Write the reactions of D-glucose which cannot be explained by its open-chain structure. How can cyclic structure of glucose explain these reactions?
he open chain structure of glucose explained most of its properties. However, it could not explain the following facts.
(i) Despite having an aldehydic (-CHO) group, glucose does not undergo certain characteristic Reactions of aldehydes. For example,
(a) Glucose does not react with ammonia.
(b) Glucose does not react with sodium bisulphite (NaHSO3) to form addition product.
(c) Glucose does not give Schiff's test and 2, 4-DNP test like other aldehydes.
(ii) Glucose reacts with hydroxylamine (-NH2OH) to form an oxime but glucose pentaacetate does not react with hydroxylamine. This shows that -CHO groups is not present in glucose pentaacetate.
(iii) D (+) – Glucose exists in two stereoisomeric forms i.e., α -D-glucose and β-D-glucose. These two forms are crystalline and have different melting points and optical rotations.
(iv) An aqueous solution of glucose shows mutarotation, i.e., its specific rotation gradually decreases from +110 ° to + 52.5 ° in case of α -glucose and increases from +19.7 ° to + 52.5 ° in case of β-glucose.
(v) Glucose forms isomeric methyl glucosides. When glucose is heated with methanol in the presence of dry hydrogen chloride gas, it gives two isomeric monomethyl derivatives known as methyl α -D-glucoside (m.p. = 438 K or 165 °C) and methyl β-D-glucoside (m.p. = 380 K or 107 °C).
These results shows that glucose does not have open chain form structure
The letters ' D ' or ' L' before the name of a stereoisomer of a compound indicate the correlation of configuration of that particular stereoisomer.
This refers to their relation with one of the isomers of glyceraldehydes. Predict whether the following compound has ‘D' or ‘L' configuration.
Which monosaccharide units are present in starch, cellulose and glycogen and which linkages link these units?
Assertion (A): Vitamin D can be stored in our body.
Reason (R): Vitamin D is fat soluble vitamin.
Some enzymes are named after the reaction, where they are used. What name is given to the class of enzymes which catalyse the oxidation of one substrate with simultaneous reduction of another substrate?
Protein found in a biological system with a unique three dimensional structure and biological activity is called a native protein. When a protein in its native form, is subjected to a physical change like change in temperature or a chemical change like, change in pH, denaturation of protein takes place. Explain the cause.
Assertion (A): β-glycosidic linkage is present in maltose.
Reason (R): Maltose is composed of two glucose units in which C-l of one glucose unit is linked to C-4 of another glucose unit.
Classify the following into monosaccharides and disaccharides. Ribose, 2-deoxyribose, maltose, galactose, fructose and lactose.
In fibrous proteins, polypeptide chains are held together by
(a) van der Waals forces (b) disulphide linkage
(c) electrostatic forces of attraction (d) hydrogen bonds
Which of the following terms are correct about enzyme?
(a) Proteins (b) Dinucleotides
(c) Nucleic acids (d) Biocatalysts
α-Helix is a secondary structure of proteins formed by twisting of polypeptide chain into right handed screw like structures. Which type of interactions are responsible for making the a-helix structure stable?
Match the following enzyme given in Column I with the reactions they catalyse given in Column II.
Assertion (A): Glycine must’be taken through diet.
Reason (R): It is an essential amino acid.
What products would be formed when a nucleotide from DNA containing thymine is hydrolysed?
When RNA is hydrolysed, there is no relationship among the quantities of different bases obtained. What does this fact suggest about the structure of RNA?
Optical rotations of some compounds along with their structures are given below which of them have D configuration.
Carbohydrates are classified on the basis of their behaviour on hydrolysis and also as reducing or non-reducing sugar. Sucrose is a .
(a) monosaccharide (b) disaccharide
(c) reducing sugar (d) non-reducing sugar
Assertion (A): In presence of enzyme, substrate molecule can be attacked by the reagent effectively.
Reason (R): Active sites of enzymes hold the substrate molecule in a suitable position.
How do you explain the presence of all six carbon atoms in glucose in a straight chain?
Match the vitamins given in Column I with the deficiency disease they cause given in Column II.
Assertion (A): All naturally occurring a-amino acids except glycine are optically active.
Reason (R): Most naturally occurring amino acids have L-configuration.
Enumerate the reactions of D-glucose which cannot be explained by its open chain structure.
Structure of a disaccharide formed by glucose and fructose is given below. Identify anomeric carbon atoms in monosaccharide units.
Three structures are given below in which two glucose units are linked. Which of these linkages between glucose units are between C1 and C4 and which linkages are between C1 and C6?
