CBSE Class 12 Chemistry HOTs Biomolecules

MULTIPLE CHOICE QUESTIONS

Question. Which of the following statement is not true about glucose?
(a) it is an aldohexose
(b) on heating with HI it forms n-hexane
(c) it is present in furanose form
(d) it does not give 2, 4-DNP test

Answer. C

Question. Which of the following acids is a vitamin?
(a) aspartic acid
(b) ascorbic acid
(c) aoiphic acid
(d) saccharic acid

Answer. B

Question. Which of the following base is not present in RNA?
(a) adenine
(b) uracil
(c) thymine
(d) cytosine

Answer. C

Question. Which of the following vitamins can be stored in our body?
(a) vitamin B₁
(b) vitamin B₂
(c) vitamin B₆
(d) vitamin B₁₂

Answer. D

Question. Which one given below is non-reducing sugar?
(a) glucose
(b) sucrose
(c) maltose
(d) lactose

Answer. B

Question. In a protein molecule amino acids are linked together by:
(a) peptide bond
(b) dative bond
(c) glycosidic bond
(d) phospodiestes bond

Answer. A

Question. In DNA1 the complementary bases are:
(a) adenine and thynine ; guanine and eytosine
(b) adenine and thymine; guanine and uracil
(c) adenine and guanine; thymine and cytosine
(d) uracil and adenine; cytosine and guanine

Answer. A

Question. Deficiency of vitamin B₁, cause the disease:
(a) convulsions
(b) beri-beri
(c) cheilosis
(d) sterility

Answer. B

Question. One strand of DNA has the sequence. ATGCTT, the sequence of complementary strand would be:
(a) TCCGAA
(b) TACGTA
(c) TACGAA
(d) TAGCTA

Answer. C

Question. The correct statement regarding RNA and DNA is:
(a) The sugar component RNA is arabinose and sugar in DNA is ribose
(b) The sugar component in RNA is 2'deoxyribose and the sugar component in DNA is arabinose.
(c) The sugar component in RNA is arabinose and the sugar component in DNA is 2'-deoxyribose.
(d) The sugar component in RNA is ribose and sugar component in DNA is 2'-deoxyribose.

Answer. D

Question. Which of the following vitamin given below is water soluble?
(a) vitamin C
(b) vitamin D
(c) vitamin K
(d) vitamin E

Answer. A

Question. In both DNA and RNA, base and phosphate esterlinkage are at
(a) C′5 and C′2 respectively of sugar molecule
(b) C21 and C51 respectively of sugar molecule
(c) C′3 and C51 respectively of sugar molecule
(d) C51 and C11 respectively of sugar molecule

Answer. C

Question. The two functional groups present in a typical carbohydrates are:
(a) —OH and —COOH
(b) —CHO and —COOH
(c) > C==O and —OH
(d) —CHO and —COCl

Answer. C

Question. The presence or absence of hydroxyl group on which carbon atom of sugar differentiates RNA and DNA.
(a) 1st
(b) 2nd
(c) 3rd
(d) 4th

Answer. B

Question. Which of the following is called invert sugar
(a) lactose
(b) sucrose
(c) maltose
(d) glucose

Answer. B

Question. Carbohydrates which give two molecules of mono-saccharides are called disaccharides. These are:
(a) maltose
(b) cellulose
(c) maltase
(d) lactose

Answer. A,D

Question. Starch is a mixture of:
(a) amylom
(b) amylopectin
(c) amylose
(d) β-D-glucose

Answer. B,C

Question. Which of the following contain transition metal?
(a) Vitamin B-12
(b) Chlorophyl
(c) Haemoglobin
(d) RNA

Answer. A,C

Question. Which of the following has glycosidic linkage?
(a) Maltose
(b) Anylose
(c) galactose
(d) sucrose

Answer. A,B,D

Question. Fibrous proteins are present in:
(a) myosin
(b) albumin
(c) collagen
(d) fibroin

Answer. A,C,D

Assertion and Reasoning Type

The question given below consist of an Assertion and the Reason. Use the following key to choose the appropriate answer.
(a) Assertion and reason both are CORRECT and reason is the CORRECT explanation of the assertion.
(b) Assertion and reason both are wrong statements.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.
(e) Assertion and reason both are correct statements but reasson is not correct explanation of assertion.

Question. Assertion : A solution of sucrose in water is dextro rotatory but on hydrolysis in presence of little HCl it becomes laevorotatory.
Reason : Sucrose on hydrolysis gives unequal amount of glucose and fructose as a result sign of rotation changes.

Answer. C

Question. Assertion : Fructose does not contain aldehyde group but still reduce Tollen's reagent.
Reason : In the presence of base, fructose undergoes rearrangement to form glucose and mannose.

Answer. A

Matching Column Type

Question. Match the carbohydrate in Column I with its characteristic given in Column II
Column-I                              Column-II
(A) Lactose                        (p) Ketohexose
(B) Starch                         (q) Disaccharide
(C) Sucrose                       (r) Polysaccharide
(D) Fructose                     (s) on hydrolysis gives β-D-glucose and β-D-galactose
(a) A–s, B–r, C–p, D–q
(b) A–p, B–q, C–r, D–s
(c) A–r, B–s, C–p, D–q
(d) A–s, B–r, C–q, D–p

Answer. (a)—(q, s), (b)—(r), (c)—(q), (d)—(p)

Question. Match the carbohydrate in Column I with its characteristic given in Column II
Column-I                          Column-II
(A) Keratin                    (p) protein
(B) Haemoglobin           (q) β-pleated protein
(C) Riboflavin                (r) α-amino acid
(D) Glycine                   (s) Water soluble vitamin
(a) A–p, B–q, C–s, D–r
(b) A–q, B–p, C–s, D–r
(c) A–q, B–p, C–r, D–s
(d) A–s, B–r, C–q, D–p

Answer. (a)—(p, q), (b)—(p), (c)—(s), (d)—(r) 

VERY SHORT ANSWER TYPE QUESTIONS 

Question. Name polysaccharides which is stored in the liver of animals.
Answer. Glycogen. 

Question. What structural feature is required for a carbohydrate to behave as reducing sugar ?
Answer. The carbonyl group of any one monosaccharide present in carbohydrate should be free. 

Question. Give the significance of (+) sign in the name D-(+)-glucose.
Answer. (+) sign indicates dextro-rotatory nature of glucose. 

Question. Glucose is an aldose sugar but it does not react with sodium hydrogen sulphite.
Give reason.
Answer. The – CHO group reacts with – OH group at C-5 to form a cyclic hemiacetal. 

Question. Why is sucrose called invert sugar ?
Answer. When sucrose is hydrolysed by water, the optical rotation of solution changes from positive to negative. 

Question. Name the amino acid which is not optically active.
Answer. Glycine. 

Question. Give reason :
Amylase present in the saliva becomes inactive in the stomach.
Answer. HCl present in stomach decreases the pH. 

Question. Which forces are responsible for the stability of α-helical structure of proteins ?
Answer. Hydrogen bonding. 

Question. Which nucleic acid is responsible for carrying out protein synthesis in the cell ?
Answer. RNA (Ribonucleic acid) 

Question. When RNA is hydrolysed, there is no relationship among quantities of different bases obtained. What does this fact suggest about structures of RNA ?
Answer. RNA is single stranded. 

Question. What type of linkage holds together the monomers of DNA and RNA ?
Answer. Phosphodiester linkage. 

Question. Give the Howarth projection of D-glucopyranose.
Answer.

Question. Name the vitamin responsible for coagulation of blood.
Answer. Vitamin K. 

Question. Where does the water present in the egg go after boiling the egg ?
Answer. On boiling, during denaturation process water gets absorbed in denaturated proteins. 

Question. What is native state of protein ?
Answer. The energetically most stable shape of the protein at normal pH and temperature is called native state.

SHORT ANSWER TYPE QUESTIONS 

Question. Define the following terms in relation to proteins :
(i) Peptide linkage (ii) Denaturation
Answer. (i) Peptide linkage : A link between two amino acids with loss of water − CO – NH – peptide linkage.
(ii) A process that changes the three dimensional structure of native protein is called denaturation of protein. It results into breaking of hydrogen bonds and disulphide linkages. Thus, a completely denatured protein has a shape of random coil.

Question. List the reactions of glucose which cannot be explained by its open chain structure.
Answer. (i) Despite having the aldehyde group, glucose does not give 2, 4 DNP test or Schiff’s test.
(ii) It does not form hydrogensulphite addition product with NaHSO₃.
(iii) The penta acetate of glucose does not react with hydroxylamine indicating the absence of free – CHO group.

Question. Explain what is meant by :
(i) Biocatalyst
Answer. (i) Biocatalysts are the catalysts which increases the rate of metabolism/ biochemical reactions.

Question. Explain the following terms :
(i) Invert sugar (ii) Polypeptides
Answer. (i) An equimolar mixture of glucose and fructose produced on hydrolysis of sucrose is called invert sugar. It is called so because sucrose is dextro rotatory whereas its hydrolysis product is laevo rotatory.
(ii) Polypeptides are polymers of amino acids containing less than 100 amino acids. For example, oxytocin, vasopressin, etc.

Question. Explain what is meant by :
(i) Glycosidic linkage
Answer. (i) The linkage between the monosaccharide units through oxygen is called glycosidic linkage.

Question. Name the product of hydrolysis of sucrose. Why is sucrose not a reducing sugar ?
Answer. On hydrolysis, sucrose gives equimolar mixture of D-(+)-glucose and D-(−)- fructose. Sucrose is not a reducing sugar as glucose and fructose are linked through their reducing centres in structure of sucrose.

Question. State clearly what are known as nucleotides and nucleosides.
Answer. A nucleoside contain only two basic components of nucleic acids i.e., pentose sugar and nitrogenous base.
A nucleotide contains all the three basic components of nucleic acids i.e., a phosphoric acid group, pentose sugar and nitrogenous base.

Question. Describe what do you understand by primary structure and secondary structure of proteins.
Answer. Primary structure of proteins : The protein in which amino acids linked with each other in a specific sequence is said to be the primary structure of that protein.
Secondary structure of proteins : It refers to the shape in which a long polypeptide chain can exist i.e., α-helix and β-pleated structure.

Question.What is essentially the difference between α-form of glucose and β-form of glucose ? Explain.
Answer. α-form of glucose and β-form of glucose differ only in the configuration of the hydroxyl group at C₁ in cyclic structure of glucose/hemiacetal form of glucose.

Question. What are anomers ? Give the structures of two anomers of glucose.
Answer. Monosaccharides which differs in configuration at functional gp-c-atom (C₁ and C₂), e.g., α-glucose and β-glucose.

More Questions

(ii) between C and G there exist three hydrogen bonds :

- - - - - - - - - -

C - - - - - - - - - - G

- - - - - - - - - -

 

Q.6 When RNA in hydrolysed there is no relationship among the quantities of four bases obtained like DNA. What does this fact indicate about structure of RNA ?

Answer. This indicate that RNA has a single strand structure.

 

Q.7. Where does the water present in the egg go after boiling the egg ?

Answer. After boiling, the water soluble globular protein of egg while get denatured and it cogulates into hard and rubbery insoluble mass.

 

Q.8. Which vitamin is helpful in healing wound and cuts ? What is the chemical name of this vitamin ?

Answer. Vitamin-C is helpful in healing wounds and cuts, its chemical name is Ascorbic acid.

 

2 MARKS QUESTIONS

 

Q.1. What type of bonding helps in stabilising the α-helix structure of proteins ?

Answer. In a α-helix structure, polypeptide chain of amino acids coils as a right handed screw because of the formation of all possible Hydrogen bonds between — NH group at each amino residue and > C = 0 group of adjacent turn of helix.

 

Q.2. Name the water insoluble fraction of Starch. Name the monomer of this.

Answer. Amylopectin is water insoluble fraction of starch. It is a polymer of α-glucose.

 

Q.3. What are the products of hydrolysis of (i) lactose (ii) sucrose. Also name the enzyme used for reaction. Lactase

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Q. 4. How will you prove that all the carbon atoms of glucose are in straight chain ?

Answer. The reaction of glucose with HI gives n-hexane and it proves that all sin-carbon-atom are in straight chain.

Heat n-hexane

 

Q. 5. Enumerate two reactions of glucose which cannot be explained by its open chain structure.

Answer. (i) Glucose does not give Schiff‘s Test although it contains aldehyde group.

(ii) Glucose does not form crystaline product with NaHSO₃.

 

Q. 6. B-complex is an often prescribed Vitamin. What is complex about it ? What is its usefulness ?

Answer. It is a type of Vitamin which contains B1, B2, B6 and B12. It required to release energy from food and to promote healthy skin and muscles. Its deficiency causes beri-beri (Vitamin B₁) and Anaemia (Vitamin B₁₂).

 

Q. 7. What are anomers ? Give two points of difference between two anomer of glucose.

Answer. The pair of optical Isomers which differ in the orientation of H and OH gp only at C₁ Carbon atom are called anomers.

Difference between two anomers of glucose :

α-D (+) glucose β-D (+) glucose

(1) The specific rotation is + 111°. (1) The specific rotation is + 19.2°.

(2) The – OH gp at C1 is below the plane. (2) The – OH gp at C_–1 is above the plane.

VERY SHORT ANSWER TYPE QUESTIONS 

Question. Why is cellulose not digested in human body ?
Answer. It is due to the fact that human beings do not have enzyme to digest cellulose.

Question. Name the enzyme that is used to dissolve blood clots ?
Answer. Streptokinase.

Question. Name two diseases caused due to deficiency of enzymes.
Answer. Albinism and phenyl keto urea.

Question. Give one example of : (a) water soluble, (b) fat soluble vitamins.
Answer. (a) Vitamin C (b) Vitamin D

Question. Name a protein which is insoluble in water.
Answer. Keratin.

Question. Name the deficiency disease resulting from lack of Vitamin ‘A’ in the diet.
Answer. Night blindness, Xerophthalmia.

Question. Mention two important functions of carbohydrates in plants.
Answer. Major energy source, storage molecules like starch in plants.

Question. Name two of the different types of RNA molecules found in cells of organisms.
Answer. tRNA, mRNA, rRNA.

Question. The deficiency of which vitamin causes the disease pernicious anaemia ?
Answer. Vitamin B12.

Question. Why are carbohydrates generally optically active ?
Answer. Because they contain one or more chiral atom.

Question. During curdling of milk, what happens to sugar present in it ?
Answer. Lactose changes to lactic acid.

Question. What are the products of hydrolysis of lactose ?
Answer. β-D-galactose and β-D-glucose.

Question. The two strands in DNA are not identical but complementary. Explain.
Answer. Base pairing rule is followed; A = T and G ≡ C.

Question. If one strand of DNA has the sequence 5’-G-G-A-C-T-A-C-T-3’, what is the sequence of bases in the complementary strand ?
Answer. 3’-C-C-T-G-A-T-G-A-5’

Question. What are monosaccharides ?
Answer. Sugars which cannot be hydrolysed to give simpler units or compounds.

Question. What is the difference between native protein and denatured protein ?
Answer. Proteins found in a biological system with unique 3D-structure and biological activity is called native protein. When native protein is subjected to physical and chemical change, protein loses its biological activity and is called denatured protein.

Question. Amino acids are amphoteric in nature. Explain.
Answer. It can react with acid and base both as per the following reaction :

SHORT ANSWER-I TYPE QUESTIONS  

Question. Write the hydrolysed product of :
(i) Maltose (ii) Cellulose
Answer. (i) α-D-glucose (ii) β-D-glucose

Question. (i) Acetylation of glucose with acetic anhydride gives glucose penta-acetate.Write the structure of penta acetate.
(ii) Explain why glucose penta acetate does not react with hydroxylamine ?
Answer.

(ii) The molecule of glucose penta acetate has a cyclic structure in which – CHO is involved in ring formation.

Question. What are vitamins ? How are they classified ?
Answer. Vitamins are a group of biomolecules (other than carbohydrates, fats and proteins) most of which cannot be produced by body but must be supplied in small amount to perform specific biological functions of the body.
Types :
(i) Water soluble vitamins : Vitamin B and C.
(ii) Fat soluble vitamins : Vitamin A, D, E and K.

Question. Write the products of oxidation of glucose with :
(i) Bromine water
(ii) Nitric acid
Answer.

Question. State two main differences between globular and fibrous proteins.
Answer. Globular protein                                  Fibrous protein
(i) They form a α-helix structure.            (i) They have β-pleated structure.
(ii) They are water soluble.                    (ii) They are water insoluble.

Question. (i) Name the disease caused by deficiency of vitamin D.
(ii) Why cannot vitamin C be stored in our body ?
Answer. (i) Rickets.
(ii) Vitamin C is a water soluble vitamin which is excreted in urine and cannot be stored in our body.

Question. Name the constituents of starch and what is the difference between them ?
Answer. Amylose : A linear polymer of α-glucose, water soluble.
Amylopectin : Branched polymer of α-glucose, water insoluble

Question. What are essential and non-essential amino acid ? Give two examples of each type.
Answer. Essential amino acids are those which are not produced in our body and required to be supplied from outside, e.g., valine, leucine.
Non-essential amino acids are those which are produced by our body, e.g., glycine, alanine.

Question. Give reasons :
(i) On electrolysis in acidic solution amino acids migrate towards cathode while in alkaline solution these migrate towards anode.
(ii) The monoamino monocarboxylic acids have two pKa values.
Answer.

(ii) Due to zwitter ion formation.

Question. Coagulation of egg white on boiling is an example of denaturation of protein.
Explain it in terms of structural changes.
Answer. Protein albumin present in egg white gets denatured i.e., 2º & 3º structures are destroyed and 1º structure is retained.

Question. Describe two important functions of nucleic acids.
Answer. (i) DNA is responsible for transfer of heredity information from one generation to another.
(ii) RNA is responsible for protein synthesis.

SHORT ANSWER-II TYPE QUESTIONS 

Question. (i) Deficiency of which vitamin causes scurvy ?
(ii) What type of linkage is responsible for the formation of proteins ?
(iii) Write the product formed when glucose is treated with HI.
Answer. (i) Vitamin C.
(ii) Peptide linkage.
(iii) n-hexane.

Question.Differentiate between the following :
(i) Secondary and tertiary structure of protein
(ii) α-helix and β-pleated sheet structure of protein
(iii) Fibrous and globular protein
Answer. (i) Secondary structure is responsible for the shape of protein α-helix and β-pleated sheets in which polypeptide chains have peptide bonds.
Tertiary structure represents overall folding of polypeptide chain and give rise to the fibrous or globular molecular shape.
(ii) α-helix structure : The peptide chains coiled up to form right handed helix involving H-bonding (Intramolecular).
β-pleated sheets : The peptide chains lie side by side together by intermolecular hydrogen bonding.

Question. (i) Name the four bases present in DNA.
(ii) Which of them is not present in RNA ?
(iii) Give the structure of a nucleotide of DNA.
Answer. (i) Adenine, Guanine, Thymine, Cytosine.
(ii) Thymine.

Question. Glucose or sucrose are soluble in water but cyclohexane and benzene are insoluble in water. Explain.
Answer. Glucose contain 5 – OH groups and sucrose contain eight – OH groups, because of this they form intermolecular hydrogen bonding, so they are soluble in water.
But benzene and cyclohexane doesn’t contain – OH groups hence doesn’t form intermolecular hydrogen bonding, so they are not soluble in water.

1 Mark Question

1 How many chiral centres are there in D-(-)-Fructose?

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

3 Why do monosaccharides form cyclic structures?