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Carbohydrates BMB

99 important questions on Carbohydrates BMB

What is the main function of cellulose in human nutrition?

Cellulose is a major constituent of fiber, the non-digestable carbohydrate. It decreases the absorption of glucose and cholesterol from the intestine and increases the bulk of feces.

What is the composition of keratan sulfate?

D-Galactose, N-acetyl-glucosamine 6-sulfate

How does hyaluronic acid function in connective tissues?

Hyaluronic acid forms a gel around the ovum and is found in the ground substance of synovial fluid of joints and vitreous humor of eyes.

What are the most common disaccharides among oligosaccharides?

Among the oligosaccharides, disaccharides are the most common. These include the reducing disaccharides namely lactose (milk sugar) and maltose (malt sugar) and the non-reducing sucrose (cane sugar).

What is chitin composed of?

Chitin is composed of N-acetyl D-glucosamine units held together by β (1 → 4) glycosidic bonds.

What are polysaccharides and their primary functions?

Polysaccharides, or glycans, consist of repeat units of monosaccharides or their derivatives, held together by glycosidic bonds. They are primarily concerned with structural functions and storage of energy.

What is sucrose composed of, and how are its components linked?

Sucrose is made up of α-D-glucose and β-D-fructose, held together by a glycosidic bond (α1→β2) between C1 of α-glucose and C2 of β-fructose.

How do polysaccharides differ from proteins and nucleic acids in terms of structure?

Polysaccharides are linear as well as branched polymers, unlike proteins and nucleic acids which are only linear polymers.

What is the significance of glucose in mammals?

Glucose is the most important energy source of carbohydrates to mammals.

How is dermatan sulfate structurally related to chondroitin 4-sulfate?

Dermatan sulfate is structurally related to chondroitin 4-sulfate with an inversion in the configuration around C5 of D-glucuronic acid to form L-iduronic acid.

What happens during the inversion of sucrose?

During inversion, sucrose (dextro) is hydrolysed to glucose and fructose, changing from dextrorotatory (+66.5°) to levorotatory (−28.2°).

What are the two types of polysaccharides?

Homopolysaccharides: Yield only a single type of monosaccharide.
Heteropolysaccharides: Yield a mixture of a few monosaccharides or their derivatives.

What are the carbohydrate reserves of plants and animals?

Starch and glycogen are the carbohydrate reserves of plants and animals respectively. Cellulose, exclusively found in plants, is the structural constituent.

What is glucovanillin and its significance?

Glucovanillin (vanillin-D-glucoside) is a natural substance that imparts vanilla flavour.

What medical use does dextrose have?

Dextrose (glucose in solution in dextrorotatory form) is frequently used in medical practice.

What is agar used for in the laboratory?

A major component of microbial culture media, and in electrophoresis.

How is lactose structured, and what are its properties?

Lactose is composed of β-D-galactose and β-D-glucose held together by β (1→4) glycosidic bond. It exhibits reducing properties and forms osazones.

What is starch and its significance?

Starch is the carbohydrate reserve of plants and is the most important dietary source for higher animals. It is found in cereals, roots, tubers, and vegetables.

What happens to monosaccharides when treated with concentrated sulfuric acid?

Monosaccharides undergo dehydration with an elimination of 3 water molecules.

What are cardiac glycosides and their function?

Cardiac glycosides (steroidal glycosides) like digoxin and digitoxin contain the aglycone steroid and they stimulate muscle contraction.

What is the function of inulin in medical assessments?

Inulin, a polymer of fructose, is used to assess renal function by measuring glomerular filtration rate (GFR).

What are mucopolysaccharides and their role?

Mucopolysaccharides (glycosaminoglycans) are the essential components of tissue structure. They provide the matrix or ground substance of extracellular tissue spaces in which collagen and elastin fibers are embedded.

What is formed when hexoses undergo dehydration?

Hexoses give hydroxymethyl furfural.

What is the Lobry de Bruyn-van Ekenstein transformation?

It is the formation of a common enediol from D-fructose and D-mannose.

What is the significance of sucrose in the food industry?

Sucrose is used as a sweetening agent in food industry and is hydrolysed by the enzyme sucrase to glucose and fructose, which are absorbed.

What are the components of starch and their characteristics?

Starch consists of two polysaccharide components:

Water soluble amylose (15-20%)
Water insoluble amylopectin (80-85%)

What are pectins and where are they found?

Pectins contain galactouronate and rhamnose, found in apples and citrus fruits.

What is the role of the enzyme hyaluronidase in semen?

The enzyme hyaluronidase degrades the gel around the ovum, allowing effective penetration of sperm.

What are glycoproteins and their significance?

Glycoproteins are a group of biochemically important compounds with a variable composition of carbohydrate (1-90%), covalently bound to protein.

Why can't mammals digest cellulose?

Mammals cannot digest cellulose due to lack of the enzyme that cleaves β-glycosidic bonds.

How does the mucopolysaccharide heparin function in the body?

The mucopolysaccharide heparin is an anticoagulant (prevents blood clotting).

What is the chemical basis of the Molisch test?

Furfural can condense with phenolic compounds to form colored products.

What is the role of enediols in sugar reduction?

Enediols are highly reactive and act as powerful reducing agents in alkaline solutions.

What is the structure of glycogen at branching points?

Glycogen has α (1 → 6) glycosidic bonds at branching points.

What is the effect of phlorhizin on experimental animals?

Phlorhizin produces renal damage in experimental animals.

What is the difference between sucrose and lactose in terms of osazone formation?

Sucrose is a non-reducing sugar and cannot form osazones, while lactose exhibits reducing properties and forms osazones.

How are sugars classified based on their reducing properties?

Sugars are classified as reducing or non-reducing based on the presence of a free aldehyde or keto group of anomeric carbon.

How is amylopectin structured compared to amylose?

Amylopectin is a branched chain with α (1 → 6) glycosidic bonds at the branching points and α (1 → 4) linkages elsewhere. It looks like a branched tree with 20–30 glucose units per branch.

How are sugar acids formed?

Sugar acids are formed by oxidation of aldehyde or primary alcohol group in monosaccharide.

What tests are used to identify reducing sugars in the laboratory?

Benedict’s test, Fehling’s test, and Barfoed’s test.

What does the Mucic acid test detect?

Galactose when treated with nitric acid forms insoluble mucic acid crystals.

What are sugar alcohols and how are they produced?

Sugar alcohols (polyols) are produced by reduction of aldoses or ketoses.

What is the role of amylase in the hydrolysis of starch?

Amylase hydrolyses starch by acting specifically on α (1 → 4) glycosidic bonds to liberate dextrins, and finally maltose and glucose units.

What happens when enediol forms reduce cupric ions?

They reduce cupric ions (Cu²⁺) of copper sulphate to cuprous ions (Cu⁺), forming a yellow precipitate of cuprous hydroxide or a red precipitate of cuprous oxide.

What are dextrins and how are they produced?

Dextrins are the breakdown products of starch by the enzyme amylase or dilute acids, identified by iodine colouration as soluble starch (blue), amylodextrin (violet), erythrodextrin (red), and achrodextrin (no colour).

What is the polysaccharide employed for the assessment of kidney function?

Inulin

What is involved in osazone formation?

The first two carbons (C₁ and C₂) are involved in osazone formation.

What is the optical rotation of freshly prepared α-glucose?

The specific optical rotation of a freshly prepared glucose (α anomer) solution in water is +112.2°.

What occurs during the oxidation of the aldehyde group in glucose?

Oxidation of the aldehyde group (CHO) results in the formation of gluconic acid.

What are amino sugars and how are they formed?

Amino sugars are formed when one or more hydroxyl groups of monosaccharides are replaced by amino groups.

What is a racemic mixture?

A racemic mixture is when D- and L-isomers are present in equal concentration and does not exhibit any optical activity.

How are Haworth projection formulae depicted?

Haworth projection formulae are depicted by a six-membered ring pyranose or a five-membered ring furanose.

What is N-acetylneuraminic acid (NANA) and its importance?

N-acetylneuraminic acid (NANA) is a derivative of N-acetylmannose and pyruvic acid, important in glycoproteins and glycolipids.

What is the result of oxidizing the terminal alcohol group in glucose?

Oxidation of the terminal alcohol group (CH₂OH) leads to the production of glucuronic acid.

What is inulin and where is it found?

Inulin is a polymer of fructose, i.e., fructosan, found in dahlia bulbs, garlic, onion, etc., and is used for assessing kidney function through glomerular filtration rate (GFR).

What is glycogen and where is it primarily found?

Glycogen is the carbohydrate reserve in animals, found in high concentration in liver, followed by muscle, brain, and also in plants without chlorophyll.

How is the configuration of D-aldoes depicted?

The configuration of D-aldoes starting from D-glyceraldehyde is depicted in Fig.2.2, representing Kiliani-Fischer synthesis.

What is the equilibrium mixture composition of D-glucose anomers?

63% β-anomer and 36% α-anomer

How are monosaccharides classified based on the functional group?

Aldoses: Aldehyde group (\(H-C=O\))
Ketoses: Keto group (\(C=O\))

What are the cyclic forms of glucose known as?

The cyclic forms of glucose are known as α-D-glucopyranose and α-D-glucofuranose.

What is the general formula for the reduction of monosaccharides?

H–C=O + 2H → H–C–OH

What are deoxysugars and their significance?

Deoxysugars are sugars with one oxygen less than the parent molecule, important in DNA.

What distinguishes the members of each pair in Figure 2.2?

The configuration around C2 (red) distinguishes the members of each pair.

What are the corresponding alcohols for D-Glucose and D-Galactose?

D-Glucose is reduced to D-Sorbitol, and D-Galactose is reduced to D-Dulcitol.

If two monosaccharides differ in configuration around a single carbon atom, they are known as what?

Epimers

What is mutarotation in the context of fructose?

Conversion of pyranose ring to furanose ring with a specific optical rotation of −92° at equilibrium.

What is referred to as aglycone in glycosides?

The non-carbohydrate moiety when present.

What is L-Ascorbic acid and its structure?

L-Ascorbic acid (vitamin C) is a water-soluble vitamin, closely resembling a monosaccharide.

What is the structure of epimers glucose and galactose?

Structures of epimers (glucose and galactose are C4-epimers while glucose and mannose are C2-epimers).

What are the types of monosaccharides based on the number of carbon atoms?

Trioses (3C)
Tetroses (4C)
Pentoses (5C)
Hexoses (6C)
Heptoses (7C)

What pathological conditions can result from the accumulation of sorbitol and dulcitol?

Cataract, peripheral neuropathy, nephropathy.

What is the role of epimerases?

Epimerases catalyse the reaction of epimerization.

What is tautomerization or enolization in monosaccharides?

The process of shifting a hydrogen atom from one carbon atom to another to produce enediols.

What is the interconversion of epimers known as?

The interconversion of epimers (e.g., glucose to galactose and vice versa) is known as epimerization.

What is the occurrence and biochemical importance of dihydroxyacetone?

Found in cells as phosphate; Its 1-phosphate is an intermediate in glycolysis.

What is the occurrence of D-Erythrose and its biochemical importance?

Widespread; Its 4-phosphate is an intermediate in carbohydrate metabolism.

What is the significance of glyceraldehyde in carbohydrate structure?

Glyceraldehyde is the simplest monosaccharide with one asymmetric carbon atom and is the reference carbohydrate for all other carbohydrates.

What determines if a sugar is D- or L-series?

The spatial orientation of –H and –OH groups on the carbon atom adjacent to the terminal primary alcohol carbon determines if the sugar is D- or L-series.

What is maltose composed of?

Maltose is composed of two α-D-glucose units held together by α (1 → 4) glycosidic bond.

What are the occurrences and biochemical importance of D-Ribose?

Occurrence: Widespread as a constituent of RNA and nucleotides
Biochemical importance: For the structure of RNA and nucleotide coenzymes (ATP, NAD⁺, NADP⁺)

What is the empirical formula for carbohydrates?

The empirical formula for carbohydrates is (CH2O)n where n ≥ 3.

What are oligosaccharides and how are they classified?

Oligosaccharides contain 2-10 monosaccharide molecules and are subdivided into disaccharides, trisaccharides, etc.

What are the functions of carbohydrates?

They are the most abundant dietary source of energy.
Carbohydrates are precursors for many organic compounds.
Participate in the structure of cell membrane and cellular functions.
They are structural components of many organisms.
Serve as the storage form of energy (glycogen).

What is the role of D-Deoxyribose in metabolism?

As a constituent of DNA; For the structure of DNA.

What is the optical activity of sugars?

Optical activity is a characteristic feature of compounds with asymmetric carbon atoms, causing rotation of polarized light.

How is D-Ribulose produced and what is its importance?

Produced during metabolism; It is an important metabolite in hexose monophosphate shunt.

What is stereoisomerism in monosaccharides?

Stereoisomerism refers to compounds with the same structural formula but different spatial configurations.

How are carbohydrates classified?

Carbohydrates are classified into three major groups—monosaccharides, oligosaccharides, and polysaccharides.

What is the occurrence and function of D-Xylose?

As a constituent of glycoproteins and gums; Involved in the function of glycoproteins.

What is the biochemical importance of D-Xylulose?

Excreted in urine in essential pentosuria.

What is the occurrence and biochemical role of D-Lyxose?

Heart muscle; As a constituent of lyxoflavin of heart muscle.

What are the occurrences and biochemical importance of D-Glucose?

Occurrence: As a constituent of polysaccharides (starch, glycogen, cellulose) and disaccharides (maltose, lactose, sucrose). Also found in fruits.
Biochemical importance: The 'sugar fuel of life'; excreted in urine in diabetes. Structural unit of cellulose in plants.

What is the occurrence and biochemical importance of D-Galactose?

As a constituent of lactose (milk sugar); Converted to glucose, failure leads to galactosemia.

Where is D-Mannose found and what is its biochemical role?

Found in plant polysaccharides and animal glycoproteins; For the structure of polysaccharides.

What is the occurrence and biochemical importance of D-Fructose?

Fruits and honey, as a constituent of sucrose and inulin; Its phosphates are intermediates of glycolysis.

What is the occurrence and biochemical importance of D-Sedoheptulose?

Found in plants; Its 7-phosphate is an intermediate in hexose monophosphate shunt, and in photosynthesis.

What is the occurrence and biochemical importance of sucrose?

As a constituent of cane sugar and beet sugar, pineapple; Most commonly used table sugar supplying calories.

What is the occurrence and biochemical importance of lactose?

Milk sugar; Exclusive carbohydrate source to breast fed infants. Lactase deficiency (lactose intolerance) leads to diarrhea and flatulence.

What is the occurrence and biochemical importance of maltose?

Product of starch hydrolysis, occurs in germinating seeds; An important intermediate in the digestion of starch.

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Chapter 2 Carbohydrates BMB

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