BIOMOLECULES
Introduction:
In this Unit, Structures and functions of some of biomolecules will be discuss. The structure and functions of biomolecules inside the living being is studied in biochemistry. Living systems are made up of various complex biomolecules such as carbohydrates, proteins, enzymes, lipids, vitamins, hormones, nucleic acids and compounds for storage and exchange of energy such as ATP, etc.
Carbohydrates:
Classification of Carbohydrates
On the basis of their behaviour upon hydrolysis, carbohydrates can be divided into three main groups:
Monosaccharides: A carbohydrate which cannot be hydrolyzed into simpler unit of polyhydroxy aldehyde or ketone is called monosaccharide. About 20 monosaccharides are known to occur in nature. e.g., glucose, fructose, ribose etc.
Oligosaccharides: A carbohydrate which upon hydrolysis yields 2–10 unit of monosaccharide is called oligosaccharide. They are further classified as disaccharides, trisaccharides, etc., depending upon the number of monosaccharides, they provide on hydrolysis. For example, sucrose is a disaccharide which on hydrolysis yields two unit of monosaccharides i.e., glucose and fructose whereas raffinose is a trisaccharide which on hydrolysis yields three unit of monosaccharides i.e., glucose, fructose and galactose.
Polysaccharides: A high molecular mass carbohydrate which upon hydrolysis yields a large number of monosaccharide units is called polysaccharide e.g., starch, cellulose, glycogen, gums, etc.
(C6H10O5)n + nH2O ⟶ nC6H12O6
Sugar and non-sugars : In general monosaccharides and oligosaccharides, are crystalline solids, soluble in water and sweet to taste, are collectively known as sugars. The polysaccharides, on the other hand, are amorphous insoluble in water and tasteless, are known as non-sugars.
Reducing and non-reducing carbohydrates : The carbohydrates containing free aldehydic or ketonic group can reduce Fehling’s solution and Tollen’s reagent are known as reducing carbohydrates. All monosaccharides whether aldose or ketose are reducing in nature. The carbohydrates in which the reducing parts are not free cannot reduce Fehling’s solution and Tollen’s reagent are known as non-reducing carbohydrates. All polysaccharides like starch, cellulose, glycogen etc. are non-reducing carbohydrates.
Monosaccharides
If a monosaccharide contains an aldehyde group, it is known as an aldose and if it contains a keto group, it is known as a ketose.
Glucose
Glucose occurs in nature in free as well as in the combined forms. It is present in sweet fruits and honey. Ripe grapes contain ~20% of glucose.
Preparation of Glucose
From Sucrose (Cane Sugar): When sucrose is boiled with dilute HCl or H2SO4 in alcoholic solution, glucose and fructose are obtained in equimolar proportion.
C12H22O11 + H2O ⟶ C6H12O6 + C6H12O6
From Starch : When starch is boiled with dilute H2SO4 at 393 K under pressure, glucose is obtained. This is the commercial method for the preparation of glucose.
(C6H10O5)n + nH2O ⟶ nC6H12O6
Structure of Glucose: Glucose is an aldohexose and is the monomer of many larger carbohydrates like starch, cellulose etc. It is the most abundant organic compound on the Earth.
Cyclic Structure of Glucose: It was proposed that glucose can form a six-membered ring in which –OH at C-5 can add to the –CHO group and can form a cyclic hemiacetal structure. This explains the absence of –CHO group and also the existence of glucose in α and β-anomeric forms as
The two cyclic hemiacetal forms of glucose differ only in the configuration of the hydroxyl group at C-1, called anomeric carbon and the corresponding α and β-forms are called anomers. It should be noted that α and β-forms of glucose are not mirror images of each other, hence are not enantiomers.
Fructose
Fructose is an important ketohexose. It is obtained by the hydrolysis of sucrose. On the basis of molecular weight determination, elemental analysis and various reaction its molecular formula is found to be C6H12O6 and open chain structure of it can be written as
Fructose also exists in two cyclic forms like glucose i.e., α-D-(–) - fructose and β-D- (–) - fructose. The five membered cyclic structure of fructose is formed by the involvement of –OH at C-5 and carbonyl group. The five-membered ring of fructose is named as furanose with analogy to the compound furan.
Disaccharides
The disaccharides are composed of two units of monosaccharides. On hydrolysis with dilute acids or specific enzymes they give the corresponding monomers.
C12H22O11 + H2O ⟶ C6H12O6 + C6H12O6
In disaccharides the two monosaccharides units are joined together by an oxide linkage formed by the loss of a water molecule and the linkage is known as glycosidic linkage.
Sucrose
Sucrose is formed by the glycosidic linkage between C-1 of α-D-(+)-glucose and C-2 of β-D-(–) fructose:
Maltose
Maltose is formed by the glycosidic linkage between C-1 of one glucose unit to the C-4 of another glucose unit.
Lactose
Lactose is found in milk so it is also known as milk sugar. It is formed by the glycosidic linkage between C-1 of α-D-galactose unit and C-4 of β-D-glucose unit. Lactose is a reducing sugar.
Polysaccharides
Polysaccharides are long chain polymer of monosaccharides joined together by glycosidic linkages. For example, starch, cellulose, glycogen etc. They mainly act as the food storage or structural materials.
Starch (C6H10O5)n
Starch is the main storage polysaccharide of plants. High content of starch is found in cereals, roots, tubers and some vegetables. Starch is a polymer of α-D-(+) Glucose coming of two components namely Amylose and Amylopectin.
Amylose is water soluble component, which constitutes about 15 - 20% of starch. It is a straight chain polysaccharide containing α-D-(+)-glucose units joined together by β-glycosidic linkage involving C-1 of one glucose unit and C-4 of the next.
Amylopectin is a branched chain polysaccharide insoluble in water. It constitutes about 80 – 85% starch. It is a branched chain polymer of α-D-glucose units in which chain is formed by C-1 - C-4 glycosidic linkage whereas branching occurs by C-1 – C-6 glycosidic linkage.
Cellulose
Cellulose is a straight chain polysaccharide composed of only β-D-glucose units. In cellulose there is β-glycosidic linkages between C-1 of one glucose unit and C-4 of the next glucose unit. Cellulose occurs mainly in plants and it is the most abundant organic substance in plant kingdom.
Glycogen
Its structure is similar to amylopectin with more branching than in amylopectin. It is also known as animal starch. In body, carbohydrates are stored as glycogen and when the body needs glucose, enzymes break the glycogen down to glucose. Glycogen is present in liver, muscle and brain.
Note : Carbohydrates are essential for life in both plants and animals. Carbohydrates are stored in plant as starch and in animals as glycogen.
Proteins:
Proteins are high molecular mass complex biopolymer of α-amino acids present in all living cells. They occur in every part of the body and form the fundamental basis of structure and functions of life. The term protein is derived from the Greek word “proteios” which means of prime importance. Proteins are the most abundant biomolecules of the living system. Chief sources of proteins are milk, cheese, pulses, peanuts, fish etc.
Amino Acids : The compound containing –NH2 and –COOH functional groups are known as amino acid, depending upon the relative position of –NH2 group with respect to –COOH group, amino acids are classified into α, β, γ, δ and so on amino acid. Hydrolysis of proteins gives only α-amino acids represented as
Essential and non-essential amino acids : The amino acids which cannot be synthesized in the body are known as essential amino acids which must be taken through diet. The amino acids, which can be synthesized in the body are known as non-essential amino acids.
Peptides : When amino acids are joined together by amide bonds, they form larger molecules called peptides and proteins.
Polypeptide : A dipeptide contains two amino acids linked by one peptide linkage, a tripeptide contains three amino acids linked by two peptide linkages and so on. When number of such amino acids is more than ten, then the products are called polypeptides.
Classification of Protein
On the basis of molecular shape, proteins are classified into two types :
Fibrous Proteins : When the polypeptide chains run parallel and are held together by hydrogen and disulphide bonds, then fibre-like structure is formed, known as fibrous proteins. Such proteins are insoluble in water. For example: Keratin, Myosin etc.
Globular Proteins : When the polypeptide chains coil around to give a spherical shape, the formation of globular protein takes place. Such proteins are usually soluble in water. For example : Insulin, Albumins etc.
Primary, Secondary, Tertiary & Quaternary Structures of Proteins :
Primary Structure : Proteins may have one or more polypeptide chains. Each polypeptide in a protein has amino acids linked with each in a specific sequence and it is this sequence of amino acids that is said to be the primary structure of that protein.
Secondary Structure : The secondary structure of protein refers to the shape in which a long polypeptide chain can exist. They are found to exist in two different types of structure namely α-helix and β-pleated sheet structure.
Tertiary Structure : The tertiary structure of proteins represents overall folding of the polypeptide chains i.e., further folding of secondary structure. It gives rise to two major molecular shapes namely fibrous and globular.
Quaternary Structure : Some of the proteins are composed of two or more polypeptide chains referred to as sub units. The spatial arrangement of these subunits with respect to each other is known as quaternary structure.
Denaturation of Proteins : The loss in biological activity of a protein due to unfolding of globules and uncoiling of helix is called denaturation of protein. During denaturation secondary and tertiary structures are destroyed but primary structure remains intact. The coagulation of egg white on boiling is a common example of denaturation.
Enzymes:
Colloidal solution of protein which works as biological catalyst is known as enzyme. All enzymes are globular proteins. Zymase, Invertase, Maltase, Lactase, Emulsin, Urease, Pepsin, Trypsin, α-Amylase etc are the example of enzyme.
Note : The enzymes work best at an optimum temperature range of 298 K to 313 K. Their activity decreases with decrease or increase in temperature and stops at 273 K.
Vitamins:
Vitamins are organic compounds which are essential for normal growth of life for animals, some bacteria and micro organism. Vitamins are not synthesized by animals (except vitamin D). Vitamins are supplied to the organism through food. They are essential dietary factor.
Classification
Vitamins are classified in two categories :
Water Soluble Vitamins : Vitamin-B-complex and vitamin-C are water soluble.
Fat Soluble Vitamins : Vitamin-A (Retinol), Vitamin-D (Calciferol), Vitamin-E (Tocopherol), Vitamin-K (Phylloquinone).
Nucleic Acid:
The particles in nucleus of the cell, responsible for heredity are called chromosomes which are made up of proteins and another type of biomolecules called nucleic acid. These are natural biopolymers made of nucleotide units i.e., polynucleotides. Nucleic acid contain the elements carbon, oxygen, nitrogen and phosphorous.
Hormones:
Hormones are molecules that act as intercellular messengers. These are produced by endocrine glands in the body and are poured directly in the blood stream which transports them to the site of action. Hormones have several functions in the body. They help to maintain the balance of biological activities in the body. Testosterone is the major sex hormone produced in males.
Topic 1: Carbohydrates
1. Which of the following properties of glucose cannot be explained by its open chain structure? (NCERT PAGE-413)
(i) Glucose does not form hydrogen sulphite with NaHSO3
(ii) On oxidation with HNO3 glucose gives saccharic acid.
(iii) Glucose is found to exist in two different crystalline forms which are named as a and b.
(a) (ii) only (b) (i) and (iii)
(c) (ii) and (iii) (d) (i) and (ii)
2. Which of the following statements is incorrect regarding glucose? (NCERT PAGE-413 & 414)
(a) It is an aldohexose.
(b) It is also known as dextrose
(c) It is monomer of cellulose.
(d) It is the least abundant organic compound on earth
3. Glucose gives silver mirror test with Tollen’s reagent. It shows the presence of (NCERT PAGE-412)
(a) acidic group (b) alcoholic group
(c) ketonic group (d) aldehyde group
4. When glucose reacts with bromine water, the main product is
(NCERT Page-413)
(a) gluconic acid (b) glyceraldehyde
(c) saccharic acid (d) acetic acid
5. Glucose does not react with (NCERT Page-415)
(a) Br2/H2O (b) H2NOH (c) HI (d) NaHSO3
6. Reduction of glucose by HI suggest that (NCERT Page-413)
(a) presence of OH groups
(b) presence of –CHO group
(c) cyclic structure of glucose
(d) six carbon atoms are arranged in straight chain
7. Which is the least stable form of glucose ? (NCERT Page-415)
(a) a-D-Glucose (b) b-D-Glucose
(c) Open chain structure (d) All are equally stable
8. The -D glucose and -D glucose differ from each other due to difference in carbon atom with respect to its (NCERT Page-415)
(a) conformation (b) configuration
(c) number of OH groups (d) size of hemiacetal ring
9. Cellulose is a polymer of (NCERT Page-419)
(a) Glucose (b) Fructose (c) Ribose (d) Sucrose
10. Carbohydrates are stored in the body as (NCERT Page -419)
(a) sugars (b) starch (c) glucose (d) glycogen
11. Lactose is made of (NCERT Page -418)
(a) a-D-glucose only
(b) a-D-glucose and b-D-glucose
(c) a-D-galactose and b-D-glucose
(d) b-D-galactose and b-D-glucose
12. Which of the following monosaccharides are present as five membered cyclic structure (furanose structure)? (NCERT Page -416)
(i) Ribose (ii) Glucose (iii) Fructose (iv) Galactose
(a) (i) and (ii) (b) (i) and (iii) (c) (iii) and (iv) (d) (ii) and (iii)
13. Invert sugar is (NCERT Page -417)
(a) chemically inactive form of sugar
(b) equimolecular mixture of glucose and fructose
(c) mixture of glucose and sucrose
(d) a variety of cane sugar
14. Chemically amylose is a _________ with 200-1000 (NCERT Page -418)
-D-(+)-glucose units held by ______ glycosidic linkage
(a) long unbranched chain, C1- C6.
(b) branched chain, C1 - C4.
(c) long unbranched chain, C1- C4.
(d) branched chain, C1- C6.
15. Which of the following is incorrect about cellulose? (NCERT Page -419)
(a) It is a major constituent of cell wall of plant cells.
(b) It is a branched chain disaccharide
(c) It is composed of only b-D-glucose units.
(d) The glycosidic linkage between two units is found between C1 of one unit and C4 of next unit
16. Which of the following statement(s) is/are correct? (NCERT Page -416 & 417)
(i) Glucose is reducing sugar (ii) Sucrose is reducing sugar
(iii) Maltose is non reducing sugar (iv) Lactose is reducing sugar
(a) (i) and (ii) only (b) (i) and (iii) only
(c) (i) and (iv) only (d) All of these
17. Read the following statements and choose the correct option? (NCERT Page -418)
(i) Starch is a polymer of -glucose.
(ii) Starch consists of amylose and amylopectin.
(iii) Amylose is insoluble in water.
(iv) Amylopectin is soluble in water.
(a) (i) (iii) and (iv) (b) (i), (ii) and (iii) (c) (i) and (ii) (d) (iii) and (iv)
18. Select the false statement about the cyclic glucose. (NCERT Page -414 & 415)
(a) If the OH group is added to CHO group it will form cyclic hemiacetal structure
(b) Glucose form Six-membered ring in which –OH is at C–5 position
(c) Melting point of a-glucose is 423 K and of b-glucose is 419 K
19. When -D-glucose and -D-glucose are dissolved in water in two separate beakers I and II respectively and allowed to stand, then – (NCERT Page -417)
(a) specific rotation in beaker I will decrease while in II will increase upto a constant value
(b) the specific rotation of equilibrium mixture in two beakers will be different
(c) the equilibrium mixture in both beakers will be leavorotatory
(d) the equilibrium mixture in both beakers will contain only cyclic form of glucose
20. Sucrose in water is dextro-rotatory, []D= + 66.4º. When boiled with dilute HCl, the solution becomes leavo-rotatory, []D= -20º. In this process the sucrose molecule breaks into (NCERT Page -417)
(a) L-glucose + D-fructose (b) L-glucose + L-fructose
(c) D-glucose + D-fructose (d) D-glucose + L-fructose
Topic 2: Proteins
21. One of essential a-amino acids is (NCERT Page -421)
(a) lysine (b) serine (c) glycine (d) proline
22. Denaturation of proteins leads to loss of its biological activity by
(NCERT Page -421)
(a) Formation of amino acids
(b) Loss of primary structure
(c) Loss of both primary and secondary structures
(d) Loss of both secondary and tertiary structures
23. Amino acids generally exist in the form of Zwitter ions. This means they contain (NCERT Page -422)
(a) basic-NH2 group and acidic -COOH group
(b) the basic-NH3+ group and acidic -COO- group
(c) basic-NH2 and acidic -H+ group
(d) basic -COO- group and acidic -NH3+ group
24. Proteins are polypeptides of (NCERT Page -422)
(a) b-amino acids (b) a-hydroxy acids
(c) D-a-amino acids (d) L-a-amino acids
25. Globular proteins are present in (NCERT Page -423)
(a) blood (b) hair (c) nails (d) all of these
26. Which of the following is not a fibrous protein? (NCERT Page -422)
(a) Keratin (b) Myosin (c) Insulin (d) Both (a) and (b)
27. Primary structure of a protein is (NCERT Page -423)
(a) sequence in which a-amino acids are linked to one another
(b) sequence in which amino acids of one polypeptide chain are joined to other chain
(c) the folding patterns of polypeptide chains (d) the pattern in which the polypeptide chains are arranged
28. The helical structure of protein is stabilized by (NCERT Page -423)
(a) dipeptide bonds (b) hydrogen bonds
(c) ether bonds (d) peptide bonds
29. Secondary structure of protein is mainly governed by (NCERT Page -423)
(a) hydrogen bonds (b) covalent bonds
(c) ionic bonds (d) disulphide bonds
30. The secondary structure of a protein refers to (NCERT Page -423)
(a) fixed configuration of the polypeptide backbone
(b) - helical backbone
(c) hydrophobic interactions
(d) sequence of - amino acids
31. Coagulation of protein is known as (NCERT Page -424)
(a) dehydration (b) decay (c) deamination (d) denaturing
32. Which of the following terms refers to the overall three dimensional shape of a protein. (NCERT Page -423 & 424)
(a) Primary structure (b) Secondary structure
(c) Tertiary structure (d) Quaternary structure
Topic 3: Enzymes
33. Which of the following is incorrect regarding enzymes? (NCERT Page -425)
(a) Most of them are globular proteins.
(b) They are very specific for a particular reaction but not for a particular substrate.
(c) They are generally named after the compound or class of compounds upon which they work.
(d) All the above statements are incorrect.
34. Enzymes are essential as biocatalysts. They function in (NCERT Page -425)
(a) aqueous medium, temp = 30-35ºC; pH=7
(b) organic medium
(c) aqueous medium under extreme pH conditions
(d) None of these
35. Which of the following statements is incorrect? (NCERT Page -425)
(a) Enzymes are organic catalysts
(b) Enzymes have a very large turnover number
(c) Enzymes action is specific
(d) Enzymes always require a coenzyme in their catalytic action.
Topic 4: Vitamins
36. Among the following vitamins the one whose deficiency causes rickets (bone deficiency) is : (NCERT Page -426)
(a) Vitamin A (b) Vitamin B (c) Vitamin D (d) Vitamin C
37. Vegetable oils like wheat gram oil, sunflower oil etc. are the good source of (NCERT Page -426)
(a) vitamin K (b) vitamin E (c) vitamin D (d) vitamin A
38. Which is a fat soluble vitamin? (NCERT Page -426)
(a) Vitamin A (b) Vitamin B6 (c) Vitamin C (d) Vitamin B2
39. Assertion : Vitamin D cannot be stored in our body (NCERT Page -426)
Reason : Vitamin D is fat soluble vitamin and can not be excreted from the body with urine.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.
Topic 5: Nucleic Acids
40. The presence or absence of hydroxyl group on which carbon atom of sugar differentiates RNA and DNA? (NCERT Page -428)
(a) 1st (b) 2nd (c) 3rd (d) 4th
41. Which of the following is correct about H-bonding in (NCERT Page -428)
nucleotide?
(a) A --- A and T --- T (b) G --- T and A --- C
(c) A --- G and T --- C (d) A --- T and G --- C
42. In DNA the linkages between different nitrogenous bases are (NCERT Page-428)
(a) peptide linkage (b) phosphate linkage
(c) H-bonding (d) glycosidic linkage
43. The double helical structure of DNA was proposed by (NCERT Page -429)
(a) Watson and Crick (b) Meichers
(c) Emil Fischer (d) Khorana
44. When adenine is attached to ribose sugar, it is called adenosine. To make a nucleotide from it, it would require (NCERT Page -429)
(a) oxygenation (b) addition of a base
(c) addition of phosphate (d) hydrogenation
45. Which of the following is not present in a nucleotide? (NCERT Page -429)
(a) Guanine (b) Cytosine (c) Adenine (d) Tyrosine
Topic 6: Hormones
46. Oxytocin hormone is produced by (NCERT Page -431)
(a) pituitary (b) adrenals (c) hypothalamus (d) thyroid
47. Which of the followings is the more scientific definition of hormone? (NCERT Page -430)
(a) They are extracellular messengers.
(b) They always act at distantly located target organ.
(c) They are the products of well organized endocrine glands.
(d) They are non-nutrient chemicals that act as intercellular messengers.
TOPIC 1: Carbohydrates and Lipids
1. Which of the following statement is true?
1) Epimers are also anomers. 2) Anomers are also epimers.
3) Both of the above statements are true. 4) Neither of the two statement is true.
2. The artificial sweetener that has the highest sweetness value in comparison to cane sugar is:
1) Sucralose 2) Aspartame 3) Saccharin 4) Alitame
3. What is the structure of L-glyceraldehyde?
4. Which of the following statements is incorrect?
1) Maltose gives two molecules of glucose only. 2) Cellulose and sucrose are polysaccharides.
3) Polysaccharides are not sweet in taste. 4) Polysaccharides are also known as non-sugars.
5. Rapid interconversion of -D-glucose and -D-glucose to solution is known as
1) Racemization 2) asymmetric induction
3) Fluxional isomerization 4) mutarotation
6. Natural glucose is termed D-glucose because:
1) – OH on the second carbon is on the right side in Fischer projection.
2) – OH on the sixth carbon is on the right side in Fischer projection.
3) – OH on the fifth carbon is on the right side in Fischer projection.
4) It is dextrorotatory.
7. In cells the net production of ATP molecules generated from one glucose molecule is
1) 46 2) 32 3) 38 4) 40
8. Which of the following gives positive Fehling solution test?
1) Protein 2) Sucrose 3) Glucose 4) Fats
9. Which of the following properties of glucose cannot be explained by its open chain structure?
(i) Glucose does not form hydrogen sulphite with NaHSO3.
(ii) On oxidation with HNO3 glucose gives saccharic acid.
(iii) Glucose is found to exist in two different crystalline forms which are named as and .
1) (ii) only 2) (i) and (iii) 3) (ii) and (iii) 4) (i) and (ii)
10. -D- Glucose and - D-glucose differ from each other due to difference in one carbon with respect to its
1) Size of hemiacetal ring 2) number of OH groups
3) Configuration 4) conformation
11. Which of the following does not reduce Benedict’s solution?
1) Glucose 2) Fructose 3) Sucrose 4) Aldehyde
12. Glucose gives silver mirror with Tollen’s reagent. It shows the presence of
1) An acidic group 2) an alcoholic group 3) a ketonic group 4) an aldehydic group
13. Which of the following statements is incorrect regarding glucose?
1) It is an aldohexose. 2) It is also known as dextrose
3) It is monomer of cellulose. 4) It is the least abundant organic compound on earth.
14. The highest calorific value is found in
1) Proteins 2) fats 3) vitamins 4) carbohydrates
15. Isomerization of glucose produces
1) galactose 2) fructose 3) mannose 4) allose
16. The most common disaccharide has the molecular formula
1) C10H18O9 2) C10H20O10 3) C18H22O11 4) C12H22O11
17. In fructose, the possible optical isomers are
1) 12 2) 8 3) 16 4) 4
18. What happens when H2SO4 is treated with sugar?
1) Oxidation 2) Reduction 3) Dehydration 4) Hydrolysis
19. Table sugar is a
1) Disaccharide of D-glucose and D-fructose. 2) A monosaccharide.
3) A disaccharide containing two glucose units. 4) D-glucose.
20. Complete hydrolysis of cellulose gives
1) D-fructose 2) D-ribose 3) D-glucose 4) L-glucose
21. Invert sugar is
1) Chemically inactive form of sugar 2) Equimolecular mixture of glucose and fructose
3) Mixture of glucose and sucrose 4) a variety of cane sugar
22. An organic compound with the formula C6H12O6 forms a yellow crystalline solid with phenylhydrazine and gives a mixture of sorbitol and mannitol when reduced with sodium. Which among the following could be the compound?
1) Fructose 2) glucose 3) mannose 4) sucrose
23. Which one of the following is the reagent used to identify glucose?
1) Neutral ferric chloride 2) Chloroform and alcoholic KOH
3) Ammoniacal silver nitrate 4) Sodium ethoxide
TOPIC 2: Amino Acids, Proteins and Enzymes
24. Globular proteins are present in
1) blood 2) egg 3) milk 4) all of these
25. Among the following organic acids, the acid present in rancid butter is:
1) Pyruvic acid 2) Lactic acid 3) Butyric acid 4) Acetic acid
26. A strongly alkaline solution of a monoaminodicarboxylic acid contains how many basic groups?
1) 1 2) 2 3) 3 4) 4
27. Which of the following protein destroys the antigen when it enters in body cell?
1) Antibodies 2) Insulin 3) Chromoprotein 4) Phosphoprotein
28. The number of essential amino acids in man is
1) 8 2) 10 3) 18 4) 20
29. Which of the following is not a fibrous protein?
1) Keratin 2) Myosin 3) Insulin 4) Both 1) and 2)
30. The helical structure of protein is stabilized by
1) dipeptide bonds 2) hydrogen bonds 3) ether bonds 4) peptide bonds
31. Which functional group participates in disulphide bond formation in proteins?
1) Thioester 2) Thioether 3) Thiol 4) Thiolactone
32. Lactase enzyme hydrolyses
1) Proteins to amino acids. 2) Fats to fatty acids.
3) Glucose to ethyl alcohol. 4) Polysaccharides to monosaccharides.
33. Which of the following tests is not used for testing proteins?
1) Millon’s test 2) Molisch’s test 3) Biuret test 4) Ninhydrin test
34. Which of the following statements is incorrect?
1) In -helix structure a polypeptide chain forms all possible hydrogen bonds by twisting into a right
handed screw.
2) In -structure of proteins all peptide chains are stretched out to nearly maximum extension.
3) During denaturation 1° and 2° structures are destroyed but 3° structure remains intact.
4) All the above statements are incorrect.
35. The enzyme which hydrolyses triglycerides to fatty acids and glycerol is called
1) Maltase 2) lipase 3) zymase 4) pepsin
36. Which one of the following metals is required as co-factor by all enzymes utilizing ATP in phosphate transfer?
1) K 2) Ca 3) Na 4) Mg
37. Tertiary structure of protein arises due to
1) Folding of polypeptide chain
2) Folding, coiling and bonding of polypeptide chain
3) Linear sequence of amino acid in polypeptide chain
4) Denatured proteins
38. An electric current is passed through an aqueous solution
(buffered at pH = 6.0) of alanine (pI = 6.0) and ariginine
(pI = 10.2). The two amino acids can be separated because
1) Alanine migrates to anode, and arginine to cathode.
2) Alanine migrates to cathode, and arginine to anode.
3) Alanine does not migrate, while arginine migrates to cathode.
4) Alanine does not migrate, while arginine migrates to anode.
39. Coagulation of protein is known as
1) Dehydration 2) decay 3) deamination 4) denaturing
40. Imino acid among these compounds is
1) Serine 2) proline 3) tyrosine 4) lysine
41. Which of the following terms refers to the overall three dimensional shape of a protein.
1) Primary structure 2) Secondary structure
3) Tertiary structure 4) Quaternary structure
42. Which amino acid is achiral?
1) Alanine 2) valine 3) proline 4) None of these
43. The strongest form of intermolecular bonding that could be formed involving the residue of the amino acid serine is.
1) Ionic bond 2) hydrogen bond
3) van der Waal’s interactions 4) none of the above
44. Insulin production and its action in human body are responsible for the level of diabetes. This compound belongs to which of the following categories?
1) An enzyme 2) A hormone 3) A co-enzyme 4) An antibiotic
TOPIC 3: Vitamins and Hormones
45. Vitamin K is associated with the disease:
1) Scurvy 2) Beri-beri 3) Blood coagulation 4) Sore throat
46. Vitamin B12 contains
1) Ca(II) 2) Fe(II) 3) Co(III) 4) Zn(II)
47. Vitamin B6 is known as
1) pyridoxine 2) thiamine 3) tocopherol 4) riboflavin
48. Night blindness is caused by deficiency of:
1) Vitamin B12 2) Vitamin A 3) Vitamin C 4) Vitamin E
49. Vegetable oils like wheat gram oil, sunflower oil etc. are the good source of
1) vitamin K 2) vitamin E 3) vitamin D 4) vitamin A
50. Match the columns
Column - I Column - II
1) Vitamin B6 (p) Fat soluble
2) Vitamin K (q) Xerophthalmia
3) Vitamin D (r) Convulsions
4) Vitamin A (s) Delayed blood clotting
1) A – (p,q), B – (p,s), C – (p), D – (r)
2) A – (r), B – (p,s), C – (p), D – (p, q)
3) A – (p,s), B – (r), C – (p), D – (p,q)
4) A – (r), B – (p,s), C – (p,q), D – (p)
51. Biotin is an organic compound present in yeast. Its deficiency in diet causes dermatitis and paralysis. It is also known as
1) Vitamin H 2) Vitamin B3 3) Vitamin B12 4) Vitamin D
52. Match List I (name of vitamin) with List II (deficiency result/ disease) and select the correct answer using the codes given below the lists :
List I List II
I. Ascorbic acid A. Beri-beri
II. Retinol B. Cracked lips
III. Riboflavin C. Scurvy
IV. Thiamine D. Night blindness
1) I - B, II - A, III - C, IV - D 2) I - A, II - B, III - C, IV - D
3) I - D, II - C, III - B, IV - A 4) I - C, II - D, III - B, IV – A
TOPIC 4 : Nucleic Acids
53. In DNA, the complimentary bases are:
1) Adenine and thymine; guanine and cytosine
2) Adenine and thymine ; guanine and uracil
3) Adenine and guanine; thymine and cytosine
4) Uracil and adenine; cytosine and guanine
54. When adenine is attached to ribose sugar, it is called adenosine. To make a nucleotide from it, it would require
1) oxygenation 2) addition of a base 3) addition of phosphate 4) hydrogenation
55. a - Helix is found in
1) DNA 2) RNA 3) lipid 4) carbohydrates
56. Which of the following is not present in a nucleotide?
1) Guanine 2) Cytosine 3) Adenine 4) Tyrosine
57. A sequence of how many nucleotides in messenger RNA makes a codon for an amino acid?
1) Three 2) Four 3) One 4) Two
58. The chemical change in DNA molecule that could lead to synthesis of protein with an altered amino acid sequence is called
1) replication 2) lipid formation 3) cellular membrane 4) mutation
59. Which of the following statements regarding DNA fingerprinting is incorrect?
1) It is used in forensic laboratories for identification of criminals.
2) It cannot be altered by surgery.
3) It is different for every cell and cannot be altered by any known treatment.
4) It is used to determine paternity of an individual.
60. The process by which synthesis of protein takes place based on the genetic information present in m-RNA is called
1) Translation 2) Transcription 3) Replication 4) Messenger hypothesis
1. The difference between amylose and amylopectin is [2018]
1) Amylopectin has linkage and - linkage
2) Amylose has - linkage and - linkage
3) Amylopectin has - linkage and -linkage
2. Which of the following compounds can form a zwitterion? [2018]
1) Aniline 2) Acetanilide 3) Glycine 4) Benzoic acid
3. Which of the following statements is not correct: 2017]
1) Ovalbumin is a simple food reserve in egg-white.
2) Blood proteins thrombin and fibrinogen are involved in blood clotting.
3) Denaturation makes the proteins more active.
4) Insulin maintains sugar level in the blood of a human body.
4. In a protein molecule various amino acids are linked together by [2016]
1) a-glycosidic bond 2) b-glycosidic bond 3) peptide bond 4) dative bond
5. The correct statement regarding RNA and DNA, respectively is [2016]
1) The sugar component in RNA is arabinose and the sugar component in DNA is 2'-deoxyribose.
2) The sugar component in RNA is ribose and the sugar component in DNA is 2'-deoxyribose.
3) The sugar component in RNA is arabinose
4) The sugar component in RNA is 2'-deoxyribose and the sugar component in DNA is arabinose
6. Which one given below is a non-reducing sugar? [2016]
1) Maltose 2) Lactose 3) Glucose 4) Sucrose
7. D (+) glucose reacts with hydroxylamine and yields an oxime. The structure of the oxime would be
[2014]
8. Which of the following hormones is produced under the condition of stress which stimulates glycogenolysis in the liver of human beings? [2014]
1) Thyroxin 2) Insulin 3) Adrenaline 4) Estradiol
9. The non-essential amino acid among the following is : [2019]
(1) valine (2) leucine (3) alanine (4) lysine
10. Which structure(s) of proteins remains(s) intact during denaturation process? [2019-ODISSA]
(1) Both secondary and tertiary structures (2) Primary structure only
(3) Secondary structure only (4) Tertiary structure only
11. Deficiency of which vitamin causes osteomalacia? (2020-COVID-19) (1) Vitamin A (2) Vitamin D (3) Vitamin K (4) Vitamin E
12. Which of the following statement is not true about glucose? (2020-COVID-19)
(1) It is an aldohexose. (2) It contains five hydroxyl groups.
(3) It is a reducing sugar. (4) It is an aldopentose.
13. The RBC deficiency is deficiency disease of : [NEET-2021]
1. Vitamin 2. Vitamin 3. Vitamin 4. Vitamin
NCERT LINE BY LINE QUESTIONS – ANSWERS
1. (b) 2. (d) 3. (d) 4. (a) 5. (d) 6. (d) 7. (c) 8. (b) 9. (a) 10. (d)
11. (d) 12. (b) 13. (b) 14. (c) 15. (b) 16. (c) 17. (c) 18. (c) 19. (a) 20. (c)
21. (a) 22. (d) 23. (d) 24. (d) 25. (a) 26. (c) 27. (a) 28. (b) 29. (b) 30. (b)
31. (d) 32. (c) 33. (b) 34. (a) 35. (d) 36. (c) 37. (b) 38. (a) 39. (d) 40. (b)
41. (d) 42. (c) 43. (a) 44. (c) 45. (d) 46. (c) 47. (d)
TOPIC WISE PRACTICE QUESTIONS – ANSWERS
NEET PREVIOUS YEARS QUESTIONS-ANSWERS
NCERT LINE BY LINE QUESTIONS – SOLUTIONS
1. (b) To explain the properties which can not be explained by open chain structure of glucose it was proposed that one of the –OH groups may add to the –CHO group and forms a cyclic hemiacetal structure as shown below.
2. (d) It is the most abundant organic compound on earth.
3. (d) Tollen’s reagent is reduced by glucose due to aldehydic group and gives grey colour as silver metal.
4. (a) Glucose contains an aldehyde group. It is oxidised into acidic group by bromine water and gluconic acid is formed
5. (d) Weak reagent like NaHSO3 is unable to open the chain and can’t react with glucose. This explains the inability of glucose to form aldehyde bisulphite compound.
6. (d)
7. (c) Open chain structure is unstable and converted to cyclic.
8. (b) -D glucose and -D glucose are the isomers which differ in the orientation (configuration) of H and OH groups around C1 atom.
9. (a) We know that cellulose (C6H12O5)n is the chief constituent of cell walls of plants. It is the most abundant organic substance found in nature. It is a polymer of glucose with 3500 repeat units in a chain.
10. (d) Carbohydrates are stored in the body as glycogen.
11. (d) Lactose (milk sugar) is a disaccharide, it is made of b-D-galactose and b-D-glucose
12. (b)
13. (b)
14. (c) Chemically amylose is a long unbranched chain with 200-1000 a-D-(+)-glucose units held by C1-C4 glycosidic linkage.
15.b
16. (c) Sucrose is non-reducing in nature. It does not contain a free aldehydic or ketonic group. Maltose is a reducing sugar
17. (c) Amylose is water soluble component which constitutes about 15-20% of strach. Amylopectin is insoluble in and constitutes about 80-85% of starch.
18. (c) Melting point of a-glucose® 419 K and b-glucose is 323 K.
19. (a) -D-glucose or -D-glucose when dissolved in water and allowed to stand, following equilibrium is stablised, which is called mutarotation.
20. (c) The hydrolysis of sucrose by boiling with mineral acid or by enzyme invertase or sucrase produces a mixture of equal molecules of D(+) glucose and
D(-) Fructose.
21. (a)
22. (d)
23. (d) Zwitter ion contains both +ve and -ve charge. Proton of -COOH group is transferred to the -NH2 group.-NH3+ group is acidic since it can donate a proton and -COO- group is basic since it can accept a proton.
24. (d) Proteins are highly complex, natural compounds, composed of a large number of different a-amino-acids joined together with peptide linkage, i.e., they are naturally
occuring polypeptides.
25. (a) Globular proteins is present in blood. These are soluble in water.
26. (c) Insulin is an example of globular protein.
27. (a) The sequence in which the a-amino acids are linked to one another in a protein molecule is called its primary structure.
28. (b)
29. (b) The -helix structure is formed when the chain of -amino acids coils as a right handed screw (called -helix) because of the formation of hydrogen bonds between amide groups of the same peptide chain, i.e., NH group in one unit is linked to carbonyl oxygen of the third unit by hydrogen bonding. This hydrogen bonding between different units is responsible for holding helix in a position.
30. (b) The secondary structure of a protein refers to the shape in which a long peptide chain can exist. There are two different conformations of the peptide linkage present in protein, these are -helix and -conformation. The a helix always has a right handed arrangement. In -conformation, all peptide chains are stretched out to nearly maximum extension and then laid side by side and held together by intermolecular hydrogen bonds. The structure resembles the pleated folds of drapery and therefore is known as -pleated sheet.
31. (d) 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, the native conformation of the molecule is disrupted and proteins so formed are called denaturated proteins. The denaturation may be reversible or irreversible. The coagulation of egg on boiling is an example of irreversible protein denaturation. However, it has been shown now that in some cases, the process is actually reversible. The reverse process is called renaturation.
32. (c) Tertiary structure indicates the overall structure of the protein.
33. (b) Enzymes are highly specific for a particular reaction and also for a particular
substrate.
34. (a)
35. (d) Enzymes may or may not require a coenzyme for their catalytic action.
36. (c) Deficiency of vitamin D causes rickets.
37. (b) Vitamin E is mainly present in vegetable oils like wheat gram oil, sunflower oil, etc.
38. (a) Vitamin A or retinol.
39. (d) Vitamin D is a fat soluble vitamin and can be stored in the body since it is not excreted out of the body.
40. (b) RNA has D (-) - Ribose and the DNA has 2-Deoxy D (-) - ribose as the carbohydrate unit.
From the structures it is clear that 2nd carbon in DNA does not have OH group.
41. (d)
. The hydrogen bonds are formed between the base (shown by dotted lines). Because of size and geometrics of the bases, the only possible pairing in DNA are between G(Guanine) and C(Cytosine) through three H-bonds and between A (Adenine) and T (Thymine) through two Hbonds.
42. (c) The base pairs of the two strands of DNA are linked together through H-bonds.
43. (a)
44. (c)
45. (d) Tyrosine is an a-amino acid, and not a purine.
46. (c) Oxytocin hormone is produced by hypothalamus gland and is secreted by the posterior pituitary gland into the blood stream.
47. (d)
TOPIC WISE PRACTICE QUESTIONS - SOLUTIONS
1. (2) Epimers are those diastereomers which differ in the configuration of only one chiral carbon which may be C1, C2, C3, etc.; while anomers are diastereomers that differ in the configuration of a specific chiral carbon which is C1 in aldoses and C2 in ketoses.
2. (4) Alitame is an artificial sweetner that is 2,000 times as sweet as sugar.
3. (4)
4 . (2) Sucrose is an oligosaccharide and cellulose is a polysaccharide.
5. (4)
6. (3) Fischer gave the prefix “D” to compounds whose bottom chiral carbon has its OH to the right. So natural glucose is called D-glucose or dextrose.
7. 3)
Net ATP molecules evolved = 38
8. 3) Glucose contains aldehyde group.
9. 2) To explain the properties which can not be explained by open chain structure of glucose it was proposed that one of the –OH groups may add to the –CHO group and forms a cyclic hemiacetal structure as shown below.
10. (3) and -D-glucoses differ in the arrangement of groups around one carbon atom (C1) i.e., they differ in configuration at C1, hence these are also known as anomers.
11. 3) Sucrose does not have free –CHO or –CO group, hence it does not reduce Benedict’s solution. Remember that fructose has an a-hydroxy ketonic group, which is also reducing group (difference from ordinary ketonic group)
12. (4) Glucose + Tollen’s reagent Gluconic acid + Ag-mirror
13. (4) It is the most abundant organic compound on earth.
14. (2) 1 g fat provides 37 kJ of energy on oxidation, while 1 g carbohydrate on oxidation gives 17 kJ of energy. Hence, fat has highest calorific value.
15. (2)
16. (4)
17. (2) Fructose has 3 chiral centres and hence number of optical isomers are 23 = 8
18. 3) 19. 1) 20. 3) 21. 2)
22. 1) Since the compound forms a yellow crystalline solid, i.e. osazone with phenylhydrazine, it may be an aldohexose or a ketohexose. Further, since on reduction, compound forms a mixture of sorbitol and
mannitol, it must be a ketohexose, i.e. fructose. Recall that glucose on reduction gives only one alcohol
glucitol (Sorbitol)
23. (3) Glucose contains aldehyde group due to which it gives positive test with ammoniacal silver nitrate.
24. (4) All these are the examples of globular proteins. These are soluble in water.
25. (3) Butyric acid also known as butanoic acid is found in milk, and butter and is a product of anaerobic
fermentation.
26. (3) In strongly alkaline solution of an amino acid, all of its —COOH groups are converted into —COO–. Thus a strongly alkaline solution of a monoaminodicarboxylic acid will have one —NH2 and two —COO– groups, all of which are basic in nature. Further remember that —NH2 group is more basic than –COO– group.
27. (1) When antigens enter into the body cells and destroy them, then antibodies being proteins are synthesised in the body and combine with antigens and destroy these by forming inactive complexes. Therefore antibodies destroy antigens.
28. (2) There are 20 amino acids in man, out of which 10 are essential.
29. (3) Insulin is an example of globular protein.
30. (2) The a-helix structure is formed when the chain of amino acids coils as a right handed screw (called -helix) because of the formation of hydrogen bonds between amide groups of the same peptide chain, i.e., NH group in one unit is linked to carbonyl oxygen of the third unit by hydrogen bonding. This hydrogen bonding between different units is responsible for holding helix in a position.
31. (3)
32. (4)
33. (2) Molisch test is used for testing carbohydrates.
34. (3) During denaturation 2° and 3° structures are destroyed but 1° structure remains intact.
35. (2) Triglycerides are lipids, hence these are hydrolysed by lipases to glycerol and fatty acids.
36. (4) Mg acts as a cofactor to the enzyme as it forms complex with phosphate group of ATP that is utilized in the transfer of ATP phosphate.
37. (2) In this structure of protein, atoms are highly coiled and form a spherical form.
38. (3) At the given pH (6) of the solution, alanine (pI = 6.0),exists as a dipolar ion while arginine (pI = 10.2) exists as a cation. Hence on passing an electric current, alanine will not migrate to any electrode, while arginine will migrate to cathode.
39. (4) 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, the native conformation of the molecule is disrupted and proteins
so formed are called denaturated proteins.
40. (2) Proline contains imino (secondary amino), NH group.
41. (3) Tertiary structure indicates the overall structure of the protein.
42. (4) All are chiral.
43. (2) Serine contains a hydroxyl functional group on its side chain and so the strongest possible interaction will be hydrogen bonding where the hydroxyl group could act as a hydrogen bond donor or hydrogen bond acceptor.
44. (2) Insulin is a biochemically active peptide hormone secreted by pancreas.
45. (3)
46. (3) Vitamin B12, also called cyanocobalamine, is antipernicious anaemia vitamin.
47. (1) Vitamin B6 is called pyridoxine. It is found in fruits, green-vegetables, milk, etc.
48. (2) Vitamin A.
49. (2) Vitamin E is mainly present in vegetable oils like wheat gram oil, sunflower oil, etc.
50. (2) 51. (1)
52. (4) Ascorbic acid - Scurvy
Retinol - Night blindness
Riboflavin - Cracked lips
Thiamine - Beri-Beri
53. (1) In DNA the complimentary base are adenine and thymine. Guanine and cytosine. The genetic
information for cell is contained in the sequence of bases A, T, G and C in DNA molecule.
54. (3)
55. (1) DNA has double stranded a-helical structure. Amount of A = T and that of G = C.
56. (4) Tyrosine is an -amino acid, and not a purine or pyrimidine.
57. (1) The sequence of bases in mRNA are read in a serial order in groups of three at a time. Each triplet of
nucleotides (having a specific sequence of bases) is known as codon. Each codon specifies one amino acid. Further since, there are four bases, therefore, 43 = 64 triplets or codons are possible.
58. (4)
59. (3) DNA fingerprinting is same for every cell and cannot be altered by any known treatment.
60. (1) Synthesis of polypeptide is known as translation. For this process three types of RNA are essential.
NEET PREVIOUS YEARS QUESTIONS-EXPLANATIONS
1. (1) Amylose and amylopectin are polymers of -D-glucose, so -link is not possible. Amylose is
linear with 1 4 -linkage whereas amylopectin is branched and has both 1 4 and 1 6 -linkages
2. 3)
3. 3) Due to denaturation of proteins, helix get uncoiled and protein loses its biological activity.
4. 3)Peptide bond
5. (2) Sugar in DNA is 2-deoxyribose whereas sugar in RNA is ribose.
6. (4) Sucrose is non-reducing disaccharide as the two monosaccharide units are linked through their
respective carbonyl groups.
7. (4) Glucose reacts with hydroxyl amine to form an oxime
8. 3) Adrenaline is a hormone produced by adrenal glands during high stress or exciting situations. This powerful hormone is part of the human body’s acute stress response system, also called the fight or flight response.
9. 3)non-essential amino acid . alanine Essential amino acid . valine, leucine, lysine
10. 2) During denaturation 2° and 3° structures are destroyed but 1° structure remains intact
11 2) Deficiency of vitamin D causes osteomalacia (soft bones and joint pain in adults)
12. 4)
13. 4) vitamin -
