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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5337_Библиотеки_им_академика_М_И_Перельмана.pdf
6. The structural formula for polysaccharides is:
A. (C6H10O5)n B. (C6H12O5)n
C. (C6H10O6)n D. (C6H10O6)n
7. The procedure of osmosis is act opposite when
compared with:
A. Effusion B. Diffusion
C. Active transport D. Coagulation
8. Milk sugar is also known as:
A. Galactose B. Lactose
C. Fructose D. Sucrose
9. If two sugars have different congurations only
around on carbon atom then these types of sugars
called:
A. Anomers B. Epimers
C. Isomers D. Stereoisomers
10. In the following reaction, glucose represents
α-D-glucose + 1120→ + 52.50 ← + 190 βD-glucose
A. Optical isomerism B. Mutarotation
C. Epimerisation D. Optical isomerism
11. Which molecule has double energy content than
carbohydrates ?
A. Fatty acids B. Wax
C. Glycerol D. Acylglycerol
12. The carbohydrate of the blood group substances
is:
A. Sucrose B. Fucose
C. Arabinose D. Glucose
13. The structure which favours protein synthesis is:
A. Nucleus B. Ribosome
C. Mitochondrion D. Cell membrane
14. In which glycosaminoglycan uronic acid is absent?
A. Dermatan sulphate
B. Chondroitin sulphate
C. Keratan sulphate
D. All of the above
15. Osazones synthesis is not possible with:
A. Sucrose B. Glucose
C. Fructose D. All of these
16. Sugar alcohol is:
A. Mannitol B. Trehalose
C. Xylulose D. Arabinose
17. A carbohydrate, known commonly as invert sugar,
is:
A. Fructose B. Sucrose
C. Glucose D. Lactose
18. Which biomolecule is a potential source of energy?
A. Carbohydrates B. Vitamins
C. Lipids D. Proteins
19. Sucrose is composed of:
A. Glucose + glucose B. Glucose + galactose
C. Glucose + sucrose D. Glucose + fructose
20. The monosaccharide units are linked by 1 → 4
glycosidic linkage in:
A. Maltose B. Sucrose
C. Cellulose D. Cellobiose
21. Disaccharide molecule synthesised by joining of
their monosaccharide units by 1,1-glycosidic bond.
A. Lactose B. Maltose
C. Trehalose D. Sucrose
22. Name the pathway for glucose synthesis by noncarbohydrate precursors.
A. Glycogenesis B. Glycolysis
C. Gluconeogenesis D. Glycogenolysis
23. The homopolysaccharide used for intravenous
infusion as plasma substitute is:
A. Agar B. Inulin
C. Pectin D. Starch
24. The fatty acid’s transportation from mitochondria
occurs through:
A. Active transport B. Facilitated transfer
C. Pinocytosis D. None of these
25. Those structures which have same structural
formula but the different spatial congurations
are known as:
A. Stereoisomers B. Anomers
C. Optical isomers D. Both A and C
26. Gluconeogenesis is inhibited through:
A. Glucagon B. Norepinephrine
C. Insulin D. Glucocorticoids
27. Liver glycogen breakdown is stimulated by:
A. Insulin B. Glucagon
C. Adrenaline D. Both B and C
28. Erythromycin contains:
A. Dimethyl amino sugar
B. Trimethyl amino sugar
C. Sterol and sugar
D. Glycerol and sugar
29. Which structure of the cell is known as “The
powerhouse of the cell”?
A. Nucleus B. Cytoplasm
C. Mitochondria D. Peroxisomes
30. In a sucrose medium in the presence of leuconostoc
mesenteroids, a glucose polymer is formed:
A. Dextrans B. Dextrin
C. Galactose D. Insulin
31. Which disorder may be proceed due to the
congenital galactosaemia?
A. Mental retardation B. Premature cataract
C. Death D. All of these
32. Hormone responsible to regulate blood glucose
level by activation of gluconeogenesis?
A. Norepinephrine B. Glucagon
C. Insulin D. Epinephrine
Section 3 Biochemistry
379378
33. A positive Benedict’s test is not given by:
A. Sucrose B. Lactose
C. Maltose D. Glucose
34. Amylopectin has approximated the following
number of branches:
A. 14 B. 50
C. 40 D. 80
35. Urine’s specic gravity increases in case of
A. Diabetes mellitus
B. Glomerulonephritis
C. Obsessive-compulsive disorder
D. Hypercalcaemia
36. Number of stereoisomers of glucose is:
A. 4 B. 8
C. 16 D. None of these
37. Maltose can be synthesised by hydrolysis of the
following substance:
A. Starch B. Dextrin
C. Glycogen D. All of these
38. Α-D-glucuronic acid found in
A. Hyaluronic acid B. Chondroitin sulphate
C. Heparin D. All of these
39. Which of the following is absent in mature
erythrocytes?
A. Glycolytic enzymes B. HMP shunt enzymes
C. Pyridine nucleotide D. ATP
40. The compositional building block of inulin is:
A. Glucose B. Fructose
C. Mannose D. Maltose
41. ________ sugar is an example of aldose sugar.
A. Glycerose B. Ribulose
C. Erythrulose D. Dihydoxyacetone
42. An example of an epimeric pair is ________ .
A. Glucose and fructose
B. Glucose and galactose
C. Galactose and mannose
D. Lactose and maltose
43. A carbohydrate found only in milk is:
A. Glucose B. Galactose
C. Lactose D. Maltose
44. ________ is known as beet root sugar.
A. Ribulose B. Maltose
C. Sucrose D. Lactose
45. Choose the false statement(s) about glycogen
metabolism.
I.
Release of epinephrine enhances glycogenolysis.
II.
cAMP is a secondary messenger that stimulates
an increase in glycogenesis.
III.
Insulin performs dephosphorylation and
Section 3 Biochemistry
activation of glycogen synthase enzyme.
IV.
Glucagon increases glycogen breakdown.
A. II only B. V only
C. III and IV D. II and I
46. How many ATP molecules are yield in glycolysis of
one mole of glucose (under anaerobic conditions)?
A. 4 B. 2
C. 9 D. 8
47. One of the important epimer of glucose is:
A. Arabinose B. Fructose
C. Xylose D. Galactose
48. Iodine produces red colour when mixed with:
A. Starch B. Dextrin
C. Glycogen D. Inulin
49. Compositional repeating units of hyaluronic acid
are:
A. N-acetyl glucosamine and D-glucuronic acid
B. N-methyl galactosamine and D-glucuronic acid
C. N-acetyl glucosamine and glucose
D. N- methyl galactosamine and fructose
50. Amylose is made-up of:
A. Starch B. Cellulose
C. Glycogen D. None of these
51. Choose false option about reactions and enzymes
used in the glycolytic pathway?
A. Triose phosphate isomerase is considered as a
“perfect enzyme” due to its property— product
is formed immediately as enzyme and substrate
collide.
B. Phosphoglucose isomerase responsible for the
conversion of the glucose ring to a fructose ring
C. Domains of phosphoglycerate kinase clamp
down on the substrate so as to eliminate water
from the reaction
D. ATP and citrate activated phosphofructokinase.
52. Iodine solution produces no colour with:
A. Cellulose B. Starch
C. Dextrin D. Glycogen
53. The aldose sugar is:
A. Dihydoxyacetone B. Fructose
C. Ribulose D. Glycerose
54. Lactate formed in muscles can be utilised through:
A. HMP shunt
B. Glucose-alanine cycle
C. Cori’s cycle
D. Citric acid cycle
55. The synthesis of glucose from lactate, glycerol, or
amino acids is called:
A. Glycogenolysis B. Glycolysis
C. Lipolysis D. Gluconeogenesis
56. The major sugar found in insect hemolymph is
________ .
A. Pectin B. Trihalose
C. Glycogen D. Maltose
57. The major source of carbohydrate in a typical
Western diet is:
A. Starch B. Cellulose
C. Glycogen D. Sucrose
58. Glucose-6-phosphatase is absent in:
A. Liver and kidneys
B. Liver and muscles
C. Kidneys and adipose tissue
D. Muscles and adipose tissue
59. The sugar present in DNA is:
A. Ribose B. Deoxyribose
C. Xylose D. Galactose
60. Below critical body temperature, when living
organisms are cooled, in their cells metabolic reactions
stop functioning normally. This happened due to:
A. Their enzymes lose the proper spatial
arrangement
B. Substrates bound to enzyme active sites
permanently
C. The activation energy threshold for the reaction
is increased
D. Absence of sufficient molecular motion for
substrates to proper interaction
61. Glucose-6-phosphatase is absent or decient in:
A. Von Gierke’s disease
B. Pompe’s disease
C. Cori’s disease
D. McArdle’s disease
62. Debranching enzyme is not present in
A. Cori’s disease B. Andersen’s disease
C. Von Gierke’s disease D. Addison’s disease
63. The average pH of urine is
A. 6.0 B. 7.2
C. 8.7 D. 1.9
64. Oxidation of galactose with concentrated HNO
produces
A. Mucic acid B. Glucuronic acid
C. Saccharic acid D. Gluconic acid
65. Which of the following pathways is not useful for
triacylglycerol production?
A. Glycerol-3-phosphate pathway
B. Glyoxylate pathway
C. Monoacylglycerol pathway
D. Kennedy pathway
66. Which pathway is an example of amphibolic
pathway?
A. HMP shunt B. Glycolysis
C. Citric acid cycle D. Gluconeogenesis
67. What is lipolysis?
A. Hydrolysis of triacylglycerol
B. Formation of lipids
C. Breakdown of ketone bodies
D. Formation of ketone bodies
68. Ethanol inhibits luconeogenesis through:
A. Inhibiting glucose-6-phosphatase
B. Inhibiting PEP carboxykinase
C. Change NAD+ into NADH and inhibit the
availability of pyruvate
D. Change NAD+ into NADH and inhibit the
availability of lactate
69. The following substances are cell inclusions,
except:
A. Melanin B. Glycogen
C. Lipids D. Centrosome
70. In the condition of starvation, ketone bodies are
used as an energy source by:
A. Erythrocytes B. Brain
C. Liver D. All of these
71. If the mean rate of oxygen consumption of a male
athlete during a training session is 2 L/min, then
his rate of energy expenditure is:
A. 300 kJ/min B. 100 kJ/min
C. 80 kJ/min D. 40 kJ/min
72. In glucose, the orientation of the –H and –OH
groups around the carbon atom 5 adjacent to the
terminal primary alcohol carbon determines:
A. D or L series
B. Epimers
C. Dextro or levorotatory
D. α and β anomers
73. How many isomers of glucose are found?
A. 14 B. 12
C. 9 D. 16
74. Obesity increases the risk of:
A. Hypertension
B. Diabetes mellitus
C. Cardiovascular disease
D. All of the above
75. Normally, if the intensity of exercise is higher, the
greater the proportional contribution of:
3
A. Aerobic energy production
B. Anaerobic energy production
C. The Krebs’ cycle to the generation of ATP
D. The electron transfer chain to the generation of
ATP
76. For the prevention of which disorder iodised salt
is recommended?
A. Hypertension B. Angina
C. Endemic goitre D. None of these
77. Mucopolysaccharides are:
A. Homopolysaccharides
B. Hetropolysaccharides
C. Proteins
D. Amino acids
78. Production of rRNA (in mammalian cells) occurs
in:
A. Endoplasmic reticulum
B. Peroxisomes
C. Nucleolus
D. Nucleus
79. Fructose diphosphate accumulation would:
A. Inhibit glycolysis and gluconeogenesis
B. Stimulate glycolysis and gluconeogenesis
C. Stimulate glycolysis and inhibit gluconeogenesis
D. Inhibit glycolysis and stimulate gluconeogenesis
Section 3 Biochemistry
381380
80. Denition of charge of the cell is:
A. It is a difference between the charge at the
outside and inside of a cell membrane
B. It is produced by the sodium-potassium ATPase
C. The overall rate of energy use by the cell
D. The amount to which the total adenine
nucleotide pool is phosphorylated
81. An early feature of kidney impairment is:
A. Impairment of the capacity of the tubule to
perform osmotic work
B. Decrease in maximal tubular excretory capacity
C. Suppressed filtration factor
D. Suppressed renal plasma flow
82. Those patients who are suffering from Von Gierke’s
disease are not able to perform gluconeogenesis
due to the presence of defective:
A. Lactate dehydrogenase
B. Glucose-6-phosphatase
C. Pyruvate carboxylase
D. None of the above
83. When Benedict’s solution boiled, it is not reduced
by:
A. Sucrose B. Milk sugar
C. Maltose D. Fructose
84. Mitochondrial DNA is:
A. Circular double-stranded
B. Circular single-stranded
C. Linear double helix
D. None of the above
85. Cellulose is made-up of the molecules of:
A. α-glucose B. β-glucose
C. Both of the above D. None of these
86. Boat and chair conformations are found:
A. In pyranose sugars
B. In any sugar without axial -OH groups
C. In any sugar without equatorial -OH groups
D. Only in d-glucopyranose
87. In EM pathway 2-phosphoglycerate is converted to
A. Phosphoenol pyruvate
B. Enol pyruvate
C. Di-hydroxy acetone phosphate (DHAP)
D. 1,3-bisphosphoglycerate
88. Endurance training increases the muscle’s capacity to:
A. Contract faster
B. Breakdown phosphocreatine
C. Burn fat and carbohydrate
D. Generate energy anaerobically
89. Glycogen structure includes a branch in between
____________ glucose units.
A. 6–12 B. 8–14
C. 6–10 D. 12–18
90. Instead of glucuronic acid, chondroitin sulphate
Section 3 Biochemistry
B has:
A. Gluconic acid B. Glucuronic acid
C. Induronic acid D. Sulphonic acid
91. Which pathway(s) and/or combination(s) of
pathways is/are able to change a molecule of
glucose to 6 molecules of carbon dioxide?
A. Gluconeogenesis, glycolysis
B. Glycolysis and gluconeogenesis
C. Gluconeogenesiss
D. Pentose phosphate pathway with
gluconeogenesis
92. Active transport of sugar is depressed by the agent:
A. Oxaloacetate B. Fumarate
C. Malonate D. Succinate
93. The conversion of alanine into glucose is known
as:
A. Glycolysis
B. Oxidative decarboxylation
C. Specific dynamic action
D. Gluconeogenesis
94. Phosphorylation of glucose into glucose-
6-phosphate occurs in the presence of the
following enzyme:
A. Hexokinase B. Glucokinase
C. Phosphofructokinase
D. Both A and B
95. Honey has the hydrolytic product of:
A. Lactose B. Maltose
C. Inulin D. Starch
96. Two major products of pentose phosphate
pathway are:
A. Nicotinamide adenine dinucleotide and ribose-
5-phosphate
B. Flavine adenine dinucleotide and glucose-
5-phosphate
C. FAD and CoA D. NADPH and NAD
97. Out of 24 moles of ATP produced in TCA cycle,
2 molecules of ATP can be produced at “substrate
level” through which of the following reactions?
A. Citric acid→ Isocitric acid
B. Isocitrate→ Oxaloacetate
C. Succinic acid→ Fumarate
D. Succinyl CoA→ Succinic acid
98. The conversion of one molecule of glucose into
two molecules of pyruvate results in the net
formation of:
A. Six molecules of water
B. Two molecules of ATP
C. Three molecules of ATP
D. Thirty-eight molecules of ATP
99. Gluconeogenesis is increased in which of the
following conditions?
A. Diabetes insipidus B. Diabetes mellitus
C. Hypothyroidism D. Liver diseases
100. Which of the following metabolites integrates
glucose and fatty acid metabolism?
A. Acetyl-CoA B. Pyruvate
C. Citrate D. Lactate
101. The Golgi complex:
A. Produces proteins
B. Generates ATP
C. Facilitate by providing a pathway for
transporting chemicals
D. Synthesizes glycoproteins
102. Cerebrosides consist of most of this sugar:
A. Glucose B. Fructose
C. Galactose D. Arabinose
103. Glycolysis is the name given to the pathway
involving the conversion of:
A. Glycogen to glucose-6-phosphate
B. Glycogen or glucose to fructose
C. Glycogen or glucose to pyruvate or lactate
D. Glycogen or glucose to pyruvate or acetyl-CoA
104. The chief form of glucose in solution is:
A. Acyclic form B. Glucofuranose
C. Glucopyranose D. None
105. After which period of time does maximal dynamic
exercise become predominantly aerobic?
A. 10 seconds B. 30 seconds
C. 1 minute D. 4 minutes
106. _______________ amino sugar is present in the
bacterial cell wall.
A. N-acetylmuramic acid
B. Sialic acid
C. Aminoglycoside
D. Azide
107. In the hexose monophosphate shunt examples of
dehydrogenase enzymes are:
A. NAD+ B. NADP+
C. FAD D. FMN
108. Which of these is a hereditary disease caused due
to an error in amino acid metabolism?
A. Homocystinuria
B. Albinism
C. Phenylketonuria
D. Branched-chain ketoaciduria
109. In case of the total oxidation of acetyl-CoA (in
TCA cycle), the number of ATP molecules of ATP
generated are:
A. 6 B. 12
C. 11 D. 9
110. The cellular organelles called “suicide bags” are:
A. Lysosomes B. Ribosomes
C. Nucleolus D. Golgi’s bodies
111. Rothera test is not given by:
A. β-hydroxy butyrate B. Bile salts
C. Glucose D. None of these
112. Polysaccharides are:
A. Acids B. Proteins
C. Oils D. Polymers
113. The fastest method to synthesize ATP molecules
during exercise is through:
A. Glycolysis
B. Phosphocreatine breakdown
C. Krebs’ cycle
D. Glycogen breakdown
114. Substrate level phosphorylation in TCA cycle is
in step:
A. Isocitrate dehydrogenase
B. Malate dehydrogenase
C. Aconitase
D. Succinate thiokinase
115. One molecule of glucose produces how many
molecules of CO2 in EM-TCA cycle.
A. 6 B. 3
C. 1 D. 2
116. Brain gets energy from ketone bodies if availability
of glucose is:
A. Constant B. Less
C. High D. Zero
117. The NAG6 substrate is hydrolysed by human
lysozyme to form:
A. 6 glucosamines + 6 acetic acids
B. NAG4 + NAG2
C. NAG3 + NAG3
D. NAG3
118. Glucagon and epinephrine:
A. Inhibit gluconeogenesis and stimulates
glycolysis
B. Stimulate gluconeogenesis and glycolysis
C. Stimulate gluconeogenesis and inhibit glycolysis
D. Inhibit gluconeogenesis and glycolysis
119. Following enzyme is required for glycolysis:
A. Pyruvate kinase
B. Pyruvate carboxylase
C. Glucose-6-phosphatose
D. Glycerokinase
120. A 33-year-old woman has been fasting for the
religious reason for several days. Her brain has
reduced its need for glucose by using the following
substance as an alternative source of energy:
A. Fatty acids
B. Beta hydroxy butyrate
C. Glycerol
D. Beta carotene
121. When O2 supply is not sufficient, pyruvate
changed into:
A. Phosphopyruvate B. Acetyl-CoA
C. Lactate D. Alanine
122. Anaerobic metabolism refers to the generation of
ATP:
A. In the absence of ADP
B. Without using glycogen
C. Without using oxygen
D. In the absence of available oxygen
Section 3 Biochemistry
383382
123. Inner membrane of the mitochondrion has the
enzymes of the:
A. Krebs’ cycle
B. Electron transport chain
C. Glycogen molecules
D. Triacylglycerol molecules
124. It is required to the conversion of pyruvic acid into
__________ before entering into TCA cycle.
A. Acetyl-CoA B. Lactate
C. α-ketoglutarate D. Citrate
125. A molecule of amylopectin contains 1500 glucose
residues and is branched after every 30 residues.
How many reducing ends are there?
A. 0 B. 1
C. 2 D. 5
126. Lactose is obtained by which of the following
reactions?
A. UDP galactose and glucose
B. UDP glucose and galactose
C. Glucose and galactose
D. Glucose, galactose and UTP
127. Coenzyme of transketolase is:
A. NAD+ B. FP
C. TPP D. Pyridoxol phosphate
128. The enzymes of glycolysis are located in the:
A. Mitochondrion B. Nucleus
C. Cytoplasm D. Lysosomes
129. Breakdown of glycogen in exercising muscle is
triggered by:
A. Insulin B. Cortisol
C. Amylase D. None of these
130. Polysaccharides:
A. Contain many monosaccharide units which
may or may not be of the same kind
B. Function mainly a storage or structural
compounds
C. Are present in huge amounts in connective
tissue
D. All of the above
131. __________ above are absent in saliva.
A. Hormones
B. Amylase
C. Bacteria-killing enzymes
D. Antibodies
132. Aerobic resynthesis of ATP occurs:
A. In the mitochondria in a process called
glycogenolysis
B. In the mitochondria in a process called oxidative
phosphorylation
C. In the cytosol
D. In the sarcoplasmic reticulum
133. A regulator of the enzyme glycogen synthase is:
Section 3 Biochemistry
A. Citric acid
B. 2,3-bisphosphoglycerate
C. Pyruvate
D. All of the above
134. The less amount of carbohydrate in the diet:
A. Does not affect exercise performance in events
lasting < 10 minutes
B. Affects the pH of muscle in resting state
C. May affect high intensity exercise performance
D. All of the above
135. The following metabolic abnormalities occur in
diabetes mellitus, except:
A. Increased plasma FFA
B. Increased pyruvate carboxylase activate
C. Decreased lipogenesis
D. Decreased gluconeogenesis
136. Fructose is metabolised by:
A. Fructose-1-phosphate pathway
B. Fructose-6-phosphate pathway
C. Glyceraldehyde-3-phosphate pathway
D. Both A and B
137. In standard 20 amino acids, only one amino acid
named ___________ is optically inactive.
A. Alanine B. Glycine
C. Glucocine D. Lysine
138. Fatty acids transportation along cell membrane
occurs through:
A. Active transport B. Facilitated transport
C. Diffusion D. Phagocytosis
139. The following enzyme is necessary for the HMP
shunt pathway:
A. Glucose-6-phosphatase
B. Phosphorylase
C. Aldolase
D. Glucose-6-phosphate dehydrogenase
140. Humans are unable to digest:
A. Starch
B. Complex carbohydrates
C. Denatured proteins
D. Cellulose
141. If the more negative standard reduction potential
of a redox pair, the greater the tendency to:
A. Lose electrons
B. Gain electrons
C. Lose/gain electrons
D. Lose and gain electrons
142. Glucokinase:
A. Is found in most of the mammalian tissues
B. Is important for glucose phosphorylation
primarily after taking a carbohydrate rich diet
C. Is widely distributed in prokaryotes
D. None of the above
143. In lysozyme catalysis, which of the following does
not contribute?
A. The abnormally high PKa of Glu35
B. The strained conformation of the D sugar
C. Synthesis of a covalent intermediate at Asp52
D. Synthesis of a covalent intermediate at Ser195
144. ___________ required for coordinated maintenance
of glucose and glycogen metabolism.
A. NAD
+
B. Fructose-2,6-bisphosphate
C. Glycogen
D. Fructose-1,6-bisphosphate
145. During vigorous exercise, pyruvate produced by
glycolysis is converted to:
A. Acetate
B. Lactate
C. Monosodium phosphate
D. Pyruvic acid
146. N-acetylneuraminic acid is an example of:
A. Sialic acid B. Mucic acid
C. Glucuronic acid D. Hippuric acid
147. Which of the following reactions is unique to
gluconeogenesis?
A. Lactate → pyruvate
B. Phosphoenolpyruvate → pyruvate
C. Oxaloacetate → phosphoenolpyruvate
D. Glucose-6-phosphate → fructose-6-phosphate
148. The total net generation of ATP through substrate-
level phosphorylation in glycolysis is:
A. 2 ATP molecules from glucose and 3 ATP
molecule from glycogen
B. 2 ATP molecules from glucose and 4 ATP
molecule from glycogen
C. 3 ATP molecules from glucose and 4 ATP
molecule from glycogen
D. 3 ATP molecules from glucose and 2 ATP
molecule from glycogen
149. Enzymes required for the electron transport chain
are present in the:
A. Ribosomes
B. Endoplasmic reticulum
C. Lysosomes
D. Inner mitochondrial membrane
150. The heptose–ketose sugar formed as a result of a
chemical reaction in the HMP shunt is:
A. Sedoheptulose B. Galactoheptose
C. Glucoheptose D. Mannoheptose
ANSWER KEY
1. C 2. B 3. D 4. B 5. A 6. A 7. B 8. B 9. B 10. B 11. D 12. B 13. B 14. C
15. A 16. A 17. B 18. A 19. D 20. A 21. B 22. B 23. A 24. B 25. A 26. C 27. D 28. A
29. C 30. A 31. D 32. B 33. A 34. D 35. A 36. C 37. D 38. C 39. C 40. B 41. A 42. B
43. C 44. C 45. A 46. B 47. D 48. C 49. A 50. A 51. D 52. A 53. D 54. C 55. D 56. B
57. A 58. D 59. B 60. D 61. A 62. A 63. A 64. A 65. B 66. C 67. A 68. C 69. D 70. B
71. D 72. D 73. D 74. D 75. B 76. C 77. A 78. C 79. C 80. D 81. A 82. B 83. A 84. A
85. A 86. A 87. A 88. C 89. D 90. C 91. D 92. C 93. D 94. D 95. C 96. A 97. D 98. B
99. B 100. A 101. D 102. C 103. C 104. C 105. C 106. A 107. B 108. C 109. B 110. D 111. A 112. D
113. B 114. D 115. A 116. B 117. B 118. C 119. A 120. B 121. C 122. C 123. B 124. A 125. B 126. A
127. C 128. C 129. D 130. D 131. D 132. B 133. C 134. C 135. B 136. D 137. B 138. B 139. D 140. D
141. A 142. B 143. D 144. B 145. B 146. C 147. C 148. A 149. D 150. A
3. Proteins
Proteins are large complex biological molecules made
up of one or more amino acids’ chains.
Proteins are essential to perform lots of vital functions
in all living organisms like for catalysing metabolic
reactions, DNA replication, to show response against
the stimulus, transport substances, etc.
Proteins are different as they have different sequences
of amino acids in their structure and this sequence of
amino acids is decided by the genes.
Protein get folded into a specific three-dimensional
structure; this three-dimensional structure is the
determinant factor of proteins activity.
Amino acids linked each other by peptide bonds and
formed polypeptide.
The sequence of amino acids in a protein is determined
by the gene.
During the synthesis of a protein or after synthesis the
residue in a protein are sometimes chemically modified
by a specific procedure called post-translational
modification which is responsible to change the
physiochemical properties like folding, stability, activity
and ultimately the functions of the protein.
Sometimes, non-peptide groups are also attached to
proteins known as prosthetic groups or cofactors.
Section 3 Biochemistry
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Proteins play a vital role and participate in almost each
process of cells.
Some proteins act as an enzyme.
Proteins also perform mechanical functions like in
muscle contraction by actin and myosin.
Some proteins take part in cell signalling, immunity, cell
adhesion and the cell division.
Proteins are important part of animal’s diet because
animals cannot synthesise each and every amino acid.
They need and must obtain essential amino acids from
food.
By digestion, animals splitted ingested protein into free
amino acids that are then used in metabolism reactions.
Amino acids are divided into three main categories
Essential: Those essential amino acids that cannot be
produced in human body:
z
Histidine
z
Isoleucine
z
Leucine
z
Lycine
z
Methionine
z
Phenylalanine
z
Threonine
z
Tryptophan
z
Valine.
Denaturation
It is a process that involves a transformation in which a
protein’s well-defined, folded structure (formed under
physiological conditions) changed into an unfolded
state (under non-physiological conditions). It happens
because of the breakdown of weaker chemical bonds
and interactions.
Denaturation occurs quickly and completely under a
narrow range of conditions.
Slowly reversible.
When proteins undergo denaturation, the cells go
through a variety of changes or alterations like, first
loosening, then tightening.
When a protein loses its three-dimensional structure, it
also losses its function.
Denaturation causes alterations in the physical, chemical
and biological properties of protein molecules.
During the denaturation of proteins, some of its bonds
begin to break, and it unfolds:
Nonessential: Nonessential amino acids are made by
the body from essential amino acids or in the normal
breakdown of proteins they are:
Alanine
Asparagine
Glutamic acid
Aspartic acid
Conditional: Conditional amino acids are usually not
essential, except in times of illness and stress they include:
Arginine
Cysteine
Proline
Tyrosine
Ornithine
Glutamine
Glycine
Serine.
Structure of proteins
Most of the proteins have a unique three-dimensional
structure.
Primary structure— amino acid sequence.
Secondary structure— repeated structures regularly that
are stabilised by a hydrogen bond. Like alpha helix, beta
sheets and turn.
Tertiary structure— the three-dimensional structure of a
functional protein.
Quaternary structure— some of the proteins are composed
Section 3 Biochemistry
of two or more polypeptide chains referred to as subunits.
The spatial arrangement of these subunits is known as
quaternary structure.
Agents of denaturation
Heat
Violent shaking
Detergents
Heavy metals like Hg
X-rays
Chaotropic agents like urea, lithium perchlorate
UV radiation
Acids and alkalis
Organic solvents
Altered pH.
Agents of denaturation
These are broadly classified as:
Physical agents: Heat, violent shaking, X-rays, UV
radiation.
Chemical agents: Acids, alkalies, organic solvents (ether,
alcohol), salts of heavy metals (Pb, Hg), urea, salicylate.
Colour reactions of protein/amino Acids
Reaction Specic group or amino acids
Biuret reaction Two peptide linkage
Folin-Coicalteau’s test Phenolic groups (Tyr)
Ninhydrin test α-Amino acids
Sulphur test Sulphydryl groups (Cys)
Xanthoproteic
reactions
Classification of Protein
Benzene rings of aromatic amino
acids
Million’s reaction Phenolic group (Tyr)
Hopkins-Cole reaction Indole ring (Trp)
Nitroprusside reaction Sulphydryl groups (Cys)
Careful denaturation is sometimes reversible (known as
renaturation). Hemoglobin undergoes denaturation in the
presence of salicylate by removal of salicylate, hemoglobin
is renatured.
Coagulation: The term ‘coagulum’ refers to a semi-solid
viscous precipitate of protein. Irreversible denaturation
results in coagulation. Coagulation is optimum and
requires lowest temperature at isoelectric pH, albumins
and globulins (to a lesser extent) are coagulable proteins.
Heat coagulation test is commonly used to detect the
presence of albumin in the urine.
Section 3 Biochemistry
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Urea cycle
Also known as Krebs-Henseleit urea cycle and ornithine
cycle
First substance of urea cycle—Ornithine
Urea is synthesized in liver
Transportation to kidneys (for excretion in urine)
Urea is the end-product of amino acid (protein)
metabolism
The urea cycle is a five-step cyclic process, with five
different enzymes.
Mitochondria—contain two enzymes (carbamoyl
phosphate synthase-I, ornithine transcarbamylase)
Cytosol— contains the remaining three enzymes of the
urea cycle (argininosuccinate synthase, argininosuccinase,
arginase).
Regulation of urea cycle
Rate limiting enzyme in urea cycle— carbamoyl
phosphate synthase.
Activation of carbamoyl phosphate synthase is done by
N acetylglutamate (NAG).
It is synthesised with the help of glutamate and acetyl
CoA molecules in the presence of synthase and degraded
in the presence of hydrolase.
Normal range of creatinine excretion in adult males is
15 mmol per day.
Muscular dystrophy or paralysis may cause decreased
excretion of creatinine in urine.
The amount of creatinine in urine—indicator for 24 hours
urine sample collection.
Stored creatine phosphate (high energy compound)
storage site—muscle.
Indicator of the metabolic process of muscle contraction—
interconversion of phosphocreatine and creatine.
Amount of creatinine produced related to muscle mass.
NH3 + CO2 + Aspartate → Urea + Fumarate
The urea cycle consumes 4 high energy phosphate bonds.
Fumarate formed in the 4th step may be converted to
malate.
1 NADH is generated when malate is oxidised into
oxaloacetate (1 NADH = 2.5 ATP).
So, net energy expenditure is only 1.5 high energy
phosphates.
Section 3 Biochemistry
The urea cycle and TCA cycle are interlinked and it is
called urea bicycle
Transamination
In this process, a new amino acid and keto acid are formed
due to the transfer of an amine group (of amino acid) to a
keto acid. Transaminases enzymes catalyse this reaction.
Different organs like the liver, kidney, heart and brain have
an adequate amount of these enzymes.
Mechanism of transamination
Step 1: Transfer of amino group from amino acid 1 to the
coenzyme PLP and form pyridoxamine phosphate. Amino
acid 1 is converted to keto acid 2.
Step 2: Amino group from pyridoxamine phosphate is
then transferred to a keto acid 1 to generate a new amino
acid 2 and enzyme with PLP is regenerated.
Transamination reaction