MCQs in Biochemistry for Medical Students (With Explanatory Answers) Arti S Pandey
Chapter Notes

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Biomolecules, Enzymes and MetabolismChapter 1

1. Examples of carbohydrates include:
  1. Glucose, sucrose, cholesterol
  2. Albumin, fructose, glycogen
  3. Glucosamine, starch, maltose
  4. Glutamate, ribose, cellulose
2. Hexoses are carbohydrates with:
  1. Six monosaccharide units
  2. Three disaccharide units
  3. Six carbon atoms
  4. Six OH groups
3. A carbohydrate on hydrolysis yields 5 monosaccharide units. It belongs to the class of:
  1. Oligosaccharides
  2. Monosaccharides
  3. Disaccharides
  4. Polysaccharides
4. Pentoses are:
  1. Oligosaccharides
  2. Monosaccharides
  3. Disaccharides
  4. Polysaccharides
5. D-glucose and L-glucose are:
  1. Stereoisomers
  2. Optical isomers
  3. Anomers
  4. Epimers
6. Glucose is also called dextrose because:
  1. Its solution rotates plane polarized light to the right
  2. It is present in the D-glucose isomeric form
  3. 2Dextrose indicates its anomeric form
  4. It represents its furanose structure in solution
7. Epimerization at carbon 2 of glucose will lead to the formation of:
  1. Mannose
  2. Fructose
  3. Galactose
  4. Ribose
8. Which of the following pentoses is a constituent of nucleic acids and coenzymes:
  1. Ribulose
  2. Ribose
  3. Xylulose
  4. Arabinose
9. Lactose is formed by:
  1. β 1→4 linkage between β-D-glucose and β-D-galactose
  2. β 1→4 linkage between β-D-galactose and β-D-glucose
  3. α1→4 linkage between β-D-galactose and β-D-glucose
  4. β 1→2 linkage between β-D-galactose and β-D-glucose
10. Cellulose is important in diet because:
  1. It releases glucose on oxidation
  2. It is a storage polysaccharide
  3. It forms the bulk in diet
  4. It is a structural polysaccharide
11. Glycogen is:
  1. A storage polysaccharide in animals
  2. Is composed mainly of amylose
  3. Consists of α1→4 and α1→6 glycosidic linkages
  1. i and iii
  2. i and ii
  3. iii only
  4. i only
12. Glycosaminoglycans (GAGs) are:
  1. branched polysaccharides
  2. unbranched homopolysaccharides
  3. unbranched repeating disaccharide units
  4. unbranched repeating units of glucosamine
13. GAGs may consist of a combination of:
  1. Glucose, glucosamine, glucuronic acid
  2. Galactosamine, glucuronic acid, phosphate
  3. Galactosamine, iduronic acid, sulfate
  4. Glucosamine, glucuronic acid, phosphate
314. Which of the following is NOT glycosaminoglycans?
  1. Heparin
  2. Heparan sulfate
  3. Hyaluronic acid
  4. Antithrombin III
15. GAGs are degraded in:
  1. Intestine
  2. Liver
  3. Endoplasmic reticulum
  4. Lysosomes
16. Mucopolysaccharidosis results from:
  1. Excessive storage of glycogen in tissues
  2. Deficiency of a lysosomal hydrolase
  3. Defective synthesis of GAGs
  4. Inability of GAGs to associate with proteins
17. Glycoproteins:
  1. Are proteins having oligosaccharide chains attached to protein backbones
  2. Are proteins with covalently linked GAGs
  3. Are proteins with >95% carbohydrate content
  4. Are proteins with covalently linked glucose molecules
18. Which of the following is NOT a glycoprotein?
  1. Collagen
  2. Ceruloplasmin
  3. Mucin
  4. Albumin
19. Which of the following solvents will NOT dissolve a lipid?
  1. Ethanol
  2. Benzene
  3. Water
  4. Chloroform
20. A diet deficient in lipid might:
  1. Make a person healthier
  2. Result in vit. K deficiency
  3. Prevent heart disease
  4. Not have any effect
21. A simple lipid consists of:
  1. Fatty acid + glycerol
  2. Fatty acid+ glycerol + phosphate
  3. Fatty acid + glycerol + serine
  4. Fatty acid + carbohydrate
22. Which of the following is not a fatty acid?
  1. Eicosanoids
  2. Palmitic acid
  3. Linolenic acid
  4. Cholesterol
23. Eicosanoids are derived from:
  1. Arachidonic acid
  2. Arachidic acid
  3. Linoleic acid
  4. Linolenic acid
424. The main lipid constituent of membranes is:
  1. Cholesterol
  2. Phospholipids
  3. Triacylglycerols
  4. Glycolipids
25. Which of the following phospholipid is a second messenger?
  1. Phosphatidylcholine
  2. Phosphatidylglycerol
  3. Phosphatidylserine
  4. Phosphatidylinositol
26. The correct association of cardiolipin, dipalmitoyl lecithin, phosphatidylinositol and sphingomyelins, respectively is:
  1. Cell membrane, lung surfactant, mitochondrial membrane, brain
  2. Heart, storage, hormone, brain
  3. Mitochondrial membrane, lung surfactant, second messenger, nerves
  4. Mitochondrial membrane, lung surfactant, second messenger, muscle
27. Gangliosides are:
  1. Phospholipids
  2. Glycosphingolipids
  3. Steroids
  4. Eicosanoids
28. Cholesterol is a precursor for:
  1. Bile acids, adrenal hormones and vitamin D
  2. Bile pigments, steroids, vitamin D
  3. Bile pigments, sex hormones, coprostanol
  4. Bile salts, thyroid hormones, ceramides
29. A lipid bilayer is not present in:
  1. The cell membrane
  2. A liposome
  3. A micelle
  4. The mitochondrial membrane
30. Proteins are polymers of:
  1. Fatty acids
  2. Glucuronic acid
  3. Citric acid
  4. Amino acids
31. Proteins differ from each other in structure and function due to differences in:
  1. Quarternary structure
  2. Tertiary structure
  3. Secondary structure
  4. Primary structure
32. Which of the following constitutes the primary structure of proteins?
  1. Nature of amino acids
  2. Sequence of amino acids
  3. 5Composition of amino acids
  4. Content of amino acids
33. Consider the following peptides:
Peptide A- NH3+- Ala-Gly-Met-Cys-Lys-Pro-Ala-Glu-COO Peptide B- NH3+- Ala-Met-Gly-Lys-Cys-Pro-Ala-Glu-COO. Peptides A and B have ________ of amino acids and ___________ primary structure.
  1. Same number, therefore the same
  2. Different sequence, the same
  3. Same kinds, the same
  4. Different sequence, therefore different
34. Protein structures are stabilized by:
  1. Covalent bonds
  2. Hydrogen bonds
  3. Hydrophobic interactions
  1. i and ii
  2. ii and iii
  3. iii only
  4. i only
35. A super secondary structure of protein is not:
  1. The same as a “motif”
  2. Formed from combinations of secondary structures
  3. The same as a “domain”
  4. Formed from α helices, β strands and β bends
36. The tertiary structure of a protein does not contain:
  1. Alpha helices, hydrogen bonds, polypeptide subunits
  2. Beta sheets, supersecondary motifs, hydrophobic interactions
  3. Disulfide bonds, alpha helices, beta sheets
  4. Electrostatic interactions, hydrophobic interactions, disulfide linkages
37. Quarternary structure of protein occurs in:
  1. All proteins
  2. Monomeric proteins only
  3. Dimeric proteins
  4. Mono- and dimeric proteins
38. Which of the following is not a property of an amino acid?
  1. It has an asymmetric center
  2. It is both an acid as well as a base
  3. It possesses a secondary structure
  4. It can form chains by combining with other amino acids
639. The substitution of a single amino acid in a protein will:
  1. Have no consequence
  2. Denature the protein
  3. Disrupt protein structure as well as function
  1. ii only
  2. i only
  3. i and iii
  4. ii and iii
40. Protein denaturation refers to:
  1. Disruption of primary structure
  2. Disruption of quarternary structure
  3. Unfolding of tertiary structure
  4. Insolubility of protein
41. Enzymes:
  1. Increase the rate of a chemical reaction
  2. Decrease the rate of a chemical reaction
  3. Increase or decrease the rate of a chemical reaction
  4. Do not affect the rate of a chemical reaction
42. Which of the following statements is correct?
  1. All enzymes are proteins
  2. All proteins are enzymes
  3. Enzymes are consumed during catalysis
  4. Enzymes are proteins or nucleic acids
43. Which of the following is the correct IUBMB classification of enzymes, for classes 1 through 6?
  1. Oxidoreductases, lyases, ligases, isomerases, transferases, hydrolases
  2. Oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases
  3. Oxidoreductases, hydrolases, lyases, transferases, ligases, isomerases
  4. Oxidoreductases, transferases, hydrolases, ligases, isomerases, lyases
44. Which class of enzymes will catalyze the removal of a hydrogen atom?
  1. Transferases
  2. Lyases
  3. Hydrolases
  4. Oxidoreductases
745. Urease catalyzes the following reaction. Urea + H2O → CO2 + NH3. It belongs to:
  1. Lyases
  2. Transferases
  3. Hydrolases
  4. Oxidoreductases
46. A decarboxylase catalyzes the removal of a CO2 molecule by cleaving a C-C bond. For example, Pyruvate → Acetaldehyde + CO2. This is an example of:
  1. A hydrolase
  2. A lyase
  3. A ligase
  4. A transferase
47. Enzymes that transfer a phosphate group from ATP to a substrate molecule are called:
  1. Phosphatases
  2. ATPases
  3. Kinases
  4. Phosphorylases
48. In an enzyme catalyzed reaction, products are formed:
  1. On the surface of the enzyme
  2. At the active site of the enzyme
  3. After their release from the enzyme
  4. By conversion of the enzyme
49. Enzymes act by:
  1. Lowering the free energies of reactants and products
  2. Changing the equilibrium of the reaction
  3. Destabilizing the transition state
  4. Providing an alternate reaction pathway with lowered activation energy
50. The figure shown on page 8 represents:
  1. The Michaelis–Menten curve
  2. The lineweaver–Burke plot
  3. Activity of allosteric enzymes
  4. Constant increase in enzyme activity with substrate concentration
51. The point marked “X” in the figure mentioned for “50” defines:
  1. Optimum substrate concentration
  2. Michaelis–Menten constant
  3. Maximum velocity of the reaction
  4. Initial reaction velocity
zoom view
Figure 1:
52. Maximum Velocity (Vmax) is reached by an enzyme catalyzed reaction when:
  1. Half the active sites on the enzyme are occupied
  2. All the active sites on the enzyme are occupied
  3. Substrate concentration is at Km
  4. Enzyme concentration is much larger than substrate concentration
53. Enzyme activity:
  1. Rises constantly with temperature
  2. Falls constantly with temperature
  3. Rises with temperature and then falls as temperature keeps rising
  4. Falls with increase in temperature and then rises with further increase
54. Cellular enzymes are _______ at very high temperatures (100 °C) due to ___________.
  1. Active, energy provided by heat
  2. Inactive, denaturation
  3. Active, lowering of activation energy
  4. Inactive, raised activation energy
55. The optimum pH for enzyme activity is:
  1. 7
  2. 2
  3. 10
  4. variable for different enzymes
956. Pepsin is a digestive enzyme which is functional in the stomach. Its optimum pH is:
  1. 7
  2. 7.4
  3. 2
  4. 8
57. The optimum pH of alkaline phosphatase is:
  1. 9
  2. 7
  3. 4
  4. 2
58. Trypsin is a digestive enzyme with a pH optimum at 6. If the pH is raised to 10 or lowered to 2, it will _____ its activity due to _______.
  1. Lose, denaturation
  2. Gain, solubilization
  3. Continue, no change
  4. Modify, adaptability
59. The Lineweaver Burke plot shows the:
  1. Inhibition of enzyme activity
  2. The variation of 1/v with 1/[s]
  3. The variation of v with [s]
  4. Hyperbolic relationship between v and [s]
60. Inhibitors of enzymes act by:
  1. Decreasing the rate of enzyme catalyzed reactions
  2. Denaturing the enzyme
  3. Binding to the substrate of the enzyme
  4. Increasing the activation energy of the reaction
61. If an increase in substrate concentration leads to a recovery of enzyme activity in the presence of an inhibitor, this inhibition was likely:
  1. An irreversible inhibition
  2. A noncompetitive inhibition
  3. A competitive inhibition
  4. A repression
62. Penicillin is an antibiotic that binds covalently to an enzyme required by the bacteria for synthesis of its cell wall. This is an example of:
  1. Covalent modification
  2. Reversible inhibition
  3. Irreversible inhibition
  4. Allosteric inhibition
63. A competitive inhibitor binds to the _______ and acts by increasing the enzyme _____ for the substrate.
  1. Substrate, Km
  2. Substrate binding site, Km
  3. 10Substrate binding site, affinity
  4. Substrate, Vmax
64. Succinate (OOC-CH2-CH2-COO) is a substrate for succinate dehydrogenase. Malonate (OOC-CH2-COO) will act as a ______ inhibitor of succinate dehydrogenase.
  1. Noncompetitive
  2. Competitive
  3. Irreversible
  4. Allosteric
65. The first enzyme for the pathway for heme biosynthesis is inhibited by heme. This type of inhibition is:
  1. Competitive
  2. Noncompetitive
  3. Irreversible
  4. Feedback
66. Which of the following is NOT a way to regulate enzymes in a living cell?
  1. Induction and repression
  2. Feedback inhibition
  3. Allosteric activation
  4. Irreversible inhibition
Refer to the figure below for problems 67–70
67. In the figure below, the shape of curve B:
  1. Shows the activity of a monomeric enzyme
  2. Shows Michaelis–Menten kinetics
  3. Shows Allosteric enzyme activity
  4. Is hyperbolic
68. An enzyme showing kinetics as illustrated by curve B will show behavior depicted by curve D in the presence of:
zoom view
Figure 2:
  1. 11A positive modulator
  2. Excess of substrate
  3. A negative modulator
  4. Excess of enzyme
69. An enzyme showing kinetics shown by curve B will show behavior depicted by curve C in the presence of:
  1. A positive modulator
  2. A negative modulator
  3. Excess substrate
  4. Excess of enzyme
70. Hexokinase and glucokinase catalyze the phosphorylation of glucose with kinetics represented by curves A and B, respectively. Which of the following is true while comparing these two enzymes?
  1. Hexokinase has a higher Km for glucose
  2. Glucokinase has a lower affinity for glucose
  3. Both enzymes become saturated at the same concentration of glucose
  4. Hexokinase and glucokinase are coenzymes
71. Glycogen phosphorylase, an enzyme that hydrolyzes glycogen, is activated when phosphorylated on a serine residue. This is an example of:
  1. Covalent modification
  2. Allosteric activation
  3. Zymogen activation
  4. Enzyme induction
72. The hormone insulin is released in response to high blood glucose levels and causes an increase in the synthesis of enzymes involved in glycolysis. This is an example of:
  1. Covalent modification
  2. Zymogen activation
  3. Enzyme induction
  4. Allosteric activation
73. Raised activity of an enzyme which is physiologically absent from plasma indicates
  1. Increased cell division
  2. Increased cell turnover
  3. Increased synthesis of enzyme
  4. zymogen activation
74. Creatine kinase (CK) occurs in brain, skeletal muscle and heart, where it catalyzes the phosphorylation of creatine. These three forms of CK are called
  1. Apoenzymes
  2. Coenzymes
  3. Isoenzymes
  4. Holoenzymes
1275. CK activity is raised in serum during myocardial infarction due to a rise in:
  1. CK-MM
  2. CK-MB
  3. CK-BB
  4. CK-MB and CK-MM
76. Appearance of which form of creatine kinase will specifically indicate heart damage?
  1. CK-MB and CK- MM
  2. CK-MM
  3. CK-MB
  4. CK-BB
77. Coenzymes are ________ without which enzymes are _________.
  1. Metal ions, inactive
  2. Nonprotein molecules, active
  3. Organic molecules, inactive
  4. Protein molecules, inactive
78. Which of the following is present in DNA?
  1. Adenosine
  2. Deoxyuridine
  3. Cytidine
  4. Deoxyadenosine
79. Nucleotides are formed from:
  1. A nitrogenous base and phosphate
  2. A nitrogenous base, ribose sugar and phosphate
  3. A nitrogenous base and ribose sugar
  4. A nitrogenous base, a hexose sugar and phosphate
80. DNA strands are formed by formation of phosphodiester linkages between:
  1. Nitrogenous bases
  2. Deoxyribose sugars
  3. Deoxyribose sugars and nitrogenous bases
  4. Phosphates
81. The two sequences 5’-AGTCCGTTA-3’ and 3’-ATTGCCTGA-5’ are:
  1. Complementary
  2. The same
  3. Reverse
  4. Antiparallel
82. Which of the following is correct base pairing in DNA?
  1. A≡T
  2. A=C
  3. G=C
  4. C≡G
83. Tm is the temperature at which:
  1. DNA starts melting
  2. DNA starts reannealing
  3. 13Half of the DNA helix is single stranded
  4. DNA is completely denatured
84. Nucleosomes are formed when:
  1. DNA coils around histones
  2. DNA supercoils on itself
  3. DNA becomes circular
  4. DNA is packed into the nucleus
85. Which of the following is true of introns and exons?
  1. Introns are translated into a protein
  2. Exons are excluded from translation
  3. Exons and introns are transcribed into RNA
  4. Only exons are translated into protein
86. The central dogma of molecular biology refers to:
  1. The replication of DNA
  2. The occurrence of DNA in the nucleus
  3. All nucleic acid molecules
  4. The flow of information from DNA to RNA to protein
87. A gene is:
  1. The DNA of a cell
  2. A character that is transferred from parent cell to daughter cells
  3. A part of DNA that gives rise to a functional protein
  4. Composed of exons only
88. Genetic expression is:
  1. The formation of a final functional product from DNA
  2. The formation of an exact replica of a gene
  3. The transfer of characters from parent to offspring
  4. The expression of all DNA in daughter cells
89. RNAs are different from DNA in that they:
  1. Do not carry genetic information
  2. Are not a part of central dogma
  3. Cannot form base pairs
  4. Are single stranded
90. Which of the following will not be seen in an RNA molecule?
  1. A=U
  2. Deoxyribose
  3. Uracil
  4. Phosphodiester linkage
1491. Which of the following associations is correct?
  1. mRNA- anticodon
  2. rRNA- catalysis
  3. tRNA- poly A tail
  4. tRNA- codon
92. Which of the following acts as a template for protein synthesis?
  1. DNA
  2. rRNA
  3. tRNA
  4. mRNA
93. Ribozymes are:
  1. Enzymes that cleave RNA
  2. rRNA that acts as an enzyme
  3. tRNA that acts as an enzyme
  4. Enzymes that synthesize RNA
94. Dietary carbohydrates, proteins and triglycerides are processed after absorption into the blood, in the form of:
  1. Polysaccharides, peptides and triglycerides
  2. Disaccharides, peptides and fatty acids
  3. Monosaccharides, amino acids, fatty acids and glycerol
  4. Monosaccharides, amino acids and triglycerides
95. Carbohydrates, proteins and lipids present in the diet are metabolized to the common intermediate:
  1. Pyruvate
  2. Acetyl CoA
  3. CO2 and H2O
  4. Glucose
96. Carbohydrates, proteins and lipids present in the diet are metabolized to the final product:
  1. CO2 and H2O
  2. Acetyl CoA
  3. Pyruvate
  4. ATP
97. Glucose is catabolized through:
  1. Gluconeogenesis, β oxidation and TCA cycle
  2. Transamination and urea cycle
  3. Glycolysis, TCA cycle and electron transport chain
  4. Pentose phosphate pathway, β oxidation, TCA cycle
98. The product of glycolysis in the presence and absence of oxygen are, respectively:
  1. Acetyl CoA and ketone bodies
  2. Glycogen and ATP
  3. Pyruvate and lactate
  4. Lactate and acetyl CoA
1599. Gluconeogenesis is:
  1. Glycolysis in reverse
  2. Synthesis of glycogen from glucose
  3. Synthesis of glucose from lactate
  4. Synthesis of glucose from CO2 and H2O
100. Glycogenesis and glycogenolysis occur in response to:
  1. Low and high blood glucose respectively
  2. A well-fed state and starvation respectively
  3. A diet high in lipids
  4. Heavy exercise and well-fed state, respectively
101. Amino acids undergo _______ and their carbon chains enter _________.
  1. Transamination, urea cycle
  2. Transamination, TCA cycle
  3. Deamination, protein synthesis
  4. Protein synthesis, glycolysis
102. Fatty acids are metabolized through:
  1. Glycolysis and oxidative phosphorylation
  2. Oxidative phosphorylation and β oxidation
  3. β oxidation and ketogenesis
  4. Transamination and ketogenesis
103. TCA cycle produces __________ which enters __________ to produce energy.
  1. Acetyl CoA, ketogenesis
  2. NADH, fatty acid synthesis
  3. Reducing equivalents, the electron transport chain
  4. GTP, oxidative phosphorylation
104. Lipids are stored as ________ in the _________ while protein is stored chiefly as _________.
  1. Fatty acids, liver, albumin
  2. Cholesterol, arteries, immunoglobulins
  3. Phospholipids, membranes, muscle
  4. Triglycerides, adipose, muscle
105. __________transfer through the electron transport chain is coupled to the generation of _______ through ___________.
  1. Electron, ATP, oxidative phosphorylation
  2. NADH, H2O, oxidation
  3. 16Reducing equivalent, NADH, reduction
  4. NADH, ATP, substrate phosphorylation
106. The end product of glycolysis in a cell without mitochondria is:
  1. Pyruvate
  2. Acetyl CoA
  3. Lactate
  4. ATP
107. Glucose transporters 1–14 transport glucose into cells through:
  1. Simple diffusion
  2. Primary active transport
  3. Secondary active transport
  4. Facilitated diffusion
108. Glycolysis:
  1. Uses 4 net ATPs
  2. Generates 4 net ATPs
  3. Generates 2 net ATPs
  4. Uses 2 net ATPs
109. The ATP synthesized during the process of glycolysis is formed by:
  1. Substrate level phosphorylation
  2. Oxidative phosphorylation
  3. ATP synthase
  4. Oxidative dephosphorylation
110. ________ and _______ convert glucose to glucose-6-phosphate in liver and muscle, respectively.
  1. Hexokinase, glucokinase
  2. GLUT4, GLUT 2
  3. GLUT 2, glucokinase
  4. glucokinase, hexokinase
111. A higher Km of glucokinase for glucose prevents:
  1. Uptake of glucose by hepatocytes after a carbohydrate rich meal
  2. Uptake of glucose by hepatocytes when blood glucose is low
  3. Uptake of glucose by peripheral tissues when blood glucose is low
  4. Secretion of insulin by the β pancreatic cells
112. Glycolysis is inhibited during an energy-rich state through inhibition of key enzymes, one of which is phosphofructokinase 1(PFK 1). Which of the following will inhibit PFK 1?
  1. AMP
  2. Fructose 6 phosphate
  3. ATP
  4. Insulin
17113. Fructose 2,6 bisphosphate:
  1. Activates PFK1
  2. Activates Fructose 1,6 bisphosphatase
  3. Formation is activated by glucagon
  4. Formation is inhibited by insulin
114. The reaction catalyzed by glyceraldehyde-3 phosphate dehydrogenase:
  1. Generates ATP
  2. Utilizes ATP
  3. Generates NADH
  4. Utilizes NADH
115. ATP is synthesized from ________of the intermediates 1,3 bis phosphoglycerate and phosphoenolpyruvate and the process is called ________.
  1. Phosphorylation, covalent modification
  2. Oxidation, oxidative phosphorylation
  3. Reduction, reductive phosphorylation
  4. High-energy phosphates, substrate-level phosphorylation
116. Pyruvate kinase is activated by the glycolytic intermediate Fructose 1,6 Bis Phosphate and inhibited by phosphorylation. These two modules of regulation are, respectively:
  1. Allosteric activation, feedback inhibition
  2. Feed forward activation, covalent modification
  3. Feed back inhibition, allosteric activation
  4. Covalent modification, covalent inhibition
117. RBCs can generate ATP only from:
  1. Glycolysis
  2. Oxidative phosphorylation
  3. Tricarboxylic acid cycle
  4. Gluconeogenesis
118. Which of the following glycolytic enzyme deficiencies is a known cause of nonspherocytic hemolytic anemia?
  1. PFK1
  2. PFK2
  3. Pyruvate kinase
  4. Hexokinase
119. The end product of glycolysis in RBCs is ______ because of a lack of _______.
  1. Phosphoenolpyruvate, pyruvate kinase
  2. Lactate, oxygen
  3. Pyruvate, lactate dehydrogenase
  4. Lactate, mitochondria
18120. During a block of blood flow to tissues, tissue cells will produce _____ due to a lack of ______, in order to continue making ______.
  1. CO2, RBCs, glucose
  2. Pyruvate, energy, ATP
  3. Lactate, enzymes, pyruvate
  4. Lactate, O2, ATP
121. Glycolysis is _____ by insulin and _______ by glucagon.
  1. Inhibited, activated
  2. Activated, inhibited
  3. Not influenced, influenced
  4. Influenced, not influenced
122. Figure 3 shows the structure of:
  1. A cell wall
  2. A nuclear membrane
  3. Mitochondrial membrane
  4. Cell membrane
123. “A” and “B” are respectively:
  1. Nonpolar and polar regions
  2. Hydrophilic and hydrophobic regions
    zoom view
    Figure 3:
  3. 19Phospholipid and triglyceride regions
  4. Internal and external regions
124. “H” is a ______ molecule which gives the membrane its _______ character.
  1. Hydrophobic, bipolar
  2. Cholesterol, fluid
  3. Carbohydrate, rigid
  4. Cholesterol, nonpolar
125. A and B are formed, respectively by:
  1. COO groups and carbon chains
  2. Glycerol and fatty acids
  3. Phosphatidyl derivatives and acyl chains
  4. Acyl groups and phosphatidylglycerols
126. The outer layer of the membrane will have all of the following lipids as a regular component, except:
  1. Phosphatidylethanolamine
  2. Phosphatidylinositol
  3. Sphingomyelin
  4. Phosphatidylcholine
127. C and D are:
  1. Integral and peripheral proteins, respectively
  2. Peripheral and integral proteins, respectively
  3. Peripheral proteins
  4. Integral proteins
128. E and F together form:
  1. A proteoglycan
  2. A glycoprotein
  3. A glycolipid
  4. Glycocalyx
129. Gases, such as O2 and CO2 move from a region of higher concentration across the plasma membrane, to a region of low concentration, till equilibrium is reached. This type of transport across membrane is:
  1. Facilitated diffusion
  2. Active transport
  3. Simple diffusion
  4. Gated channel transport
130. Glucose is transported into cells through transporters down a concentration gradient. This is an example of:
  1. Facilitated diffusion
  2. Active transport
  3. Simple diffusion
  4. Gated channel transport
20131. On arrival of an action potential at the neuron, channels in the axonal membrane open to let in Na+. This is an example of:
  1. A voltage-gated channel
  2. Simple diffusion
  3. Facilitated diffusion
  4. Active transport
132. CFTR (Cystic fibrosis transmembrane conductance regulator) is a membrane protein that opens in response to phosphorylation by ATP to transport Cl from the intestinal cell into the intestinal lumen. This is an example of:
  1. Voltage-gated channel
  2. Ligand-gated channel
  3. Active transport
  4. Facilitated diffusion
133. Na+ is continuously transported out of the cell by the Na+-K+ ATPase in exchange of K+ even though Na+ concentration is high outside the cell. This is an example of:
  1. Ligand-gated channel
  2. Voltage-gated channel
  3. Active transport
  4. Facilitated diffusion
134. Na+ is transported into the intestinal cell from the lumen down its concentration gradient which is created by the Na+-K+ ATPase. Several molecules like glucose and amino acids are co-transported with Na+ as it travels down its concentration gradient. This type of transport is:
  1. Facilitated diffusion
  2. Secondary active
  3. Primary active
  4. Voltage-gated channel
135. Macromolecules and fluid from extracellular space can be transported inside the cell through:
  1. Active transport
  2. Exocytosis
  3. Facilitated transport
  4. Endocytosis
136. Cells release their contents into the extracellular space by:
  1. Phagocytosis
  2. Exocytosis
  3. Pinocytosis
  4. Endocytosis21
All other choices include molecules that are not carbohydrates, albumin is a protein, cholesterol is a lipid and glutamate is an amino acid.
Hexoses are MONO saccharides with 6 carbon atoms. Six monosaccharide units will make an oligosaccharide.
Oligosaccharides consist of less than 10 monosaccharide units.
Pentoses are monosaccharides with 5 carbon atoms (just as hexoses are monosaccharides with 6 carbon atoms in question 2).
Stereoisomers which differ in the placement of H and OH groups on carbon 5 only. Each of D and L forms can either be dextro- or levo- rotatory, which is NOT what D and L here stand for.
A solution of glucose is dextrorotatory.
Ribose, a component of deoxyribose nucleic acid (DNA) and nicotinamide adenine dinucleotide (nicotinamide + adenine + ribose + phosphate), which is one example.
When the linkages are indicated, the correct sequence of placing the monosaccharides should be followed. Hence, it is not a, although the linkage and constituents are correct.
Cellulose is an important source of fiber or bulk in the diet. It cannot be utilized for energy or storage as it cannot be digested by humans due to lack of the enzyme that can break β1→4 linkages between glucose units of cellulose. Some cellulose can be broken down for energy by the gut bacteria, but is not significant for humans.
Glycogen is a storage polysaccharide in animals which is highly branched. Amylose is not branched and is a main constituent of starch.
GAGs are repeating units of disaccharides, one of which is an amino derivative of glucose or galactose and the other is a uronic acid, either of which can be sulfated.
Amino sugar + uronic acid + sulfate.
Antithrombin III is a protein.
The lysosomes by lysosomal hydrolytic enzymes.
Mucopolysaccharidoses are a class of lysosomal storage disorders. Abormal amounts of GAGs accumulate in the tissues because they cannot be broken down due to a lack of one of their hydrolytic enzymes in the lysosomes.
A protein backbone with short oligosaccharides attached which consist of several different monosaccharides and their derivatives. Carbohydrate content does not exceed 85%.
All plasma proteins are glycoproteins except albumin. Collagen is also a glycoprotein.
Lipids are hydrophobic and do not dissolve in water
A lipid-deficient diet can result in deficiency of fat-soluble vitamins, Vit. K being one of them.
Simple lipids are esters of fatty acids with alcohols.
Cholesterol is a steroid.
Eicosanoids are derived from C20 fatty acids with multiple double bonds. Arachidic acid is not unsaturated and linoleic and linolenic acids have 18 carbons only.
Although all choices can be found in membranes, the phospholipids form a bilayer and form a membrane, in which other lipids can be incorporated.
Bile acids are synthesized from cholesterol. Bile pigment, however, is a product of breakdown of heme.
A micelle is a single layer of phospholipids with nonpolar tails facing the interior
All differences in structure (and function) is a result of different sequences of amino acids in different proteins, i.e. the primary structure.
A peptide with the sequence Ala-Gly-Met-Glu-Cys has a different primary structure than Glu-Cys-Ala-Gly-Met, even though the amino acids in both peptides are the same.
As explained in 32.
Protein structures are stabilized by noncovalent interactions.
Supersecondary structures are formed from the basic α helices, β strands and β bends and are also known as motifs. Motifs combine to form domains of a tertiary structure.
Tertiary structures occur within a single polypeptide, if subunits occur, the protein has quarternary structure.
Quarternary structure can occur only if a protein has 2 or more subunits.
If the substitution occurs on the surface of the protein, it might not have any consequence. If it occurs at a site involved in protein folding, it will disrupt the structure and function of the protein, as occurs in many genetic diseases.
When the organized tertiary structure is disrupted, as due to heat or strong acids and bases, the protein is said to be denatured. The separation of subunits of a protein is not denaturation, nor is the breaking of the peptide bond. Denaturation does not refer to precipitation of proteins, as precipitation (insolubility) can occur without denaturation also.
Enzymes always increase the rate of a chemical reaction.
Most of the known enzymes are proteins, but some types of RNAs also show catalytic activity, e.g. the 23S ribosomal RNA.
The mnemonic “Oh To Have Loved in Life’ helps remember the correct classification, when the starting letter of each word is taken, i.e. OTHLIL. The first L is for lyases and ligases come last. It is important to remember the classes in the correct sequence. For example, transferases are group 2 and lyases are group 4.
The removal of a hydrogen atom is the removal of H+ and an e. The loss of an electron is oxidation, so the class of enzymes that will catalyze hydrogen atom removal will be oxidoreductases.
An enzyme which cleaves a bigger molecule with the utilization of a water molecule is a hydrolase. Digestive enzymes which carry out the hydrolysis of biomolecules in our diet are hydrolases.
This is also a reaction where the cleavage of a bond occurs. However, here there is no addition of a water molecule. Such cleavage of a C-C or C-N bond are catalyzed by lyases.
The word kinase originates from the Greek word “kinein” meaning “to move”. Kinases move a phosphate group from an energy-rich molecule, such as ATP to another molecule. Note that phosphatases catalyze the removal of a phosphate group from a molecule with the addition of a water molecule and are hence, hydrolases. Kinases on the other hand are transferases.
The active site of the enzyme helps to convert the substrate into products according to the reaction E+S→ES→EP→E+P. Products dissociate from the enzyme once formed.
An enzyme does not alter the free energies of reactants or products, nor does it change the equilibrium. It does lower the “activation energy” which is the energy required by the reactants to reach transition state.
Although the activity does increase with substrate concentration, the increase in activity is not constant, it rises sharply, then becomes slower and then becomes steady and does not change. So “d” would be the wrong answer.
This is the Michaelis–Mentens constant or Km.
The velocity of an enzyme catalyzed reaction rises till it is saturated with substrate or in other words, all of its substrate binding sites have been occupied.
The behavior of enzymes with changes in temperature can be visualized as a bell shape, the highest peak of this is the optimum temperature Tm, at which enzyme activity is maximum. If an enzyme is inactive, raising the temperature will raise its activity till Tm is reached, after which the activity falls, as high heat will denature the enzyme and it will lose its activity.
As explained for 53.
Different enzymes have different optimum pH.
The pH in the stomach is very low (~2) due to the secretion of HCl.
We can guess this from the name of the enzyme. The word “alkaline” suggests that it works under alkaline or basic conditions. A pH of 9 amongst the various choices is alkaline.
Extremes of pH from pH optimum for an enzyme will cause it to denature and become inactive.
Inhibitors bind to enzymes to affect the binding of substrates and their conversion to products, hence slowing down the reaction.
Competitive inhibitors bind to the same site as the substrates. When substrate concentration is large compared to the inhibitor, there is a higher probability of the substrate binding to its site compared to an inhibitor.
Irreversible inhibitors usually form covalent links with the enzyme which are hard to break.
The affinity of the enzyme for its substrate is lowered, hence Km is higher.
The similarity in structures of succinate and malonate suggests that there can be competition for the same binding site.
When the final product of a pathway inhibits an enzyme at the beginning of this pathway, this is feedback inhibition. In this case, feedback inhibition is carried out by repression and allosteric inhibition.
Regulation of enzymes requires that enzymes should be able to switch on and off. Irreversible inhibition will not allow an enzyme that has been switched off to be switched back on.
curve B is sigmoid, i.e has the shape of an “S”, a shape shown by allosteric enzyme kinetics.
Curve B will shift to the right when the enzyme is bound by a negative modulator, raising its Km for the substrate.
Curve B will shift to the left when the enzyme is bound by a positive modulator, decreasing the Km for the substrate and hence, increasing its affinity for the same.
Glucokinase and hexokinase are isozymes catalyzing the same reaction, but showing different kinetic behavior. A higher Km (and hence lower affinity) of glucokinase is apparent from the curve.
Phosphorylation of enzyme proteins occurs on serine/threonine/tyrosine residues, amino acids with an –OH group in the side chain, through a covalent linkage. This is a very common way of regulation of enzymes, as this is reversible.
Synthesis of an enzyme is increased by increasing the expression of the gene that codes for it, a process called “induction”.
Enzymes “leak” into the plasma when cells undergo necrosis and are being replaced by new cells (cell turnover), as occurs in injury.
Heart muscle contains both CK-MB and CK-MM and both will contribute to the rise in total CK activity in serum.
CK-MB is specific to heart and when this isozyme is raised in proportion to total CK, heart damage, usually due to an infarct, is confirmed.
Coenzymes are nonprotein organic molecules without which enzymes are inactive.
The ribose sugars in DNA are the deoxy form, so deoxy is added to the name when ribose is included. Adenine + deoxyribose forms deoxyadenosine.
The deoxyribose sugars are connected through a phosphodiester linkage.
A base sequence is always read from the 5’ to the 3’ end.
Three hydrogen bonds between C and G and two between A and T.
When half the DNA has “melted”, i.e. separated from its partner in the double helix.
Exons are “ex”pressed, so will be transcribed and translated, but not the introns, which are removed before translation.
A sequence of DNA consisting of introns as well as exons together, which will get translated into a structural or functional protein (the phenotype). All DNA does not form genes. Only 10% of our DNA is expressed, and this needs to be explicit in the definition of a gene.
A gene is said to be “expressed” when the protein (or sometimes RNA) that it codes for has been formed. Transfer of characters defines inheritance rather than the expression of genes. Some characters might be transferred from parent to offspring but might not be expressed, as they might be recessive.
Some RNAs (tRNA) fold on themselves and form base pairs, are a part of central dogma and carry genetic information from DNA to protein.
All polymeric biomolecules of the diet are broken down into their constituents for absorption.
Acetly CoA forms the common intermediate for the main biochemical pathways for metabolism of carbohydrates, lipids and protein.
The final product of oxidation of dietary carbohydrates, fats and protein is CO2 and H2O, as energy in the form of ATP is generated.
Pyruvate, the aerobic glycolytic product is converted to acetyl CoA which enters TCA, from which reducing equivalents in the form of NADH are generated which are transported through the electron transport chain to generate ATP through oxidative phosphorylation.
It is not the reverse of glycolysis as three key reactions are different.
An energy-rich state will cause glucose to be stored “for later”, in the form of glycogen, while in a scarcity of glucose, stores of glycogen are hydrolyzed to release glucose into the blood stream.
Most amino acids on transamination form intermediates of TCA cycle, or products that are later channeled into the TCA cycle.
TCA produces reducing equivalents in the form of NADH which are then channeled into the electron transport chain.
TGs are the main storage form of lipids in the adipose tissue, while muscle serves as a store of protein.
ETC and oxidative phosphorylation are coupled processes.
Lactate is formed when pyruvate cannot be channeled into TCA. Since the latter occurs in mitochondria, cells and mitochondria have no use of converting pyruvate to acetyl CoA. Instead, lactate is generated.
Glucose is transported into cells through many different kinds of transporters. GLUT 1–14 transport glucose down a concentration gradient.
2 ATPs are used in the preparatory phase and 4 ATPs are generated in the second phase, giving a net yield of 2 ATPs
When high-energy substrates or intermediates are used to phosphorylate ADP and make ATP, it is termed substrate level phosphorylation.
Glucokinase is present in the liver, hexokinase is present in all tissues.
A higher Km ensures that glucokinase in the liver will not function unless the concentration of glucose in the blood is high. When this is so, glucokinase converts glucose to glucose 6 phosphate in the hepatocytes and most of this is directed towards storage as glycogen.
An energy-rich state is signified by a high concentration of ATP.
Fructose 2, 6 bisphosphate is the most potent activator of PFK1.
A dehydrogenase will catalyze the transfer of electrons. In this reaction, the electrons are transferred from glyceraldehyde 3 phosphate to NAD to form NADH.
The “high energy” phosphates from intermediates are utilized to form ATP from ADP.
The activation is allosteric, and an intermediate formed at the beginning of the pathway activates an enzyme near the end of the pathway (feed forward). Phosphorylation and dephosphorylation are covalent modifications of enzymes.
Because they lack mitochondria, the glycolytic intermediate, pyruvate, is converted to lactate which travels through blood to the liver to get converted to glucose through gluconeogenesis, which comes back to RBCs for glycolysis.
The other glycolytic enzyme that can cause nonspherocytic hemolytic anemia is phosphoglucoisomerase. Another enzyme resulting in the same is glucose 6 phosphate dehydrogenase which is an enzyme of another glucose metabolic pathway called the HMP shunt pathway.
A block in blood flow will result in hypoxia, or low O2, which will encourage pyruvate to be utilized through the anaerobic glycolytic pathway to lactate which is transported out of the RBC. This ensures that glycolysis continue to occur with the generation of ATP through substrate level phosphorylation.
Insulin activates pathways that will lower blood glucose and glucagon will do the opposite.
Although the basic membrane structure or the cell and its organelles is the same, specific characteristics exist for each type. A cell membrane will show surface carbohydrates.
Hydrophilic or polar regions face outward in the packing of the lipid bilayer, while hydrophobic chains or nonpolar regions, face inward.
Cholesterol ring is distinguishable from similar structures in the membrane, notably carbohydrates, which are never integral. Because of the cholesterol molecules, the membrane has fluidity which allows the protein molecules to move laterally within the membrane.
The lipid bilayer is made up mainly of phospholipids. The phosphatidyl derivatives are charged and face away from the interior. The latter is formed by the acyl chains of phosphoacylglycerols.
The distribution of phospholipids between the outer and inner layer is asymmetric. Phosphatidylinositol occurs only in the inner membrane, from where, on stimulation, its acts as a second messenger to transmit signals into the cell.
The ligand in this case is the phosphate group which binds to the transport protein.
A transport ‘against” concentration gradient will require energy and is always “active”.
Since this transport utilized a primary active transport of the Na+–K+ ATPase which creates the gradient, it is “secondary active”. If Na+–K+ ATPase is inhibited, secondary transport depending on this primary transport will also stop.
Larger molecules and fluid will need invagination of the cell membrane to form vesicles which are internalized and the contents fuse with lysosomes in the cytosol.
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