NEET AIPMT Biology Chapter Wise Solutions – Biomolecules
Contents
NEET AIPMT Biology Chapter Wise SolutionsPhysicsChemistry
1. The chitinous exoskeleton of arthropods is formed by the polymerisation of (AIPMT 2015)
(a) N – acetyl glucosamine
(b) lipoglycans
(c) keratin sulphate and chondroitin sulphate
(d) D – glucosamine.
2. Which of the following biomolecules does have a phosphodiester bond? (AIPMT 2015)
(a) Amino acids in a polypeptide
(b) Nucleic acids in a nucleotide
(c) Fatty acids in a diglyceride
(d) Monosaccharides in a polysaccharide
3. Which one of the following statements is incorrect? (AIPMT 2015, Cancelled)
(a) The competitive inhibitor does not affect the rate of breakdown of the enzyme-substrate complex.
(b) The presence of the competitive inhibitor decreases the Km of the enzyme for the substrate.
(c) A competitive inhibitor reacts reversibly with the enzyme to form an enzyme-inhibitor complex.
(d) In competitive inhibition, the inhibitor molecule is not chemically changed by the enzyme.
4. Select the option which is not correct with respect to enzyme action. (AIPMT 2014)
(a) Substrate binds with enzyme at its active site.
(b) Addition of lot of succinate does not reverse the inhibition of succinic dehydrogenase by malonate.
(c) A non-competitive inhibitor binds the enzyme at a site distinct from that which binds the substrate.
(d) Malonate is a competitive inhibitor of succinic dehydrogenase.
5. Which one of the following is a non – reducing carbohydrate? (AIPMT 2014)
(a) Maltose
(b) Sucrose
(c) Lactose
(d) Ribose 5-phosphate
6. A phosphoglyceride is always made up of (NEET 2013)
(a) a saturated or unsaturated fatty acid esterified to a glycerol molecule to which a phosphate group is also attached.
(b) a saturated or unsaturated fatty acid esterified to a phosphate group which is also attached to a glycerol molecule.
(c) only a saturated fatty acid esterified to a glycerol molecule to which a phosphate group is also attached.
(d) only an unsaturated fatty acid esterified to a glycerol molecule to which a phosphate group is also attached.
7. Macromolecule chitin is (NEET2013)
(a) sulphur containing polysaccharide
(b) simple polysaccharide
(c) nitrogen containing polysaccharide
(d) phosphorous containing polysaccharide.
8. Transition state structure of the substrate formed during an enzymatic reaction is (NEET2013)
(a) transient and unstable
(b) permanent and stable
(c) transient but stable
(d) permanent but unstable.
9. The essential chemical components of many coenzymes are (NEET 2013)
(a) carbohydrates
(b) vitamins
(c) proteins
(d) nucleic acids
10. Which of the following statements about enzymes is wrong? (Karnataka NEET 2013)
(a) Enzymes are denatured at high temperatures.
(b) Enzymes are mostly proteins but some are lipids also.
(c) Enzymes are highly specific.
(d) Enzymes require optimum pH and temperature for maximum activity.
11. Uridine, present only in RNA is a (Karnataka NEET 2013)
(a) nucleoside
(b) nucleotide
(c) purine
(d) pyrimidine.
12. The figure shows a hypothetical tetrapeptide portion of a protein with parts labelled A-D. Which one of the following options is correct? (Karnataka NEET 2013)
(a) D is the acidic amino acid-glutamic acid.
(b) C is an aromatic amino acid-tryptophan.
(c) A is the C-terminal amino acid and D is N-terminal amino acid.
(d) A is a sulphur containing amino acid methionine.
13. Which one out of A – D given below correctly represents the structural formula of the basic amino acid? (Prelims 2012)
(a) C
(b) D
(c) A
(d) B.
14. Which one is the most abundant protein in the animal world? (Prelims 2012)
(a) Trypsin
(b) Haemoglobin
(c) Collagen
(d) Insulin.
15. The given diagrammatic representation shows one of the categories of small molecular weight organic compounds in the living tissues. Identity the category shown and the one blank component “X” in it. (Prelims 2012)
Category Component
(a) Cholesterol Guanine
(b) Amino acid NH2
(c) Nucleotide Adenine
(d) Nucleoside Uracil.
16. Which one of the following is wrong statement? (Prelims 2012)
(a) Anabaena and Nostoc are capable of fixing nitrogen in free-living state also.
(b) Root nodule forming nitrogen fixers live as aerobes under free-living conditions.
(c) Phosphorus is a constituent of cell membranes, certain nucleic acids and all proteins.
(d) Nitrosomonas and Nitrobacter are chemo- autotrophs.
17. Which one of the following biomolecules is correctly characterized? (Main 2012)
(a) Lecithin – a phosphorylated glyceride found in cell membrane.
(b) Palmitic acid’ – an unsaturated fatly acid with 18 carbon atoms.
(c) Adenylic acid – adenosine with a glucose phosphate molecule.
(d) Alanine amino acid – contains an amino group and an acidic group anywhere in the molecule.
18. The curve given below shows enzymatic activity in relation to three conditions (pH, temperature and substrate concentration). What do the two axes (x and y) represent? (Prelims 2011)
x-axis Y-axis
(a) enzymatic activity pH
(b) temperature enzyme activity
(c) substrate concentration enzymatic activity
(d) enzymatic activity temperature
19. Which one of the following enzymes carries out the initial step in the digestion of milk in humans?
(a) pepsin
(b) rennin
(c) lipase
(d) trypsin
20. Which one of the following structural formulae of two organic compounds is correctly identified along with its related function? (Prelims 2011)
B : adenine – a nucleotide that makes up nucleic acids
A: triglyceride – major source of energy
B : uracil – a component of DNA
A : lecithin – a component of cell membrane.
21. Three of the following statements about enzymes are correct and one is wrong. Which one is wrong? (Main 2010)
(a) enzymes require optimum pH for maximal activity
(b) enzymes are denatured at high temperature but in certain exceptional organisms they are effective even at temperatures 80° – 90°C
(c) enzymes are highly specific
(d) most enzymes are proteins but some are lipids.
22. The figure given below shows the conversion of a substate into product by an enzyme. In which one of the four options (a-d) the components of reaction labelled as A, B, C and D are identified correctly? (Main 2010)
23. Carbohydrates are commonly found as starch in plants storage organs. Which of the following five properties of starch (1-5) make it useful as a storage material? (Prelims 2008)
(1) easily translocated
(2) chemically non-reactive
(3) easily digested by animals
(4) osmotically inactive
(5) synthesized during photosynthesis.
The useful properties are
(a) (1), (3) and (5)
(b) (1) and (5)
(c) (2) and (3)
(d) (2) and (4).
24. Cellulose is the major component of cell walls of (Prelims 2008)
(a) Pseudomonas
(b) Saccharomyces
(c) Pythium
(d) Xanthomonas.
25. A competitive inhibitor of succinic dehydrogenase is (Prelims 2008)
(a) a-ketoglutarate
(b) malate
(c) malonate
(d) oxaloacetate
26. Modem detergents contain enzyme preparations of (Prelims 2008)
(a) thermoacidophiles
(b) thermophiles
(c) acidophiles
(d) alkaliphiles.
27. About 98 percent of the mass of every living organism is composed of just six elements including carbon, hydrogen, nitrogen, oxygen and (2007)
(a) sulphur and magnesium
(b) magnesium and sodium
(c) calcium and phosphorus
(d) phosphoms and sulphur.
28. An organic substance bound to an enzyme and essential for its activity is called (2006)
(a) isoenzyme
(b) coenzyme
(c) holoenzyme
(d) apoenzyme.
29. The catalytic efficiency of two different enzymes can be compared by the (2005)
(a) formation of the product
(b) pH of optimum value
(c) K value
(d) molecular size of the enzyme.
30. Which one of the following statements regarding enzyme inhibition is correct? (2005)
(a) competitive inhibition is seen when a substrate competes with an enzyme for binding to an inhibitor protein
(b) competitive inhibition is seen when the substrate and the inhibitor compete for the active site on the enzyme
(c) non-competitive inhibition of an enzyme can be overcome by adding large amount of substrate
(d) non-competitive inhibitors often bind to the enzyme irreversibly.
31. Enzymes, vitamins and hormones can be classified into a single category of biological chemicals, because all of these (2005)
(a) help in regulating metabolism
(b) are exclusively synthesized in the body of a living organism as at present
(c) are conjugated proteins
(d) enhance oxidative metabolism.
32. Which of the following is the simplest amino acid? (2005)
(a) alanine
(b) asparagine
(c) glycine
(d) tyrosine.
33. Nucleotides are building blocks of nucleic acids. Each nucleotide is a composite molecule formed by (2005)
(a) base-sugar-phosphate
(b) base-sugar-OH
(c) (base-sugar-phosphate)n
(d) sugar-phosphate.
34. Carbohydrates, the most abundant biomolecule on earth, are produced by (2005)
(a) some bacteria, algae and green plant cells
(b) fungi, algae and green plant cells
(c) all bacteria, fungi and algae
(d) viruses, fungi and bacteria.
35. In which one of the following enzymes, is copper necessarily associated as an activator? (2004)
(a) carbonic anhydrase
(b) tryptophanase
(c) lactic dehydrogenase
(d) tyrosinase.
36. The major role of minor elements inside living organisms is to act as (2003)
(a) co-factors of enzymes
(b) building blocks of important amino acids
(c) constituent of hormones
(d) binder of cell structure
37. Lipids are insoluble in water because lipid molecules are (2002)
(a) hydrophilic
(b) hydrophobic
(c) neutral
(d) zwitter ions.
38. Which of the following is a reducing sugar (2002)
(a) galactose
(b) gluconic acid
(c) p-methyl galactoside
(d) sucrose.
39. Enzyme first used for nitrogen fixation (2001)
(a) nitrogenase
(b) nitroreductase
(c) transferase
(d) transaminase.
40. Role of enzyme in reactions is to/as (2000)
(a) decrease activation energy
(b) increase activation energy
(c) inorganic catalyst
(d) none of the above.
41. Which factor is responsible for inhibition of enzymatic process during feed back? (2000)
(a) substrate
(b) enzymes
(c) end product
(d) temperature.
42. Enzymes are not found in (2000)
(a) fungi
(b) algae
(c) virus
(d) cyanobacteria.
43. ATP is (2000)
(a) nucleotide
(b) nucleoside
(c) nucleic acid
(d) vitamin.
44. Which of the following have carbohydrate as prosthetic group (2000)
(a) glycoprotein
(b) chromoprotein
(c) lipoprotein
(d) nucleoprotein.
45. Some of the enzymes, which are associated in converting fats into carbohydrates, are present in (1999)
(a) microsomes
(b) glyoxysomes
(c) liposomes
(d) golgi bodies.
46. Cellulose, the most important constituent of plant cell wall is made up of (1998)
(a) branched chain of glucose molecules linked by P-1,4 glycosidic bond in straight chain and a-1, 6 glycosidic bond at the site of branching
(b) unbranched chain of glucose molecules linked by P-1, 4 glycosidic bond
(c) branched chain of glucose molecules linked by a-1, 6 glycosidic bond at the site of branching
(d) unbranched chain of glucose molecules linked by a-1, 4 glycosidic bond.
47. Lactose is composed of (1998)
(a) glucose + galactose
(b) fructose + galactose
(c) glucose + fructose
(d) glucose + glucose.
48. Co-factor (prosthetic group) is a part of holoenzyme. It is (1997)
(a) loosely attached organic part
(b) loosely attached inorganic part
(c) accessory non-protein substance attached firmly
(d) none of these.
49. Which is a typical example of ‘feedback inhibition’? (1996)
(a) cyanide and cytochrome reaction
(b) sulpha drugs and folic acid synthesizer bacteria
(c) allosteric inhibition of hexokinase by glucose 6-phosphate
(d) reaction between succinic dehydrogenase and succinic acid.
50. In which of the following groups are all polysaccharides? (1996)
(a) sucrose, glucose and fructose
(b) maltose, lactose and fructose
(c) glycogen, sucrose and maltose
(d) glycogen, cellulose and starch.
51. What are the most diverse molecules in the cell? (1996)
(a) lipids
(b) mineral salts
(c) proteins
(d) carbohydrates.
52. Which purine base is found in RNA? (1996)
(a) thymine
(b) uracil
(c) cytosine
(d) guanine.
53. The enzyme enterokinase helps in the conversion of (1995)
(a) caesinogen into caesin
(b) trypsinogen into trypsin
(c) pepsinogen into pepsin
(d) proteins into polypeptides.
54. The nuclease enzyme, which begins its attack from free end of a polynucleotide, is (1994)
(a) polymerase
(b) endonuclease
(c) exonuclease
(d) kinase.
55. Which of the following nucleotide sequences contains 4 pyrimidine bases? (1994)
(a) GATCAATGC
(b) GCUAGACAA
(c) UAGCGGUAA
(d) both (b) and (c).
56. The four elements that make up 99% of all elements found in a living system are (1994)
(a) C, H, O and P
(b) C,N,OandP
(c) H, O, C and N
(d) C, H, O and S.
57. Which is wrong about nucleic acids? (1993)
(a) DNA is single stranded in some viruses
(b) RNA is double stranded occasionally
(c) length of one helix is 45 A in B-DNA
(d) one turn of Z-DNA has 12 bases.
58. Glycogen is a polymer of (1993)
(a) galactose
(b) glucose
(c) fructose
(d) sucrose.
59. In RNA, thymine is replaced by (1992)
(a) adenine
(b) guanine
(c) cytosine
(d) uracil.
60. Amino acids are mostly synthesised from (1992)
(a) mineral salts
(b) fatty acids
(c) volatile acids
(d) a-ketoglutaric acid.
61. Which is distributed more widely in a cell? (1992)
(a) DNA
(b) RNA
(c) chloroplasts
(d) sphaerosomes.
62. Amino acids are produced from (1992)
(a) proteins
(b) fatty acids
(c) essential oils
(d) a-keto acids.
63. Living cell contains 60 – 95% water. Water present in human body is (1992)
(a) 60-65%
(b) 50-55%
(c) 75-80%
(d) 65-70%.
64. Adenine is (1992)
(a) purine
(b) pyrimidine
(c) nucleoside
(d) nucleotide.
65. Enzymes having slightly different molecular structure but performing identical activity are (1991)
(a) holoenzymes
(b) isoenzymes
(c) apoenzymes
(d) coenzymes.
66. A nucleotide is formed of (1991)
(a) Purine, pyrimidine and phosphate
(b) Purine, sugar and phosphate
(c) Nitrogen base, sugar and phosphate
(d) Pyrimidine, sugar and phosphate.
67. DNA is composed of repeating units of (1991)
(a) ribonucleosides
(b) deoxyribonucleosides
(c) ribonucleotides
(d) deoxyribonucleotides.
68. A segment of DNA has 120 adenine and 120 cytosine bases. The total number of nucleotides present in the segment is (1991)
(a) 120
(b) 240
(c) 60
(d) 480.
69. The basic unit of nucleic acid is (1991)
(a) pentose sugar
(b) nucleoid
(c) nucleoside
(d) nucleotide.
70. Mineral associated with cytochrome is (1991)
(a) Cu
(b) Mg
(c) Cu and Mg
(d) Fe.
71. Which is not consistent with double helical structure of DNA? (1990)
(a) A = T, C = G
(b) density of DNA decreases on heating
(c) A + T/C + G is not constant
(d) both (a) and (b).
72. RNA does not possess (1988)
(a) uracil
(b) thymine
(c) adenine
(d) cytosine.
73. In double helix of DNA, the two DNA strands are (1988)
(a) coiled around a common axis
(b) coiled around each other
(c) coiled differently
(d) coiled over protein sheath.
Explanations
1. (a)
Chitin is a structural polysaccharide that constitutes the exoskeleton of arthropods. It is a complex carbohydrate in which N-acetyl glucosamine monomers are joined together by 1, 4-β-linkages. Chitinous exoskeleton provides strength and elasticity to arthropods.
2. (b)
3. (b)
Competitive inhibition is a reversible inhibition where inhibitor competes with the normal substrate for the active site of enzyme. A competitive inhibitor is usually chemically similar to the normal substrate and therefore, fits into the active site of an enzyme and binds with it. The inhibition is thus due to substrate analogue. The enzyme, now cannot act upon the substrate and reaction products are not formed. E.g., the activity of succinate dehydrogenase is inhibited by malonate. Km value or Michaelis constant is defined as the substrate concentration at which half of the enzyme molecules are forming enzyme substrate (ES) complex, or concentration of the substrate when the velocity of the enzyme reaction is half the maximal possible. A smaller Km, value indicates greater affinity of the enzyme for its substrate, hence, shows a quicker reaction. The competitive inhibitor decreases the affinity of enzyme for substrate, thus increases the Km, value.
4. (b)
The reduction of activity of succinate dehydrogenase by malonate is an example of competitive inhibition. Competitive inhibition is a reversible inhibition where inhibitor competes with the normal substrate for the active site of enzyme. A competitive inhibitor is usually similar to the normal substrate and, therefore, fits into the active site of an enzyme and binds with it. The enzyme, now cannot act upon the substrate and reaction products are not formed. Hence, action of an enzyme may be reduced or inhibited. Since a competitive inhibitor occupies the site only temporarily, the enzyme action is not permanently affected. Thus, addition of a lot of succinate can reverse the inhibition of succinic dehydrogenase by malonate.
5. (b)
In non-reducing sugars, a free aldehyde or ketonic group is absent. Sucrose is a non-reducing sugar formed by condensation of one molecule each of glucose and fructose with release of a water molecule. A glycosidic bond is established between carbon atom 1 of glucose and carbon atom 2 of fructose.
6. (a)
Phosphoglycerides are the triesters of fatty acids (either saturated or unsaturated) and glycerol to which a phosphate group is also attached.
7. (c)
Chitin is a polysaccharide comprising chains of N-acetyl-D-glucosamine, a derivative of glucose. Chitin is structurally very similar to cellulose and serves to strengthen the supporting structures of various invertebrates. It is a major constituent of fungal cell walls and of the exoskeleton of insects and other arthropods.
8. (a)
Transition state is formation of unstable intermediate structural state. During this, substrate bonds are broken and new bonds are established that transform the substrate molecules into products. This state is transient and highly unstable.
9. (b)
Coenzyme is the non protein organic group which gets attached to the apoenzyme to form holoenzyme or conjugate enzyme. It helps in removing a product of chemical reaction besides bringing contact between the substrate and the enzyme. Most of the coenzymes are made of water soluble vitamins B and C, e.g., thiamine, riboflavin, nicotinamide, pyridoxine.
10. (b)
The enzymes are organic catalysts or biocatalysts which catalyse biochemical reactions at the body temperature. They regulate the rate of biochemical reactions without being utilised in these reactions. Enzymes are mostly proteins but some are RNA (ribozymes). No lipid working as enzymes are known.
11. (a)
A nucleoside is pentose sugar and base together, without the phosphate group. Uracil is present as uridine in RNA only.
Uracil + Ribose → Uridine.
12. (None of the options is correct)
A – Serine (Neutral – Polar)
B – Cysteine(Neutral – Polar)
C – Tyrosine(Neutral – Polar) ‘
D – Not an amino acid
13. (b)
Basic amino acids have an additional amino group without forming amides thus they are diamino monocarboxylic acids e.g., arginine, lysine, etc.
14. (c)
Collagen is an insoluble fibrous protein found extensively in the connective tissue of skin, tendons and bone. Collagen accounts for over 30% of the total body proteins of mammals and it is the most abundant animal protein.
15. (d)
The given structure corresponds with the structure of ribose sugar. As it lacks a phosphoric acid hence it can be a nucleoside not a nucleotide.
16. (c)
Phosphorus is present in plasma membrane in the form of phospholipid bilayer. It is an essential component of all nucleic acids not ‘certain’ nucleic acids. Moreover, phosphorus is never found in proteins.
17. (a)
Lecithin is a triglyceride lipid where one fatty acid is replaced by phosphoric acid which is linked to additional nitrogenous group called choline. It is a common membrane lipid. It is an amphipathic phospholipid having both hydrophilic polar and hydrophobic nonpolar groups. The hydrocarbon chains of two fatty acids function as hydrophobic non-polar tails whereas the phosphate and choline behave as hydrophilic polar head group of the molecule. Palmitic acid is a saturated fatty acid (as it does not possess double bonds in its carbon chain) and contains 16 carbon atoms with formula Cl6H32O2. Adenylic acid or adenosine monophosphate is a nucleotide formed by union of adenine (nitrogenous base), ribose (pentose sugar) and phosphate. It is formed through phosphorylation of nucleoside as phosphate combines with sugar molecule at its 5′ carbon atom. Amino acids are organic acids with carboxylic group (-COOH) having amino group (-NH2) generally attached to a-carbon or carbon next to carboxylic group. Alanine is a nonpolar and neutral amino acid having one methyl group and having amino group attached to carbon next to carboxylic group.
18. (b)
Enzymes generally function in a narrow range of temperature and pH. Each enzyme shows its highest activity at a particular temperature and pH called the optimum temperature and optimum pH. Activity declines both below and above the optimum values. X-axis always represents temperature or pH and Y axis represents enzyme activity.
19. (a)
Milk is coagulated by pepsin in stomach because adult human being lacks renin, so first step in digestion of milk is carried out by pepsin.
20. (d)
‘A’ is a structural formula of lecithin. It is probably the most common phospholipid. Phospholipids are major components in the lipid bilayers of cell membrane.
21. (d)
Most enzymes are proteins but some are RNA enzymes e.g., ribozymes. Ribozymes are RNA molecules that exhibit enzyme (catalytic) activities. Ribozymes provide resistance to several viruses which is being applied in biotechnology in producing cDNA that encode for ribozyme and to integrate it into the host plant genome for developing resistant plants.
22. (b)
A – Transition state
B – Potential energy
C – Activation energy without enzyme
D – Activation energy with enzyme
23. (d)
Starch is the major storage carbohydrate of plants. In most plant species it is accumulated in the chloroplast of leaves, whereas in storage organ it accumulates in amyloplast as reserve starch. It is the osmotically inactive form of photosynthetic product and is a hexosan polysaccharide made of large number of glucose unit so, chemically non reactive.
24. (c)
The cell wall of most fungi consist of chitin or cellulose. In Pythium, the hyphal wall contains cellulose whereas, in yeast the cell wall is thin and is composed of chitin in combination with other compounds (carbohydrates, glucan and mannan). The bacterial cell wall contains N-acetyl glucosamine andN-acetyl muramic acid.
25. (c, d)
Competitive inhibitor is a substrate analogue that combines reversibly to the free enzyme at the active site, without getting transformed e.g., malonate or oxaloacetate, which resemble succinate in structure and inhibit the activity of succinate dehydrogenase. Such competitive inhibitors are often used
26. (d)
Modern detergents contain enzyme preparation of alkaline protease which are called alkaliphiles, for removing protein stain.
27. (d)
Living organisms requires 6 elements in relatively large amounts. C, H, O, N, P, S. These elements contribute to the structural organization of living organisms. Phosphorus is important constituent of nucleic acids, sulphur and nitrogen constituent of amino acids. Carbon, hydrogen, oxygen are frame work element. Nitrogen forms DNA base pairs. Smaller quantities of the elements required are Na, K, Mn, Ca, Fe, Mg, Cl, Mg, Cl, I, Co, Bo. Plants obtained their supplies of material from air, water, and soil. Animals obtained these by eating plants and drinking water. All-are present in rocks and are released by erosion and weathering into soils, rivers, lakes and oceans. Some such as N, 0, and C are also present in the atmosphere. The movement of the nutrient element through the biosphere is called the biogeochemical cycle. e.g. Carbon, nitrogen, sulphur, phosphorus, oxygen and water cycles.
28. (b)
Enzymes are simple if they are made of only proteins (e.g. pepsin, amylase etc.) while conjugate enzymes have an additional non-protein cofactor which may be organic or inorganic. Loosely attached organic cofactor is coenzyme. It plays an accessory role in enzyme catalyzed processes often by acting as a donor or acceptor of a substance involved in the reaction. ATP and NAD are common coenzymes. Isozymes are closely related variants of enzymes. It has similar function as another enzyme but has a different set of amino acids. Holoenzyme is the intact enzyme cofactor complex. Apoenzyme is an enzyme without its cofactor. It is the protein molecule to which a coenzyme will bind to produce the holoenzyme.
29. (c)
K value or Michaelis constant is defined as v ‘ m the substrate concentration at which half of the enzyme molecules are forming (ES) complex or concentration of the substrate when the velocity of the enzyme reaction is half the maximal possible. The Km varies from enzyme to enzyme and is used in characterizing the different enzymes. A smaller Km value indicates greater affinity of the enzyme for its substrate, hence, shows a quicker reaction. Km value is a constant characteristic of an enzyme for its conversion of a substrate.
30. (b)
Km Competitive inhibition is a reversible inhibition where inhibitor competes with the normal substrate for the active site of enzyme. A competitive inhibitor is usually chemically similar to the normal substrate and therefore, fits into the active site of an enzyme and binds with it. The inhibition is thus due to substrate analogue. The enzyme, now cannot act upon the substrate and reaction products are not formed. Hence, action of an enzyme may be reduced or inhibited. Since a competitive inhibitor occupies the site only temporarily, the enzyme action is not permanently affected. The activity of succinate dehydrogenase is inhibited by malonate and is the most common example of competitive inhibition.
31. (a)
Enzymes control all the life processes. They increase the rate of a biological reaction. The magnitude of increase may be greater than those affected by other catalysts. Vitamins are accessory indispensable food factor, organic in nature (organic acid, amino acid esters, alcohols, steroids etc.) required by an organism in small amounts to maintain normal growth and regulate the metabolic processes. Hormones are biologically active organic substance that are produced in minute quantities by some specialized organs and exert physiological effects at sites remote from their origin.
32. (c)
Amino acids are the essential constituents of all living cells. They are the building blocks of proteins. Chemically, amino acids are nitrogenous compounds having both-an acidic carboxyl (-COOH) group and a basic amino (-NH2) group. The general structural formula of the amino acids is
Glycine is considered as the simplest amino acid as it has one amino group, one carboxylic group and no substituent functional group.
33. (a)
Each nucleotide consists of three distinct units – a phosphate group derived from phosphoric acid, a pentose sugar and a ring shaped nitrogenous base. The base-sugar combination without phosphate group is called nucleoside. A nucleotide is formed by the reaction of sugar portion of a nucleoside with phosphoric acid through dehydration synthesis, e.g. Adenosine monophosphate – composed of ribose, adenine and phosphate.
34. (a)
Carbohydrates are organic compounds synthesized in the chlorophyll containing cells of some bacteria, algae and green plant cells, during photosynthesis. Certain photoautotrophic bacteria eg. Green sulphur bacteria and purple sulphur bacteria contain pigments like chlorobium chlorophyll and bacteriochlorophyll respectively that helps them in photosynthesis. During photosynthesis carbon dioxide is reduced into carbohydrates by water and oxygen is liberated.
35. (d)
The additional nonprotein cofactor may be inorganic and are termed as activators. They are minerals of different types like Ca, Fe, Cu, Zn, Mn etc. Copper is associated as an activator with tyrosinase. It is widely distributed in plants, animals and man. It is also known as polyphenol oxidase or catecholase. It oxidizes tyrosine to melanin in mammals and causes the cut surfaces of many fruits and vegetable to darken.
36. (a)
Minor element are those which are required in quantity of less than milligram/gram of dry matter but they are essential for proper growth and development of an organism e.g., Cl, Mn, B, Zn, Cu, Mo etc. These elements work as non-protein cofactor in enzymes e.g., Zn, Cu etc. They also take part in oxidation reduction reactions eg. Cu, with variable valency. Chloride ion enhances activity of salivary amylase. Zinc is required for activity of carbonic anhydrase and alcohol dehydrogenase, etc.
37. (b)
Lipid molecules are insoluble or sparingly soluble in water but are freely soluble in organic solvents like ether, alcohol and benzene. Insolubility of lipids in water is due to the fact that the polar groups they contain are much smaller than their nonpolar portions. The nonpolar chains are long complex hydrophobic hydrocarbon chains. If shaken in water lipids often form small droplets or micelles. The complex formed is called emulsions. These non polar proteins give them water repellent or hydrophobic property.
38. (a)
All those sugars which have free aldehyde or ketone group are called reducing sugars. These are able to reduce cupric ions (Cu+2) into cuprous ions (Cu+). The two common test are Benedict’s test and Fehling’s test. Both tests employ alkaline solution of copper sulphate which is blue in colour with reducing sugar it gives orange to brick red precipitation. Galactose is a reducing sugar. It gives brownish red precipitate with Fehling reagent and with Benedict’s reagent it gives yellow, red or green precipitate confirming the presence of sugar. Sucrose, starch are non-reducing sugars.
39. (a)
Nitrogen fixation involves conversion of atmospheric nitrogen to ammonia. It is done with the help of nitrogenase enzyme which occurs inside thick walled heterocysts of the blue green algae. These provide suitable anaerobic environment for nitrogenase activity even in aerobic conditions.
40. (a)
All molecules require certain amount of energy for activation (to overcome energy barrier) before they can react. This energy is called activation energy. This energy is recovered when products are formed. The essence of an enzyme is its ability to speed up (catalyze) a reaction by making or breaking specific covalent bonds (bonds in which atoms are held together by sharing of electrons). Enzymes act by somehow lowering the temperature at which a given bond is unstable i.e., they speedup a reaction by lowering the activation energy. It is the magnitude of the activation energy which determines how fast the reaction will proceed.
41. (c)
Feedback inhibition or end product inhibition is the inhibition of the activity of an enzyme catalysing some early reactions of the series by the end product of the metabolic pathway. For example a substrate A is converted into a product F through B, C, D and E intermediate products. As the concentration of end product F increases, it diffuses to allosteric enzyme (E,) causing a reduced synthesis of the product B which in turn lowers the rate of enzymatic reactions in rest of the pathway.
42. (c)
Viruses do not have enzymes so they cannot synthesize proteins. They multiply only inside the living host cell and for multiplication and metabolism they take over the machinery of the host cell. They lack their own cellular machinery and enzymes.
43. (a)
ATP is a nucleotide as it is composed of adenine, ribose sugar and phosphoric acid. There are two additional phosphate groups attached to the phosphate group of AMP. The last two phosphate molecules are connected by high energy bonds.
44. (a)
Glycoproteins are proteins that contain sugars like carbohydrates as prosthetic group. In most glycoproteins, the linkage is between asparagine and N-acetyl-D-glucosamine. Some glycoproteins are immunoglobulins, membrane proteins and muscle proteins. These are formed in Golgi apparatus in the process of glycosylation and are important components of plasma membrane in which they extend throughout the lipid bilayer. Lipoproteins are protein complexed with lipids like triglycerides, phospholipids etc. Nucleoproteins are proteins associated with nucleic acids and chromoproteins are proteins associated with pigments e.g., cytochrome, phytochrome.
45. (b)
Glyoxysomes are microbodies found in fungi and germinating oil seeds that are involved in converting fat into carbohydrates. They contain enzymes for P oxidation of fatty acids and glyoxylate cycle. Glyoxylate cycle is a metabolic pathway in plants and microorganisms that is a modified form of the Krebs’ cycle. It utilizes fats as a source of carbon and enables the synthesis of carbohydrate from fatty acids by avoiding the stages of the Krebs’ cycle in which carbon dioxide is released. It occurs in tissues rich in fats, such as those of germinating seeds; the enzymes involved in the cycle, which have not been found in mammals, are contained in organelles (microbodies) called glyoxysomes.
46. (b)
Cellulose is the most abundant carbohydrate. Cellulose molecule is composed of 1600 to 6000 glucose molecules joined together. Those polymers form long twisting macromolecules of cellulose. The chains are unbranched and linear. The successive glucose residues are joined together by β -1-4, linkages.
47. (a)
Lactose is popularly known as milk sugar. It is a disaccharide composed of one molecule of glucose and one molecule of galactose. The covalent bond that joins these two monosaccharide units is called glycosidic bond or glycosidic linkage. It is a reducing sugar.
48. (c)
Enzymes are simple if they are made of only proteins (e.g. pepsin, amylase etc.) while conjugate enzymes have an additional non-protein cofactor which may be organic or inorganic. Loosely attached organic cofactor is coenzyme. It plays an accessory role in enzyme catalyzed processes often by acting as a donor or acceptor of a substance involved in the reaction. ATP and NAD are common coenzymes. Isozymes are closely related variants of enzymes. It has similar function as another enzyme but has a different set of amino acids. Holoenzyme is the intact enzyme cofactor complex. Apoenzyme is an enzyme without its cofactor. It is the protein molecule to which a coenzyme will bind to produce the holoenzyme.
49. (c)
Feedback inhibition or end product inhibition occurs when the end product of a metabolic pathway inhibits the activity of an enzyme catalysing some early reactions of the series. The end product is the inhibitor and the enzyme inactivated is called allosteric enzyme. The enzyme is regulated by modulators that bind noncovalently at site other than the active site. An example of feedback inhibition is the inhibition of the activity of the enzyme hexokinase by glucose 6-phosphate in glycolysis.
This enzyme catalyses conversion of glucose into glucose 6-phosphate but as the reaction proceeds, increase in concentration of glucose 6-phosphate inhibits the activity of hexokinase.
50. (d)
Polysaccharides are complex long chain carbohydrates which are formed by dehydrate synthesis or polymerisation of more than 10 but generally very large number of units called monosacccharides. Starch, glycogen and cellulose are all polysaccharides. Starch is a glucosan homopolysaccharide which is the main reserve food of plants. Glycogen is also a glucosan homopoly¬saccharide which is the major reserve food of fungi, animals and some bacteria. It is also called animal starch. Cellulose is the structural polysaccharide of plant cell walls, some fungi, protists. It is a fibrous glucosan homopolysaccharide of high tensile strength.
51. (c)
Proteins show enormous diversity because of different proportions and sequences of twenty amino acid within the protein molecule. A large number of permutations and combinations of these amino acids are responsible for the unlimited variety of proteins. Proteins are the most abundant and most varied of the macromolecules having one or more polypeptides (chains of amino acids). The proteins constitute almost 50% of the total dry weight of the cell. Proteins may be simple or conjugated. Among conjugated, proteins may be phosphoprotein, glycoprotein, nucleoprotein, chromoprotein, lipoprotein, flavoprotein, metallo protein etc. Functionally proteins may be structural protein, enzymes, hormones, respiratory pigment etc.
52. (d)
The bases are of two types-purines and pyrimidines. The purine derivatives adenine (A) and guanine (G) are double ring structures whereas pyrimidine derivatives thymine, cytosine and uracil are single ring structures. Thymine (T) and cytosine (C) are found in DNA and cytosine (C) and uracil (U) is found in RNA.
53. (b)
The enzyme enterokinase which is also known as enteropeptidase helps in the conversion oftrypsinogen into trypsin. Trypsin acts on proteins and breaks them for digestion. It occurs in the brush borders of duodenum.
54. (c)
Exonuclease activity means cleavage of nucleotides only at the end while endonuclease breaks DNA strand at an internal position. DNA polymerase I has 3′ – 5′ exonuclease activity which removes any nucleotide which mispair during elongation of growing strand. A small segment of DNA polymerase I also shows 5′ – 3′ exonuclease activity which removes DNA segment which comes as an obstmction in way of growing DNA strand. Polymerase catalyses the elongation of a polymeric molecule.
Endonucleases are very specific and cut DNA at very specific nucleotide sequences. These are called restriction enzymes. Kinase is an enzyme that can transfer a phosphate group.
55. (a)
In the given question there are 4 pyrimidines as 2 cytosine and 2 thymine in option ‘a’.
56. (c)
Carbon, hydrogen, oxygen and nitrogen are called four big elements of living body they make up about 99% of the mass of most cells. These are lightest elements that are capable of forming covalent bonds. It is known that the strength of covalent bond is inversely related to the atomic weights of the bonded atoms. As C, H, O and N are lightest elements so the bonds they form are the strongest covalent bonds. So that the compounds formed are stable, varied in size and shapes. Carbon constitutes more than 50% of the dry matter. It has been observed that human body contains 0.5% hydrogen, 18.5% carbon, 65% oxygen and 3.3% nitrogen. Other elements are present in very lesser amount.
57. (c)
The DNA duplex model proposed by Watson and Crick is right handed spiral and is called B-DNA. Its one complete turn is 34Å long and has 10 base pairs.
58. (b)
Glycogen (animal starch) is a polysaccharide consisting of a highly branched polymer of glucose occurring in animal tissues, especially in liver and muscle cells. It is the major store of carbohydrate energy in animal cells.
59. (d)
In RNA and DNA, purines are the same. The two purines are adenine and guanine. The two pyrimidines are cytosine and thymine in DNA but in RNA thymine is replaced by uracil.
60. (d)
Amino acids are mostly synthesized from a ketogluaric acid. These are the precursors of amino acids. A five carbon compound formed during Krebs’ cycle is a a-ketoglutaric acid which is the first diearboxylic acid formed. Pyruvic acid converted into alanine, a-ketoglutaric acid into glutamic acid, OAA into aspartic acid, polymerization of such amino acids results into formation of proteins.
61. (b)
RNA occurs in the nucleus as well as in the cytoplasm of the eukaryotic cells and in prokaryotic cell, it is found in the cytoplasm. DNA is found in the nucleus, mitochondria and chloroplast. Chloroplast and sphaerosomes are found only in cytoplasm.
62. (a)
Proteins are large-sized polymeric macromolecules having one or more polypeptides (chains of amino acids). Amino acids are formed after digestion of proteins. Amino acids are organic acids (with carboxylic group – CO OH) having amino group (NH2) generally attached to a-carbon or carbon next to the carboxylic group. Carboxylic group provides an acidic property to the amino acid while amino group gives it a basic reaction.
63. (d)
Water is the most abundant substance of living beings. The water content of actively living cells varies between 60-95%. In human beings maximum water content is found in the embryo 90 – 95%. Water content decreases thereafter in adult and the aged where it is 65 – 70%.
64. (a)
The bases are of two types-purines and pyrimidines. The purine derivatives adenine (A) and guanine (G) are double ring structures whereas pyrimidine derivatives thymine, cytosine and uracil are single ring structures. Thymine (T) and cytosine (C) are found in DNA and cytosine (C) and uracil (U) is found in RNA.
65. (b)
Enzymes having slightly different molecular structures but performing identical activities are called isoenzymes. Over 100 enzymes are known to have isoenzymes. Thus a-amylase of wheat endosperm has 16 isozymes, lactic dehydrogenase has 5 isoenzymes in man. Holoenzyme is a complex comprising an enzyme molecule and its cofactor. Apoenzyme is an inactive enzyme that must associate with a specific cofactor molecule or ion in order to function. Coenzyme is an organic nonprotein molecule that associates with an enzyme molecule in catalysing biochemical reactions.
66. (c)
Nucleotide is an organic compound consisting of a nitrogen-containing purine or pyrimidine base linked to a sugar (ribose or deoxyribose) and a phosphate group.
67. (d)
DNA is the largest macromolecule in the organisms. It is a long, double chain of deoxy- ribonucleotide, or deoxyribotide units. The two deoxyribonucleotide chains are twisted around a common axis to form a right-handed double helix (spiral) that encloses a cylindrical space in it. Each deoxyribonucleotide unit, in turn, consists of three different molecules phosphate, (PO3-4), a 5-carbon deoxyribose sugar (C5H10O4) and a nitrogenous base.
68. (d)
According to ChargafFs rules, the amount of adenine is always equal to that of thymine, and the amount of guanine is always equal to that of cytosine i. e A = T (120) and G = C (120), therefore, the total no. of nucleotides would be 120 x 4 = 480.
69. (d)
The nucleic acids (DNA and RNA) are the molecules having complex structure and very high molecular weights. The nucleic acid is composed of a large number of nucleotide molecules joined into a linear, unbranched chain. Nucleotide is an organic compound consisting of a nitrogen-containing purine or pyrimidine base linked to a sugar (ribose or deoxyribose) and a phosphate group.
70. (d)
Cytochromes are generally membrane-bound hemoproteins that contain heme groups and carry out electron transport. The heme group is a highly conjugated ring system (which means its electrons are very mobile) surrounding a metal ion, which readily interconverts between the oxidation states. For many cytochromes the metal ion present is that of iron, which interconverts between Fe2+ (reduced) and Fe3+ (oxidized) states (electron-transfer processes) or between Fe2+ (reduced) and Fe3+ (formal, oxidized) states (oxidative processes). Cytochromes are thus capable of performing oxidation and reduction.
71. (c)
The density of DNA decreases on heating as hydrogen bonds breakdown. According to ChargafFs rules, the amount of adenine is always equal to that of thymine, and the amount of guanine is always equal to that of cytosine i.e A = T and G = C. The base ratio A + T/ G + C may vary form species to species, but is constant for a given species.
72. (b)
In RNA and DNA, purines are the same. The two purines are adenine and guanine. The two pyrimidines are cytosine and thymine in DNA but in RNA thymine is replaced by uracil.
73. (a)
According to Watson-Crick model, the DNA molecule consists of two long, parallel chains which are joined together by short crossbars at regular intervals. The two chains are spirally coiled around a common axis in a regular manner to form a right handed double helix.
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