Adenine (A)

Nucleic Acids Purine

These are biological polymers. They function as the chemical Nitrogenous Guanine (G)
carriers of cell’s genetic information. base in DNA Thymine (T)
DNA (Deoxyribose nucleic acid) Pyrimidine
Nucleic Cytosine (C)
acids RNA (Ribose nucleic acid) l
DNA has A == T, C ≡≡ G

1. DNA 2. RNA (Ribose Nucleic Acid)

(Deoxyribose Nucleic Acid) l
It is also a polymer of nucleotide units but in it, the
nucleotide unit contains ribose sugar instead of
l
DNA is the polymer of nucleotide.
deoxyribose sugar.
l
It is a genetic material. l
RNA has uracil (U) instead of thymine (T).
l
It has double helical structure. l
RNA molecules are of three types, these are messenger
l
Nucleotide has deoxyribose sugar, phosphate and RNA (mRNA), ribosomal RNA (rRNA) and transfer RNA
nitrogenous base. (t RNA). They perform different functions.
l
Nucleoside has deoxyribose sugar and nitrogenous base. A
unit formed by the attachment of a base to 1′-position of
sugar is known as nucleoside.
Biological Functions of Nucleic Acids
l
DNA has an ability of self duplication during cell division
l
In nucleosides, the sugar carbons are numbered as 1′ , 2′ , 3′
and identical DNA strand are transferred to daughter cell.
etc., in order to distinguish these from the bases. When
In this way, DNA is responsible for maintaining the identity
nucleoside is linked to phosphoric acid at 5′-position of
of different species of organisms over million of years.
sugar moiety, we get a nucleotide.
l
RNA molecules synthesised various types of proteins in the
l
Nucleotides are joined together by phosphodiester linkage
cell but the message for the synthesis of a particular type of
between 5′ and 3′ carbon.
protein is present in DNA.

DAY PRACTICE SESSION 1

FOUNDATION QUESTIONS EXERCISE

1 Which one given below is a non-reducing sugar? 6 Which one of the following does not exhibit the
ª NEET 2016, Phase I phenomenon of mutarotation? ª CBSE-AIPMT 2010
(a) Lactose (b) Glucose (a) (+) sucrose (b) (+) lactose
(c) Sucrose (d) Maltose (c) (+) maltose (d) (−) fructose
2 Number of chiral carbon atoms in β-D-(+)-glucose is 7 D-(+)-glucose reacts with hydroxylamine and yields an
(a) five (b) six (c) three (d) four oxime.The structure of the oxime would be ª CBSE-AIPMT 2010
3 The term anomers of glucose refers to — NOH
CH— CH — NOH
 
(a) isomers of glucose that differ in configuration at carbons H—C—OH HO—C—H
one and four (C-1 and C - 4)  
HO—C—H HO—C—H
(b) a mixture of D-glucose and L-glucose (a)  (b) 
(c) enantiomers of glucose HO—C—H H—C—OH
 
(d) isomers of glucose that differ in configuration at carbon H—C—OH H—C—OH
one C -1  
CH2OH CH2OH
4 Artificial sweetener which is stable under cold conditions
CH — NOH CH—NOH
only is ª CBSE-AIPMT 2014  
(a) saccharine (b) sucralose HO—C—H H—C—OH
 
(c) aspartame (d) alitame H—C—OH HO—C—H
(c)  (d) 
5 The change in the optical rotation of freshly prepared HO—C—H H—C—OH
solution of glucose is known as  
H—C—OH H—C—OH
(a) tautomerism (b) racemisation  
(c) specific rotation (d) mutarotation CH2OH CH2OH
 8 Which one of the following sets of monosaccharides forms 19 Which of the following has an imino ( NH) group
sucrose? ª CBSE-AIPMT 2012 instead of an amino group (—NH 2 ) ?
(a) α-D-galactopyranose and α-D-glucopyranose (a) Proline (b) Isoleucine
(b) α-D-glucopyranose and β -D-fructofuranose (c) Tyrosine (d) Serine
(c) β -D-glucopyranose and α-D-fructofuranose 20 Which of the following compounds can form a Zwitter
(d) α-D-galactopyranose and β -D-fructofuranose ion? ª NEET 2018
9 Sucrose (cane sugar) is a disaccharide. One molecule of (a) Benzoic acid (b) Acetanilide
sucrose on hydrolysis gives _____. (c) Aniline (d) Glycine
(a) 2 molecules of glucose 21 Which functional group participates in disulphide
(b) 2 molecules of glucose + 1 molecule of fructose bond formation in proteins?
(c) 1 molecule of glucose + 1molecule of fructose (a) Thiolactone (b) Thiol
(d) 2 molecules of fructose (c) Thioether (d) Thioester
10 Which of the following is an example of ketohexose? 22 Which one of the following is a conjugated protein?
(a) Mannose (b) Galactose (c) Maltose (d) Fructose (a) Phosphoprotein (b) Glycoprotein
11 Which one of the following statements is not true regarding (c) Chromoprotein (d) All of these
(+) lactose? ª CBSE-AIPMT 2011 23 Which of the following statements is not correct?
(a) (+) lactose is a β -glycoside formed by the union of a ª NEET 2017
molecule of D-(+)-glucose and a molecule of (a) Insulin maintains sugar level in the blood of a
D-(+)-galactose human body
(b) (+) lactose is a reducing sugar and does not exhibit (b) Ovalbumin is a simple food reserve in egg white
mutarotation (c) Blood proteins thrombin and fibrinogen are involved
(c) (+) lactose, C12H22O11 contains 8 —OH groups in blood clotting
(d) On hydrolysis, (+) lactose gives equal amount of (d) Denaturation makes the proteins more active
D-(+)-glucose and D-(+)-galactose
24 Which of the following contains cobalt?
12 Hydrolysis of sucrose is called (a) Vitamin-A (b) Vitamin-C
(a) inversion (b) esterification (c) Vitamin-B12 (d) Vitamin-K
(c) hydration (d) saponification
25. Which of the following acid is a vitamin?
13 Which one of the following biomolecules is insoluble in (a) Aspartic acid (b) Ascorbic acid
water? (c) Adipic acid (d) Saccharic acid
(a) α-keratin (b) Haemoglobin
(c) Ribonuclease (d) Adenine
26 Which of the following hormones is produced under
the condition of stress which stimulates
14 Complete hydrolysis of cellulose gives glycogenolysis in the liver of human beings?
(a) D-fructose (b) D-ribose (c) D-glucose (d) L-glucose ª CBSE-AIPMT 2014
15 The difference between amylose and amylopectin is (a) Thyroxine (b) Insulin
ª NEET 2018 (c) Adrenaline (d) Estradiol
(a) amylopectin have 1 → 4 α-linkage and 1 → 6 β-linkage 27 Deficiency of vitamin B1 causes the disease
(b) amylose have 1 → 4 α-linkage and 1 → 6 β-linkage ª CBSE-AIPMT 2012
(c) amylopectin have 1 → 4 α-linkage and 1 → 6 α-linkage (a) convulsions (b) beri-beri
(d) amylose is made up of glucose and galactose (c) cheilosis (d) sterility
16 In a protein molecule various amino acids are linked together 28 The pyrimidine bases present in DNA are
by ª NEET 2016, Phase I (a) cytosine and adenine (b) cytosine and guanine
(a) β-glycosidic bond (b) peptide bond (c) cytosine and thymine (d) cytosine and uracil
(c) dative bond (d) α-glycosidic bond
29 DNA and RNA contain four bases each. Which of the
17 Casein contained in milk is a/an following base is not present in RNA?
(a) carbohydrate (b) lipid (a) Adenine (b) Uracil
(c) protein (d) important molecule (c) Thymine (d) Cytosine
18 Which of the following set consists only of essential amino 30 The couplings between base units of DNA is through
acids? (a) hydrogen bonding (b) electrostatic bonding
(a) Alanine, tyrosine, cystine (b) Leucine, lysine, tryptophan (c) covalent bonding (d) van der Waals’ forces
(c) Alanine, glutamine, lycine (d) Leucine, proline, glycine
DAY THIRTY FOUR BIOMOLECULES 399

DAY PRACTICE SESSION 2

PROGRESSIVE QUESTIONS EXERCISE

1 In both DNA and RNA, heterocyclic base and phosphate 8 An organic compound consumes 4 moles of periodic
ester linkages are at acid to form following copounds, per mole of the starting
(a) C 5′ and C1′ respectively of the sugar molecule compound HCHO, 3HCOOH and CHOCOOH. The
(b) C1′ and C 5′ respectively of the sugar molecule organic compound is
(c) C ′2 and C ′5 respectively of the sugar molecule (a) glucose (b) fructose
(d) C 5′ and C 2′ respectively of the sugar molecule (c) gluconic acid (d) sorbitol
2 The correct statement about the following disaccharide is 9 Which of the following statements is not true about
CH2OH glucose?
H2COH O (a) It is an aldohexose
O H
H H (b) On heating with HI it forms n-hexane
H (c) It is present in furanose form
H OH
OH H CH2OH (d) It does not give 2,4-DNP test
OH OCH2CH2O
10 Optical rotations of some compounds along with their
H OH OH H structures are given below which of them have D
(I) (II) configuration.
CH2OH
(a) Ring (I) is pyranose with α-glycosidic link CHO
|
(b) Ring (I) is furanose with α-glycosidic link
CHO H OH C==O
(c) Ring (II) is furanose with α-glycosidic link
(d) Ring (II) is pyranose with α-glycosidic link HO H HO H
H OH
3 A compound give negative test with ninhydrin and H OH H OH
CH2OH
positive test with Benedict’s solution. The compound is H OH H OH
(a) a protein CH2OH CH2OH
(b) an amino acid
(+) rotation (+) rotation (–) rotation
(c) a lipid
(d) a monosaccharide
I II III

4 Insulin production of its action in human body are (a) I, II and III (b) II and III
responsible for the level of diabetes. This compound (c) I and II (d) Only III
belongs to which of the following categories? 11 Identify the correct statement regarding enzymes.
(a) A coenzyme (b) A hormone (a) Enzymes are specific biological catalysts that can
(c) An enzyme (d) An antibiotic normally function at very high temperatures (T ~ 100 K)
5 RNA and DNA are chiral molecules, their chirality is (b) Enzymes are normally heterogeneous catalysts that are
due to very specific in their action
(a) L-sugar component (c) Enzymes are specific biological catalysts that cannot be
(b) chiral bases poisoned
(c) D-sugar component (d) Enzymes are specific biological catalysts that possess
(d) chiral phosphate ester units well defined active sites
6 In an amino acid, the carboxyl group ionises at 12 In an electric field, if an amino acid migrate towards
pKa1 = 2.34 and ammonium ion at pKa2 = 9.6. The cathode, the pH of the solution is said to be
isolectric point of the amino acid is at pH (a) less than pI (b) more than pI
(a) 5.97 (b) 2.34 (c) 9.60 (d) 6.97 (c) equal to pI (d) 7
7 The enzyme which facilitates internal rearrangement in 13 The correct statement in respect of protein haemoglobin
3-phosphoglyceric acid to form 2-phosphoglyceric acid is is that it
(a) aldolase (a) acts as an oxygen carrier in the blood
(b) triose phosphate isomerase (b) forms antibodies and offers resistance to diseases
(c) phosphoglycero mutase (c) functions as a catalyst for biological reactions
(d) pyruvate kinase (d) maintains blood sugar level
14 Which statement is incorrect about peptide bond (c) C—N bond length in proteins is smaller than usual bond
O length of C—N bond
 • • (d) None of the above
C  N H  ?
15 The α-D glucose and β-D-glucose differ from each other
(a) C—N bond length in proteins is longer than usual bond due to difference in carbon with respect to its
length of C—N bond
(a) conformation (b) configuration
(b) Spectroscopic analysis show planar structure of
(c) number of —OH groups (d) size of hemiacetal ring
 C NH group

O

ANSWERS
SESSION 1 1 (c) 2 (a) 3 (d) 4 (c) 5 (d) 6 (a) 7 (d) 8 (b) 9 (c) 10 (d)
11 (b) 12 (a) 13 (a) 14 (c) 15 (c) 16 (b) 17 (c) 18 (b) 19 (a) 20 (d)
21 (b) 22 (d) 23 (d) 24 (c) 25 (b) 26 (c) 27 (b) 28 (c) 29 (c) 30 (a)
SESSION 2 1 (a) 2 (a) 3 (d) 4 (b) 5 (c) 6 (a) 7 (c) 8 (c) 9 (c) 10 (a)
11 (d) 12 (a) 13 (a) 14 (c) 15 (b)

Hints and Explanations

SESSION 1 3 Anomers of glucose are cyclic diastereomers differ
1 Sucrose is non-reducing sugar because reducing part of in configuration at C-1 existing in two forms α and β
O respectively.
 4 Aspartame is the only artificial sweetener which is stable at lower
glucose (— C — H) and fructose ( C == O) are involved in temperature and decomposes at higher temperature. It is also
glycosidic linkage. called Nutra sweet. It’s relative sweetness value is 180.
CH2OH 5 A spontaneous change in the specific rotation of a solution of an
O optically active compound is called mutarotation. Hemiacetal
H H forms of α and β-D-glucose are stable in solid state but in
H
aqueous solution, there is opening of the cyclic structure which
OH H gives solution of constant specific rotation.
HO O Glycosidic
linkage
H HO HO H H—C O H OH
H OH H OH H OH
O
HOH2C HO H HO H HO H
OH CH2OH
H H OH H OH H OH
H
H H O H OH H O
OH
Sucrose CH2OH CH2OH CH2OH
While, lactose, glucose and maltose are reducing sugars. β
D-glucose α
Specific rotation
[α] = +113°
2 HO * H [α] = +10° + 52.6°
C
* 6 Reducing sugars that exist in hemiacetal and hemiketal forms,
OH—C—OH undergo mutarotation in aqueous solution.
*

O—C—H O Among the given carbohydrates, only sucrose is a non-reducing
 sugar as in it, the hemiacetal and hemiketal groups of glucose
*
H—C—OH

and fructose are linked together through O-atom and thus, not
* free. Due to the absence of free hemiacetal or hemiketal group,
H—C
 sucrose does not exhibit mutarotation.
CH2OH
β-D(+)-glucose (dextro)
Chiral carbon atoms = 5 .
 7 CH—NOH 16 Two amino acids in a protein are linked by a peptide bond.
 e.g. glycylalanine is formed when carboxyl group of glycine
CH O CH NOH H—C—OH combines with the amino group of alanine.
N H2 OH 
(CHOH)4 (CHOH)4 or HO—C—H H2N — CH2 — CO OH + H2 N — CH COOH
_ 
H2O
H—C—OH –H2O H CH3
CH2 OH CH2OH
Glucose oxime
 Alanine
H—C—OH
H2N — CH2 — CO — NH — CH — COOH

CH2OH Peptide linkage
CH3
8 Sucrose is composed of α-D-glucopyranose and a Glycylalanine (Gly-Ala)
β-D-fructofruanose units which are joined by α, β-glycosidic
linkage between C-1 of the glucose unit and C-2 of the fructose 17 Casein contained in milk is a protein.
unit. 18 Essential amino acids (10) are as follows:
CH2OH (i) Arginine (vi) Methionine
O (ii) Histidine (vii) Phenylalanine
H H (iii) Isoleucine (viii) Threonine
H
(iv) Leucine (ix) Tryptophan
OH H (v) Lysine (x) Valine
HO
COOH
Glycosidic linkage
H HO
19 Proline; HN———H
O CH2
HOH2C O

20 Ion containing positive as well as negative charge is called

H HO CH OH Zwitter ion.
H 2
Among the given options, only glycine (H2N CH2 COOH) is
OH H an amino acid which contains both acidic (acquiring negative
Structure of sucrose
charge) and basic group (acquiring positive charge). Glycine
can form a Zwitter ion. It is because glycine behave like salts
rather than simple amines or carboxylic acids. In aqueous solution,
9 C12H22O11 + H2O → C 6H12O 6 + C 6H12O 6 the carboxyl group can lose a proton and amino group can
Sucrose Glucose Fructose accept a proton giving rise to a dipolar ion known as Zwitter ion.
10 Fructose is an example of ketohexose while glucose is an H
example of aldohexose. 
H  C  C OO −
11 Lactose is a reducing sugar and all reducing sugars show 
mutarotation. NH3
+
12 On hydrolysis, sucrose gives an equimolar mixture of
Zwitter ion
D-(+ )-glucose and D-(− ) fructose.
C12H22O11 + H2O → C 6H12O 6 + C 6H12O 6 The pH at which the amino acid has no net charge is called
Sucrose ( + ) Glucose ( − ) Fructose
isoelectric point. The isoelectric point of glycine is 5.97.

Here, the configuration of sucrose changes (gets inverted) after 21 Disulphide bond may be reduced to thiol by means of reagents,
hydrolysis, thus its hydrolysis is called inversion. i.e. NaBH4 , which shows the presence of thiol group in
disulphide bond formation.
13 α-keratin is water insoluble fibrous protein. It is the major
constituent of nail, hair and skin. 22 Conjugated proteins on hydrolysis give a non-protein portion
14 Cellulose is a polysaccharide, composed of D-glucose units alongwith α-amino acid. The non-protein portion is called
which are joined by β -glycosidic linkages. prosthetic group.

H+
(C 6H10O 5 )n + nH2O → nC 6H12O 6 Protein Prosthetic group
Cellulose D -glucose
Phosphoprotein Lipid (e.g. lecithin)
15 Starch contains two components amylose and amylopectin. Glycoprotein Sugar
Chemically, amylose is a long unbranched chain with 200-1000 Chromoprotein Coloured matter such as
α-D- (+ )-glucose units held by C1-C 4 glycosidic linkage. red coloured protophyrin
Amylopectin is a branched chain polymer of α -D-glucose
units in which chain is formed by C1-C 4 glycosidic linkage Since, all of them have non-protein part hence, all of them are
where branching occurs by C1-C 6 glycosidic linkage. conjugated proteins.
23 Denaturation of protein occur when it is subjected to physical 3 Proteins gives blue voilet colour with ninhydrin while
change like change in temperature or chemical change like carbohydrate gives negative test with ninhydrin. Carbohydrates
change in pH, the hydrogen bonds are disturbed. As a result, give brown red precipitate with benedict’s solution. Hence,
globules unfolds and helix get uncoiled so that protein losses its compound is monosaccharide.
biological activity. Hence, the denaturation of protein makes the 4 Insulin is a proteinaceous hormone. It is secreted by pancreas
protein inactive is not correct. and controls the metabolism of glucose and maintains glucose
24 Vitamin B12 contains cobalt and its chemical name is level in the blood.
cyanocobalamin. Its deficiency causes pernicious anaemia. 5 RNA and DNA molecules have ribose and deoxyribose sugar
25 Vitramin C is also known as ascorbic acid. respectively. Both are chiral, their chirality is due to D-ribose or
deoxyribose sugar component.
26 Epinephrine (adrenaline) hormone produced, the adrenal
2.34 + 9.6
medulla that helps the body to respond to emergency situations. 6 pH (at isoelectric point) = = 5.97
This stimulates glycogenolysis in the liver of human beings. 2
27 Deficiency of vitamin B1 causes beri-beri, which causes loss of 7 The internal rearrangement of 3-phosphoglyceric acid into
2-phospho glyceric acid takes place in the presence of enzyme
appetite and vigour, weak heart beat etc.
phosphoglyceromutase.
28 The pyrimidine bases present in DNA are cytosine and thymine 4HIO
while adenine and guanine are purine bases. 8 CH2 CH CH CH CH COOH →
4
HCHO
    
29 In RNA, uracil is present instead of thymine. OH OH OH OH OH
Gluconic acid + 3HCOOH + C HCOOH
30 In DNA, the two strands are held together by hydrogen bonds. 
For example guanine is bonded to cytosine and adenine to 9 Glucose is present in pyranose form. O
thynine by hydrogen bonding. 10 In all the three structures (I, II and III), the configuration of OH at
C-1 is towards right and hence, all have D-configuration.
SESSION 2 11 Enzymes have well defined active sites and their action are
1 Synthesis of RNA/DNA from phosphoric acid, ribose and specific in nature. They are called biological catalysts and work
cytosine is given below : at optimum temperature between 25 to 40°C.
Dehydration 12 Cations move towards cathode and when pH < pI, thus cationic
NH2
form dominates.
OH 5 4
3N
5
O
13 Haemoglobin act as an oxygen carrier in the blood because four
O P—OH HOCH2 OH 1 2
6
N Fe 2+ ions of haemoglobin can bind with 4 molecules of O 2 and
4 1
O
OH from oxyhaemoglobin.
H H H
H H Hb + O 2 → Oxyhaemoglobin
3 NH2
2
14 Peptide bond is formed by the reaction of COOH group of one
OH OH 5 4
3N amino acid with the NH2 group of another amino acid and
6 2 represented as
OH 1 _
O O O
–2H2O 5'
O P—O— CH2 O N   +
4' 1' —C—NH— —C —NH—
OH
H
H H As partial double bond character found betweenC N bond, the
H
3' bond length of C N in protein should be smaller than usual
2'
C N bond.
OH OH
15 The isomer having the hydroxyl group ( OH) on the right is
Thus, ester linkages are at C 5 ′ and C1 ′ of sugar molecule. called α-D-glucose and one having the hydroxyl group ( OH)
2 Ring A is pyranose (6 membered ring containing one O-atom) on the left is called β-D-glucose. Such pairs of optical isomers
with α-glycosidic linkage and ring II is furanose with β -glycosidic which differ in the configuration only around C1 atom are called
linkage. anomers. Thus α-D-glucose and β-D-glucose are anomers.