Carbohydrates MCQ - Biotechnology Engineering (BT) MCQ

The glucose and fructose in sucrose are linked by glucose fructose linkage.

Trehalose, is a disachharides that is made up of α -D-glucopyranosyl-(1 → 1)-α -D-glucopyranoside units. While inulin is polysaccharides, raffinose is trisaccharide and cellulose is polysaccharides.

Idose, Allose, Altrose, Gulose, Galactose, Mannose, Stachyose and Glucose are all hexose sugars, while xylose is an example of pentose sugar.

Cellulose, the most abundant compound known, is the structural fiber of plants and bacterial walls. It is a polysaccharide consisting of chains of glucose residues linked by β 1 → 4 bonds. Since humans do not have intestinal hydrolases that attack β 1 → 4 linkages, cellulose cannot be digested but forms an important source of “bulk" in the diet. Lactose is a disaccharide of glucose and galactose found in milk. Amylose is an unbranched polymer of glucose residues in α-1.4 linkages. Glycogen is a branched polymer of glucose with both α-1.4 and α-1, 6 linkages. Maltose is a disaccharide of glucose, which is usually the breakdown pro duct of amylose.

A reducing sugar is capable of acting as a reducing agent, because it has free aldehyde or a free ketone group. Sucrose and trehalose both don’t have free aldehyde and ketone group, so they are non-reducing.

Starch is made up of repeating units of alpha D glucose. In aqueous solution, glucose occurs predominantly as cyclic (ring) structure in which the carbonyl group of glucose forms a covalent bond with oxygen of hydroxyl group at C-5 position of the same glucose molecule, resulting in formation of hemiacetal winch contains an additional asymmetric carbon atom. Thus cyclic form of glucose can exist in two stereoisomeric forms called α and β. Therefore, anomers are isomeric forms of monosaccharides that differ only in their configuration about the hemiacetal or hemiketal carbon atom

Epimers are the pair of carbohydrates that have difference in the rotation of atoms across single carbon atom. If they differ across 2nd carbon atoms, molecules are named as C-2 Epimers. If they differ across 4th carbon atoms, molecules are named as C-4 Epimers.

Hemiacetal is forimed due to reaction between aldehyde and internal hydroxyl groups of the carbohydrates. If hemiacetal reacts with one more sugar through alcohol group they lead to the formation of acetal hi linear structure carbohydrates are neither hemiacetal nor acetal. Glucose is a aldehyde sugar and aldehyde sugars on cyclization tonus hemiacetal. Fructose is a ketose sugar and ketose sugars on cyclization form Hemiketal. Hemiacetals / Hemiketal contain an additional asymmetric carbon atom and thus can exist in 2 stereo isomeric forms α and β.

Gluconic acid is formed due to oxidation at C1 alone, while Glucuronic acid is formed when oxidation occurs at C6 only. Oxidation product of glucose which is oxidized at both C1 and C6 is formed in presence of strong oxidizing agent and is known as Glucaric acid.

A sugar molecule in which OH (hydroxyl group) is replaced by a amino group, is called an amino sugar. Bacterial cell walls are made up of peptidoglycan. Peptidoglycan is a polymer consisting of sugars and amino acid. The sugar component consists of alternating residues of β (1, 4) linked X acetyl glucosamine (NAG) and N acetyl muramic acid. In N acetyl muramic acid (NAM), lactic acid is ether linked to the oxygen at C-3 of N acetyl glucosamine.

Carbohydrates reaction with phenyl hydrazine leads to the formation of Osazone.


All reducing sugars form osazones. Glucose is a reducing sugar hence it forms osazone. Sucrose does not form osazone crystals because it is a non-reducing sugar as it has no free carbonyl group. Sucrose is made
up of glucose and fructose. The linkage in sucrose is Glucose

Inulin is extracted from the roots of Dahelia and used for the determination of Glomerular filtration rate. The monomeric unit of inulin is fructose and glucose.

Amylose being a linear polymer without branching forms a helical shape in which iodine fits well, while iodine cannot bind to the sheet link structure of cellulose. The binding of iodine is mild in case of amylopectin, as amylopectin is a branched chain molecule, so cannot trap the molecule of iodine, meaning the colour of iodine remains reddish violet. Hence Amylose gives blue colour, amylopectin gives violet colour and cellulose does not change the colour of iodine.

Mutarotation is the change in the optical rotation because of the change in the equilibrium between two anomers. when the corresponding stereocenters interconvert. Cyclic sugars show mutarotation as α and β anomeric forms interconvert.
During mutarotation optical activity does not change from positive to negative but increases or decreases. For example-In α glucose specific rotation is +112.2 but in its anomeric form β -Glucose, the specific rotation is +18.7.

Mannose and Glucose are C2 Epimers, while Glucose and Galactose are C4 epimers. Glucose and fructose are not epimers but functional isomers. Alpha D Glucose and Beta D glucose are anomers.
(Anomers and epimers are both diastereomers, but an epimer is a stereoisomer that differs in configuration at any single stereogenic center, while an anomer is actually an epimer that differs in configuration at the acetal/hemiacetal carbon.)

Those polysaccharides which consist of two or more different kind of monosaccharide are called as heteropolysachharides
Cellobiose is a disaccharide with the formula C₁₂H₂₂O₁₁. Cellobiose. a reducing sugar, coznsists of two β-glucose molecules linked by a β (1 → 4) bond.
Heparin: The most common disaccharide unit is composed of a 2-O-sulfated iduronic acid and 6-O-sulfated. N-sulfated glucosamine. IdoA(2S)-GlcNS(6S).
Peptidoglycan: The sugar component consists of alternating residues of β -(1, 4) linked X-acetylglucosamine (NAG) and X-acetylmuramic acid (NAM) C'hondroitin sulfate: linear heteropolysaccharide consisting of repeatins disaccharide units of slucuronic acid and salactosamine

Statement (a) is correct. Allose is a hexose. It has 4 chiral centres. Therefore, the number of isomers of allose are 2ⁿ = 2⁴ = 16.
Statement (c) is correct. Trehalose is a disaccharide formed by 1-1 glycosidic bond between the two alpha glucose units. Therefore in trehalose, anomeric carbon of both glucose are involved in glycosidic linkage so it is a non-reducing sugar and also does not exhibit mutarotation.
Statement (d) is incorrect
α.D glucose and β D glucose are anomers. Isomeric forms of monosaccharides that differ only in their configuration about the hemiacetal or hemiketal carbon atoms are called anomers. D glucose and D galactose are C-4 epimers.
Two sugars that differ only in the configuration around one carbon atom are called epimers. D galactose differs from D glucose in the configuration around 4^th carbon atom.

The number of stereoisomers will be 8 (number of stereoisomers = 2n where n is number of chiral centres). So each molecule will have one enantiomer while remaining will be the Diasteromers. So in this case pintose will have one enantiomer and remaining 6 molecules will be its Diasteromers.

Let us assume that the percentage of alpha anomer is x, so the percentage of beta anomer will be
100-x. The net optical activity will be the result of individual contribution of each anomer.
i.e. 112.2(x/100) + 18.7 (100-x/100) = 100
112x - 18.7 x = 10000 – 1870
X = 86.9

In order to calculate the net optical activity add the contribution of each component
(20% sucrose was hydrolyzed means – 20% glucose, 20% fructose and 80 % sucrose)
0.2 x 52.7 – 92 x .2 + 0.8 x 66.7 = 45.5

Fust, calculate the growth per second:
0.3 m/day = 3 x 10^-6 m/s
(24 h/day)(60 min/h)(60 s/min)
Given that each glucose residue increases the length of the cellulose chain by 0.5 nm(5 x 10^-10 m), the number of residues added per second is 3 x 10^-6 ms = 6,000 residues/s
5 x 10^-10 m/residue