4751 to 4800 MCQs for Lab Technician and Technologist Exam Preparation
5000 Plus MCQs for Lab Technician and Technologists are designed to test the knowledge and proficiency of laboratory professionals who work in the field of clinical laboratory science. These questions cover a wide range of topics related to laboratory science, including anatomy, physiology, microbiology, chemistry, and hematology.
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Questions 4751 to 4800
Our body can get pentoses from:
- a) Glycolytic pathway
- b) Uromic acid pathway
- c) TCA cycle
- d) HMP shunt
Explanation:
The HMP shunt (Hexose Monophosphate Shunt), also known as the Pentose Phosphate Pathway, is the primary metabolic pathway responsible for generating pentose sugars (like Ribose-5-phosphate) which are essential for the synthesis of DNA and RNA.
Why other options are incorrect:
Why other options are incorrect:
- • Glycolytic pathway: This pathway breaks down glucose to produce pyruvate and energy (ATP); it does not produce pentoses as a primary product.
- • Uromic acid pathway: This is an alternative pathway for glucose oxidation that produces glucuronic acid, but it is not the main source of pentose sugars for the body.
- • TCA cycle: This occurs in the mitochondria to oxidize acetyl-CoA into CO2 and water to produce high-energy electrons; it is not involved in pentose synthesis.
Conversion of glucose to glucose-6-phosphate in human liver is by:
- a) Hexokinase only
- b) Glucokinase only
- c) Hexokinase and glucokinase
- d) Glucose-6-phosphate dehydrogenase
Explanation:
In the human liver, the phosphorylation of glucose to glucose-6-phosphate is catalyzed by both Hexokinase and Glucokinase (Hexokinase IV). While Hexokinase is present in almost all tissues to provide glucose for basic cellular needs, Glucokinase is specifically highly active in the liver and pancreas to handle high glucose levels after meals.
Why other options are incorrect:
Why other options are incorrect:
- • Hexokinase only: Incorrect because the liver is unique for having a significant amount of Glucokinase in addition to Hexokinase.
- • Glucokinase only: Incorrect because while Glucokinase is the “liver-specific” enzyme, standard Hexokinase is still present in liver cells.
- • Glucose-6-phosphate dehydrogenase: This enzyme is involved in the Pentose Phosphate Pathway (HMP shunt) to oxidize G6P; it does not create G6P from glucose.
The following is an enzyme required for glycolysis:
- a) Pyruvate kinase
- b) Pyruvate carboxylase
- c) Glucose-6-phosphatase
- d) Glycerokinase
Explanation:
Pyruvate kinase is the enzyme that catalyzes the final step of glycolysis, converting phosphoenolpyruvate (PEP) to pyruvate while generating one molecule of ATP. It is one of the three irreversible regulatory enzymes of the glycolytic pathway.
Why other options are incorrect:
Why other options are incorrect:
- • Pyruvate carboxylase: This is a key enzyme in gluconeogenesis (the synthesis of glucose), not glycolysis. It converts pyruvate into oxaloacetate.
- • Glucose-6-phosphatase: This enzyme is involved in gluconeogenesis and glycogenolysis; it removes the phosphate group from glucose-6-phosphate to release free glucose into the blood.
- • Glycerokinase: This enzyme is involved in lipid metabolism, specifically the phosphorylation of glycerol to glycerol-3-phosphate.
The normal glucose tolerance curve reaches peak at:
- a) 15 min
- b) 1 hr
- c) 2 hrs
- d) 2 ½ hrs
Explanation:
In a standard Oral Glucose Tolerance Test (OGTT), blood glucose levels in a healthy individual typically rise and reach their maximum concentration (peak) about 1 hour after the ingestion of the glucose load. After this peak, insulin action causes the levels to fall back toward baseline.
Why other options are incorrect:
Why other options are incorrect:
- • 15 min: This is too early; the glucose is still being absorbed from the gastrointestinal tract and hasn’t reached its maximum concentration in the blood.
- • 2 hrs: By two hours, a normal curve should be showing a significant decline in glucose levels as it is cleared by the tissues. This timing is often used for diagnostic cut-offs for diabetes.
- • 2 ½ hrs: At this stage, blood glucose should be near fasting levels or even slightly below (postprandial dip) in a healthy person.
Oxidative decarboxylation of pyruvate requires:
- a) NADP+
- b) Cytochromes
- c) pyridoxal phosphate
- d) COASH
Explanation:
The oxidative decarboxylation of pyruvate to Acetyl-CoA is catalyzed by the Pyruvate Dehydrogenase (PDH) complex. This multi-enzyme complex requires five essential cofactors: TPP, Lipoic acid, CoA-SH (COASH), FAD, and NAD+.
Why other options are incorrect:
Why other options are incorrect:
- • NADP+: The PDH complex specifically uses NAD+ as an electron acceptor, not NADP+ (which is more common in anabolic pathways like fatty acid synthesis).
- • Cytochromes: These are electron carriers found in the Electron Transport Chain (ETC) in the inner mitochondrial membrane, not in the PDH complex.
- • Pyridoxal phosphate (PLP): This is the active form of Vitamin B6 and is primarily involved in amino acid metabolism (transamination), not pyruvate decarboxylation.
Glucose tolerance is increased in:
- a) Diabetes mellitus
- b) Adrenalectomy
- c) Acromegaly
- d) Thyrotoxicosis
Explanation:
Increased glucose tolerance means the body is able to clear glucose from the blood very efficiently or maintains lower blood sugar levels. Adrenalectomy (removal of the adrenal glands) results in a deficiency of glucocorticoids like cortisol. Since cortisol is a “diabetogenic” hormone that normally raises blood sugar, its absence leads to increased insulin sensitivity and higher glucose tolerance.
Why other options are incorrect:
Why other options are incorrect:
- • Diabetes mellitus: This is characterized by decreased glucose tolerance because the body cannot effectively move glucose into cells.
- • Acromegaly: Caused by excess Growth Hormone, which antagonizes insulin action, leading to decreased glucose tolerance.
- • Thyrotoxicosis: Excess thyroid hormones increase the rate of glucose absorption from the gut and can lead to decreased glucose tolerance (hyperglycemia).
Glucose tolerance is decreased in:
- a) Diabetes mellitus
- b) Hypopituitarisme
- c) Addison’s disease
- d) Hypothyroidism
Explanation:
Decreased glucose tolerance refers to the body’s inability to effectively clear glucose from the blood, leading to prolonged hyperglycemia. Diabetes mellitus is the most common cause of this, resulting from either insulin deficiency (Type 1) or insulin resistance (Type 2).
Why other options are incorrect:
Why other options are incorrect:
- • Hypopituitarisme: A deficiency in pituitary hormones (like Growth Hormone and ACTH) leads to increased glucose tolerance because these hormones normally act as insulin antagonists.
- • Addison’s disease: This is chronic adrenal insufficiency. The lack of cortisol (a hormone that increases blood sugar) results in a tendency toward hypoglycemia and increased glucose tolerance.
- • Hypothyroidism: A decrease in thyroid hormones generally slows the rate of glucose absorption from the gastrointestinal tract, often leading to a flat glucose tolerance curve (which is technically an increase in tolerance).
During glycolysis, Fructose 1, 6 diphosphate is decomposed by the enzyme:
- a) Enolase
- b) Fructokinase
- c) Aldolase
- d) Diphosphofructophosphatose
Explanation:
The enzyme Aldolase (specifically Aldolase A in muscle and Aldolase B in liver) is responsible for the cleavage (decomposition) of Fructose 1,6-bisphosphate into two three-carbon molecules: Dihydroxyacetone phosphate (DHAP) and Glyceraldehyde 3-phosphate (G3P).
Why other options are incorrect:
Why other options are incorrect:
- • Enolase: This enzyme acts later in glycolysis, catalyzing the dehydration of 2-phosphoglycerate to form phosphoenolpyruvate (PEP).
- • Fructokinase: This enzyme is involved in the specialized metabolism of fructose (fructolysis), converting fructose to fructose-1-phosphate.
- • Diphosphofructophosphatose: (Commonly known as Fructose-1,6-bisphosphatase) This is a key enzyme in gluconeogenesis that removes a phosphate group; it does not decompose the carbon skeleton.
The following enzyme is required for the hexose monophosphate shunt pathway:
- a) Glucose-6-phosphatase
- b) Phosphorylase
- d) Glucose-6-phosphate dehydrogenase
Explanation:
Glucose-6-phosphate dehydrogenase (G6PD) is the first and rate-limiting enzyme of the Hexose Monophosphate (HMP) shunt, also known as the Pentose Phosphate Pathway. It catalyzes the conversion of glucose-6-phosphate into 6-phosphogluconolactone while reducing NADP+ to NADPH.
Why other options are incorrect:
Why other options are incorrect:
- • Glucose-6-phosphatase: This enzyme is used in gluconeogenesis and glycogenolysis to release free glucose into the blood; it is not part of the HMP shunt.
- • Phosphorylase: (Glycogen phosphorylase) This enzyme is responsible for the breakdown of glycogen into glucose-1-phosphate.
- • Aldolase: This is a glycolytic enzyme that cleaves fructose-1,6-bisphosphate into two three-carbon fragments.
Dehydrogenase enzymes of the hexose monophosphate shunt are:
- a) NAD+ specific
- b) NADP+ specific
- c) FAD specific
- d) FMN specific
Explanation:
The dehydrogenase enzymes in the Hexose Monophosphate (HMP) shunt, namely Glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase, are NADP+ specific. They reduce NADP+ to NADPH, which is essential for fatty acid synthesis and maintaining glutathione in a reduced state to protect cells from oxidative damage.
Why other options are incorrect:
Why other options are incorrect:
- • NAD+ specific: NAD+ is primarily used in catabolic pathways like Glycolysis and the TCA cycle to generate NADH for ATP production.
- • FAD / FMN specific: These are flavin-based cofactors usually associated with the Electron Transport Chain or specific mitochondrial dehydrogenases (like succinate dehydrogenase), but not the HMP shunt.
Under anaerobic conditions the glycolysis of one mole of glucose yields ______moles of ATP:
- a) One
- b) Two
- c) Eight
- d) Thirty
Explanation:
Under anaerobic conditions (lack of oxygen), glucose is converted into lactate. During this process, a total of 4 ATP are produced by substrate-level phosphorylation, but 2 ATP are consumed in the initial steps, resulting in a net yield of 2 ATP per mole of glucose.
Why other options are incorrect:
Why other options are incorrect:
- • One: This is incorrect as the pathway net gain is specifically two molecules.
- • Eight: This value was traditionally associated with aerobic glycolysis (including the ATP generated from NADH via the respiratory chain), but is not applicable to anaerobic conditions.
- • Thirty: (or 32) This represents the total ATP yield of complete aerobic respiration (Glycolysis + TCA cycle + Oxidative Phosphorylation), not just anaerobic glycolysis.
Glycogen is converted to glucose-1-phosphate by:
- a) UDPG transferase
- b) Branching enzyme
- c) Phosphorylase
- d) Phosphatase
Explanation:
The enzyme Glycogen Phosphorylase (often simply called Phosphorylase) is the key enzyme in glycogenolysis. It breaks the $\alpha$-1,4-glycosidic bonds in glycogen by adding an inorganic phosphate, releasing glucose-1-phosphate.
Why other options are incorrect:
Why other options are incorrect:
- • UDPG transferase: Also known as Glycogen Synthase, this enzyme is involved in glycogen synthesis (glycogenesis), not breakdown.
- • Branching enzyme: This enzyme works during glycogenesis to create $\alpha$-1,6-glycosidic bonds to form branches in the glycogen molecule.
- • Phosphatase: Specifically Glucose-6-phosphatase, this enzyme converts Glucose-6-phosphate into free glucose in the liver; it does not act directly on glycogen to produce glucose-1-phosphate.
Which of the following is NOT an enzyme involved in glycolysis?
- a) Enolase
- b) Aldolase
- c) Hexokinase
- d) Glucose oxidase
Explanation:
Glucose oxidase is an enzyme that catalyzes the oxidation of glucose to hydrogen peroxide and D-glucono-δ-lactone. While it is widely used in laboratory biosensors and test strips to measure blood glucose levels, it is not an enzyme found in the human glycolytic pathway.
Why other options are incorrect:
Why other options are incorrect:
- • Enolase: This is the ninth enzyme of glycolysis, responsible for converting 2-phosphoglycerate to phosphoenolpyruvate (PEP).
- • Aldolase: This is the fourth enzyme of glycolysis, which cleaves Fructose-1,6-bisphosphate into two three-carbon sugars (DHAP and G3P).
- • Hexokinase: This is the first enzyme of glycolysis, responsible for phosphorylating glucose into glucose-6-phosphate.
The Tricarboxylic acid (TCA) cycle to be continuous requires the regeneration of:
- a) Pyruvic acid
- b) oxaloacetic acid
- c) α-oxoglutaric acid
- d) Malic acid
Explanation:
The TCA cycle (Krebs cycle) is a true cycle because it begins and ends with oxaloacetic acid (OAA). In the first step, OAA condenses with Acetyl-CoA to form Citrate. Through a series of redox reactions, OAA is eventually regenerated so it can combine with a new molecule of Acetyl-CoA, allowing the cycle to continue.
Why other options are incorrect:
Why other options are incorrect:
- • Pyruvic acid: Pyruvate is the precursor that is converted into Acetyl-CoA; it is not an intermediate that is regenerated within the cycle itself.
- • α-oxoglutaric acid: (Alpha-ketoglutarate) This is an intermediate within the cycle, but it is not the molecule that “closes the loop” to restart the process.
- • Malic acid: Malate is the immediate precursor to oxaloacetate, but it is the oxidation of malate into OAA that completes the cycle.
Dehydrogenation of succinic acid to fumaric acid requires the following hydrogen carrier:
- a) NAD+
- b) NADP+
- c) flavoprotein
- d) Glutathione
Explanation:
The enzyme Succinate Dehydrogenase (which is also Complex II of the Electron Transport Chain) catalyzes the conversion of succinate to fumarate. This enzyme is a flavoprotein because it uses FAD (Flavin Adenine Dinucleotide) as its hydrogen carrier. The free energy change of this specific reaction is insufficient to reduce NAD+, which is why FAD is required.
Why other options are incorrect:
Why other options are incorrect:
- • NAD+: While NAD+ is the carrier for most other dehydrogenases in the TCA cycle, it cannot be used for the succinate to fumarate step because the redox potential of the succinate/fumarate pair is not high enough to reduce NAD+.
- • NADP+: This carrier is primarily used for reductive biosynthesis (like in the HMP shunt) and is not used in the TCA cycle.
- • Glutathione: This is a tripeptide used as a major antioxidant to protect cells from oxidative stress; it does not function as a hydrogen carrier in the TCA cycle.
The tissues with the highest total glycogen content are:
- a) Muscle and kidneys
- b) Kidneys and liver
- c) Liver and muscle
- d) Brain and Liver
Explanation:
Glycogen is primarily stored in the liver and skeletal muscle. While the liver has a higher concentration of glycogen per gram of tissue (to maintain blood glucose), the skeletal muscle contains the largest total amount of glycogen in the body because of its much greater total mass.
Why other options are incorrect:
Why other options are incorrect:
- • Kidneys: Although the kidneys can perform gluconeogenesis, they store very negligible amounts of glycogen compared to the liver and muscle.
- • Brain: The brain has very limited glycogen stores (found mainly in astrocytes). It relies on a continuous supply of glucose from the bloodstream for its high energy demands.
- • Muscle and kidneys / Kidneys and liver: Any option including the kidneys is incorrect because their contribution to total body glycogen is minimal.
Rothera test is not given by:
- a) β-hydroxy butyrate
- b) bile salts
- c) Glucose
- d) None of these
Explanation:
Rothera’s test is used to detect ketone bodies (acetone and acetoacetate) in urine. Although β-hydroxybutyrate is clinically classified as a ketone body, it does not give a positive Rothera test because it lacks the keto (=O) group; it has a hydroxyl (-OH) group instead.
Why other options are incorrect:
Why other options are incorrect:
- • Bile salts: While bile salts also do not give a positive Rothera test (they are detected by Hay’s test), in biochemistry exams, this question specifically tests the knowledge that β-hydroxybutyrate is the “Rothera-negative” ketone body.
- • Glucose: Glucose is detected by Benedict’s or Fehling’s test, not Rothera’s.
- • None of these: This is incorrect as Option A is the specific biochemical answer regarding ketone body testing.
Gluconeogenesis is increased in the following condition:
- a) Diabetes insipidus
- b) Diabetes Mellitus
- c) Hypothyroidism
- d) Liver diseases
Explanation:
In Diabetes Mellitus, gluconeogenesis is significantly increased. Due to a lack of insulin or insulin resistance, the body cannot effectively use glucose from the blood. High levels of counter-regulatory hormones (like glucagon and cortisol) stimulate the liver to synthesize new glucose from non-carbohydrate sources (amino acids, glycerol, and lactate) to try and provide energy, which further worsens hyperglycemia.
Why other options are incorrect:
Why other options are incorrect:
- • Diabetes insipidus: This is a condition related to water balance and ADH (antidiuretic hormone) deficiency; it does not directly affect glucose metabolism or gluconeogenesis.
- • Hypothyroidism: This condition slows down the overall metabolic rate, typically leading to a decrease in the rate of gluconeogenesis.
- • Liver diseases: Since the liver is the primary site of gluconeogenesis, severe liver damage (such as cirrhosis or hepatitis) reduces the capacity of the organ to produce glucose, often leading to hypoglycemia.
The oxidation of lactic acid to pyruvic acid requires the following vitamin derivative as the hydrogen carrier:
- a) Lithium pyrophosphate
- b) Coenzyme A
- c) NAD+
- d) FMN
Explanation:
The conversion of lactic acid to pyruvic acid is catalyzed by the enzyme Lactate Dehydrogenase (LDH). This reaction requires NAD+ (Nicotinamide Adenine Dinucleotide) as a hydrogen carrier, which is reduced to NADH. NAD+ is derived from Vitamin B3 (Niacin).
Why other options are incorrect:
Why other options are incorrect:
- • Lithium pyrophosphate: This is not a standard biological cofactor; it is likely a distractor for Thiamine pyrophosphate (TPP).
- • Coenzyme A: CoA is involved in the transfer of acyl groups (like in Acetyl-CoA), not in the simple dehydrogenation of lactate to pyruvate.
- • FMN: Flavin Mononucleotide is a carrier found in the respiratory chain (Complex I) and some oxidases, but it is not the cofactor for Lactate Dehydrogenase.
Physiological glycosuria is met with in:
- a) Renal glycosuria
- b) Alimentary glycosuria
- c) Diabetes Mellitus
- d) Alloxan diabetes
Explanation:
Alimentary glycosuria is considered a physiological condition. It occurs in healthy individuals after the ingestion of a very large amount of carbohydrates. The rapid absorption of glucose exceeds the renal threshold (approximately 180 mg/dL) temporarily, leading to the appearance of glucose in the urine despite there being no underlying disease.
Why other options are incorrect:
Why other options are incorrect:
- • Renal glycosuria: This is a condition where the renal threshold for glucose is lower than normal due to a defect in the renal tubules; while often benign, it is categorized as a renal abnormality rather than a standard physiological response.
- • Diabetes Mellitus: This is a pathological glycosuria caused by insulin deficiency or resistance leading to chronic hyperglycemia.
- • Alloxan diabetes: This refers to diabetes experimentally induced in laboratory animals using the chemical alloxan, which destroys pancreatic beta cells; it is purely pathological.
Two examples of substrate level phosphorylation in EM pathway (Glycolysis) of glucose metabolism are in the reactions of:
- a) 1,3 bisphosphoglycerate and phosphoenol pyruvate
- b) Glucose-6 phosphate and Fructo-6-phosphate
- c) 3 phosphoglyceraldehyde and phosphoenolpyruvate
- d) 1,3 diphosphoglycerate and 2-phosphoglycerate
Explanation:
Substrate-level phosphorylation is the direct formation of ATP from ADP and a high-energy intermediate. In the Embden-Meyerhof (EM) pathway, this occurs at two steps:
Why other options are incorrect:
- When 1,3-bisphosphoglycerate is converted to 3-phosphoglycerate by phosphoglycerate kinase.
- When phosphoenolpyruvate (PEP) is converted to pyruvate by pyruvate kinase.
Why other options are incorrect:
- • Glucose-6 phosphate / Fructo-6-phosphate: These reactions involve isomerization and phosphorylation that consume ATP (in the preparatory phase), rather than producing it.
- • 3 phosphoglyceraldehyde: This is a reactant in the oxidation step that produces NADH, but it does not directly donate a phosphate to ADP to form ATP.
- • 2-phosphoglycerate: This is an intermediate formed from 3-phosphoglycerate; the reaction does not involve the production of energy in the form of ATP.
The number of molecules of ATP produced by the total oxidation of acetyl CoA in TCA cycle is:
- a) 6
- b) 8
- c) 10
- d) 12
Explanation:
In the total oxidation of one molecule of Acetyl CoA via the TCA cycle and oxidative phosphorylation, the energy yield (based on traditional biochemical calculations) is 12 ATP:
Why other options are incorrect:
- 3 NADH: Yields 9 ATP (3 ATP per NADH)
- 1 FADH2: Yields 2 ATP (2 ATP per FADH2)
- 1 GTP: Yields 1 ATP (Substrate-level phosphorylation)
- Total: 9 + 2 + 1 = 12 ATP.
Why other options are incorrect:
- • 6 / 8: These numbers do not correspond to the complete oxidation of Acetyl CoA in the mitochondria.
- • 10: This is the modern revised yield based on updated P:O ratios. However, in the context of most standard medical MCQs where 12 is an option, 12 is usually the expected traditional answer.
Substrate level phosphorylation in TCA cycle is in the step catalyzed by:
- a) Isocitrate dehydrogenase
- b) Malate dehydrogenase
- c) Aconitase
- d) Succinate thiokinase
Explanation:
The only step in the TCA cycle that involves substrate-level phosphorylation is the conversion of Succinyl-CoA to Succinate. This reaction is catalyzed by Succinate thiokinase (also known as Succinyl-CoA synthetase). During this step, the high-energy thioester bond of Succinyl-CoA is cleaved to generate GTP (or ATP), which is a direct form of cellular energy.
Why other options are incorrect:
Why other options are incorrect:
- • Isocitrate dehydrogenase: This enzyme catalyzes an oxidative decarboxylation that produces NADH, not a direct phosphate transfer to a nucleoside.
- • Malate dehydrogenase: This enzyme catalyzes the oxidation of malate to oxaloacetate, which produces NADH.
- • Aconitase: This is an isomerase enzyme that simply rearranges citrate into isocitrate; it does not produce any energy carriers.
Fatty acids cannot be converted into carbohydrates in the body as the following reaction is not possible:
- a) Conversion of glucose-6-phosphate into glucose
- b) Fructose 1,6-bisphosphate to fructose-6-phosphate
- c) Transformation of acetyl CoA to pyruvate
- d) Formation of acetyl CoA from fatty acids
Explanation:
In the human body, fatty acids are broken down into Acetyl CoA through beta-oxidation. While Acetyl CoA can enter the TCA cycle, it cannot be used for the net synthesis of glucose because the Pyruvate Dehydrogenase (PDH) reaction (which converts Pyruvate to Acetyl CoA) is irreversible. Humans lack the enzymes (the glyoxylate shunt) to bypass this step and turn Acetyl CoA back into Pyruvate or Oxaloacetate for gluconeogenesis.
Why other options are incorrect:
Why other options are incorrect:
- • Glucose-6-phosphate to glucose: This reaction is perfectly possible and is catalyzed by the enzyme Glucose-6-phosphatase in the liver.
- • Fructose 1,6-bisphosphate to fructose-6-phosphate: This is a key regulatory step in gluconeogenesis, catalyzed by Fructose-1,6-bisphosphatase.
- • Acetyl CoA from fatty acids: This is the standard process of Beta-oxidation, which happens continuously in the mitochondria to produce energy from fat.
Tissues form lactic acid from glucose. This phenomenon is termed as:
- a) Aerobic glycolysis
- b) Oxidation
- c) Oxidative phosphorylation
- d) Anaerobic glycolysis
Explanation:
Anaerobic glycolysis is the transformation of glucose to lactate (lactic acid) when limited amounts of oxygen are available. This commonly occurs in muscle tissues during intense exercise.
Why other options are incorrect:
Why other options are incorrect:
- • Aerobic glycolysis: This process occurs in the presence of oxygen and typically results in pyruvate, which then enters the Krebs cycle.
- • Oxidation: This is a broad chemical term referring to the loss of electrons; while glycolysis involve redox reactions, it is not the name of the specific pathway that produces lactic acid.
- • Oxidative phosphorylation: This is the final stage of cellular respiration occurring in the mitochondria where ATP is formed using energy from the electron transport chain.
One molecule of glucose gives __ molecules of CO2 in EM-TCA cycle.
- a) 6
- b) 3
- c) 1
- d) 2
Explanation:
A single molecule of glucose contains 6 carbon atoms. During complete aerobic respiration (Glycolysis followed by the TCA cycle), all 6 carbon atoms are eventually oxidized and released as 6 molecules of CO2 (2 during the transition reaction and 4 during the TCA cycle itself).
Why other options are incorrect:
Why other options are incorrect:
- • 3: This represents the number of CO2 molecules released from only one molecule of pyruvate, not a whole glucose molecule.
- • 1: A single molecule of glucose is far more complex and yields multiple CO2 molecules during decarboxylation steps.
- • 2: Two molecules of CO2 are released per turn of the TCA cycle, but since one glucose produces two pyruvates, the cycle turns twice.
One molecule of glucose gives __ molecules of CO2 in one round of HMP shunt.
- a) 6
- b) 1
- c) 2
- d) 3
Explanation:
In the HMP shunt (also known as the Pentose Phosphate Pathway), the oxidative phase involves the conversion of Glucose-6-phosphate to Ribulose-5-phosphate. During this process, one carbon atom is removed from each glucose molecule and released as one molecule of CO2.
Why other options are incorrect:
Why other options are incorrect:
- • 6: This is the total number of CO2 molecules produced if glucose underwent complete oxidation via Glycolysis and the TCA cycle.
- • 2 or 3: The stoichiometry of the oxidative phase of the HMP shunt specifically results in the release of only one carbon atom (as CO2) per glucose molecule processed.
The 4 rate limiting enzymes of gluconeogenesis are:
- a) Glucokinase, Pyruvate carboxylase, phosphoenol pyruvate carboxykinase and glucose-6-phosphatase
- b) Pyruvate carboxylase, phosphoenol pyruvate carboxykinase, fructose 1,6 diphosphatase and glucose-6-phosphatase
- c) Pyruvate kinase, pyruvate carboxylase, phosphoenol pyruvate carboxykinase and glucose-6-phosphatase
- d) Phospho fructokinase, pyruvate carboxylase, phosphoenol pyruvate carboxykinase and fructose 1, 6 diphosphatase
Explanation:
Gluconeogenesis is the process of synthesizing glucose from non-carbohydrate precursors. It must bypass the three irreversible steps of glycolysis using four specific enzymes:
1. Pyruvate carboxylase
2. Phosphoenolpyruvate carboxykinase (PEPCK)
3. Fructose 1,6-bisphosphatase
4. Glucose-6-phosphatase.
Why other options are incorrect:
Why other options are incorrect:
- • Glucokinase: This is a glycolytic enzyme (catalyzes glucose to glucose-6-phosphate), not a gluconeogenic one.
- • Pyruvate kinase: This is the final enzyme of glycolysis; gluconeogenesis uses Pyruvate carboxylase and PEPCK to bypass this step.
- • Phosphofructokinase (PFK): This is the key rate-limiting enzyme of glycolysis, whereas gluconeogenesis uses Fructose 1,6-bisphosphatase for the reverse reaction.
For glycogenesis, Glucose should be converted to:
- a) Glucuronic acid
- b) Pyruvic acid
- c) UDP glucose
- d) Sorbitol
Explanation:
UDP-glucose (Uridine diphosphate glucose) is the “activated” form of glucose required for glycogenesis. The enzyme glycogen synthase can only add glucose units to a growing glycogen chain if the glucose is donated by UDP-glucose.
Why other options are incorrect:
Why other options are incorrect:
- • Glucuronic acid: This is formed in the Uronic Acid Pathway and is used for detoxification and the synthesis of glycosaminoglycans.
- • Pyruvic acid: This is the end product of glycolysis, which is the breakdown of glucose for energy, not the storage of glucose.
- • Sorbitol: This is produced via the polyol pathway; while it is a derivative of glucose, it is not involved in the synthesis of glycogen.
Fluoride inhibits __ and arrests glycolysis.
- a) Glyceraldehyde-3-phosphate dehydrogenase
- b) Aconitase
- c) Enolase
- d) Succinate dehydrogenase
Explanation:
Fluoride (specifically sodium fluoride) inhibits the enzyme Enolase. It does this by forming a complex with magnesium and phosphate, which removes the magnesium ions ($Mg^{2+}$) required as a cofactor for the enzyme’s activity, effectively stopping glycolysis. This is why fluoride is added to blood collection tubes for glucose estimation.
Why other options are incorrect:
Why other options are incorrect:
- • Glyceraldehyde-3-phosphate dehydrogenase: This enzyme is inhibited by iodoacetate, not fluoride.
- • Aconitase: This is an enzyme of the TCA cycle (not glycolysis) and is inhibited by fluoroacetate.
- • Succinate dehydrogenase: This is an enzyme of the TCA cycle and is inhibited by malonate through competitive inhibition.
One of the following statement is correct:
- a) Glycogen synthase ‘a’ is the phosphorylated
- b) cAMP converts glycogen synthase b to ‘a’
- c) Insulin converts glycogen synthase b to a
- d) UDP glucose molecules interact and grow into a Glycogen tree
Explanation:
Insulin promotes the storage of glucose as glycogen. It triggers the dephosphorylation of glycogen synthase (converting the inactive ‘b’ form into the active ‘a’ form) through the activation of protein phosphatase-1 and the inhibition of Glycogen Synthase Kinase-3 (GSK3).
Why other options are incorrect:
Why other options are incorrect:
- • Option a: Glycogen synthase ‘a’ is the dephosphorylated (active) form. The ‘b’ form is the phosphorylated (inactive) form.
- • Option b: cAMP activates Protein Kinase A, which phosphorylates glycogen synthase, converting the active ‘a’ form to the inactive ‘b’ form (stopping glycogenesis).
- • Option d: UDP-glucose molecules do not interact spontaneously; they require the enzyme Glycogen synthase to add units to a primer and the Branching enzyme to create the “tree” structure.
Amylo 1, 6 glucosidase is called:
- a) Branching enzyme
- b) Debranching enzyme
- c) Glucantransferase
- d) Phosphorylase
Explanation:
The Debranching enzyme is a bifunctional enzyme that handles the breakdown of glycogen branches. One of its activities is Amylo-1,6-glucosidase, which specifically hydrolyzes the $\alpha(1 \to 6)$ glycosidic bond at the branch point, releasing a free glucose molecule.
Why other options are incorrect:
Why other options are incorrect:
- • Branching enzyme: Also known as Amylo-(1,4 $\to$ 1,6)-transglycosylase, this enzyme creates branches rather than removing them.
- • Glucantransferase: This is the other activity of the debranching enzyme (4-alpha-D-glucanotransferase) which moves a tri-saccharide unit from one branch to another.
- • Phosphorylase: Glycogen phosphorylase only breaks $\alpha(1 \to 4)$ bonds; it cannot act on the $\alpha(1 \to 6)$ bonds at branch points.
Glucose enters the cells by:
- a) Insulin independent transport
- b) Insulin dependent transport
- c) Enzyme mediated transport
- d) Both (insulin independent transport) and (insulin dependent transport)
Explanation:
Glucose entry into cells occurs through two main mechanisms depending on the tissue type:
Why other options are incorrect:
- Insulin-Dependent: Occurs primarily in skeletal muscle and adipose tissue via GLUT4 transporters, which require insulin to move to the cell surface.
- Insulin-Independent: Occurs in the brain, liver, red blood cells, and kidneys via other transporters like GLUT1, GLUT2, and GLUT3, or via SGLT (sodium-glucose linked transporters) in the intestines and renal tubules.
Why other options are incorrect:
- • Option a & b: These are individually true but incomplete, as the body utilizes both mechanisms.
- • Option c: Glucose transport is mediated by transporter proteins (carriers), not enzymes. While enzymes like Hexokinase process glucose after it enters, the transport itself is a physical translocation process.
Glycogen while being acted upon by active phosphorylase is converted first to:
- a) Glucose
- b) Glucose 1-phosphate and Glycogen with 1 carbon less
- c) Glucose-6-phosphate and Glycogen with 1 carbon less
- d) 6-Phosphogluconic acid
Explanation:
The enzyme Glycogen phosphorylase catalyzes the phosphorolytic cleavage (phosphorolysis) of the $\alpha(1 \to 4)$ glycosidic linkages in glycogen. This reaction uses inorganic phosphate to release glucose units one by one in the form of Glucose 1-phosphate, leaving the remaining glycogen chain shorter by one glucose molecule.
Why other options are incorrect:
Why other options are incorrect:
- • Glucose: Free glucose is only released during glycogenolysis by the “debranching enzyme” ($\alpha-1,6$-glucosidase activity) at the branch points.
- • Glucose-6-phosphate: This is formed in the next step of the pathway, where Phosphoglucomutase converts Glucose 1-phosphate into Glucose 6-phosphate.
- • 6-Phosphogluconic acid: This is an intermediate in the Pentose Phosphate Pathway (HMP Shunt), not a product of glycogen breakdown.
When O2 supply is inadequate, pyruvate is converted to:
- a) Phosphopyruvate
- b) Acetyl CoA
- c) Lactate
- d) Alanine
Explanation:
Under anaerobic conditions (inadequate oxygen), the enzyme Lactate Dehydrogenase (LDH) converts pyruvate to Lactate. This reaction is crucial because it regenerates $NAD^+$ from $NADH$, allowing glycolysis to continue and produce ATP even without oxygen.
Why other options are incorrect:
Why other options are incorrect:
- • Phosphopyruvate: Also known as PEP, this is the precursor to pyruvate in glycolysis, not a product of pyruvate.
- • Acetyl CoA: Pyruvate is converted to Acetyl CoA only when oxygen is adequate, so it can enter the TCA cycle in the mitochondria.
- • Alanine: Pyruvate can be converted to Alanine via transamination, but this is a pathway for amino acid metabolism rather than a direct response to oxygen debt.
Reactivation of inactive liver phosphorylase is normally favoured by:
- a) Insulin
- b) Epinephrine
- c) ACTH
- d) Glucagon
Explanation:
Glucagon is the primary hormone that stimulates glycogen breakdown (glycogenolysis) in the liver. It binds to its receptor, increasing intracellular cAMP, which activates protein kinase A. This kinase then activates phosphorylase kinase, which finally phosphorylates (reactivates) liver phosphorylase.
Why other options are incorrect:
Why other options are incorrect:
- • Insulin: This hormone promotes glycogen synthesis and favors the inactivation of phosphorylase through dephosphorylation.
- • Epinephrine: While it can activate liver phosphorylase during “fight or flight” responses, it is primarily the major regulator of muscle phosphorylase. Glucagon is the more specific “normal” regulator for liver glycogen.
- • ACTH: Adrenocorticotropic hormone acts on the adrenal cortex to stimulate the release of cortisol; it does not have a direct mechanism for reactivating liver phosphorylase.
Before pyruvic acid enters the TCA cycle it must be converted to:
- a) Acetyl CoA
- b) Lactate
- c) α-ketoglutarate
- d) Citrate
Explanation:
Pyruvate (pyruvic acid) is the end product of glycolysis in the cytoplasm. To enter the TCA cycle (Kreb’s cycle) in the mitochondria, it must undergo oxidative decarboxylation to form Acetyl CoA. This “bridge” or “link” reaction is catalyzed by the Pyruvate Dehydrogenase Complex (PDC).
Why other options are incorrect:
Why other options are incorrect:
- • Lactate: Pyruvate is converted to lactate only under anaerobic conditions; this does not lead into the TCA cycle.
- • α-ketoglutarate: This is an intermediate within the TCA cycle itself, but it is not the entry molecule for pyruvate.
- • Citrate: Citrate is the first product of the TCA cycle, formed when Acetyl CoA condenses with oxaloacetate. Pyruvate must become Acetyl CoA first before citrate can be made.
The hydrolysis of Glucose-6-phosphate is catalysed by a specific phosphatase which is found only in:
- a) Liver, intestines and kidneys
- b) Brain, spleen and adrenals
- c) Striated muscle
- d) Plasma
Explanation:
The enzyme Glucose-6-phosphatase is essential for releasing free glucose into the blood. It is found in the liver, kidneys, and intestinal mucosa. These are the primary organs capable of performing gluconeogenesis and glycogenolysis to maintain systemic blood glucose levels.
Why other options are incorrect:
Why other options are incorrect:
- • Striated muscle: Muscle lacks Glucose-6-phosphatase. Therefore, muscle glycogen can only be used locally for energy (glycolysis) and cannot be converted to free glucose to raise blood sugar levels.
- • Brain, spleen and adrenals: These tissues lack the enzyme; they are consumers of glucose rather than producers for the rest of the body.
- • Plasma: Enzymes involved in intracellular metabolism like phosphatases are not functionally active in the plasma for glucose regulation.
The formation of citrate from oxalo acetate and acetyl CoA is:
- a) Oxidation
- b) Reduction
- c) Condensation
- d) Hydrolysis
Explanation:
The first step of the TCA cycle is a condensation reaction catalyzed by the enzyme Citrate Synthase. It involves the joining of the 2-carbon Acetyl group from Acetyl CoA with the 4-carbon Oxaloacetate to form the 6-carbon Citrate.
Why other options are incorrect:
Why other options are incorrect:
- • Oxidation & Reduction: While the TCA cycle as a whole involves several redox (oxidation-reduction) steps where $NAD^+$ is reduced to $NADH$, this specific first step is a synthetic condensation, not a redox reaction.
- • Hydrolysis: Although the thioester bond of Acetyl CoA is hydrolyzed during this process to release the CoA-SH molecule, the primary classification of the reaction that builds the citrate molecule is a condensation.
Which one of the following is a rate limiting enzyme of gluconeogenesis?
- a) Hexokinase
- b) Phosphofructokinase
- c) Pyruvate carboxylase
- d) Pyruvate kinase
Explanation:
Pyruvate carboxylase is one of the four key rate-limiting enzymes of gluconeogenesis. It catalyzes the conversion of pyruvate to oxaloacetate in the mitochondria. This is the first “bypass” reaction required to overcome the irreversible nature of the final step of glycolysis.
Why other options are incorrect:
Why other options are incorrect:
- • Hexokinase: This is a rate-limiting enzyme for glycolysis (the breakdown of glucose), not gluconeogenesis.
- • Phosphofructokinase: This is the primary regulatory and rate-limiting enzyme of glycolysis.
- • Pyruvate kinase: This is the final enzyme of glycolysis. In gluconeogenesis, this step is bypassed by Pyruvate carboxylase and PEPCK.
The number of ATP produced in the succinate dehydrogenase step is:
- a) 1
- b) 2
- c) 3
- d) 4
Explanation:
The succinate dehydrogenase step in the TCA cycle involves the oxidation of succinate to fumarate. During this process, FAD is reduced to FADH₂. In the Electron Transport Chain, each molecule of FADH₂ yields approximately 2 ATP (classically calculated; 1.5 ATP in modern bioenergetics).
Why other options are incorrect:
Why other options are incorrect:
- • 1: One ATP (or GTP) is produced via substrate-level phosphorylation in the previous step (Succinyl CoA to Succinate), but not by succinate dehydrogenase.
- • 3: Three ATP molecules are produced from NADH (formed in steps like Isocitrate Dehydrogenase or Malate Dehydrogenase), not FADH₂.
- • 4: There is no single step in the TCA cycle that directly or indirectly produces 4 ATP molecules from one substrate molecule.
Which of the following reaction gives lactose?
- a) UDP galactose and glucose
- b) UDP glucose and galactose
- c) Glucose and Galactose
- d) Glucose, Galactose and UTP
Explanation:
Lactose is synthesized in the mammary glands by the enzyme Lactose Synthase. This reaction requires the activated form of galactose, which is UDP-galactose, to react with a molecule of D-glucose.
Why other options are incorrect:
Why other options are incorrect:
- • UDP glucose and galactose: UDP-glucose is used in glycogen synthesis and the uronic acid pathway, but it is not the donor of the sugar moiety for lactose synthesis.
- • Glucose and Galactose: These are the simple monosaccharides that result from the breakdown (hydrolysis) of lactose, but they cannot spontaneously join together without activation (UDP).
- • Glucose, Galactose and UTP: While UTP is necessary to activate galactose into UDP-galactose in previous steps, the direct enzymatic reaction that produces lactose specifically uses the UDP-galactose intermediate.
UDP Glucuronic acid is required for the biosynthesis of:
- a) Chondroitin sulphates
- b) Glycogen
- c) Lactose
- d) Starch
Explanation:
UDP-glucuronic acid is an essential intermediate in the uronic acid pathway. It serves as the donor of glucuronic acid for the synthesis of glycosaminoglycans (GAGs) like Chondroitin sulphate, Hyaluronic acid, and Heparin. It is also vital for the detoxification of bilirubin and various drugs in the liver.
Why other options are incorrect:
Why other options are incorrect:
- • Glycogen: The biosynthesis of glycogen (glycogenesis) requires UDP-glucose as the building block.
- • Lactose: Lactose synthesis in the mammary glands requires UDP-galactose and glucose.
- • Starch: Starch is a plant polysaccharide; its synthesis typically involves ADP-glucose rather than UDP-glucuronic acid.
Which one of the following can convert glucose to vitamin C?
- a) Albino rats
- b) Humans
- c) Monkeys
- d) Guinea pigs
Explanation:
Most mammals, including albino rats, can synthesize Vitamin C (ascorbic acid) from glucose via the Uronic Acid pathway. The process involves the conversion of glucose to L-gulonolactone, which is then converted to ascorbic acid by the enzyme L-gulonolactone oxidase.
Why other options are incorrect:
Why other options are incorrect:
- • Humans, Monkeys, and Guinea pigs: These species lack the gene for the enzyme L-gulonolactone oxidase due to an evolutionary mutation. Therefore, they cannot synthesize Vitamin C and must obtain it from their diet.
Which one of the following cannot convert glucose to Vitamin C?
- a) Albino rats
- b) Dogs
- c) Monkeys
- d) Cows
Explanation:
Monkeys (along with humans, apes, and guinea pigs) cannot synthesize Vitamin C from glucose. This is because they lack the final enzyme in the uronic acid pathway, L-gulonolactone oxidase, which is necessary to convert L-gulonolactone into ascorbic acid.
Why other options are incorrect:
Why other options are incorrect:
- • Albino rats, Dogs, and Cows: Most mammals possess the functional L-gulonolactone oxidase enzyme in their liver or kidneys, allowing them to produce sufficient Vitamin C internally to meet their biological needs.
Transketolase has the coenzyme:
- a) NAD+
- b) FP
- c) TPP
- d) Pyridoxol phosphate
Explanation:
Transketolase is a key enzyme in the Pentose Phosphate Pathway (HMP Shunt). It requires TPP (Thiamine Pyrophosphate), the active form of Vitamin B1, as a coenzyme to transfer two-carbon units from a ketose to an aldose. Measuring erythrocyte transketolase activity is often used as a clinical test for thiamine deficiency.
Why other options are incorrect:
Why other options are incorrect:
- • NAD+: This coenzyme is used by dehydrogenases involved in redox reactions, such as Lactate dehydrogenase or Malate dehydrogenase.
- • FP (Flavoprotein/FAD): These serve as electron carriers for enzymes like Succinate dehydrogenase in the TCA cycle.
- • Pyridoxol phosphate (PLP): This is the active form of Vitamin B6 and is primarily required for transamination and decarboxylation reactions in amino acid metabolism.
Two conditions in which gluconeogenesis is increased are:
- a) Diabetes mellitus and atherosclerosis
- b) Fed condition and thyrotoxicosis
- c) Diabetes mellitus and Starvation
- d) Alcohol intake and cigarette smoking
Explanation:
Gluconeogenesis is the process of synthesizing glucose from non-carbohydrate sources. It increases during Starvation to maintain blood glucose levels for the brain, and in Diabetes Mellitus because the lack of insulin (or insulin resistance) fails to suppress glucose production in the liver.
Why other options are incorrect:
Why other options are incorrect:
- • Atherosclerosis: This is a vascular disease involving plaque buildup and does not directly stimulate glucose production.
- • Fed condition: In a fed state, high insulin levels actually inhibit gluconeogenesis to prevent blood sugar from rising too high.
- • Alcohol intake: Alcohol metabolism actually inhibits gluconeogenesis by depleting NAD+, which can lead to hypoglycemia.
- • Cigarette smoking: While harmful to health, it is not a primary physiological trigger for the gluconeogenesis pathway.
Acetyl CoA is not used for the synthesis of:
- a) Fatty acid
- b) Cholesterol
- c) Pyruvic acid
- d) Citric acid
Explanation:
In humans and animals, the conversion of Pyruvic acid to Acetyl CoA (via the Pyruvate Dehydrogenase complex) is irreversible. Therefore, Acetyl CoA cannot be used to synthesize Pyruvic acid.
Why other options are incorrect:
Why other options are incorrect:
- • Fatty acid: Acetyl CoA is the primary building block for long-chain fatty acid synthesis (lipogenesis).
- • Cholesterol: Acetyl CoA provides all the carbon atoms needed for the synthesis of the cholesterol molecule through the mevalonate pathway.
- • Citric acid: In the first step of the Krebs cycle (TCA cycle), Acetyl CoA condenses with oxaloacetate to form Citric acid.
The total glycogen content of the body is about __ gms.
- a) 100
- b) 200
- c) 300
- d) 500
Explanation:
In a healthy adult, the total glycogen content is approximately 500 grams. This is distributed primarily between the muscle (approx. 400g, used for local energy) and the liver (approx. 100g, used to maintain blood glucose levels).
Why other options are incorrect:
Why other options are incorrect:
- • 100: This only accounts for the glycogen stored in the liver, ignoring the much larger pool in the skeletal muscles.
- • 200/300: These values are significant underestimates for an average adult with normal muscle mass in a well-fed state.
The total Glucose in the body is __ gms.
- a) 10–15
- b) 20–30
- c) 40–50
- d) 60–80
Explanation:
The total amount of glucose present in the body at any given time is approximately 20–30 grams. Most of this glucose is found in the blood and extracellular fluids, while smaller amounts are stored in tissues.
Why other options are incorrect:
Why other options are incorrect:
- • 10–15: This is lower than the normal total glucose content of the body.
- • 40–50: This exceeds the usual total amount of glucose present in the body.
- • 60–80: This is much higher than the normal total glucose content.
Answer Key Summary
The questions are typically designed to assess the technical skills and knowledge required for the laboratory profession, including the ability to analyze laboratory test results, perform laboratory procedures, and maintain laboratory equipment.
To prepare for these MCQs, candidates should have a thorough understanding of the key concepts and principles of laboratory science. They should also be familiar with common laboratory equipment and procedures, as well as laboratory safety protocols.
Candidates may also benefit from studying specific laboratory science textbooks or taking online courses that cover the material tested in the MCQs. Additionally, practicing sample MCQs and reviewing the answers can help candidates identify areas where they may need to improve their knowledge or skills.
Overall, the MCQs for lab technologists are designed to be challenging and comprehensive, requiring candidates to demonstrate a high level of proficiency in the field of laboratory science.
📚 This article may have been prepared using trusted medical literature, clinical guidelines, textbooks, and peer-reviewed sources.
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