Class 12 Chemistry · Chapter 10
Short answer:
Ye Class 12 Chemistry Part II ka final chapter hai — Biomolecules. NCERT exercise me 14 questions hain (carbohydrates classification aur mutarotation se lekar protein structure levels, denaturation, vitamin deficiency diseases aur DNA-RNA differences tak). Is page me poore 14 exercise questions solve kiye gaye hain, plus reference tables (protein structure levels, vitamin-deficiency table, DNA vs RNA comparison), 6 common exam mistakes, aur board-style PYQs.
Biomolecules woh organic compounds hain jo living organisms ke andar structure aur function ke liye zaroori hain. Ye chapter chaar major classes cover karta hai — carbohydrates (energy source), proteins (structure aur enzymes), vitamins (micronutrients), aur nucleic acids (genetic information). Board exam me structure-based aur classification-based questions bohot common hain, isliye definitions aur diagrams dono clear hone chahiye.
Chapter 10 Summary — 5 Minute Revision
1. Carbohydrates
Carbohydrates optically active polyhydroxy aldehydes ya ketones hain, ya woh compounds jo hydrolysis pe aise banate hain. Inhe saccharides bhi kehte hain.
- Monosaccharides: Simplest carbohydrate jo hydrolysis se aur chhote units me nahi tootta. E.g. glucose (C6H12O6), fructose, ribose.
- Oligosaccharides: Hydrolysis pe 2-10 monosaccharide units dete hain. Sabse common hain disaccharides (2 units) — sucrose, maltose, lactose.
- Polysaccharides: Bahut saari monosaccharide units polymerised — starch, cellulose, glycogen. Ye generally sweet nahi hote isliye non-sugars kehlate hain.
Reducing vs non-reducing sugar: Agar sugar Tollens' ya Fehling's reagent ko reduce kar sake (free -CHO ya free ketonic group ki wajah se), toh reducing sugar hai. Sab monosaccharides (aldoses aur ketoses dono) reducing hote hain. Disaccharides me — maltose aur lactose reducing hain (free anomeric OH available), lekin sucrose non-reducing hai kyunki glucose ka C1 aur fructose ka C2 dono anomeric carbons glycosidic bond me involved hain — free anomeric OH bacha hi nahi.
Glucose ki open-chain structure: CHO-(CHOH)4-CH2OH. Lekin glucose ki kaafi properties (jaise aldehyde test na dena reliably, mutarotation) open-chain se explain nahi hoti — isliye cyclic structure propose hui.
Cyclic structure aur mutarotation: Glucose ka C1 (aldehyde carbon) aur C5 ka -OH group intramolecularly react karke six-membered ring (pyranose) banate hain — is process me C1 naya asymmetric centre ban jaata hai jise anomeric carbon kehte hain. Do cyclic forms banti hain: α-D-glucose aur β-D-glucose, jo sirf C1 pe OH ki orientation me differ karte hain (anomers). Jab pure α ya pure β form ko water me dissolve karte hain, unka specific rotation gradually change hoke ek equilibrium value pe aa jaata hai (+52.5°) — is phenomenon ko mutarotation kehte hain. Ye isliye hota hai kyunki solution me α aur β forms open-chain form ke through interconvert hote rehte hain jab tak equilibrium mixture (~36% α + 64% β) nahi ban jaata.
Fructose: Ketohexose hai, cyclic form me five-membered ring (furanose) banata hai.
Disaccharides: Sucrose (glucose + fructose, α1-β2 glycosidic linkage, non-reducing), Maltose (glucose + glucose, α1-4 linkage, reducing), Lactose (glucose + galactose, β1-4 linkage, reducing — milk sugar).
Polysaccharides: Starch (amylose — unbranched, α1-4 linked; amylopectin — branched, α1-4 + α1-6), Cellulose (unbranched, β1-4 linked — plant cell wall), Glycogen (highly branched, animal storage form — "animal starch").
2. Proteins
Proteins amino acids ke polymers hain, jo peptide bond se jude hote hain.
Amino acids: General structure me ek amino group (-NH2) aur ek carboxyl group (-COOH) same carbon (α-carbon) se attached hote hain — isliye inhe α-amino acids kehte hain.
- Essential amino acids: Jo body synthesize nahi kar sakti, diet se lene padte hain (e.g. valine, leucine).
- Non-essential amino acids: Body khud synthesize kar sakti hai (e.g. glycine, alanine).
- Neutral amino acids: Ek -NH2 aur ek -COOH group (e.g. glycine, alanine).
- Acidic amino acids: Extra -COOH group (e.g. glutamic acid, aspartic acid).
- Basic amino acids: Extra -NH2 group (e.g. lysine, arginine).
Amino acids solid state me aur aqueous solution me zwitterion (dipolar ion) form me exist karte hain — -NH2 proton leke NH3+ ban jaata hai aur -COOH proton dekar COO- ban jaata hai.
Peptide bond: Ek amino acid ke -COOH group aur doosre amino acid ke -NH2 group ke beech, water molecule elimination ke saath bana amide linkage (-CO-NH-).
Protein structure ke levels (detail formulas table me):
- Primary structure: Sirf amino acid sequence.
- Secondary structure: Polypeptide chain ka shape — sirf hydrogen bonding se banti hai. Alpha helix aur beta pleated sheet dono isi H-bonding ke alag patterns hain.
- Tertiary structure: Overall 3D folding — secondary structures ka further folding, jo protein ko biological activity deta hai.
- Quaternary structure: Do ya zyada polypeptide subunits ka spatial arrangement (e.g. haemoglobin — 4 subunits).
Denaturation: Jab protein ko heat, pH change, ya heavy metal salts se treat karte hain, toh hydrogen bonds disturb hote hain aur globular protein unfold ho jaata hai (globule se fibrous ban jaata hai) — biological activity chali jaati hai. Important: denaturation me sirf secondary aur tertiary structure disturb hoti hai, primary structure (peptide bonds) intact rehti hai — isliye ye hydrolysis se different hai (hydrolysis me peptide bonds bhi toot jaate hain). Example: egg boiling — albumin coagulate ho jaata hai.
3. Enzymes (brief)
Enzymes globular proteins hain jo biological catalysts ki tarah kaam karte hain — biochemical reactions ko highly specific aur mild conditions (body temperature, physiological pH) pe fast karte hain. E.g. amylase starch ko maltose me convert karta hai.
4. Vitamins
Vitamins organic compounds hain jo body ko thodi matra me chahiye taaki normal functioning ho sake — inhe body synthesize nahi kar sakti (kuch exceptions chhodkar), diet se lene padte hain.
- Fat-soluble vitamins: A, D, E, K — fats/oils me store hote hain, liver aur adipose tissue me accumulate hote hain.
- Water-soluble vitamins: B-group aur C — body me store nahi hote (regularly excrete hote hain urine ke through), isliye regular intake zaroori hai.
Deficiency diseases ki full list formulas table me hai — ye highly factual recall topic hai, exact pairing yaad rakhna zaroori hai.
5. Nucleic Acids
Nucleic acids (DNA aur RNA) genetic information carry karte hain aur protein synthesis control karte hain. Ye nucleotides ke polymers hain.
Nucleotide ke 3 components: Pentose sugar + Nitrogenous base + Phosphate group. (Base + sugar mila ke sirf "nucleoside" banta hai, phosphate add hone pe "nucleotide" banta hai.)
Sugar: DNA me deoxyribose, RNA me ribose.
Bases: Purines — Adenine (A), Guanine (G) — dono me common. Pyrimidines — DNA me Cytosine (C) aur Thymine (T); RNA me Cytosine (C) aur Uracil (U) (Thymine ki jagah Uracil).
Base pairing rules: DNA (double helix, Watson-Crick model) me A pairs with T (2 H-bonds) aur G pairs with C (3 H-bonds). RNA (usually single-stranded) me protein synthesis ke time A pairs with U aur G pairs with C — kyunki RNA me Thymine hai hi nahi.
Functions: DNA — heredity information store/transfer karta hai (replication). RNA — teen types: m-RNA (message carry karta hai DNA se ribosome tak), t-RNA (amino acids transfer karta hai), r-RNA (ribosome ka structural/functional part, protein synthesis site).
Poore Class 12 Chemistry ke handwritten colour notes
IITian & district toppers ke banaye short notes — revision-ready, diagram ke saath. Board se pehle poora syllabus 3 din me revise.
Exercise Questions — Solutions (Q1–Q14)
Q1. What are monosaccharides?
Monosaccharides woh carbohydrates hain jo hydrolysis pe aur chhote polyhydroxy aldehyde ya ketone units me nahi toot sakte. Ye simplest form ke carbohydrates hain. Example: glucose (C6H12O6), fructose, ribose, galactose.
Q2. What are reducing sugars?
Woh carbohydrates jinme free aldehyde group (-CHO) ya free ketonic group (>C=O) present hota hai, jo unhe Tollens' reagent aur Fehling's solution ko reduce karne ke capable banata hai, reducing sugars kehlate hain. Sab monosaccharides (chahe aldose ho ya ketose) reducing sugars hote hain. Disaccharides me maltose aur lactose reducing hain kyunki free anomeric -OH bacha rehta hai, lekin sucrose non-reducing hai.
Q3. Write the Haworth structures of maltose and lactose.
Maltose: Do α-D-glucose units α-1,4-glycosidic linkage se jude hain (ek unit ke C1 se doosre unit ke C4 tak) — free anomeric OH doosre unit pe bacha rehta hai isliye reducing hai.
Lactose: β-D-galactose aur β-D-glucose β-1,4-glycosidic linkage se jude hain — is me bhi free anomeric OH bacha rehta hai isliye reducing hai. (Exact Haworth diagram ke liye NCERT textbook figure refer karo — is text answer me sirf linkage describe kiya gaya hai.)
Q4. What is the basic structural difference between starch and cellulose?
Starch me glucose units α-glycosidic linkage se jude hote hain (amylose — unbranched α1-4; amylopectin — branched α1-4 + α1-6). Cellulose me glucose units sirf β-glycosidic linkage (β1-4) se jude hote hain aur ye completely unbranched, linear chain hai. Ye linkage difference (α vs β) hi wajah hai ki human digestive system starch digest kar sakta hai lekin cellulose nahi.
Q5. What happens when D-glucose is treated with the following reagents? (i) HI (ii) Bromine water (iii) HNO3
(i) HI (strong reducing agent, prolonged heating): Glucose completely reduce hoke n-hexane ban jaata hai — ye prove karta hai ki glucose ki carbon chain straight/unbranched hai.
(ii) Bromine water (mild oxidising agent): Sirf -CHO group oxidise hota hai -COOH me — gluconic acid banta hai. Ye prove karta hai ki glucose me -CHO group present hai (aur cyclic form me free aldehyde nahi hota, isiliye ring structure ka support milta hai).
(iii) HNO3 (strong oxidising agent): Dono terminal groups (-CHO aur -CH2OH) oxidise hoke -COOH ban jaate hain — saccharic acid banta hai. Ye prove karta hai ki glucose me primary alcoholic group (-CH2OH) bhi present hai.
Q6. What are the expected products of hydrolysis of lactose?
Lactose ki hydrolysis se ek molecule D-galactose aur ek molecule D-glucose milta hai, jo β-1,4-glycosidic linkage se jude hote hain.
Q7. How do you explain the absence of aldehyde group in the pentaacetate of D-glucose?
D-glucose pentaacetate banane ke liye glucose cyclic (ring) form me hota hai, jisme C1 pe free -OH group hota hai (anomeric OH), free -CHO group nahi. Jab acetylation hoti hai to woh cyclic hemiacetal OH bhi acetate ban jaata hai. Isliye pentaacetate me free aldehyde group present nahi hota — ye cyclic (hemiacetal) structure ko support karta hai, open-chain structure ko nahi.
Q8. The melting points and solubility in water of amino acids are generally higher than that of the corresponding halo acids. Explain.
Amino acids solid state aur solution me zwitterion (dipolar ion, H3N+-CHR-COO-) form me exist karte hain. Zwitterionic form ki wajah se strong electrostatic (ionic) forces of attraction molecules ke beech hoti hain, jaisa ionic solids me hota hai — isliye melting point high hota hai aur polar water me solubility bhi zyada hoti hai. Halo acids me aisi zwitterion formation nahi hoti, isliye unki intermolecular forces weaker hoti hain.
Q9. Why are vitamin A and vitamin C essential to us? Give their important sources.
Vitamin A: Healthy eyes (specifically retina ki rod cells me rhodopsin banane ke liye) ke liye zaroori hai — deficiency se night blindness hoti hai. Bhi skin health maintain karta hai. Sources: fish liver oil, carrots, butter, milk.
Vitamin C: Collagen synthesis, wound healing, aur immunity ke liye zaroori hai — deficiency se scurvy hota hai (bleeding gums). Water-soluble hone ki wajah se body me store nahi hota, regular intake chahiye. Sources: citrus fruits (amla, orange, lemon), green leafy vegetables.
Q10. Why do we require carbohydrates in our diet?
Carbohydrates body ka primary energy source hain — glucose oxidation se ATP banta hai jo cellular activities ke liye energy deta hai. Excess glucose glycogen ke roop me store hota hai. Ye cell membrane structure (glycoproteins/glycolipids), fibre (dietary roughage se digestion help), aur plant structural component (cellulose) ke roop me bhi zaroori hain.
Q11. What are essential and non-essential amino acids? Give one example each.
Essential amino acids: Jo body synthesize nahi kar sakti aur diet se lena padta hai. Example: valine, leucine.
Non-essential amino acids: Jo body khud adequately synthesize kar sakti hai. Example: glycine, alanine.
Q12. Define the term co-enzyme.
Kai enzymes ki catalytic activity ke liye ek non-protein, organic small molecule ki need hoti hai jo protein part ke saath jud kar hi enzyme active karta hai — is non-protein organic molecule ko co-enzyme kehte hain. Kaafi vitamins co-enzymes ki tarah kaam karte hain (e.g. Vitamin B group ke coenzyme forms).
Q13. What is the effect of denaturation on the structure of proteins?
Denaturation me protein ki secondary aur tertiary structure disturb ho jaati hai — hydrogen bonds toot jaate hain jo secondary/tertiary structure maintain karte the. Globular protein unfold hoke fibrous ban jaata hai. Iski biological activity (enzyme activity) khatam ho jaati hai. Important: primary structure (peptide bonds, amino acid sequence) intact rehti hai — sirf 3D shape disturb hoti hai. Example: egg white ka boiling pe coagulate hona.
Q14. How are vitamins classified? Name the vitamin responsible for the coagulation of blood.
Vitamins do classes me classify hote hain solubility ke basis pe:
- Fat-soluble: A, D, E, K — body me (liver, fat tissue) store ho sakte hain.
- Water-soluble: B-group aur C — body me store nahi hote, regular intake chahiye.
Vitamin K blood coagulation (clotting) ke liye responsible hai — iski deficiency se increased blood clotting time hota hai.
Important Equations — Ek Nazar Me
| Protein structure level | Kya define karta hai |
|---|---|
| Primary structure | Sirf amino acids ka linear sequence (kaunsa amino acid kis order me hai) |
| Secondary structure | Polypeptide chain ka shape — sirf hydrogen bonding se banta hai. Do main types: α-helix aur β-pleated sheet |
| Tertiary structure | Overall 3D folding (secondary structures ka further folding) — biological activity ke liye zaroori |
| Quaternary structure | 2 ya zyada polypeptide subunits ka spatial arrangement (e.g. haemoglobin ke 4 subunits) |
↔ Table ko side me swipe karein
| Vitamin | Solubility | Deficiency disease |
|---|---|---|
| A (Retinol) | Fat-soluble | Night blindness (Xerophthalmia) |
| B1 (Thiamine) | Water-soluble | Beri-beri |
| B2 (Riboflavin) | Water-soluble | Cheilosis (mouth/lip cracking), digestive disorders |
| B6 (Pyridoxine) | Water-soluble | Convulsions |
| B12 (Cyanocobalamin) | Water-soluble | Pernicious anaemia |
| C (Ascorbic acid) | Water-soluble | Scurvy (bleeding gums) |
| D (Calciferol) | Fat-soluble | Rickets (children), Osteomalacia (adults) |
| E (Tocopherol) | Fat-soluble | Increased fragility of RBCs, muscular weakness; infertility |
| K (Phylloquinone) | Fat-soluble | Increased blood clotting time (haemorrhage) |
↔ Table ko side me swipe karein
| Feature | DNA | RNA |
|---|---|---|
| Sugar | Deoxyribose (2'-deoxy) | Ribose |
| Purine bases | Adenine, Guanine | Adenine, Guanine |
| Pyrimidine bases | Cytosine, Thymine | Cytosine, Uracil (Thymine ki jagah) |
| Strands | Double-stranded (double helix) | Usually single-stranded |
| Base pairing | A=T (2 H-bonds), G≡C (3 H-bonds) | A=U, G≡C (during protein synthesis pairing) |
| Function | Genetic information store aur transfer (heredity, replication) | Protein synthesis (m-RNA, t-RNA, r-RNA) |
| Location | Mainly nucleus | Nucleus aur cytoplasm dono |
↔ Table ko side me swipe karein
Common Mistakes — Yahan Marks Kat te Hain
- Sucrose ko reducing sugar samajhna. Sucrose non-reducing hai kyunki glycosidic bond dono anomeric carbons (glucose C1 aur fructose C2) ko involve karta hai — free anomeric OH bachta hi nahi. Sirf maltose aur lactose reducing disaccharides hain, sucrose nahi.
- DNA aur RNA ke base-pairing rules mix karna. DNA me Adenine, Thymine se pair karta hai (A-T). RNA me Thymine hota hi nahi — Adenine, Uracil se pair karta hai (A-U). Guanine-Cytosine pairing dono me same rehti hai (G-C). Ye ek high-frequency factual recall mistake hai.
- Water-soluble aur fat-soluble vitamins ko galat classify karna. Yaad rakhne ka tarika: A, D, E, K fat-soluble (in-organic solvents me dissolve, body me store hote hain). B-group aur C water-soluble hain (store nahi hote, regularly excrete hote hain — isliye inki daily intake zaroori hai).
- Protein structure ke levels ki definitions confuse karna. Secondary structure sirf hydrogen bonding se banti hai (alpha helix/beta sheet) — students isse tertiary (jo overall 3D folding hai, jisme disulfide bonds, hydrophobic interactions bhi involve hote hain) ke saath confuse kar dete hain. Primary = sirf sequence, Quaternary = multiple subunits ka arrangement.
- Denaturation ko hydrolysis samajhna. Denaturation me sirf secondary/tertiary structure (H-bonds) disturb hoti hai — peptide bonds (primary structure) intact rehte hain, biological activity chali jaati hai. Hydrolysis me peptide bonds khud toot jaate hain aur protein amino acids me break ho jaata hai. Dono alag processes hain.
- Glucose ki open-chain structure se hi saari properties explain karne ki koshish karna. Kuch properties (jaise Schiff's test negative aana, mutarotation exist karna, pentaacetate me free -CHO absent hona) sirf cyclic (hemiacetal) structure se explain hoti hain — open-chain structure inhe justify nahi kar paati. Exam me dono forms ka context samajh kar answer likhna zaroori hai.
Board-Style Important Questions
- 1 mark: Sucrose ko invert sugar kyun kaha jaata hai?
- 1 mark: RNA me thymine ki jagah kaunsa base hota hai?
- 2 marks: Reducing aur non-reducing sugar me difference batao, ek-ek example ke saath.
- 3 marks: Protein ki secondary aur tertiary structure me difference spashta karo.
- 3 marks: Denaturation of protein kya hai? Ek suitable example ke saath explain karo.
- 5 marks: DNA aur RNA ki structure me kya-kya differences hain? Table banakar explain karo.
Aksar Poochhe Jaane Wale Sawaal
Glucose open-chain hai ya cyclic?
Glucose predominantly cyclic (pyranose, six-membered ring) form me exist karta hai aqueous solution me, lekin ek chhoti equilibrium concentration open-chain form ki bhi hoti hai. Kuch reactions (jaise HCN addition) open-chain form se hoti hain, isliye dono forms samajhna zaroori hai.
Mutarotation sirf glucose me hoti hai kya?
Nahi, mutarotation kisi bhi sugar me ho sakti hai jiska cyclic hemiacetal/hemiketal structure ho aur jisme anomeric carbon free ho — jaise fructose, maltose, lactose. Sucrose me nahi hoti kyunki usme koi free anomeric carbon nahi hai.
Essential aur non-essential amino acids ki list yaad karni padegi kya?
NCERT syllabus me exact naam yaad karne ki jagah concept samajhna zaroori hai — essential woh jo body synthesize nahi kar sakti (diet se lena padta hai), non-essential woh jo body khud bana leti hai. Exam me sirf ek-ek example (jaise valine aur glycine) kaafi hota hai.
Peptide bond aur glycosidic bond me kya farak hai?
Peptide bond amino acids ke beech -CO-NH- linkage hai (amide bond, water elimination se banta hai). Glycosidic bond monosaccharides ke beech -O- linkage hai (ether-type bond, ek sugar ke anomeric carbon aur doosre sugar ke -OH ke beech). Dono condensation reactions se banate hain lekin structurally alag hain.
Kya sab fat-soluble vitamins body me store hote hain isliye overdose safe hai?
Nahi — fat-soluble vitamins (A, D, E, K) body me accumulate hote hain isliye inka excess intake toxic (hypervitaminosis) ho sakta hai, jaise Vitamin A ya D ki overdose harmful hai. Water-soluble vitamins me ye risk kam hota hai kyunki excess urine se excrete ho jaata hai.
t-RNA aur m-RNA me kya difference hai?
m-RNA (messenger RNA) DNA se genetic information copy karke ribosome tak le jaata hai — protein synthesis ka 'blueprint' hai. t-RNA (transfer RNA) specific amino acids ko ribosome tak transport karta hai jahan m-RNA ke sequence ke hisaab se protein banti hai. r-RNA ribosome ka structural component hai jahan ye synthesis hoti hai.
Class 12 Chemistry — Saare Chapters
Board exam tak sirf revision karna hai?
Class 12 Chemistry ke saare chapters ke colour handwritten short notes — diagrams, formulas aur important points ek jagah.
NCERT Kaksha ek swatantra shaikshik platform hai aur NCERT ya CBSE se aadhikarik roop se sambaddh (officially affiliated) nahi hai. Kisi galti ki jaankari dene ke liye contact kijiye.