolism and health. Most vitamins cannot be synthesized in sufficient quantity by the body and must be obtained from diet. They are classified as fat-soluble vitamins, namely A, D, E and K, and water-soluble vitamins, namely B-complex and C. Fat-soluble vitamins are stored in the liver and adipose tissue, so excess intake may cause toxicity. Water-soluble vitamins are generally not stored significantly and must be supplied regularly. NEET questions commonly ask classification, sources, functions and deficiency diseases such as night blindness, rickets, scurvy, beriberi and pernicious anaemia.
- 1Vitamins do not provide energy like carbohydrates, fats or proteins.
- 2They often function as coenzymes or parts of coenzymes.
- 3Fat-soluble vitamins can accumulate in body stores.
- 4Water-soluble vitamins are easily excreted and need regular intake.
- 5Vitamin D can be synthesized in skin under sunlight.
- 6Deficiency diseases are among the most frequently asked NEET facts.
- 7A balanced diet usually prevents vitamin deficiency.
Fat-Soluble Vitamins
Remember: All Dogs Eat Kibble = A, D, E, K are fat-soluble.
Vitamin C
C for Collagen; lack of collagen support causes bleeding gums in scurvy.
Vitamin K
K for Koagulation: Vitamin K helps blood clotting.
Bβ Beriberi
B-one causes Beri-beri: both begin with B.
Sunlight and Vitamin D
Regular exposure to sunlight helps the skin synthesize Vitamin D, which supports bone mineralization.
Citrus Fruits and Vitamin C
Lemon, orange and amla are rich in Vitamin C and help prevent scurvy.
Green Leafy Vegetables
Leafy vegetables provide vitamins such as A, K and folate, supporting vision, clotting and metabolism.
Thinking Vitamins Give Energy
Vitamins regulate metabolism but do not act as calorie-providing fuels.
Mixing Fat-Soluble and Water-Soluble
Only A, D, E and K are fat-soluble; B-complex and C are water-soluble.
Confusing Scurvy and Rickets
Scurvy is due to Vitamin C deficiency; rickets is due to Vitamin D deficiency.
Ignoring Toxicity
Fat-soluble vitamins can accumulate, so excess intake may be harmful.
This is the most important classification formula for quick revision.
Variables
A, D, E, K=Fat-soluble vitamins
B, C=Water-soluble vitamins
𧬠5. Nucleic Acids
Overview
Nucleic acids are biomolecules responsible for storage, transfer and expression of genetic information. Their monomeric units are nucleotides, each containing a nitrogenous base, pentose sugar and phosphate group. DNA contains deoxyribose sugar and bases adenine, guanine, cytosine and thymine, while RNA contains ribose sugar and uracil instead of thymine. DNA generally exists as a double helix with complementary base pairing: A-T and G-C. RNA is usually single-stranded and occurs as mRNA, tRNA and rRNA, each involved in protein synthesis. NEET questions focus on nucleotide composition, DNA-RNA differences, base pairing, types of RNA and functions of nucleic acids.
- 1DNA stores hereditary information and transfers it during cell division.
- 2RNA participates in protein synthesis.
- 3The two DNA strands are complementary and antiparallel.
- 4Hydrogen bonds stabilize base pairs: A-T has two, G-C has three.
- 5A nucleotide is formed when phosphate attaches to a nucleoside.
- 6mRNA carries genetic message from DNA to ribosome.
- 7tRNA brings amino acids during translation.
- 8rRNA is a structural and catalytic component of ribosomes.
Purines
Pure As Gold = Purines are Adenine and Guanine.
DNA vs RNA Base
DNA has T for Thymine; RNA has U for Uracil.
RNA Types
m-t-r: Message, Transfer, Ribosome. mRNA carries message, tRNA transfers amino acid, rRNA builds ribosome.
Hereditary Information
A child's traits are influenced by DNA inherited from parents, because DNA carries genetic information.
Protein Synthesis
mRNA carries instructions, tRNA brings amino acids and rRNA forms ribosomes where proteins are synthesized.
Base Pair Calculation
If a double-stranded DNA sample has 20% adenine, it also has 20% thymine, leaving 60% for G and C together.
Confusing Nucleoside and Nucleotide
Nucleoside has base and sugar only; nucleotide has base, sugar and phosphate.
Pairing A with U in DNA
A pairs with T in DNA. A pairs with U only in RNA pairing contexts.
Calling RNA Always Double-Stranded
RNA is generally single-stranded, though it may fold into complex shapes.
Forgetting Sugar Difference
DNA has deoxyribose, RNA has ribose. This difference is a favourite NEET fact.
A nucleoside lacks phosphate group.
Variables
Base=Purine or pyrimidine nitrogenous base
Pentose sugar=Ribose or deoxyribose
Nucleotides polymerize to form nucleic acids.
Variables
Nucleoside=Base attached to pentose sugar
Phosphate=Phosphoric acid residue
π©Ί 6. Hormones
Overview
Hormones are chemical messengers secreted by endocrine glands directly into blood and transported to target organs where they regulate physiological and metabolic processes. Chemically, hormones may be steroids, proteins, peptides or amino acid derivatives. They act in very small quantities and help maintain homeostasis, growth, development, metabolism, reproduction and stress responses. Important examples include insulin and glucagon for blood glucose regulation, thyroxine for metabolic rate, adrenaline for emergency response, growth hormone for body growth and sex hormones for reproductive functions. NEET questions usually test source gland, chemical nature, biological function and basic disorder associations such as diabetes mellitus, goitre, dwarfism and gigantism.
- 1Endocrine glands are ductless glands.
- 2Hormone action is specific because target cells have suitable receptors.
- 3Peptide and protein hormones generally act through membrane receptors.
- 4Steroid hormones can pass through cell membranes and affect gene expression.
- 5Negative feedback commonly regulates hormone secretion.
- 6Chemical classification is important in Chemistry: steroid, peptide/protein or amino acid derivative.
- 7Hormonal disorders in this chapter are overview-level, not detailed pathology.
Insulin vs Glucagon
INsulin puts glucose IN cells, so blood glucose decreases. Glucagon gives glucose to blood, so blood glucose increases.
Thyroxine
Thyroxine is tied to Thyroid and iodine; remember thyroid controls metabolic speed.
Adrenaline
Adrenaline = Alarm hormone: increases heartbeat, breathing and readiness during emergency.
Steroid Hormones
Sex hormones are steroid hormones: testosterone, estrogen and progesterone.
After Eating
Blood glucose rises after a meal, causing insulin release from the pancreas to help cells take up glucose.
Fear Response
During sudden danger, adrenaline increases heart rate and prepares muscles for rapid action.
Iodine and Thyroid
Low iodine intake can reduce thyroid hormone synthesis and may cause goitre.
Calling Hormones Enzymes
Hormones are messengers; enzymes are catalysts. Some hormones are proteins, but that does not make them enzymes.
Forgetting Target Specificity
Hormones circulate widely but act only on cells having specific receptors.
Confusing Insulin and Glucagon
Insulin decreases blood glucose, whereas glucagon increases blood glucose.
Assuming All Hormones Are Proteins
Hormones can be proteins, peptides, steroids or amino acid derivatives.
This summarizes how hormones function as long-distance chemical messengers.
Variables
Endocrine gland=Ductless gland secreting hormone into blood
Target organ=Organ or tissue with receptors for the hormone
Insulin and glucagon show antagonistic control of blood sugar level.
Variables
Insulin=Hormone that decreases blood glucose
Glucagon=Hormone that increases blood glucose
Formula Sheet
10Many simple sugars such as glucose and fructose follow this empirical formula, though it is not a universal definition of carbohydrates.
Variables
n=Number of carbon atoms in the monosaccharide
A peptide bond forms by condensation between the carboxyl group of one amino acid and amino group of another.
Variables
HβO=Water molecule eliminated during peptide bond formation
Nucleotides are building blocks of DNA and RNA.
Variables
Base=Purine or pyrimidine nitrogenous base
Sugar=Ribose in RNA or deoxyribose in DNA
Phosphate=Phosphoric acid residue
Many carbohydrates appear as hydrates of carbon, but this is not a strict definition because some carbohydrates do not fit exactly and some non-carbohydrates do.
Variables
x=Number of carbon atoms
y=Number of water-like HβO units
Glucose is the most common monosaccharide and an aldohexose.
Variables
Cβ=Six carbon atoms
HββOβ=Hydrogen and oxygen in 2:1 ratio
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The following reaction depicts the activity of a particular class of enzymes: Identify the enzyme class 'E' from the following options:
Match List I with List II: Choose the correct answer from the options given below :
Which of the following statements are correct regarding amino acids? A. They are substituted methanes. B. Serine is an aromatic amino acid. C. Valine is a neutral amino acid. D. Lysine is an acidic amino acid. Choose the correct answer from the options given below:
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