Chemistry

Biomolecules

Question:

Describe the term D- and L-configuration used for amino acids with examples.

Answer:

The sugars are divided into two families: the D-family and L-family which have definite configurations. These configurations are represented with respect to glyceraldehyde as the standard. The glyceraldehydes may be presented by two forms as:
D-(+)-Glyceraldehyde L-(-)-Glyceraldehyde The D-configuration has -OH attached to the carbon adjacent to -CH2OH on right while L-configuration has -OH attached to the carbon adjacent to -CH2OH on left. The sugars are called D- or L-depending upon whether the configuration of the molecule is related to D-glyceraldehyde or L-glyceraldehyde. It has been found that all naturally occurring sugars belong to D-series, e.g., D-glucose D-ribose and D-fructose.

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Biomolecules

Q 1.

The letters ' D ' or ' L' before the name of a stereoisomer of a compound indicate the correlation of configuration of that particular stereoisomer.
ncert-exemplar-problems-class-12-chemistry-biomolecules-21
This refers to their relation with one of the isomers of glyceraldehydes. Predict whether the following compound has ‘D' or ‘L' configuration.

Q 2.

Why must vitamin C be supplied regularly in diet?

Q 3.

Match the following enzyme given in Column I with the reactions they catalyse given in Column II.
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Q 4.

Name the linkage connecting monosaccharide units in polysaccharides.

Q 5.

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?

Q 6.

Aldopentoses named ribose and 2-deoxyribose are found in nucleic acids.
What is their relative configuration?

Q 7.

Which sugar in called invert sugar? Why is it called so?

Q 8.

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

Q 9.

How do you explain the presence of all six carbon atoms in glucose in a straight chain?

Q 10.

Why does compound (A) given below not form an oxime?
ncert-exemplar-problems-class-12-chemistry-biomolecules-26

Q 11.

Which monosaccharide units are present in starch, cellulose and glycogen and which linkages link these units?

Q 12.

What are the different types of RNA found in the cell?

Q 13.

What are enzymes?

Q 14.

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

Q 15.

Activation energy for the acid catalysed hydrolysis of sucrose is 6.22 kJ mol-1, while hydrolysis is catalysed by the enzyme sucrase. Explain.

Q 16.

Classify the following into monosaccharides and disaccharides. Ribose, 2-deoxyribose, maltose, galactose, fructose and lactose.

Q 17.

Optical rotations of some compounds along with their structures are given below which of them have D configuration.
ncert-exemplar-problems-class-12-chemistry-biomolecules-10

Q 18.

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?

Q 19.

How do you explain the presence of five -OH groups in glucose molecule?

Q 20.

Assertion (A): β-glycosidic linkage is present in maltose.
ncert-exemplar-problems-class-12-chemistry-biomolecules-39
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.

Q 21.

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.

Q 22.

Name the sugar present in milk. How many monosaccharide units are present in it? What are such oligosaccharides called?

Q 23.

Assertion (A): Glycine must’be taken through diet.
Reason (R): It is an essential amino acid.

Q 24.

Carbohydrates are essential for life in both plants and animals. Name the carbohydrates that are used as storage molecules in plants and animals, also name the carbohydrate which is present in wood or in the fibre of cotton cloth.

Q 25.

Differentiate between globular and fibrous proteins.

Q 26.

What is the effect of denaturation on the structure of proteins?

Q 27.

What is the difference between a nucleoside and a nucleotide?

Q 28.

Which of the following pairs represents anomers?
ncert-exemplar-problems-class-12-chemistry-biomolecules-3
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Q 29.

Which of the following carbohydrates are branched polymer of glucose?
(a) Amylose (b) Amylopectin (c) Cellulose (d) Glycogen

Q 30.

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?  

Q 31.

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?

Q 32.

Coagulation of egg white on boiling is an example of denaturation of protein. Explain it in terms of structural changes.

Q 33.

Why are vitamin A and vitamin C essential to us? Give their important sources.

Q 34.

Where does the water present in the egg go after boiling the egg?

Q 35.

What are monosaccharides ?

Q 36.

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.

Q 37.

Describe the term D- and L-configuration used for amino acids with examples.

Q 38.

What are the hydrolysis products of (i) sucrose, and (ii) lactose?

Q 39.

Enumerate the reactions of D-glucose which cannot be explained by its open chain structure.

Q 40.

The two strands in DNA are not identical but are complementary. Explain.

Q 41.

ncert-exemplar-problems-class-12-chemistry-biomolecules-15

Q 42.

ncert-exemplar-problems-class-12-chemistry-biomolecules-23

Q 43.

How do enzymes help a substrate to be attacked by the reagent effectively?

Q 44.

Assertion (A): Vitamin D can be stored in our body.
Reason (R): Vitamin D is fat soluble vitamin.

Q 45.

Glucose or sucrose are soluble in water but cyclohexane and benzene (simple six membred ring compounds) are insoluble in water Explain.

Q 46.

The melting points and solubility of amino acids in water are generally higher than those of corresponding haloacids. Explain.

Q 47.

Why cannot Vitamin C be stored in our body?

Q 48.

Write two main functions of carbohydrates in plants.

Q 49.

What are essential and non-essential amino acids? Give two examples of each type.

Q 50.

Three cyclic structures of monosaccharides are given below which of these are anomers.
ncert-exemplar-problems-class-12-chemistry-biomolecules-9