Chemical Constituents of Life; Physiological Biochemistry; Metabolisms; Clinical Biochemistry and. Download BioChemistry by U. Satyanarayana 3rd Edition PDF Free. By and which greatly exceeds what could be covered in a conventional textbook alone. U Satyanarayana. Over 40 years (30 years as Professor) of teaching experience; authored four other popular books; published about
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biochemistry by lesforgesdessalles.infoarayana and chakrapani contain basic and essential biochemistry topics at college level. My elder son, U. Chakrapani(MBBS)deservesa specialplace in this book. He made a significant contribution at everystageof its preparation-writing, verification . U Satyanarayana Biochemistry is a very popular book among the medical students of India. You can download it in PDF format here.
They are spherical or oval in shape and contain the enzyme catalase. The book has over pages with 43 chapters in total. When the polysaccharidesare composedof differenttypesof sugarsor their derivatives,they are referred to as heteropolvsaccharidesor heteroglycans. Carbohydratesalso serve as the storage form of energy glycogen to meetthe immediate energydemandsof the body. A thoroughrevisionandupdatingof eachchapterwith latestadvances-. Storageformofenergytomeetshortterm demands. Show related SlideShares at end.
The book has undergone three editions, several reprints, and revised reprints in a span of 13 years. Elsevier India. No comments. Subscribe to: Post Comments Atom. Random Post. Powered by Blogger.
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Bose Institute — Recruitment Sr. No Title Eligibility 1 Bose Top 5 natural remedies to increase hair growth. I hadthe rare privilegeof teachingmy sonashehappenedto bea studentof our college. Anda majorpartof this bookwas writtenwhilehewaslearningbiochemistry. Thus,hewasthe firstpersonto learnthesubjectof biochemistry from my handwrittenmanuscript. Thestudent-teacherrelation ratherthan the father-son hashelpedme in receivinSlconstantfeedbackfrom him and restructurethe book in a way an undergraduatestudentwould expecta biochemistrytextbookto be.
Next,I thankDr. Sivakumar Director,NationalInstituteof Nutrition, Hyderabad for his helpful sugi5lestionson the microfigures. I am gratefulto my nephew,Mr. SrinivasaRao,for helping me in drawingsomefigures. Last but not least,I thank my wife Krishna Kumari and my youngerson,Amrutpani,without whose cooperationand encouragementthis book could never have beenwritten.
The manuscriptwas carefully nurturedlike a newborn babyandthe bookhasnow becomea full-pledgedmemberof our family. I haveindividuallyandpersonallythankedall of them whonumbera fewhundreds! I onceagainexpressmy gratitudeto them. I thank my friend and colleague,Mr. JaganMohan,who has helpedme with his frequent interactionsto improvethe book,andmakeit morestudent-friendly.
I wouldlike to placeon recordmy deep senseof appreciationto my post-graduate M. Vidya DesaiSripad,whoseperiodicalacademicinteractionandfeedbackhavecontributedto the improvementof the biomedicaVclinicalaspectsin somechapters. I acknowledgethe helpof my friend,Dr. I expressmy gratitudeto Mr. Kolkata,for his wholeheartedsupportand constantencouragementin revisingthe bookin multicolour,and takingall the painsto bring it out to my satisfaction.
I thank Mr. ShyamalBhattacharyafor his excellentpage-makingand graphics-workin the book. I am indebtedto Mr. PrasenjitHalderfor the coverdesignof this book. I thank my wife, Krishna Kumari, and my younger son, Amrutpani, for their constantsupport and encouragement. I am grateful to UppalaAuthor-PublisherInterlinks, Vijayawada,for sponsoringand supportingme to bring out this edition. Iiii] DT. Biochemistry The term Biochemistrywas introducedby Carl Neubergin Biochemistrybroadlydealswith the chemistrvof life and living processes.
Thereis no exaggerationin the statement,'Thescopeof biochemistrg is asuastaslilb itself! For that matter,everymovementof life is packedwith hundredsof biochemicalreactions. Biochemistryis the mostrapidlydevelopingandmostinnovativesubjectin medicine. Thisbecomesevidentfromthe factthat over the years,the major shareof NobelPrizesearmarkedfor Medicineand Physiologyhasgoneto researchers engagedir: The disciplineof biochemistryservesas a torch light to trace the intricate complexicitiesof biology, besidesunravellingthe chemicalmysteriesof life.
Biochemicalresearchhasamplydemonstratedthat all living thingsarecloselyrelatedat the molecularlevel. Thusbiochemistryis the subjectof unity in the diversified living kingdom. Advancesin biochemistryhavetremendousimpacton humanwelfare,andhavelargelybenefitedmankind and their living styles. Theseincludethe applicationof biochernistryin the laboratoryfor the diagnosisof diseases.
SectionI dealswith the chemicalconstituentsof life-carbohydrates,lipids,proteinsandaminoacids, nucleicacidsandenzymes. SectionII physiologicalchemistryincludesdigestionandahsorption,plasmaproteins,hemoglobinand prophyrins,andbiologicaloxidation. SectionIII incorporatesall the metabolisms carbohydrates,lipids,aminoacids,nucleotides,minerals. Section[V covershormones,organfunctiontests,water,electrolyteandacid-basebalance,tissueproteins andtrodi'fluids,andnutrition. SectionV is exclusivelydevotedto molecularbiologyandbiotechnology DNA-replication,recombination, ar"lnrepair,transcriptionandtranslation,regulationof geneexpression,recombinantDNAandbiotechnology.
Section VII dealswith the basic aspectsfor learning and understandingbiochemistry bioorganic chenristry',hiophysicalchemistrytoolsof biochemistry,genetics,immunology. Each chapterin this book is carefully craftedwith colour illustrations, headingsand subheadingsto facilitatequickunderstanding. Iconsare usedat appropriateplacesto serveas 'landmarks'. The origins of biochemicalwords, confusablesin biochemistry,practicalbiochemistryand clinical biochemistrylaboratory,givenin the appendixare novelfeatures.
Thebriokis so organizedasto equipthe readerswith a comprehensiveknowledgeof biochemistry. Iiu] 6.
Nucleicacidsand Nucleotides 69 8. BflomnoXeeutrssaildthsCelll -l- hu living matter is composedof mainly six I elements-carbon, hydrogen, oxygenl nitrogen, phosphorus and sulfur. Severalother functionally importantelementsare also found in the cells.
This is attributedto the ability of carbon to form stable covalentbonds and C-C chains of unlimited length. Ghemical molecules of li e Life is composed of lifeless chemical molecules. A single cell of the bacterium, Escherichiacoli containsabout 6. The important biomolecules macromolecules with their respective building blocks and major functions are given in Table 1.
As regards lipids, it may be noted that they are not biopolymers in a strict sense,but majority of them contain fatty acids. Structural heirarehy off asn organisnl The macromolecules proteins,Iipids,nucleic acidsand polysaccharides form supramolecular assemblies e. Protein Aminoacids 2. Ribonucleicacid RNA 4. Polysaccharide glycogen Monosaccharides glucose Fundamentalbasisofstructureand functionofcell staticanddynamicfunctions. Storageformofenergytomeetshortterm demands. Lipid Fattyacids,glycerol Storagetormofenergytomeetlongterm demands;structuralcomponentsofmembranes.
Water is the solventof life and contributesto more than 60"h of the weight. This is followed by protein mostlyin muscle and lipid mostlyin adipose tissue. The carbohydratecontent is rather low which is in the form of glycogen.
The cell is the structuraland functional unit of life. The concept of cell originated from the contributionsof Schleidenand Schwann However, it was only after , the complexitiesof cell structurewere exposed. Constituent Percent 7" Weight kg Prokaryotic and eukaryotic cells The cells of the living kingdom may be divided into two categories 1.
Prokaryotes Creek: These include the variousbacteria. Eukaryotes Greek: The higher organisms animalsand plants are composedof eukaryoticcells. A comparisonof the characteristicsbetween prokaryotesand eukaryotesis listedin Table 1. The human body is composedof about cells. An eukaryoticcell is generally10 to pm in diameter. A diagrammatic representation of a typical rat liver cell is depicted in Fig. The plant cell differsfrom an animalcell by possessinga rigid cell wall mostlycomposedof cellulose and chloroplasts.
The latter are the sitesof photosynthesis. Water Protein Lipid Carbohydrate Minerals Chapter 1: Size Small generallypm Large generallypm 2. Cellmembrane Cellisenvelopedbyaflexibleplasmamembrane Distinctorganellesarefound e. Sub-cellular organelles 4, Nucleus Notwelldefined;DNAisfound asnucleoid,histonesareabsent Nucleusiswelldefined,surroundedbya membrane: DNAisassociatedwithhistones 5.
Energymetabolism Mitochondriaabsent,enzymesof energymetabolismboundto Enzymesolenergymetabolismarelocated inmitochondria membrane 6. Celldivision 7. Cytoplasm Usuallyfissionandnomitosis Mitosis 0rganellesandcytoskeleton absent Containsorganellesandcytoskeleton anetworkoftubulesandfilaments The cell consistsof well definedsubcellular organelles,envelopedby a plasma membrane. By differential centrifugation of tissue homogenate, it is possible to isolate each cellular organelle in a relatively pure form Refer Chapter The distribution of major enzymes and metabolic pathways in different cellular organelles is given in the chapter on enzymes Refer Fig.
The subcellular organellesare briefly describedin the following pages. Nucleus Nucleus is the largest cellular organelle, surroundedbv a double membrane nuclear envelope. The outer membraneis continuous with the membranesof endoplasmicreticulum. At certainintervals,the two nuclearmembranes have nuclearporeswith a diameterof about 90 nm. Theseporespermit the free passageof the products synthesizedin the nucleus into the surrounding cytoplasm. Diagrammaticrepresentationof a nt liverell.
Eukaryotic DNA is associatedwith basic protein histones in the ratio of 1: An assembly of nucleosomesconstituteschromatin fibres of chromosomes Creek'. Thus, a single human chromosomeis comoosedof abouta million nucleosomes. The number of chromosomes is a characteristic feature of the species.
Humans have 46 chromosomes,compactlypackedin the nucleus. The nucleusof the eukaryoticcell containsa dense bodv known as nucleolus. The ground materialof the nucleus is often referredto as nucleoplasm.
To the surpriseof biochemists,the enzymes of glycolysis,citric acid cycle and hexose monophosphateshunt have also been detectedin the nucleoplasm. Mitochondria The mitochondria Creek'. They are regarded as the power housesof the cell with variablesize and shape. Mitochondriaare rod-like or filamentousbodies, usuallv with dimensions of 1. The mitochondriaare comoosedof a double membrane system.
The outer membrane is smooth and completelyenvelopsthe organelle. The inner membrane is folded to form cristae Latin- crests which occupy a larger surface area. The internal chamber of mitochondriais referred to as matrix or mitosol. The componentsof electron transportchain and oxidative phosphorylation flavoprotein, cytochromesb, c1, C, a and a3 and coupling factors are buried in the inner mitochondrial membrane.
The matrixcontainsseveralenzvmes concerned with the energy metabolism of carbohydrates,lipidsandaminoacids e. The matrix enzymes also parlicipate in the synthesisof heme and urea.
Mitochondria are the principal producers of ATP in the aerobic cells. ATP, the energy currency,generatedin mitochondriais exported to all partsof the cell to provideenergyfor the cellularwork. Thus,the mitochondriaareequipped with an independent protein synthesizing machinery.
The structureand functionsof mitochondria closely resemble prokaryotic cells. Further,it is believedthat duringevolution,the aerobicbacteriadeveloped a symbiotic relationship with primordial anaerobiceukaryoticcellsthat ultimatelyled to the arrival of aerobiceukaryotes. Endoplasmic reticulum The network of membraneenclosedspaces that extends throughout the cytoplasm constitutesendoplasmicreticulum ER.
Someof these thread-like structuresextend from the nuclearporesto the plasmamembrane. A large portion of the ER is studded with ribosomesto give a granularappearancewhich is referred ro as rough endoplasmic reticulum. Ribosomes are the factories of protein biosynthesis.
During the process of cell fractionation,roughERisdisruptedto form small vesiclesknown as microsomes. It may be noted that microsomesas such do not occur in the cell. The smoothendoplasmicreticulumdoes not containribosomes. The newly synthesizedproteins are handed over to the Colgi apparatuswhich catalysethe addition of carbohydrates,lipids or sulfatemoietiesto the proteins. Thesechemical modificationsare necessaryfor the transportof proteinsacrossthe plasmamembrane.
Certainproteinsand enzymesareenclosedin membrane vesicles of Colgi apparatusand secreted from the cell after the appropriate signals. The digestiveenzymesof pancreasare oroducedin this fashion. Colgi apparatusare also involved in the membrane synthesis, particularly for the formation of intracellular organelles e.
Lysosornes Lysosomesare sphericalvesiclesenveloped by a singlemembrane. Lysosomesare regarded as the digestivetract of the cell, sincethey are actively involved in digestion of cellular substances-namely proteins, lipids, carbo- hydratesand nucleic acids.
Lysosomalenzymes are categorizedas hydrolases. The lysosomal enzymes are responsiblefor maintaining the cellular compounds in a dynamic stafe, by their degradationand recycling.
The degradedproductsleavethe lysosomes,usually by diffusion, for reutilization by the cell. Sometimes,however,certain residualproducts, rich in lipidsand proteins,collectivelyknown as Iipofuscinaccumulatein the cell. Lipofuscinis the agepigmentor wear and tearpigmentwhich has been implicatedin ageingprocess.
The digestiveenzymesof cellularcompounds are confinedto the lvsosomesin the bestinterest of the cell. Escapeof theseenzymesinto cytosol will destroythe functionalmacromoleculesof tne cell and result in many complications. The occurrence of several diseases e.
Feroxisomes Peroxisomes,also known as microbodies, are single membranecellularorganelles. They are spherical or oval in shape and contain the enzyme catalase. Accumulotion oJ lipofuscin,a pigment rich in lipids and proteins, in the cell hasbeen implicated in ogeing process. Leokageof lysosomalenzymesinto the cell degrodesseuerolfunctional macromolecules and this may leod to certain disorders e.
Peroxisome biogenesisdisorders PBDs , are a Broup of rare diseasesinvolving the enzyme activities of peroxisomes. The biochemical abnormalitiesassociatedwith PBDs incluoe increasedlevelsof very long chain fatty acids C2aand C26 and decreasedconcentrationsof plasmalogens. The most severeform of PBDsis Zellweger syndrome, a condition characterized by the absenceof functional peroxisomes.
The victimsof this diseasemav die within one vear after birth. More recent studies however, indicate that the cytoplasm actuallycontainsa complex network of protein filaments, spread throughout, that constitutes cytoskeleton. The cytoplasmicfilamentsare of three types- microtubules, actin filaments and intermediatefilaments. The filamentswhich are polymers of proteins are responsiblefor the structure,shapeand organizationof the cell.
For this purpose, the various intracellularprocessesand biochemicalreactions are tightly controlledand integrated. Divisionof a cell intotwo daughtercellsis goodexampleof the orderlyoccurrenceof an integratedseriesof cellularreactions. Apoptosisis the programmedcell death or cell suicide. This occurs when the cell has fulfilled its biologicalfunctions. Apoptosismay be regardedas a natural cell deathand it differs from the cell death caused by injury due to radiation,anoxiaetc.
Programmedcell death is a highly regulatedprocess. Life is composed ol lifeless chemical molecules. The complex biomolecules, proteins, nucleic ocids DNA and RNA , polysaccharidesand lipids are formed by the monomeric units amino acids,nucleotides,monosaccharidesand fotty acids,respectluely.
The cell is the structuroland functional unit of life. The eukoryoticcell consisfsof well det'inedsubcellulororganelles,enuelopedin a plasma membrane. The nucleus contoinsDNA, the repositoryol genetic int'ormation. DNA, in association with proteins histones ,forms nucleosomeswhich,in turn, make up the chromosomes.
The mitochondria qre the centresfor energymetobolism. Theyare the principalproducers of ATP which is exported to all parts of the cell to ptouide energylor cellular work. Endoplosmic reticulum ER ts the network of membrane enclosed spocesthat extends throughout the cytoplosm.
ER studded with ribosomes, the factorles of protein biosynfhesis, ts relerred to as rough ER. Golgi opparatus sre a cluster of membrane uesiclesto uthich the newlg synthesizedproteins are handed ouer for t'urther processing ond export.
Lysosomesare the digestiue bodiesol the cell, actiuely involued in the degradotion of cellular compounds. Peroxisomescontoln the enzymecatalosethat protects the cell lrom the toxic elfects of HrOr.
The cellular ground motrix is referred to as cytosol which, in fact, is composed of a network ot' protein t'ilaments, the cytoskeleton. Theeukaryoticcellsperform a widerangeof complex lunctionsin a well coordinatedand integrated fashion. Apoptosis is the processol programmed cell death or cell suicide. They are primarily composedof the elementscarbon, hydrogen and oxygen. The name carbohydrateliterallymeans 'hydratesof carbon'.
Someof the carbohydrates possessthe empiricalformula C. H2O nwhere n 3 3, satisfyingthat thesecarbohydratesare in fact carbonhydrates. However,thereare several non-carbohydratecompounds e. Further, some of the genuine carbohydrates e. Hencecarbohydratescannot be alwaysconsideredas hydratesof carbon. Carbohydrates may be defined as polyhydroxyaldehydes or ketones or compounds which produce them on hydrolysis.
The term 'sugar' is applied to carbohydratessoluble in water and sweet to taste. Carbohydratesare precursorsfor many organic compounds fats,amino acids. Carbohydrates asglycoproteinsand glyco- lipids participate in the structure of cell membraneand cellular functionssuch as cell growth, adhesionand fertilization. They are structuralcomponentsof many organisms.
Theseincludethe fiber cellulose of plants,exoskeletonof some insectsand the cell wall of microorganisms. Carbohydratesalso serve as the storage form of energy glycogen to meetthe immediate energydemandsof the body. They are broadlyclassifiedinto three major groups- monosaccharides, oligosaccharides and polysaccharides.
This categorizationis basedon Mono- and oligo- saccharidesare sweet to taste, crystalline in characterand soluble in water, hence thev are commonly known as sugars. FJtonosaccharides Monosaccharides Greek: They have the generalformula Cn H20 n,and they cannot be further hydrolysed.
The monosaccharidesare divided into differentcategories,based on the functionalgroupandthe numberof carbonatoms Aldoses: When the functional group in IH monosaccharidesis an aldehydel-C: When the functionalgroup is a keto lt -C: Basedon the number of carbon atoms,the monosaccharidesare regarded as trioses 3C , tetroses 4C , pentoses 5C , hexoses 6C and heptoses 7C. Thesetermsalongwith functional groupsare usedwhile namingmonosaccharides. For instance, glucose is an aldohexose while fructose is a ketohexose Table 2,1.
Thecommonmonosaccharidesand disaccha- rides of biological importanceare given in the Table 2. SSlgosaccharides Oligosaccharides Creek: Basedon the numberof monosaccharide units present, the oligo- saccharides are further subdivided to disaccharides,trisaccharidesetc. Polysace harides Polysacchari6ls Creek: They are usually tasteless non-sugars and form colloids with water. The polysaccharidesare of two types- homopolysaccharidesand heteropolysaccharides.
Stereoisomerismis an importantcharacterof monosaccharides. Stereoisomers are the compounds that have the same structural formulaebut differ in their spatialconfiguration. A carbon is said to be asymmetric when it is attached to four different atoms or groups.
Ihe number of asymmetric carbon atoms n determines the possible isomers of a given compound which is equal to 2n. Clucose contains4 asymmetriccarbons,and thus has 16 tsomers. Ghapter 2: Producedduringmetabolism i Asaconstituentofglycoproteins i anogums i ls anintermediateinuronicacidpathway i Heartmuscle i Asaconstituentolpolysaccharides starch,glycogen,cellulose and disaccharides maltose,lactose, sucrose.
Alsofoundinfruits Asaconstituentoflactose milksugar Foundinplantpolysaccharides andanimalglycoproteins Fruitsandhoney,asaconstituent ofsucroseandinulin Foundinolants i Glyceraldehyde3-phosphateisanintermediate i inglycolysis i ttst-pnosphateisanintermediateinglycolysis t Lactasedeficiency lactoseintolerance leadstodianheaandflatulence Animportantintermediateinlhedigestionof starch Maltose DandL- formsof glucosecomparedwith D and L- glyceraldehydes the reference carbohydrate.
D" and L-isomers The D and L isomersare mirror imagesof each other. The spatialorientationof -H and -OH groups on the carbon atom Cs for glucose that is adjacentto the terminal primary alcohol carbon determineswhetherthe sugaris D- or L-isomer.
The structuresof D- and L-glucosebasedon the referencemono- saccharide, D- and L-glyceraldehyde glycerose are depicted in Fig. It may be noted that the naturallyoccurring monosaccharidesin the mammaliantissuesare mostlyof D-configuration. Theenzymemachinery of cells is specific to metaboliseD-seriesof monosaccharides. This is becauseof the dextrorotatorynature of glucose. Optlcal activity of sugars Optical activity is a characteristicfeature of compounds with asymmetric carbon atom.
When a beam of polarized light is passed througha solutionof an optical isomer,it will be rotated either to the right or left. Racemicmixture does not exhibit any optical activity, since the dextro- and levorotatorv activities cancel each other.
Configuration of D-aldoses The configuration of possible D-aldoses startingfrom D-glyceraldehydeis depicted in Fig. This is a representation of Killiani- Fischersynthesis,by increasingthe chain length of an aldose,by one carbon at a time.
Thus, startingwith an aldotriose 3C ,aldotetroses 4C , aldopentoses 5C and aldohexoses 6C are formed. Of the 8 aldohexoses,glucose,mannose and galactoseare the most familiar. Among these, D-glucose is the only aldose mono- saccharidethat predominantlyoccurs in nature. Gonfiguration of D-ketoses Startingfrom dihydroxyacetone triose ,there are five keto-sugarswhich are physiologicallr important. Their structuresare given in Fig,2. Clucose and mannose are epi-'e--' q drl regardto carbon 2 C2-epimers.
The interconversionof epimers e - I r:: ThestructuralrelationshipbetweenD-aldosesshownin Fischerprojection. TheconfigurationaroundC2 ed distinguishesthemembersof eachpair. Enantiomers Enantiomers are a special type of stereoisomers that are mirror images of eachother.
The two membersare designatedas D- and L-sugars. Enantiomersof glucose are depicted in Fig. Majority of the sugarsin the higher animals includingman are of D-type Fig. The term diastereomersis used to represent the sfereoisomers that are not mirror imagesof one another. For a better understanding structure, let us consider the hemiacetals and hemiketals, producedwhen an aldehydeor a with alcohol.
H2oH C: Structuresof ketosesof physiologicalimportance. Thus, the aldehydegroup of glucoseat C1 reactswith alcohol group at C5 to form two typesof cyclic hemiacetalsnamely a and B, as depicted in Fig. The configuration of glucose is conveniently represented either by Fischer formulaeor by Haworth projectionformulae.
Fyranose and furanose structures Haworth projectionformulaeare depictedby a six-memberedring pyranose basedon pyran or a five-memberedring furanose based on furan. The cyclic formsof glucoseare known as a-D-glucopyranose and c-D-glucofuranose Fig. Anomers-nrutarotation The a and p cyclic forms of D-glucose are known as anomers.
Thev differ from each other in the configurationonly around C1 known as anomericcarbon hemiacetalcarbon. The reverseis true for B-anomer. The anomersdiffer in certainphysical and chemical properties. The a and p anomers of glucose have different optical rotations. Mutarotation is defined as the change in the specific optical rotation representing the interconversion of u and p H-C: Structuresof epimers glucoseand galactose are Co-epimerswhileglucoseand mannoseare C2-epimers.
L-Glucose D-Glucose H9. Enantiomers mirrorimages ofglucose. The cr and p formsof glucoseare interconvertiblewhich occurs through a linear form. The latter, as such, is present in a" insignificantquantitY. Mutarotation of fructose z Frur' exhibits mutarotation. And fruqt' rotation of 2. Ihe conv' to levor ': Mutarotationdepictedin Fi9.
In aqueoussolution,the p form is more predominant due to its stable conformation. The s and p formsof glucoseare interconvertiblewhich occurs through a linear form. The latter, as such, is present in an insignificantquantity. Mutarotation of fructose: Fructose also exhibits mutarotation. And fructosehas a specificoptical rotationof " at equilibrium.
Sugarspossessing anomericcarbon atom undergotautomerization in alkalinesolutions. Mutarotation of glucose representing a and p anomers A Fischer projections B Haworth projections.
Structureof glucose-pyranose and furanoseforms. Theenediolsare highlyreactive,hencesugars in alkaline solution are powerful reducing agents.
The reducingpropertyis attributedto the free aldehyde or keto group of anomeric carbon. These incfude Benedict's test, Fehling's test, Barfoed's tesf etc. The reduction is much more efficient in the alkaline medium than in the acid medium.
For instance,considerglucose: Reduetion When treatedwith reducing agentssuch as sodiumamalgam,the aldehydeor keto groupof monosaccharideis reduced to corresponding alcohol, as indicatedby the generalformula: H H-C: Mannitol is usefulto reduce intracranialtensionbv forced diuresis.
O I H-C: O I Formation of esters The alcoholic groups of monosaccharides may be esterified by non-enzymatic or enzymatic reactions. Esterificationof carbo- hydrate with phosphoric acid is a common reaction in metabolism. Glucose 6-phosphate and glucose 1-phosphateare good examples.
ATP donates the phosphate moiety in ester formation. The bond so formed is known as glycosidic bond and the non-carbohydrate moiety when present is referredto as aglycone. The monosaccharidesare held together by glycosidic bonds to result in di-, oligo- or polysaccharides seelaterfor structures. Dehydration of monosaccharides with concentrated H "SO o. Dehydration When treatedwith concentratedsulfuricacid, monosaccharidesundergodehydrationwith an eliminationof 3 water molecules.
Thus hexoses give hydroxymethylfurfuralwhile pentosesgive furfural on dehydration Fi9. Thesefurfurals can condense with phenolic compounds a-naphthol to form coloured products.
This is the chemical basisof the popular Molisch test. In case of oligo- and polysaccharides,they are firsthydrolysedto monosaccharidesby acid,and this is followed by dehydration. Osazone formation Phenylhydrazinein acetic acid, when boiled with reducing sugars, forms osazones in a reactionsummarizedin Fig,2, As is evident from the reaction, the first two carbons Cr and C2 are involved in osazone formation.
The sugars that differ in their configuration on these two carbons give the same type of osazones,since the differenceis maskedby bindingwith phenylhydrazine. Thus glucose,fructoseand mannosegive the same type needle-shaped osazones. Reducingdisaccharidesalso give osazones- maltose sunflower-shaped,and lactose powder- puff shaped.
RrcprcsentsCrto Crofglucose. The nomenclatureof glycosidic bonds is based on the Iinkagesbetweenthe carbon atomsand the status of the anomeric carbon o or p. For instance,lactose-which is formed by a bond between C1 of p-galactoseand Ca of glucose- is namedas 0. The other glycosidicbonds are describedin the structure of di- and polysaccharides. Physiologieally important glycosides 1.
Glucovanillin vanillin-D-glucoside is a naturalsubstancethat impartsvanilla flavour. Cardiac glycosides steroidalglycosides: Digoxin and digitoxin contain the aglycone steroidand they stimulatemusclecontraction.
Streptomycin, an antibiotic used in the treatmentof tuberculosisis a glycoside. Sugar acids: Oxidation of aldehyde or primaryalcoholgroupin monosaccharideresults in sugaracids.
Cluconic acid is producedfrom glucose by oxidation of aldehyde C1 group whereasglucuronicacid is formedwhen primary alcoholgroup C6 is oxidized. Sugar alcohols polyols: They are producedby reductionof aldosesor ketoses. For instance,sorbitol is formed from glucose and mannitol from mannose. The monosaccharides, on reduction,yield polyhydroxyalcohols,known as alditols. Ribitol is a constituent of flavin coenzymes; glycerol and myo-inositol are componentsof lipids. Xylitol is a sweetenerused in sugarlessgumsand candies.
Amino sugars: When one or more hydroxyl groups of the monosaccharidesare replaced by amino groups, the products formed are amino sugarse.
D-glucosamine, D-galactosamine. They are present as consti- tuentsof heteropolysaccharides. The amino groups of amino sugars are sometimes acetylated e. N-acetyl D-gluco- samrne. It is an important constituentof glycoproteins and glycolipids. The term sialicacid is usedto include NANA and its other derivatives.
Certain antibiotics contain amino sugars which may be involvedin the antibioticactivity e. These are the sugarsthat contain one oxygen lessthan that presentin the parent molecule. L-Ascorbic acid vitamin C: This is a water-solublevitamin, the structureof which closelyresemblesthat of a monosaccharide. The structuresof selected monosaccharide derivativesare depictedin Fig. Among the oligosaccharides,disaccharides are the most common Fig. As is evident from the name, a disaccharideconsistsof two monosaccharideunits similaror dissimilar held together by a glycosidic hond.
They are crystalline,water-solubleand sweetto taste. The disaccharidesare of two types '1. Reducingdisaccharideswith free aldehyde or keto group e. Non-reducingdisaccharideswith no free aldehyde or keto group e. Thefreealdehydegrouppresenton C1of second glucoseanswersthe reducingreactions,besides Structuresol monosaccharidederivatives selectedexamples.
Maltosecan be hydrolysedby dilute acid or the enzyme maltaseto liberate two moleculesof cr-D-glucose. Cellobioseis another disaccharide,identical in structurewith maltose,exceptthat the former has p 1 -r 4 glycosidiclinkage. Cellobioseis formedduringthe hydrolysisof cellulose. Suoroee Sucrose canesugar isthe sugarof commerce, mostlyproducedby sugarcane and sugarbeets.
Sucrose is made up of a-D-glucose and p- D-fructose. The reducing groups of glucose and fructose are involvedin glycosidicbond, hencesucroseis a non-reducing sugar,and it cannot form osazones. Sucroseis the major carbohydrateproduced in photosynthesis. Sucroseis the mostabundantamong the naturallyoccurring sugars. This is due to the fact that in sucrose,both the functional groups aldehyde and keto are held togetherand protectedfrom oxidativeattacks. Sucrose is an important source of dietary carbohydrate.
Sucroseis employed as a sweeteningagentin food industry. The intestinal enzyme-sucrase-hydrolysessucroseto glucose and fructosewhich are absorbed. F-aetsse Lactoseis more commonlv known as milk sugarsinceit is the disaccharidefound in milk.
Lactoseis composed ol p-D-galactoseand B-D- glucoseheld togetherby 0 1 -r a glycosidic bond. The anomericcarbonof C1glucoseis free, hence lactoseexhibits reducing propertiesand formsosazones powder-puffor hedgehogshape. Lactose of milk is the most important carbohydratein the nutritionof young mammals. It is hydrolysedby the intestinalenzyme lactase to glucoseand galactose. But, r,r,hen hydrolysed, sucrose becomes levorotatory The Structures of disaccharides -maltose, sucrose and lactose.
The processof inversionis explainedbelow. Hydrolysisof sucroseby the enzyme sucrase invertasdor dilute acid liberatesone molecure each of glucoseand fructose.
However, p-D- fructofuranoseis lessstableand immediatelygets converted to p-D-fructopyranose which is stronglylevorotatory ". Polysaccharides or simply glycans consistof repeat units of monosaccharides or their derivatives,held togetherby glycosidicbonds.
Theyareprimarilyconcernedwith two important functions-structural,and storageof energy. Polysaccharides are linear as well as branched polymers. This is in contrast to structureof proteinsand nucleicacidswhich are only linear polymers. The occurrence of branchesin polysaccharidesis due to the fact that glycosidic linkagescan be formed at any one of the hydroxylBroupsof a monosaccharide.
Polysaccharidesare of two types 1. Homopolysaccharideswhich on hydrolysis yield only a singletype of monosaccharide. They are named based on the nature of the monosaccharideunit.