Biomolecules: Class 12 Chemistry Chapter 10 Hinglish mein

Dal, chawal aur dahi ki ek plate socho. Chawal mein zyadatar starch hai, dal protein se bhari hai, aur dahi milk sugar, fat aur bahut saare helpful bacteria laata hai. Kuch hi ghanton mein tumhara body in bade molecules ko tod deta hai aur un tukdon se apni cheezein dobara banane lagta hai: muscle, blood cells, aur har baar cell divide hone par tumhare DNA ki ek nayi copy.

Living things jo molecules banate aur use karte hain, unhe biomolecules (जैव-अणु) kehte hain. Bade families hain carbohydrates, proteins, nucleic acids aur lipids, aur chhote helpers jaise vitamins, hormones aur mineral ions chemistry ko sahi track par rakhte hain. In molecules mein se koi bhi akela zinda nahi hai. Life tab banti hai jab inke hazaaron reactions paani mein, body temperature par, har ek sahi pal par, saath-saath chalte hain, aur us chemistry ki study ko biochemistry kehte hain.

Yeh unit families ko ek-ek karke leta hai: har ek kis cheez se bana hai, uske units kaise jude hain, aur uska structure uske kaam ko kaise samjhata hai. Raaste mein tum pichhle units ke ideas dobara use karoge: aldehydes, ketones, amines aur acids; optical activity aur stereocentres (Unit 6); aur chemical kinetics se activation energy.

10.1 Carbohydrates

Tumhari chai ki sugar, chapati ka starch aur cotton shirt ka cellulose, sab carbohydrates hain. Green plants inhe carbon dioxide aur paani se sunlight ki energy use karke banate hain, aur lagbhag har doosra organism, tum bhi, isi supply par jeeta hai. Family ke chhote, meethe, paani mein ghulne wale members ko sugars kehte hain, aur poori family ko saccharides bhi kehte hain, jo sugar ke Greek word se aaya hai.

Carbohydrate naam early chemistry ki ek bachi hui nishani hai. In compounds mein se kai ke formulas $\mathrm{C}{\phantom{X}}_x(\mathrm{H}{\phantom{X}}_2\mathrm{O}){\phantom{X}}_y$ mein fit hote hain: table sugar, $\mathrm{C}{\phantom{X}}_{12}\mathrm{H}{\phantom{X}}_{22}\mathrm{O}{\phantom{X}}_{11}$, ko $\mathrm{C}{\phantom{X}}_{12}(\mathrm{H}{\phantom{X}}_2\mathrm{O}){\phantom{X}}_{11}$ likh sakte hain, jaise woh carbon plus paani ho. Lekin test ke roop mein yeh formula dono taraf fail hota hai, jaisa agla example dikhata hai.

Carbohydrates mein asal mein jo common hai, woh functional groups ka ek set hai. Chemically, carbohydrate ek polyhydroxy aldehyde ya polyhydroxy ketone (optically active) hota hai, ya ek bada molecule jo hydrolysis par aise units mein toot jaata hai; polyhydroxy ka matlab bas itna hai ki usmein kai –OH groups hain.

10.1.1 Carbohydrates ka Classification

Carbohydrates ko sort karne ka sabse useful tareeka yeh poochhna hai ki hydrolysis unke saath kya karta hai (Fig. 10.1). Dilute acid ke saath ubaalne par, ya sahi enzyme ke saath treat karne par, carbohydrate apne sugar units ke beech ke links par paani leta hai, aur links toot jaate hain.

• Monosaccharides sabse simple sugars hain, woh units jinse baaki sab kuch banta hai; hydrolysis inhe usi tarah ki kisi chhoti cheez mein nahi tod sakta. Glucose, galactose aur pentose ribose iske examples hain, aur nature mein sirf lagbhag bees hi milte hain.
• Oligosaccharides (Greek oligos, yaani thode) thode se units mein tootte hain, do se das tak. Disaccharide do deta hai, trisaccharide teen, aur aise hi aage. Do-unit wala type hi tumhe sabse zyada milta hai, chahe uske dono halves same hon, jaise trehalose (glucose + glucose, insects ke blood ki sugar) mein, ya alag hon, jaise lactose (galactose + glucose) mein.
• Polysaccharides saikdon ya hazaaron units ki bahut lambi chains hain. Kyunki inka koi taste nahi hota, inhe kabhi-kabhi non-sugars kehte hain; aloo ka starch, cotton ka cellulose aur kuch pedon se risne wala gum, sab polysaccharides hain.

Ek doosra, chemical test carbohydrates ko is baat se sort karta hai ki woh reducing agents ki tarah kaam karte hain ya nahi. Sugar ko Tollens' reagent ke saath garam karo, to silver mirror banta hai; Fehling's solution ke saath garam karo, to copper(I) oxide ka brick-red precipitate aata hai. Jo sugars yeh results dete hain, woh reducing sugars (अपचायी शर्करा) hain. Har monosaccharide pass hota hai, aldoses ke saath ketoses bhi.11Fructose mein koi –CHO group nahi hai, phir bhi woh dono reagents ko reduce karta hai: unke alkaline solution mein woh ek enediol ke through aldoses mein rearrange ho jaata hai. Badi sugars ke liye jawab is par depend karta hai ki units kaise jude hain (Section 10.1.3).

10.1.2 Monosaccharides

Monosaccharide ka naam do features se rakha jaata hai: uska carbonyl group aur uske carbon atoms ki sankhya. Aldose mein chain ke ek end par aldehyde group, $-\mathrm{C}\mathrm{H}\mathrm{O}$, hota hai; ketose mein keto group, $>\mathrm{C}=\mathrm{O}$, hota hai, aksar carbon 2 par. Carbon count se triose (3 C), tetrose (4), pentose (5), hexose (6) aur heptose (7) milte hain, aur dono ideas mil kar ek word banate hain: glucose ek aldohexose hai aur fructose ek ketohexose (Table 10.1).

10.1.2.1 Glucose

Glucose woh sugar hai jo tumhara blood har cell tak le jaata hai, aur woh unit jisse starch, glycogen aur cellulose bante hain; un polymers mein bandh glucose ko bhi gino, to Earth par koi bhi organic building block isse zyada nahi hai. Pake fruits aur honey mein yeh free milta hai. Iske do purane naam iski history yaad dilate hain: grape sugar, iske sabse famous source ke naam par, aur dextrose, kyunki iska solution plane-polarised light ko right ki taraf ghumata hai.

Preparation. Glucose banane ke dono raaste hydrolysis hain. Laboratory mein starting material cane sugar hai: iske alcoholic solution ko thode se dilute mineral acid ke saath garam karne par har sucrose molecule ek glucose aur ek fructose mein toot jaata hai.

Bade scale par raw material makka ya cassava ka sasta starch hai. Pehle ise pressure vessels mein lagbhag 393 K par dilute sulfuric acid ke saath pakaya jaata tha; ab zyadatar factories enzymes amylase aur glucoamylase se kam temperature par yeh cutting karwati hain.

Structure nikaalna. X-ray methods se pehle chemists ko structures reactions se nikaalne padte the, ek baar mein ek sawaal (Fig. 10.2):

1. Har tarah ke kitne atoms? Combustion analysis aur molar-mass measurement isse tay kar dete hain: $\mathrm{C}{\phantom{X}}_6\mathrm{H}{\phantom{X}}_{12}\mathrm{O}{\phantom{X}}_6$.
2. Kya carbon skeleton branched hai? Hydrogen iodide, kaafi der tak, har oxygen hata deta hai aur n-hexane chhod deta hai, jo unbranched alkane hai.
3. Kya carbonyl group hai? Haan: hydroxylamine (oxime banata hai) aur hydrogen cyanide (add hokar cyanohydrin deta hai) ke saath glucose aldehyde ya ketone ki tarah behave karta hai.
4. Aldehyde ya ketone? Bromine water, jo C–C bonds todne ke liye bahut gentle hai, glucose ko bina ek bhi carbon khoye gluconic acid mein badal deta hai. Sirf chain ke end par wala –CHO group hi aise oxidise ho sakta hai.
5. Kitne –OH groups, aur kahan? Acetic anhydride unmein se paanch ko acetylate karta hai aur pentaacetate deta hai. Do –OH groups wala carbon paani kho deta, aur pentaacetate stable hai, isliye har –OH ka apna alag carbon hai.
6. Doosre end par kya hai? Nitric acid glucose aur gluconic acid dono ko saccharic acid mein oxidise karta hai, jiske dono ends par –COOH group hai. Doosra wala sirf C6 par ke primary alcohol group, $-\mathrm{C}\mathrm{H}{\phantom{X}}_2\mathrm{O}\mathrm{H}$, se hi aa sakta hai.

Saare clues milkar ek aldohexose ke liye open-chain formula $\mathrm{O}\mathrm{H}\mathrm{C}-(\mathrm{C}\mathrm{H}\mathrm{O}\mathrm{H}){\phantom{X}}_4-\mathrm{C}\mathrm{H}{\phantom{X}}_2\mathrm{O}\mathrm{H}$ dete hain. Phir bhi yeh formula kuch chhod deta hai. Carbons 2, 3, 4 aur 5 sab stereocentres hain, isliye $2^4=16$ stereoisomers yahi formula share karte hain. Emil Fischer ne saalon lagaye yeh nikaalne mein ki inmein se glucose kaun sa hai (unhe 1902 ka Chemistry Nobel Prize mila), aur unhone jawab ek aise style mein banaya jo aaj bhi unke naam par hai, Fischer projection: chain seedhi neeche chalti hai, C1 top par, aur har stereocentre par H aur OH left ya right point karte hain.

D aur L. Natural glucose ke Fischer projection mein C5 par wala –OH, yaani aldehyde group se sabse door wala stereocentre, right ki taraf point karta hai (Fig. 10.3). Letter D theek yahi record karta hai. Reference compound glyceraldehyde hai, sabse simple aldose, jismein sirf ek stereocentre hai. Jis enantiomer ka –OH right par hai woh D-glyceraldehyde hai aur uski mirror image L-glyceraldehyde hai. Ek sugar, jise uske sabse oxidised carbon ko top par rakh kar banaya gaya ho, D hai agar uske sabse neeche wale stereocentre ka –OH D-glyceraldehyde ki tarah same taraf point kare, aur L hai agar doosri taraf; baaki stereocentres ka label mein koi role nahi hai.

D aur L configuration batate hain, yaani space mein groups ki arrangement. Yeh kuch nahi batate ki compound plane-polarised light ko kis taraf ghumata hai; use measure karna padta hai aur alag se (+), dextrorotatory, ya (−), laevorotatory, likha jaata hai. Natural glucose D-(+)-glucose hai. D-glyceraldehyde bhi (+) nikalta hai, lekin kai D sugars (−) hain, unmein fructose bhi. Capital D aur L ko purane small d aur l se mix mat karo, jo bas (+) aur (−) ke doosre symbols the.

Open chain kahan fail hoti hai. Open-chain formula ne zyadatar reactions samjha diye, lekin kuch facts usmein fit nahi hue:

• Do standard aldehyde tests fail hote hain: Schiff's reagent colourless hi rehta hai, aur sodium hydrogensulfite, $\mathrm{N}\mathrm{a}\mathrm{H}\mathrm{S}\mathrm{O}{\phantom{X}}_3$, koi addition compound nahi banata.
• Glucose ko acetylate karo to product hydroxylamine ko ignore karta hai, yaani aldehyde group ke saath jo bhi hua, pentaacetate mein woh bacha nahi.
• Glucose do alag forms mein crystallise hota hai, jinke naam α aur β hain. Yeh alag temperatures par melt hote hain (lagbhag 146 °C aur 150 °C) aur polarised light ko alag-alag amount se ghumate hain: inke specific rotations lagbhag +112° aur +19° hain. Ek open-chain structure do isomers nahi samjha sakta.

Ring. Raasta aldehyde chemistry ke ek reaction se milta hai: ek alcohol $\mathrm{C}=\mathrm{O}$ group par add hokar hemiacetal deta hai. Glucose mein alcohol aur aldehyde dono same molecule ke hain. Chain tab tak mudti hai jab tak C5 par wala –OH C1 tak na pahunch jaaye; uska oxygen C1 se bond karta hai, aur carbonyl oxygen ek naya –OH ban jaata hai (Fig. 10.4). Result hai paanch carbons aur ek oxygen ki six-membered ring.

Ring closure se C1 ek naya stereocentre ban jaata hai, isliye yeh do tareekon se ho sakta hai. α form mein C1 par naya –OH ring ki us side point karta hai jo C5 par $\mathrm{C}\mathrm{H}{\phantom{X}}_2\mathrm{O}\mathrm{H}$ group ke opposite hai (aam taur par neeche banaya jaata hai); β form mein yeh same side (upar) point karta hai. Dono forms sirf C1 par alag hain, jise ab anomeric carbon kehte hain, aur aise isomers ke pair ko anomers (ऐनोमर) kehte hain. Paani mein α, β aur thodi si open chain ek doosre mein badalte rehte hain jab tak equilibrium na aa jaaye, lagbhag 36 % α aur 64 % β par, aur open chain 1 % se bahut kam.

Isse teeno puzzles samajh aa jaate hain. Kisi bhi pal itni kam open chain hone se Schiff's reagent jaise slow aldehyde tests mushkil se respond karte hain. Pentaacetate ring ke roop mein lock hai, C1 par acetyl group ke saath, isliye woh khulkar aldehyde nahi ban sakta. Aur α aur β hi do crystalline forms hain. Jo reactions open chain ko use karte hain, jaise Tollens' reagent se oxidation, woh phir bhi poore hote hain, kyunki equilibrium aur open chain banata rehta hai.

Kisi bhi pure crystal form ko paani mein ghol do, to rotation dheere-dheere same final value, +52.7°, ki taraf khisakta hai jaise equilibrium mixture banta hai; is drift ko mutarotation kehte hain. Ise Fig. 10.5 lab mein try karo.

Jab ring ko lagbhag edge se dikhte flat hexagon ki tarah banaya jaata hai, ring oxygen peechhe right mein aur C1 right par, to woh Haworth projection hai. Fischer projection mein right par wala group Haworth projection mein neeche point karta hai. Kyunki six-membered ring heterocycle pyran, $\mathrm{C}{\phantom{X}}_5\mathrm{H}{\phantom{X}}_6\mathrm{O}$, jaisi dikhti hai, in ring forms ko pyranoses kehte hain: α-D-glucopyranose aur β-D-glucopyranose.

10.1.2.2 Fructose

Fructose, $\mathrm{C}{\phantom{X}}_6\mathrm{H}{\phantom{X}}_{12}\mathrm{O}{\phantom{X}}_6$, glucose ka ek isomer hai jismein same unbranched six-carbon chain hai. Fark carbonyl group ka hai: C1 par aldehyde ki jagah fructose mein C2 par ketone hai, jiske ek taraf $\mathrm{C}\mathrm{H}{\phantom{X}}_2\mathrm{O}\mathrm{H}$ group (C1) aur doosri taraf baaki chain hai, aur yahi ise sabse important ketohexose banata hai. C3, C4 aur C5 par iski configuration glucose jaisi hai, isliye yeh D sugar hai, phir bhi yeh strongly laevorotatory hai: D-(−)-fructose.

Honey aur kai fruits mein free fructose hota hai, aur har sucrose molecule mein ek fructose unit hai. Same weight par yeh table sugar se zyada meetha lagta hai, isliye food banane wale ise pasand karte hain.

Ring closure glucose ki tarah hi hota hai, bas ab C5 ka oxygen keto carbon, C2, par attack karta hai (product strictly ek hemiketal hai). C2 se C5 tak aur oxygen se wapas ginne par chaar carbons aur ek oxygen ki five-membered ring milti hai, wahi ring jo heterocycle furan, $\mathrm{C}{\phantom{X}}_4\mathrm{H}{\phantom{X}}_4\mathrm{O}$, mein hai, isliye naam furanose (Fig. 10.6). Anomeric carbon C2 hai, aur phir se α aur β anomers hote hain. Paani mein fructose six-membered rings bhi bana sakta hai, lekin sucrose mein woh hamesha furanose hota hai.

10.1.3 Disaccharides

Do monosaccharides tab jud sakte hain jab ek ka –OH group doosre ke –OH group se react kare aur paani ka ek molecule nikal jaaye. Dono units ek oxygen atom, C–O–C, se bridge ho jaate hain. Yeh bridge ek glycosidic linkage (ग्लाइकोसाइडी बंध) hai, aur yeh jin carbons ko jodta hai unmein se kam se kam ek anomeric carbon hota hai. Hydrolysis, dilute acid ya enzyme se, paani wapas jodta hai aur dono monosaccharides ko free kar deta hai.

Disaccharide reducing sugar hai ya nahi, yeh uske anomeric carbons par depend karta hai. Agar ek unit ka anomeric carbon abhi bhi free hai, –OH ke saath, to woh ring khulkar aldehyde ban sakti hai, aur sugar Tollens' aur Fehling's reagents ko reduce karti hai. Agar dono anomeric carbons linkage mein bandhe hain, to koi ring nahi khul sakti aur sugar non-reducing hai. Fig. 10.7 teen common disaccharides ko compare karta hai.

Sucrose, yaani cane ya beet sugar, tumhari kitchen ki sugar hai. Iska glycosidic linkage α-D-glucose unit ke C1 ko β-D-fructose unit ke C2 se jodta hai. Yeh dono units ke anomeric carbons hain, isliye sucrose non-reducing sugar hai. Hydrolysis se glucose aur fructose barabar amounts mein milte hain (10.1.2.1 ki equation).

Sucrose plane-polarised light ko right ki taraf ghumata hai (specific rotation +66.5°). Glucose bhi dextrorotatory hai (+52.7°), lekin fructose strongly laevorotatory hai (−92.4°). Isliye jaise-jaise sucrose hydrolyse hota hai, rotation girta hai, zero se guzarta hai aur aakhir mein negative ho jaata hai. Kyunki rotation ka sign ulta (invert) ho jaata hai, glucose aur fructose ke equimolar mixture ko invert sugar (अपवृत्त शर्करा) kehte hain. Honey zyadatar invert sugar hai, jo tab banta hai jab bees nectar mein enzyme invertase milati hain.

Maltose, yaani malt sugar, woh hai jo amylase starch ko kaatne ke baad chhodta hai, tumhare munh mein ya ugte anaaj mein. Iske dono units α-D-glucose hain, α(1→4) se jude: bridge ek unit ke anomeric C1 se doosre ke C4 tak jaata hai. Isse doosre unit ka C1 free rehta hai, uski ring khulkar aldehyde ban sakti hai, isliye maltose Tollens' aur Fehling's reagents ko reduce karta hai.

Lactose sirf doodh mein milta hai. Iska galactose unit, β form mein, apne anomeric C1 se glucose unit ke C4 se bond karta hai (β(1→4) link), aur phir se glucose end par ek free anomeric carbon bachta hai: lactose bhi reducing sugar hai. Kai adults bahut kam lactase banate hain, woh enzyme jo lactose ko todta hai, isliye doodh unka pet kharab karta hai jabki dahi nahi: dahi mein bacteria pehle hi kaafi lactose use kar chuke hote hain.

10.1.4 Polysaccharides

Living world ka lagbhag saara carbohydrate polysaccharide hai. Organisms in giant molecules ko do kaamon ke liye use karte hain, fuel ke compact store ki tarah ya mazboot building material ki tarah. Inmein se teen sirf glucose se bane hain, aur yeh dikhate hain ki linkage mein chhota sa change kitne alag materials bana deta hai (Fig. 10.8).

Chawal, gehun, bajra, aloo aur tapioca ki food value mainly starch se aati hai, jo plants ka fuel store hai aur human diet mein carbohydrate ka sabse bada source. Yeh α-D-glucose ke do polymers ka mixture hai. Amylose, chhota hissa (aam taur par 15–25 %), saikdon se hazaaron units ki unbranched chain hai jo α(1→4) linkages se judi hai; yeh helix mein coil hoti hai aur garam paani mein ghul jaati hai. Amylopectin, bada hissa, paani mein nahi ghulta. Iski chains same α(1→4) links use karti hain lekin lagbhag har 20–30 units par α(1→6) linkage se ek branch nikaalti hain.

Cotton lagbhag pure cellulose hai, aur wood mein lagbhag aadha cellulose hai: yeh plant cell walls ka material hai, aur plants mein isse zyada koi organic compound nahi milta. Iski chains unbranched hain aur β-D-glucose units se bani hain jo β(1→4) linkages se judi hain. β links har chain ko seedhi aur flat rakhte hain, isliye paas wali chains aamne-saamne padi rehti hain aur hydrogen-bond karke mazboot, insoluble fibres banati hain.

Animals, yeasts aur fungi glucose ko glycogen ke roop mein store karte hain. Amylopectin jaisa bana lekin kahin zyada baar branched, lagbhag har 8–12 units par, isliye ise animal starch bhi kehte hain. Tumhare liver aur muscles mein iska zyadatar hissa hota hai, aur brain mein thoda sa. Branching hi asli baat hai: har branch ek chain end par khatam hoti hai, aur jab blood glucose girta hai, enzymes saikdon ends se ek saath glucose release karte hain.

10.1.5 Carbohydrates ki Importance

Zyadatar diets mein carbohydrates main fuel hain. Digestion starch aur sugars ko glucose mein badalta hai, aur cells glucose ko carbon dioxide aur paani mein oxidise karke nikalne wali energy pakad leti hain. Plants extra glucose ko starch ke roop mein aur animals glycogen ke roop mein baad ke liye rakh dete hain.

Materials ke roop mein carbohydrates daily life mein har jagah hain: darwaze ki lakdi, tumhare kapdon ka cotton aur rayon, notebook ka paper, kalaf lage kurte ko kadak banane wala starch, aur woh sugars jinhe yeast bread phoolne par ferment karta hai. Yeh bade molecules ke hisson ke roop mein bhi milte hain. Ribose aur deoxyribose RNA aur DNA ke backbones ka hissa hain (Section 10.5), aur cell surfaces par proteins aur lipids se judi chhoti sugar chains identity tags ki tarah kaam karti hain; jaise tumhara ABO blood group tumhare red blood cells par kuch sugar units se tay hota hai.

10.2 Proteins

1838 mein Swedish chemist Jöns Berzelius ne protein naam suggest kiya, Greek proteios se, yaani sabse pehli importance ka, aur yeh naam bilkul sahi saabit hua. Muscle, skin, baal aur nails zyadatar protein hain; waise hi woh enzymes jo tumhara khana digest karte hain, oxygen le jaane wala haemoglobin, infection se ladne wale antibodies aur insulin jaise hormones bhi. Cell mein koi aur class of biomolecule itni zyada nahi hoti aur na hi itne alag-alag kaam karti hai. Badhne aur tissue repair ke liye tumhe iski lagataar supply chahiye, aur dal, soya, paneer, ande, nuts, machhli aur chicken sab achhe sources hain.

Har protein α-amino acids (ऐमीनो अम्ल) se bani ek lambi chain hai, isliye hum unhi se shuru karte hain.

10.2.1 Amino Acids

Kisi bhi protein ko acid ke saath kaafi der ubaalo to woh α-amino acids mein toot jaata hai, jo general formula $\mathrm{H}{\phantom{X}}_2\mathrm{N}-\mathrm{C}\mathrm{H}(\mathrm{R})-\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$ wale compounds hain jinmein amino group aur carboxyl group same carbon, yaani α-carbon, par baithe hain. (Amino group ko carboxyl group se ek carbon aur door le jao to β-amino acid milta hai, phir γ, δ aur aage, lekin yeh proteins ke building units nahi hain.) Group R, yaani side chain, hi ek amino acid ko doosre se alag banata hai; kuch side chains mein ek aur functional group hota hai, jaise –OH, –SH, doosra –COOH ya doosra $-\mathrm{N}\mathrm{H}{\phantom{X}}_2$.

Biochemistry lab mein koi bhi alanine ko 2-aminopropanoic acid nahi kehta: amino acids ke wahi naam chalte hain jo discovery ke time diye gaye the, jo aksar kisi source ya property ki yaad dilate hain. Asparagine pehli baar asparagus ke juice se alag kiya gaya tha; cysteine ka naam cystine se aaya, jo bladder stones mein mila tha (Greek kystis, yaani bladder). Lambi chains ko chhota likhne ke liye har ek ka three-letter symbol (Ala, Gly…) aur one-letter code (A, G…) bhi hai. Table 10.3 proteins ke bees amino acids ko side chain ke type se group karke list karta hai.

10.2.2 Amino Acids ka Classification

Amino acids ko do tareekon se sort kiya jaata hai. Pehla tareeka acidic aur basic groups ginta hai. Ek amino group aur ek carboxyl group, jaise alanine ya serine mein, amino acid ko neutral banate hain. Extra carboxyl group wali side chain use acidic banati hai (aspartic acid aur glutamic acid), aur extra basic nitrogen group wali side chain use basic banati hai (lysine, arginine aur histidine).

Doosra sorting diet ke baare mein hai. Tumhara body bees mein se lagbhag aadhe doosre compounds se bana sakta hai; yeh non-essential amino acids hain, jaise glycine, alanine aur glutamic acid. Baaki bilkul nahi ban sakte, ya kaafi tezi se nahi bante, aur unhe khane se aana padta hai. Yeh essential amino acids (आवश्यक ऐमीनो अम्ल) hain, jaise valine, lysine aur tryptophan. Badhte bachchon ke liye aam taur par das list kiye jaate hain; adults kaafi arginine bana lete hain, isliye unke liye list nau ki hai. Anaaj mein lysine kam hota hai aur daalon mein methionine kam, isliye chawal ke saath khayi dal akele kisi ek se behtar protein deti hai.

Properties. Glycine ke kuch crystals spatula par rakho, to woh amine ya carboxylic acid jaisa bilkul behave nahi karte. Woh colourless hain, paani mein aasaani se ghulte hain aur sirf high temperatures par, aksar 200 °C se upar, decompose hote hue melt hote hain: yeh salt jaisa behaviour hai. Wajah molecule ke andar ek acid–base reaction hai (Fig. 10.9). Carboxyl group same molecule ke amino group ko ek proton de deta hai, aur ion $\mathrm{H}{\phantom{X}}_3\mathrm{N}{\phantom{X}}^{+}-\mathrm{C}\mathrm{H}(\mathrm{R})-\mathrm{C}\mathrm{O}\mathrm{O}{\phantom{X}}^{-}$ banta hai jismein ek positive aur ek negative charge hai. Aise dipolar ion ko zwitterion (ज़्विटर आयन) kehte hain, German Zwitter, yaani hybrid, se. Overall yeh neutral hai, lekin iske charged ends paas ke molecules ko strongly attract karte hain, jaise salt crystal mein ions karte hain.

Zwitterion amphoteric hota hai: yeh acids aur bases dono ke saath react karta hai. Acid daalo to $-\mathrm{C}\mathrm{O}\mathrm{O}-$ end ek proton le leta hai aur cation bachta hai; base daalo to $-\mathrm{N}\mathrm{H}{\phantom{X}}_3{\phantom{X}}^{+}$ end ek proton kho deta hai aur anion bachta hai. Yahi ek wajah hai ki proteins blood aur cells ka pH steady rakhne mein madad karte hain. Fig. 10.10 simulation dono charged ends ko point charges ki tarah treat karta hai, taaki tum dekh sako ki paas aata ion kis end ki taraf kheencha jaata hai.

Optical activity. Glycine ko chhod kar, jahan R sirf H hai, har α-amino acid mein α-carbon par chaar alag groups hote hain. Isliye woh ek stereocentre hai, aur amino acid chiral aur optically active hai. Har ek D aur L forms mein exist karta hai, jo sugars ki tarah glyceraldehyde se compare karke assign kiye jaate hain. Proteins lagbhag poori tarah L forms se bante hain: Fischer projection mein –COOH ko top par rakhne par L-amino acid ka $-\mathrm{N}\mathrm{H}{\phantom{X}}_2$ left ki taraf point karta hai.

10.2.3 Proteins ka Structure

Peptide bond. Amino acids condensation se judte hain. Ek ka carboxyl group agle ke amino group se react karta hai, paani ka ek molecule nikal jaata hai, aur ek amide link, $-\mathrm{C}\mathrm{O}-\mathrm{N}\mathrm{H}{\phantom{X}}^{-}$, banta hai (Fig. 10.11). Protein chemistry mein is amide link ko peptide bond ya peptide linkage (पेप्टाइड आबंध) kehte hain.

Is tarah jude do amino acids ek dipeptide banate hain, aur order matter karta hai. Jab alanine carboxyl group de aur glycine amino group, to product, $\mathrm{H}{\phantom{X}}_2\mathrm{N}-\mathrm{C}\mathrm{H}(\mathrm{C}\mathrm{H}{\phantom{X}}_3)-\mathrm{C}\mathrm{O}$–$\mathrm{N}\mathrm{H}-\mathrm{C}\mathrm{H}{\phantom{X}}_2-\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$ ya Ala-Gly, alanylglycine hai, jo glycylalanine (Gly-Ala) se alag compound hai. Convention ke hisaab se peptide ko free amino group wale end (N-terminus) se free carboxyl group wale end (C-terminus) tak likhte hain. Naam residues ki ginti se chalte hain: tripeptide (do peptide bonds), tetrapeptide, pentapeptide, hexapeptide aur aage.

Lagbhag das residues se zyada hone par hum bas polypeptide kehte hain. Chemists aam taur par protein word sau ya usse zyada residues wali chains ke liye rakhte hain (molar mass lagbhag 10 000 g/mol se upar), lekin yeh cut-off loose hai: insulin mein sirf 51 residues hain, do chains mein bante hue, phir bhi woh protein gina jaata hai kyunki woh ek definite working shape mein fold hota hai. Fig. 10.12 builder mein apne khud ke kuch peptides banao.

Fibrous aur globular proteins. Apne baal ke ek strand ko ande ki safedi se compare karo. Baal ek fibrous protein, keratin, se bane hain. Kai lambi chains parallel padi hain, hydrogen bonds aur disulfide (S–S) bridges se cross-linked, isliye material mazboot hai aur paani use alag nahi kar sakta. Ande ki safedi zyadatar albumin hai, ek globular protein. Har chain khud par mudkar ek compact ball ban jaati hai jiske bahar paani ko attract karne wale groups hote hain, isliye yeh ghul jaata hai.

Structure ke chaar levels. Protein ko chaar levels par describe kiya jaata hai, har ek pichhle par bana (Fig. 10.13).

Primary structure har polypeptide chain mein amino acids ka sequence hai, N-terminus se padha jaata hai. Yeh us protein ke gene se tay hota hai, aur yahi baaki sab kuch decide karta hai. Ek single amino acid badlo aur tumhare paas ek alag protein hai. Sickle-cell anaemia mein haemoglobin ki har β-chain mein ek glutamic acid ki jagah valine aa jaata hai, aur red blood cells sakht hokar sickle shapes ban jaate hain.

Secondary structure chain ke backbone ki regular local shape hai, jo ek peptide group ke $\mathrm{C}=\mathrm{O}$ aur doosre ke N–H ke beech hydrogen bonds se tiki rehti hai (Fig. 10.14). Do shapes common hain. α-helix mein chain right-handed coil mein ghoom jaati hai; har residue ka $\mathrm{C}=\mathrm{O}$ chaar residues aage wale N–H se hydrogen-bonded hota hai, isliye yeh bonds helix ke upar uske axis ke lagbhag parallel chalte hain aur har backbone $\mathrm{C}=\mathrm{O}$ aur N–H use ho jaata hai. β-pleated sheet mein chain ke hisse lagbhag poori tarah khinche zigzags ki tarah ek doosre ke paas padte hain. Har strand bagal mein apne neighbours se hydrogen-bond karta hai, aur zigzags line up hokar regular folds banate hain, kaagaz ke pankhe ki tarah.

Tertiary structure poori chain ki overall three-dimensional folding hai: uske helices, sheets aur loops saath pack hokar fibre ya globule banate hain. Yeh hydrogen bonds, cysteine side chains ke beech disulfide bridges, opposite charge wali side chains ke beech attractions (salt bridges), aur bahut saari non-polar side chains ke beech van der Waals forces se tiki rehti hai; non-polar side chains paani se door core mein ikattha hoti hain.

Kai proteins kai folded chains ki teams hote hain. Har chain ek subunit hai, aur subunits jis tarah fit hote hain woh quaternary structure hai; sirf ek chain wale protein mein yeh nahi hota. Haemoglobin classic example hai: do α-chains aur do β-chains, har ek iron wale haem group ke around mudi hui, saath pack hokar ek oxygen le jaane wala unit banati hain.

10.2.4 Proteins ka Denaturation

Garam pan mein anda todo to saaf, behti safedi kuch hi seconds mein opaque aur sakht ho jaati hai: iska main protein, albumin, denature ho gaya hai. Living cell mein har protein ki ek khaas folded shape hoti hai, uski native state, jo zyadatar weak forces se tiki rehti hai. Heat hydrogen bonds ko hila kar tod deta hai; pH change side chains ke charges badal kar salt bridges tod deta hai; alcohol, heavy-metal ions aur concentrated salt solutions bhi gadbad karte hain. Chain khul jaati hai, paas wali chains se ulajh jaati hai aur kaam karna band kar deti hai. Sirf covalent backbone bachta hai: peptide bonds, aur isliye primary structure, waise hi rehte hain, jabki secondary, tertiary aur koi bhi quaternary structure kho jaata hai. Yahi denaturation (विकृतीकरण) hai.

Kitchen mein aur bhi examples bhare hain. Garam doodh mein nimbu ka ras nichodo, to acid milk protein casein ko coagulate karke paneer bana deta hai; jab dahi jamta hai, bacteria lactose ko lactic acid mein badal kar yahi kaam dheere-dheere karte hain. Hair straightener bhi isi principle par kaam karta hai, keratin ke hydrogen bonds tod kar taaki baalon ko nayi shape di ja sake. Zyadatar denaturation, ande ko pakane ki tarah, ulta nahi kiya ja sakta.

10.3 Enzymes

Saadi bread ka ek tukda ek minute chabao to woh meetha lagne lagta hai: tumhare saliva ka amylase pehle se uske starch ko maltose mein tod raha hai. Flask mein yahi breakdown ubalte acid se hota hai, phir bhi tumhara body aise hazaaron reactions lagbhag 37 °C par, pH 7 ke paas aur paani mein chalata hai. Yeh fark enzymes (एंज़ाइम) ki wajah se hai: biological catalysts jo reactions ko bahut zyada tez kar dete hain aur khatam nahi hote, isliye thodi si amount bhi bahut kaam karti hai. Lagbhag saare enzymes globular proteins hain (kuch RNA molecules hain).

Enzymes bahut specific hote hain. Har ek aam taur par ek compound, apne substrate, par ya similar compounds ki chhoti family par kaam karta hai, aur ek hi tarah ka reaction catalyse karta hai. Zyadatar ke naam substrate ya reaction ke naam mein -ase jod kar rakhe jaate hain. Maltase maltose ko hydrolyse karta hai; sucrase, jise invertase bhi kehte hain, sucrose ko hydrolyse karta hai; lactase lactose par aur urease urea par kaam karta hai. Jo enzymes redox reactions catalyse karte hain, ek substrate ko oxidise aur doosre ko reduce karte hue, unhe oxidoreductases kehte hain.

10.3.1 Enzyme Action ka Mechanism

Kisi bhi catalyst ki tarah enzyme na reaction ka overall energy change badalta hai na uski equilibrium position. Yeh kam activation energy wala ek alag raasta deta hai (Fig. 10.15). Pehle substrate enzyme ki surface par ek chhoti pocket, active site, mein bind hokar enzyme–substrate complex banata hai. Wahan side chains substrate ko bilkul sahi orientation mein pakadti hain, jo bonds tootne hain unpar strain daalti hain aur protons aage deti ya le leti hain. Phir products nikal jaate hain aur enzyme agle substrate molecule ke liye free ho jaata hai.

1894 mein Emil Fischer ne active site ko ek lock ki tarah socha jismein sirf sahi key, yaani substrate, fit hoti hai, jo specificity samjhata hai. Ab hum jaante hain ki fit aksar induced hota hai: substrate bind hote waqt enzyme apni shape thodi badalta hai, aur uske around band ho jaata hai jaise haath ball ke around. Kyunki active site protein ki folded shape par depend karti hai, jo bhi cheez enzyme ko denature kare, jaise high temperature ya galat pH, woh uski activity khatam kar deti hai. Zyadatar human enzymes 37 °C ke paas sabse achha kaam karte hain, lekin pepsin, jo acidic stomach mein protein digest karta hai, pH 2 ke paas sabse achha kaam karta hai.

10.4 Vitamins

Lambi samudri yatraon par sailors ke daant gir jaate the aur masoodon se khoon aata tha, jab tak yeh notice nahi hua ki nimbu aur lime isse bachate hain. Polished chawal par jeene wale logon ke pair kamzor aur soojhe hue ho jaate the aur heart fail ho jaata tha. In mein se koi bhi disease kisi germ se nahi hoti. Har ek kisi khaas compound ki kami se hoti hai jo body ko bahut thodi amount mein chahiye, ek vitamin (विटामिन).

Vitamins chemically ek mixed bag hain (alcohols, amines, acids aur ring compounds), isliye unhe structure se nahi balki role se define kiya jaata hai: aise organic compounds jo body ko bahut thodi amount mein chahiye lekin woh kaafi quantity mein bana nahi sakta, isliye unhe khane se lena padta hai. Har ek ek khaas kaam karta hai, aur kami ek khaas deficiency disease ke roop mein dikhti hai. Hamare apne cells sunlight mein khuli skin mein thoda vitamin D banate hain, aur gut bacteria kuch B vitamins aur vitamin K dete hain; doosri taraf plants lagbhag saare bana lete hain, yahi ek wajah hai ki taazi sabziyan aur fruits itne important hain. Letters inke label hain, A, B, C, D, E aur K, aur B group aage ${\mathrm{B}}_1$, ${\mathrm{B}}_2$, ${\mathrm{B}}_6$, ${\mathrm{B}}_{12}$ aur doosron mein bantta hai.

Zyada bhi nuksaan kar sakta hai. Fat-soluble vitamins body mein jama hote jaate hain, aur vitamins A aur D ki badi doses zehreeli hain, isliye supplements doctor ke prescribe karne ki cheez hain, andaaze ki nahi; zyadatar logon ki zaroorat alag-alag cheezon wali diet se poori ho jaati hai.

10.4.1 Vitamins ka Classification

Vitamins ko is baat se group kiya jaata hai ki woh fat mein ghulte hain ya paani mein, aur yeh grouping batati hai ki body unhe kaise handle karta hai (Fig. 10.16).

• Fat-soluble: A, D, E aur K. Paani mein insoluble, yeh khane ke fat ke saath body mein aate hain aur liver aur body fat mein reserve mein rakhe jaate hain, isliye ek store mahinon tak chal sakta hai, aur overdose bhi.
• Water-soluble: B group aur C. Yeh blood plasma mein ghulte hain, aur jo bhi extra hai use kidneys filter karke urine mein nikaal dete hain. Vitamin ${\mathrm{B}}_{12}$ exception hai, jo liver mein saalon tak jama rehta hai; baaki ko regularly khana padta hai.

10.5 Nucleic Acids

1869 mein Friedrich Miescher ne Tübingen mein kaam karte hue use ki gayi surgical bandages se white blood cells dhoye aur unke nuclei se ek naya substance nikala, jo phosphorus se bhara aur acidic tha. Ab hum ise nucleic acid kehte hain. Iske do types hain, deoxyribonucleic acid (DNA) aur ribonucleic acid (RNA), aur dono nucleotides naam ke units ki lambi chains hain, isliye inhe polynucleotides bhi kehte hain.

Inka sabse famous kaam heredity hai, yaani characteristics ka ek generation se agli tak jaana. DNA, proteins ke around lipta hua, har cell ke nucleus mein chromosomes banata hai, aur iske sequence mein woh instructions hain jo bachche ko uske maa-baap jaisa banate hain. DNA kaise copy hota hai, padha jaata hai aur control hota hai, yeh Class 12 Biology, Chapter 5 (Molecular Basis of Inheritance) ka subject hai. Yahan hum chemistry dekhte hain: nucleic acids kis cheez se bane hain aur tukde kaise jude hain.

10.5.1 Nucleic Acids ka Chemical Composition

Nucleic acid ko acid se poori tarah tod do to sirf teen tarah ke molecules bachte hain. Ek phosphoric acid, $\mathrm{H}{\phantom{X}}_3\mathrm{P}\mathrm{O}{\phantom{X}}_4$, hai. Ek five-carbon sugar hai: β-D-ribose agar tumne RNA se shuru kiya, β-D-2-deoxyribose agar DNA se (deoxy kyunki ribose ke C2 par wala –OH H se replace ho gaya hai). Baaki flat, ring-shaped organic molecules hain jinmein bahut nitrogen hai, inhe bases kehte hain.

Kul milakar paanch bases milte hain. Adenine (A) aur guanine (G) purines hain, jinmein do fused rings hain; cytosine (C), thymine (T) aur uracil (U) pyrimidines hain, jinmein ek single ring hai. Thymine sirf DNA mein aur uracil sirf RNA mein milta hai, jabki baaki teen dono mein common hain (Table 10.6). Thymine ko uracil se sirf ek methyl group alag karta hai.

10.5.2 Nucleic Acids ka Structure

Repeating unit ko do steps mein bana hua socho (Fig. 10.17). Pehle ek base sugar se C1′ par bond karta hai; sugar ke atoms ko base ki apni numbering se alag rakhne ke liye sugar carbons par prime lagta hai (1′ se 5′). Base plus sugar ek nucleoside hai. Doosra, phosphoric acid C5′ par wale –OH ke saath ester banata hai, aur nucleoside ek nucleotide (न्यूक्लियोटाइड) ban jaata hai.

Nucleotides apne phosphate groups ke through chain mein judte hain. Ek nucleotide ke C5′ par wala phosphate usse pehle wale nucleotide ke C3′ par wale –OH ke saath doosra ester bond banata hai, isliye har phosphate do sugars ko ek phosphodiester linkage mein jodta hai. Result ek repeating backbone hai, sugar–phosphate–sugar–phosphate, jismein har sugar se ek base latka hai. Dono ends alag hain: ek par C5′ par free phosphate hai (5′ end) aur doosre par C3′ par free –OH (3′ end). Isliye sequence ek direction mein padha jaata hai, aam taur par 5′ → 3′, aur chain ke saath bases ka order nucleic acid ka primary structure hai.

Watson aur Crick ke 1953 ke model ne DNA ko uska famous secondary structure diya: do strands, opposite directions mein chalte hue, ek shared axis ke around ghoom kar double helix banate hain, backbones bahar aur bases andar ek ke upar ek (Fig. 10.18). Backbones ke beech sirf kuch khaas base pairs hi fit hote hain, aur woh hydrogen bonds se jude rehte hain: adenine thymine ke saath (do bonds) aur guanine cytosine ke saath (teen). Har pair ek do-ring purine ko ek ek-ring pyrimidine se jodta hai, isliye ladder ki har seedhi ki chaudai same hai. Isliye dono strands identical nahi balki complementary hain: ek ka sequence doosre ka sequence tay kar deta hai.

RNA aam taur par single strand hota hai. Jahan bhi bases ke chhote hisse pair kar sakte hain, wahan iske parts khud par mud kar hairpins aur loops banate hain; RNA mein uracil adenine ke saath pair karta hai. Kyunki strand ka koi partner strand nahi hai, RNA ke bases ke beech koi fixed ratio nahi hota. Cells teen main tarah ke RNA banate hain:

• messenger RNA (mRNA) gene ke instructions ki copy DNA se ribosomes tak le jaata hai;
• ribosomal RNA (rRNA) ribosome ka zyadatar hissa banata hai, woh machine jo amino acids ko jod kar proteins banati hai;
• transfer RNA (tRNA) har amino acid ko ribosome tak laata hai aur use mRNA ke instructions se match karta hai.

10.5.3 Nucleic Acids ke Biological Functions

Tumhare body ke har cell mein same DNA hai, copy ki copy, jo trillions cell divisions mein se har ek par bani. Isi sahi-sahi copying par heredity tiki hai. Cell divide hone se pehle har DNA molecule ke dono strands alag hote hain, har khula base apna partner pakad leta hai, aur do identical double helices bante hain, har daughter cell ke liye ek. Kai generations tak yahi mechanism ek species ko pehchaanne layak waisa hi rakhta hai.

DNA ke zyadatar instructions proteins ke liye hain, phir bhi DNA khud kabhi protein nahi banata. Gene ka sequence pehle mRNA mein copy hota hai; ribosome par, jiska core rRNA hai, tRNA molecules mRNA ko ek baar mein teen bases padhte hain aur matching amino acids laate hain, jinhe peptide bonds se joda jaata hai. Details biology ki hain, lekin jo chemistry tumne abhi dekhi, base pairing aur peptide bond, wahi inhe possible banati hai.

10.6 Hormones

Achanak dar lage to kuch hi seconds mein tumhara dil tez dhadakne lagta hai aur muscles ko extra fuel milta hai. Is response ka ek hissa nerves nahi balki blood mein chhoda gaya ek chemical le jaata hai. Aise messengers hormones (हॉर्मोन) hain: endocrine glands (pancreas, thyroid, adrenal glands aur doosre) dwara seedhe bloodstream mein chhode gaye molecules, jo unhe poore body mein pahuncha deta hai; sirf matching receptor wale target cells hi respond karte hain. Bahut thodi amount kaafi hai.

Chemically, hormones teen families mein aate hain:

Hormones ka ek central kaam body mein conditions ko steady rakhna hai, aur blood glucose iska achha example hai (Fig. 10.19). Khane ke baad blood mein glucose bhar jaata hai aur pancreas insulin release karta hai. Insulin muscle aur fat cells ko glucose andar lene deta hai aur liver se use glycogen ke roop mein store karwata hai, isliye level wapas gir jaata hai. Do meals ke beech, jab level girta hai, pancreas glucagon release karta hai, jo liver se glycogen tudwa kar glucose release karwata hai. Opposite directions mein kheenchte hue dono hormones blood glucose ko tight limits ke andar rakhte hain; diabetes mein yeh control fail ho jaata hai.

Doosre hormones body ko action ke liye tayyar karte hain ya uske development ko direction dete hain. Adrenal glands se epinephrine aur norepinephrine (adrenaline aur noradrenaline) achanak stimulus par fight-or-flight response laate hain: tez heartbeat aur blood mein zyada glucose. Growth hormone aur sex hormones growth aur development ko control karte hain.

Thyroxine, gardan mein thyroid gland se, amino acid tyrosine ka ek derivative hai jismein chaar iodine atoms hain; yeh body ke metabolism ki speed tay karta hai. Bahut kam hone se hypothyroidism hota hai, thakaan, susti aur weight badhne ke saath, aur bahut zyada hone se hyperthyroidism. Iodine ki kami wali diet thyroid ko raw material nahi deti, isliye woh kam kaam karne lagta hai aur phool kar goitre ban jaata hai.

Steroid hormones adrenal glands aur gonads se aate hain. Har adrenal gland ki bahari layer, cortex, do tarah ke banati hai. Ek tarah, jiska typical example cortisol hai, doosre molecules se naya glucose bana kar blood glucose badhata hai, inflammation shaant karta hai (isiliye cortisone-type creams rashes ko aaram dete hain) aur physical stress jhelne mein madad karta hai. Doosri tarah, jiska typical example aldosterone hai, kidneys ko batata hai ki kitna sodium aur paani rokna hai, aur isse blood pressure set karne mein madad karta hai. Jab adrenal cortex nasht ho jaata hai, dono kho jaate hain aur result Addison's disease hai: blood sugar kam rehta hai, muscles kamzor lagti hain, aur jo bimari ya chot doosre aaram se jhel lete hain woh jaan ke liye khatra ban sakti hai. Dono tarah ke hormones ka roz replacement patients ko theek rakhta hai.

Puberty par gonads (testes ya ovaries) apne steroids ka production badha dete hain. Testosterone male changes laata hai, jaise bhaari awaaz aur chehre par baal. Estradiol female changes laata hai aur, progesterone ke saath, monthly cycle chalata hai; progesterone ka khaas kaam uterus ki lining ko fertilised egg ke liye tayyar karna hai.