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 of the following terms are correct about enzyme?
(a) Proteins (b) Dinucleotides
(c) Nucleic acids (d) Biocatalysts
Which monosaccharide units are present in starch, cellulose and glycogen and which linkages link these units?
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?
Assertion (A): Vitamin D can be stored in our body.
Reason (R): Vitamin D is fat soluble vitamin.
Assertion (A): Deoxyribose, C5H10O4 is not a carbohydrate.
Reason (R): Carbohydrates are hydrates of carbon so compounds which follow Cx(H2O)y formula are carbohydrates.
Sucrose is dextrorotatory but the mixture obtained after hydrolysis is laevorotatory. Explain.
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
How do you explain the presence of all six carbon atoms in glucose in a straight chain?
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 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.
Aldopentoses named ribose and 2-deoxyribose are found in nucleic acids.
What is their relative configuration?
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?
Match the following enzyme given in Column I with the reactions they catalyse given in Column II.
Monosaccharides contain carbonyl group hence are classified, as aldose or ketose. The number of carbon atoms present in the monosaccharide molecule are also considered for classification. In which class of monosaccharide will you place fructose?
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?
Activation energy for the acid catalysed hydrolysis of sucrose is 6.22 kJ mol-1, while hydrolysis is catalysed by the enzyme sucrase. Explain.
Assertion (A): Glycine must’be taken through diet.
Reason (R): It is an essential amino acid.
Which of the following monosaccharides are present as five membered cyclic structure (foranose structure)?
(a) Ribose (b) Glucose (c) Fructose (d) Galactose
Structures of glycine and alanine are given below. Show the peptide linkage in glycylalanine.
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
In nucleoside a base is attached at 1′ position of sugar moiety. Nucleotide is formed by linking of phosphoric acid unit to the sugar unit of nucleoside. At which position of sugar unit is the phosphoric acid linked in a nucleoside to give a nucleotide?
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.
