5301 to 5350 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 5301 to 5350
All amino acids are optically active except:
- a) Glycine
- b) Serine
- c) Threonine
- d) Tryptophan
Explanation:
Glycine is the only amino acid that is not optically active because it lacks a chiral carbon atom. Its side chain (R-group) is a single hydrogen atom, meaning it has two identical hydrogen atoms attached to the alpha-carbon.
Why other options are incorrect:
Why other options are incorrect:
- • Serine, Threonine, and Tryptophan: These all possess a chiral alpha-carbon atom (bonded to four different groups), making them optically active.
Out of 200 different amino acids found in nature, the number of amino acids present in protein:
- a) 20
- b) 25
- c) 40
- d) 35
Explanation:
Although there are over 200 amino acids known in nature, only 20 amino acids are considered “standard” or “proteinogenic” amino acids, meaning they are encoded directly by the genetic code to build proteins.
Why other options are incorrect:
Why other options are incorrect:
- • 25, 40, and 35: These numbers do not correspond to the standard set of amino acids used in ribosomal protein synthesis across living organisms.
Enzyme catalyzed hydrolysis of proteins produces amino acids of the form:
- a) D
- b) L
- c) DL
- d) All of these
Explanation:
Proteins in living organisms are synthesized from L-amino acids. Therefore, when these proteins undergo enzyme-catalyzed hydrolysis (breakdown), they release amino acids in the L-form.
Why other options are incorrect:
Why other options are incorrect:
- • D-form: These are rarely found in nature and are not the primary constituents of biological proteins.
- • DL (Racemic mixture): This would only occur during non-biological, chemical hydrolysis or synthesis, not enzyme-catalyzed biological breakdown.
The ionizable groups of amino acids are at least:
- a) 1
- b) 2
- c) 3
- d) 4
Explanation:
Every amino acid has at least two ionizable groups: the alpha-carboxyl group (-COOH) and the alpha-amino group (-NH₂). Depending on the pH of the solution, these groups can lose or gain protons.
Why other options are incorrect:
Why other options are incorrect:
- • 1: Incorrect, as an amino acid must have both an acidic and basic center to be classified as such.
- • 3 or 4: While some amino acids (like Histidine, Lysine, or Aspartic acid) have an additional ionizable group in their side chain (R-group), the minimum number present in all amino acids is two.
The neutral amino acid is:
- a) Lysine
- b) Proline
- c) Leucine
- d) Histidine
Explanation:
Leucine is a neutral amino acid because its side chain (R-group) is a non-polar hydrocarbon (isobutyl group), which does not carry any charge at physiological pH.
Why other options are incorrect:
Why other options are incorrect:
- • Lysine: This is a basic amino acid due to the presence of an extra amino group in its side chain.
- • Histidine: This is a basic amino acid because its imidazole side chain can be protonated.
- • Proline: While often grouped with non-polar amino acids, it is technically an imino acid, and in the context of standard biochemical classifications, Leucine is the classic example of a simple neutral/non-polar amino acid.
The amino acid containing hydroxyl group:
- a) Alanine
- b) Isoleucine
- c) Arginine
- d) Threonine
Explanation:
Threonine is a polar amino acid that contains a hydroxyl (-OH) group in its side chain, which makes it capable of participating in hydrogen bonding and phosphorylation.
Why other options are incorrect:
Why other options are incorrect:
- • Alanine: Contains a simple methyl (-CH₃) group.
- • Isoleucine: Contains a non-polar hydrocarbon side chain.
- • Arginine: A basic amino acid containing a guanidino group in its side chain.
The sulphur containing amino acid:
- a) Homoserine
- b) Serine
- c) Methionine
- d) Valine
Explanation:
Methionine is one of the two standard proteinogenic amino acids that contain sulphur. Its side chain includes a thioether group (-S-CH₃). (Cysteine is the other one).
Why other options are incorrect:
Why other options are incorrect:
- • Homoserine: This is a non-proteinogenic amino acid and does not contain sulphur.
- • Serine: Contains a hydroxyl (-OH) group instead of sulphur.
- • Valine: Contains a non-polar isopropyl group and no sulphur.
The basic amino acid:
- a) Glycine
- b) Leucine
- c) Histidine
- d) Proline
Explanation:
Histidine is classified as a basic amino acid because its side chain contains an imidazole ring, which can accept a proton and become positively charged at physiological pH.
Why other options are incorrect:
Why other options are incorrect:
- • Glycine: A non-polar, neutral amino acid with a hydrogen atom as its side chain.
- • Leucine: A non-polar, neutral amino acid with an isobutyl side chain.
- • Proline: A non-polar, neutral amino acid (technically an imino acid) with a cyclic structure.
The amino acid which synthesizes many hormones:
- a) Valine
- b) Phenyl alanine
- c) Alanine
- d) Histidine
Explanation:
Phenylalanine is a precursor for the amino acid Tyrosine, which is further used to synthesize several critical hormones and neurotransmitters, including Thyroxine (thyroid hormone), Adrenaline (epinephrine), and Noradrenaline (norepinephrine).
Why other options are incorrect:
Why other options are incorrect:
- • Valine: An essential branched-chain amino acid involved primarily in energy production and muscle metabolism.
- • Alanine: Primarily involved in the glucose-alanine cycle and nitrogen transport.
- • Histidine: While it is the precursor to histamine (a signaling molecule/neurotransmitter), it is not the primary building block for the wide array of thyroid and catecholamine hormones derived from Phenylalanine.
Amino acids are insoluble in
- a) Acetic acid
- b) Chloroform
- c) Ethanol
- d) Benzene
Explanation:
Amino acids are generally insoluble in non-polar organic solvents such as chloroform. They are more soluble in water and polar solvents due to their ionic nature.
Why other options are incorrect:
Why other options are incorrect:
- • Acetic acid: Amino acids can dissolve in acidic polar media.
- • Ethanol: Many amino acids have some solubility in polar alcohols.
- • Benzene: Benzene is also a non-polar solvent, and amino acids are poorly soluble in it.
The major end product of protein nitrogen metabolism in man is:
- a) Glycine
- b) Uric acid
- c) Urea
- d) NH3
Explanation:
In humans, the nitrogen derived from the catabolism of amino acids is converted into urea in the liver through the urea cycle. Urea is then excreted by the kidneys as the primary nitrogenous waste product.
Why other options are incorrect:
Why other options are incorrect:
- • Glycine: This is a standard amino acid used to build proteins, not a waste product.
- • Uric acid: This is the end product of purine (nucleotide) metabolism, not protein metabolism.
- • NH3 (Ammonia): While toxic ammonia is produced during deamination, it is rapidly converted into urea in the liver because ammonia is highly toxic to the human body.
An amino acid not involved in urea cycle is:
- a) Arginine
- b) Histidine
- c) Ornithine
- d) Citrulline
Explanation:
The Urea cycle involves Ornithine, Citrulline, Argininosuccinate, and Arginine. Histidine is a proteinogenic amino acid and is not a functional component or intermediate of the urea cycle.
Why other options are incorrect:
Why other options are incorrect:
- • Arginine: It is one of the key intermediates that is cleaved by arginase to produce urea.
- • Ornithine: It acts as a carrier molecule that accepts a carbamoyl group to begin the cycle.
- • Citrulline: It is a critical intermediate formed after the incorporation of the first nitrogen into the cycle.
NH3 is detoxified in brain chiefly as:
- a) Urea
- b) Uric acid
- c) Creatinine
- d) Glutamine
Explanation:
Ammonia (NH₃) is highly toxic to the brain. Because the brain lacks the complete urea cycle, it detoxifies ammonia primarily by combining it with glutamate to form Glutamine, a process catalyzed by the enzyme glutamine synthetase.
Why other options are incorrect:
Why other options are incorrect:
- • Urea: Primarily formed in the liver, not the brain.
- • Uric acid: An end product of purine catabolism, not involved in ammonia detoxification.
- • Creatinine: A breakdown product of creatine phosphate in muscles, not related to ammonia detoxification.
In humans, NH3 is detoxified in liver as:
- a) Creatinine
- b) Uric acid
- c) Urea
- d) Uronic acid
Explanation:
The liver is the primary site for the detoxification of ammonia (NH₃). Through the Urea Cycle, the liver converts toxic ammonia into urea, which is a water-soluble, less toxic compound that can be safely transported in the blood to the kidneys for excretion.
Why other options are incorrect:
Why other options are incorrect:
- • Creatinine: A metabolic waste product from muscle creatine, not a detoxified form of ammonia.
- • Uric acid: The end product of purine catabolism.
- • Uronic acid: A group of sugar acids involved in metabolic pathways like the glucuronic acid pathway, not ammonia detoxification.
The body protein after eighteen years:
- a) Remains unchanged
- b) Is decomposed only slightly at intervals of one month
- c) Is in a constant state of flux
- d) Is used only for energy requirement
Explanation:
Even in an adult (after eighteen years), body proteins are not static. They are in a constant state of dynamic equilibrium or flux, where they are continuously being broken down (degraded) and resynthesized. This turnover allows the body to replace damaged proteins and adapt to changing physiological needs.
Why other options are incorrect:
Why other options are incorrect:
- • Remains unchanged: Protein turnover is a continuous biological process; it never stays static.
- • Decomposed only slightly at intervals: Protein breakdown is a continuous, ongoing process, not a periodic event.
- • Used only for energy: While protein can be used for energy, its primary role is structural and functional (enzymes, hormones, etc.), not just as a fuel source.
The only known physiological methylating agents in the animal organism are:
- a) Choline and betaine
- b) Choline and S-adenosyl methionine
- c) Betaine and S-adenosyl methionine
- d) Dimethyl glycine and betaine
Explanation:
S-adenosyl methionine (SAM) is the most important and universal methyl donor in biological systems. Choline also acts as a methyl donor after it is oxidized to betaine. These two pathways are central to the methylation processes in the animal organism.
Why other options are incorrect:
Why other options are incorrect:
- • Betaine: While it is a methyl donor, the question asks for the primary physiological agents including the most vital one, SAM.
- • Dimethyl glycine: This is a product of betaine metabolism, not a primary methylating agent itself.
In the synthesis of 1 molecule of urea in the Kreb’s-Henseleit cycle, the number of ATPs required is:
- a) 1
- b) 2
- c) 3
- d) 4
Explanation:
The synthesis of one molecule of urea requires 3 ATP molecules. Specifically, 2 ATPs are consumed during the formation of carbamoyl phosphate (by carbamoyl phosphate synthetase I) and 1 ATP is consumed to form argininosuccinate (by argininosuccinate synthetase).
Note: Since 1 ATP is converted to AMP (equivalent to 2 ATPs) in the second step, the total high-energy phosphate bonds consumed is 4, but the total number of ATP molecules required is 3.
Why other options are incorrect:
Note: Since 1 ATP is converted to AMP (equivalent to 2 ATPs) in the second step, the total high-energy phosphate bonds consumed is 4, but the total number of ATP molecules required is 3.
Why other options are incorrect:
- • 1 or 2: These amounts are insufficient to drive the energetic requirements of the urea cycle steps.
- • 4: While 4 high-energy phosphate bonds are consumed, only 3 molecules of ATP are utilized.
For biosynthesis of proteins:
- a) Amino acids only are required
- b) Amino acids and nucleic acids only are required
- c) Amino acid, nucleic acids and ATP only are required
- d) Amino acids, nucleic acids, ATP, GTP, enzymes and activators are required
Explanation:
Protein biosynthesis (translation) is a complex metabolic process. It requires:
Why other options are incorrect:
- • Amino acids: The building blocks.
- • Nucleic acids: mRNA (template), tRNA (adapters), and rRNA (ribosome structure).
- • Energy: ATP (for amino acid activation) and GTP (for initiation, elongation, and termination).
- • Enzymes/Activators: Aminoacyl-tRNA synthetases, initiation/elongation factors, and ribosomes.
Why other options are incorrect:
- • a, b, c: These options are incomplete, as they omit essential components like GTP (necessary for peptide elongation) and the specific enzymes and initiation/elongation factors required to drive the process.
Transmethylation of guanidoacetic acid gives:
- a) Creatine (or Creatine phosphate)
- b) Creatinine
- c) Choline
- d) N-methyl nicotinamide
Explanation:
The synthesis of creatine occurs in two steps. In the second step, guanidoacetic acid undergoes transmethylation by S-adenosyl methionine (SAM) to form Creatine. Creatine is subsequently phosphorylated to form Creatine phosphate in tissues like muscle.
Why other options are incorrect:
Why other options are incorrect:
- • Creatinine: This is a metabolic breakdown product of creatine, not a synthesis product of guanidoacetic acid.
- • Choline: A different molecule entirely involved in lipid metabolism and neurotransmission.
- • N-methyl nicotinamide: A methylated derivative of nicotinamide, which is a different metabolic methylation pathway.
The 2 energy-rich compounds needed for protein biosynthesis are:
- a) ATP and GTP
- b) ATP and UTP
- c) ATP and CTP
- d) ATP and TTP
Explanation:
Both ATP and GTP are required for protein synthesis.
Why other options are incorrect:
- • ATP is primarily used for the activation of amino acids (attaching them to their respective tRNA by aminoacyl-tRNA synthetases).
- • GTP is required for the initiation, the elongation (ribosomal translocation), and the termination of the polypeptide chain.
Why other options are incorrect:
- • UTP, CTP, and TTP: While these are energy-rich nucleotides, they are not the primary energy donors for the specific mechanical steps of ribosomal protein synthesis.
The following ketoacid is involved in fixing dietary NH3 into amino acid:
- a) Pyruvate
- b) Oxaloacetate
- c) Oxalosuccinate
- d) α-ketoglutarate
Explanation:
The enzyme glutamate dehydrogenase catalyzes the incorporation of ammonia (NH₃) into α-ketoglutarate to form glutamate. This is a primary pathway for the assimilation of nitrogen into amino acids in the human body.
Why other options are incorrect:
Why other options are incorrect:
- • Pyruvate: Can form alanine via transamination, but it is not the primary acceptor for fixing free ammonia.
- • Oxaloacetate: Can form aspartate via transamination, but not by fixing free NH₃ directly.
- • Oxalosuccinate: An intermediate in the Citric Acid Cycle, not involved in nitrogen fixation.
The metabolite which sustains (activates) the urea cycle is:
- a) Ornithine
- b) Citrulline
- c) Carbamoyl phosphate
- d) N-acetyl glutamate
Explanation:
N-acetyl glutamate is the essential allosteric activator of the enzyme Carbamoyl Phosphate Synthetase I (CPS-I), which is the rate-limiting step of the urea cycle. Without N-acetyl glutamate, the urea cycle cannot function efficiently to clear ammonia.
Why other options are incorrect:
Why other options are incorrect:
- • Ornithine and Citrulline: These are intermediates (substrates) of the cycle, not the metabolic regulators that sustain its activity.
- • Carbamoyl phosphate: This is a product of the rate-limiting step, not the regulator that turns the cycle “on.”
Tetrahydrofolate can be freed from N5-methyl tetrahydrofolate only by:
- a) Nor-epinephrine
- b) Ethanolamine
- c) Nicotinamide
- d) Vitamin B12
Explanation:
The “methyl trap” hypothesis states that N5-methyl tetrahydrofolate (N5-methyl THF) is a stable form of folate. The only way to remove the methyl group and regenerate free tetrahydrofolate (THF) is through the enzyme methionine synthase, which requires Vitamin B12 (cobalamin) as a coenzyme to transfer the methyl group to homocysteine, forming methionine.
Why other options are incorrect:
Why other options are incorrect:
- • Nor-epinephrine, Ethanolamine, and Nicotinamide: These substances play roles in various metabolic pathways, but they do not act as cofactors for the regeneration of tetrahydrofolate from its methyl-donor form.
Neogenesis of methyl group is:
- a) The availability of methyl group from S-adenosyl methionine
- b) The availability of methyl group from betaine
- c) Interaction between N5, N10 methylene tetrahydrofolate with a NAD+ dependent reductase
- d) Availability of methyl group from methyl B12
Explanation:
“Neogenesis” refers to the biological synthesis of the methyl group. This occurs through the reduction of N5, N10-methylene tetrahydrofolate to N5-methyl tetrahydrofolate, a reaction catalyzed by the enzyme methylene tetrahydrofolate reductase (MTHFR), which is an NADH/NADPH-dependent (often referred to as NAD+ dependent in older textbooks) process. This is the de novo production of a methyl group from a one-carbon unit.
Why other options are incorrect:
Why other options are incorrect:
- • a, b, and d: These options describe the transfer or utilization of existing methyl groups (from donors like SAM, Betaine, or Methyl-B12) rather than the synthesis (neogenesis) of the methyl group itself.
More creatinine is excreted by
- a) Adult males
- b) Adult females
- c) Children
- d) Pregnant women
Explanation:
Adult males generally excrete more creatinine than females because they usually have greater muscle mass. Creatinine is produced from creatine in skeletal muscle and is excreted mainly by the kidneys.
Why other options are incorrect:
Why other options are incorrect:
- • Adult females: Usually have less muscle mass and therefore produce and excrete less creatinine.
- • Children: Generally have less muscle mass than adult males.
- • Pregnant women: Pregnancy does not normally result in greater creatinine excretion than adult males.
A growing peptide in a ribosome can not be shifted to the adjacent ribosome because:
- a) It is firmly attached
- b) It will get the amino acid cleaved
- c) The gap between the ribosomes is too big for a shift
- d) The adjacent ribosomes have different composition
Explanation:
During translation, the growing polypeptide chain is covalently attached to a tRNA molecule (peptidyl-tRNA), which is tightly bound to the ribosome within the P-site. This firm physical linkage ensures that the chain remains associated with the specific ribosome synthesizing it until translation is terminated.
Why other options are incorrect:
Why other options are incorrect:
- • It will get the amino acid cleaved: Peptide bonds are stable during elongation; cleavage is not a factor preventing movement.
- • The gap between the ribosomes is too big: While ribosomes are spaced along the mRNA, the inability to shift is due to the molecular bond, not the physical distance.
- • The adjacent ribosomes have different composition: Ribosomes involved in protein synthesis are generally composed of the same functional subunits; composition does not prevent peptide transfer.
The first amino acid incorporated in a polypeptide in a ribosome of a human is:
- a) N formyl methionine
- b) Methionine
- c) Phenyl alanine
- d) Hydroxy lysine
Explanation:
In eukaryotes, including humans, the translation of mRNA begins with a specialized initiator tRNA that carries Methionine. Therefore, Methionine is always the first amino acid incorporated into a growing polypeptide chain.
Why other options are incorrect:
Why other options are incorrect:
- • N formyl methionine: This is the starting amino acid used by prokaryotes (bacteria) and in mitochondrial/chloroplast translation, not cytoplasmic translation in humans.
- • Phenyl alanine: This is a standard amino acid incorporated later in the chain based on the mRNA codon sequence.
- • Hydroxy lysine: This is a modified amino acid typically found in collagen; it is not used in the initial incorporation process during translation.
The first amino acid incorporated in a polypeptide in a ribosome of a bacterium is:
- a) N formyl methionine
- b) Methionine
- c) Alamine
- d) Glycine
Explanation:
In bacteria (prokaryotes), the initiator tRNA recognizes the AUG start codon and delivers N-formylmethionine (fMet). The formyl group is attached to the amino group of methionine, which serves as the signal to initiate protein synthesis.
Why other options are incorrect:
Why other options are incorrect:
- • Methionine: While used in eukaryotes, in bacteria, the methionine is specifically modified with a formyl group for initiation.
- • Alamine (Alanine): A common amino acid, but it does not serve as the initiation amino acid in ribosomal protein synthesis.
- • Glycine: Like alanine, glycine is a standard amino acid used throughout the protein chain but is not involved in the initiation process.
The integrator between the TCA cycle and urea cycle is:
- a) Fumarate
- b) Malate
- c) Pyruvate
- d) Citrate
Explanation:
The Urea cycle and the TCA cycle (Krebs cycle) are linked via the “Krebs Bicycle.” During the Urea cycle, the enzyme argininosuccinate lyase cleaves argininosuccinate into arginine and fumarate. This fumarate is released and can then enter the TCA cycle, where it is converted to malate and eventually oxaloacetate, bridging the two metabolic pathways.
Why other options are incorrect:
Why other options are incorrect:
- • Malate: While formed from fumarate in the TCA cycle, it is not the direct product released by the Urea cycle.
- • Pyruvate: A central metabolic intermediate, but it does not serve as a direct bridge between these two specific cycles.
- • Citrate: This is an intermediate of the TCA cycle, but it is not involved in the connection to the Urea cycle.
Bence Jones proteinuria is characterized by:
- a) Non-heat coagulability
- b) Heat coagulability at 100°C
- c) Heat coagulability at 45 to 60°C
- d) Precipitation at 25°C
Explanation:
Bence Jones proteins (monoclonal light chains) exhibit a unique thermal property: they precipitate out of solution when the urine is heated to between 45°C and 60°C. Characteristically, this precipitate disappears (redissolves) as the temperature is increased toward boiling (100°C).
Why other options are incorrect:
Why other options are incorrect:
- • Non-heat coagulability: Bence Jones proteins are specifically known for their temperature-dependent precipitation behavior.
- • Heat coagulability at 100°C: Most standard proteins (like albumin) coagulate at 100°C; Bence Jones proteins actually redissolve at this temperature.
- • Precipitation at 25°C: Precipitation of these proteins is strictly heat-dependent and does not occur at room temperature.
Bence Jones proteins may be excreted in urine of patients suffering from:
- a) Tuberculosis
- b) Diabetes mellitus
- c) Multiple myeloma
- d) Hyperthyroidism
Explanation:
Bence Jones proteins are immunoglobulin light chains produced in excess by malignant plasma cells. Their presence in urine is a hallmark clinical finding in patients with Multiple Myeloma, a type of cancer of the plasma cells.
Why other options are incorrect:
Why other options are incorrect:
- • Tuberculosis: Primarily a bacterial infection of the lungs; it does not lead to the monoclonal light chain production found in Bence Jones proteinuria.
- • Diabetes mellitus: Characterized by hyperglycemia and often leads to albuminuria (microalbuminuria), not Bence Jones proteins.
- • Hyperthyroidism: An endocrine disorder involving excess thyroid hormone; it is not related to plasma cell malignancy or protein light chain excretion.
Xanthurenic acid is an abnormal metabolite of:
- a) Xanthine
- b) Uric acid
- c) Tyrosine
- d) Tryptophan
Explanation:
Xanthurenic acid is a metabolite of the amino acid Tryptophan. Under normal conditions, tryptophan is metabolized into niacin. However, when there is a Vitamin B6 (pyridoxine) deficiency, the enzyme kynureninase is inhibited, causing the pathway to divert and accumulate xanthurenic acid, which is then excreted in the urine.
Why other options are incorrect:
Why other options are incorrect:
- • Xanthine/Uric acid: These are products of purine metabolism, not tryptophan metabolism.
- • Tyrosine: This amino acid follows a different catabolic pathway (leading to fumarate and acetoacetate) and does not produce xanthurenic acid.
Pyruvic acid can be obtained by transamination of alanine with:
- a) α- keto glutaric acid
- b) Acetoacetic acid
- c) β−OH butyric acid
- d) Phosphoenol Pyruvic acid
Explanation:
The transamination reaction involves the transfer of an amino group from an amino acid to an α-keto acid. In the case of alanine, the enzyme Alanine Aminotransferase (ALT) transfers the amino group to α-ketoglutaric acid, which results in the formation of pyruvic acid and glutamic acid.
Why other options are incorrect:
Why other options are incorrect:
- • Acetoacetic acid & β-OH butyric acid: These are ketone bodies and are not involved as amino group acceptors in the standard transamination of alanine.
- • Phosphoenol Pyruvic acid (PEP): This is a glycolytic intermediate; while it can be converted to pyruvate, it does not function as an amino group acceptor in a transamination reaction.
Formation of melanin from tyrosine requires the action of:
- a) Dopa decarboxylation
- b) Diamine oxidase
- c) Peroxidase
- d) Tyrosinase
Explanation:
The biosynthesis of melanin begins with the amino acid tyrosine. The enzyme Tyrosinase (a copper-containing enzyme) catalyzes the first two steps: the hydroxylation of tyrosine to L-DOPA and the oxidation of L-DOPA to DOPAquinone. Further non-enzymatic steps then lead to the production of melanin.
Why other options are incorrect:
Why other options are incorrect:
- • Dopa decarboxylation: This leads to the formation of dopamine, a neurotransmitter, not melanin.
- • Diamine oxidase: An enzyme involved in the breakdown of histamine and other polyamines, not melanin synthesis.
- • Peroxidase: While involved in some oxidative processes, it is not the specific enzyme required for the conversion of tyrosine to melanin.
In one of the following the quality of the protein synthesized is affected:
- a) Diabetes mellitus
- b) Gout
- c) Multiple myeloma
- d) Primaquine sensitivity
Explanation:
Multiple myeloma is a malignancy of plasma cells (B-cells) that leads to the uncontrolled production of abnormal, monoclonal immunoglobulin proteins (often referred to as M-proteins or Bence Jones proteins). This represents a direct production of defective or abnormal protein “quality.”
Why other options are incorrect:
Why other options are incorrect:
- • Diabetes mellitus: Primarily a disorder of glucose metabolism and insulin signaling, though it can lead to protein glycation (non-enzymatic).
- • Gout: A metabolic disorder resulting from the deposition of uric acid crystals, related to purine metabolism.
- • Primaquine sensitivity: Caused by a deficiency in the G6PD enzyme; while it involves a defective protein (enzyme), the question traditionally points to the monoclonal protein synthesis seen in myeloma.
Citrulline is an intermediate of:
- a) TCA cycle
- b) Urea cycle
- c) Pentose cycle
- d) Calvin cycle
Explanation:
In the Urea cycle, the enzyme ornithine transcarbamoylase (OTC) catalyzes the reaction between ornithine and carbamoyl phosphate to produce citrulline. Citrulline then moves to the cytoplasm to continue the cycle.
Why other options are incorrect:
Why other options are incorrect:
- • TCA cycle: Involves intermediates like citrate, isocitrate, and alpha-ketoglutarate, but not citrulline.
- • Pentose cycle: Primarily concerned with glucose metabolism and NADPH production; citrulline is not involved.
- • Calvin cycle: A photosynthetic pathway in plants involving carbon fixation; citrulline is not part of this cycle.
The semialdehydes are formed under the action of enzymes characterised as:
- a) Aldolases
- b) Peptidyl lysyl oxidases
- c) Collagenases
- d) Elastases
Explanation:
Peptidyl lysyl oxidase acts on specific lysine or hydroxylysine residues within the collagen or elastin chains. By oxidatively deaminating the ε-amino group of these residues, it converts them into allysine or hydroxyallysine (aminoadipic semialdehyde), which are reactive aldehydes essential for the formation of covalent cross-links that stabilize the protein fibers.
Why other options are incorrect:
Why other options are incorrect:
- • Aldolases: Enzymes that catalyze aldol reactions in glycolysis and the Calvin cycle, not oxidative deamination.
- • Collagenases: Enzymes that specifically break down (cleave) collagen fibers, rather than forming cross-links.
- • Elastases: Proteolytic enzymes that break down elastin, not enzymes involved in its synthesis or cross-linking.
Which of the following statement about the peptide bond is true?
- a) It is a carbon-carbon bond
- b) It has cis hydrogen and oxygen groups
- c) It is planar
- d) It has rotational freedom
Explanation:
The peptide bond is a C-N bond that exhibits partial double-bond character due to resonance between the carbonyl oxygen and the amide nitrogen. This prevents rotation around the C-N bond, causing the six atoms involved (Cα, C, O, N, H, and the next Cα) to lie in the same plane, making the peptide bond planar.
Why other options are incorrect:
Why other options are incorrect:
- • It is a carbon-carbon bond: It is actually a carbon-nitrogen (C-N) bond.
- • It has cis hydrogen and oxygen groups: Due to steric hindrance between side chains, peptide bonds almost always adopt the trans configuration, not cis.
- • It has rotational freedom: Resonance restricts rotation around the C-N bond; rotational freedom exists only at the adjacent bonds (phi and psi).
Isoenzymes for a given reaction:
- a) Have different specificities
- b) Have identical affinities for the same substrate
- c) Exhibit different electrophoretic motilities
- d) Contain similar ratios of different polypeptide chains
Explanation:
Isoenzymes (or isozymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. Because they often possess different net charges or molecular weights, they migrate differently in an electric field, allowing them to be separated and identified by electrophoresis.
Why other options are incorrect:
Why other options are incorrect:
- • Have different specificities: Isoenzymes catalyze the same reaction with the same or similar substrates.
- • Have identical affinities: While they catalyze the same reaction, they often have different Km values (affinities) for the same substrate.
- • Contain similar ratios: Isoenzymes are defined by their structural differences (often different subunit compositions), meaning their chain ratios vary.
The highest concentration of cystine can be found in:
- a) Melanin
- b) Chondroitin sulphate
- c) Myosin
- d) Keratin
Explanation:
Keratin is a fibrous structural protein that is remarkably rich in cysteine residues. These residues form extensive disulfide bridges (cystine) between polypeptide chains, which are responsible for the high degree of strength, rigidity, and resistance to chemical and enzymatic degradation seen in hair, nails, and the outer layer of the skin.
Why other options are incorrect:
Why other options are incorrect:
- • Melanin: A pigment produced from tyrosine; it is not a protein defined by high cysteine content.
- • Chondroitin sulphate: A glycosaminoglycan (carbohydrate-based), not a protein.
- • Myosin: A contractile muscle protein; while it contains cysteine, its concentration is significantly lower than that found in keratins.
One round of Edman degradation of the peptide: H2N— Gly—Arg—Lys—Phe— Asp— COOH would result in which of the following structures or their phenyl isothiocyanate derivatives?
- a) H2N—Gly—Arg—COOH + H2N—Lys— Phe— Asp—COOH
- b) H2N—Gly—Arg—Lys—Phe—COOH + Asp
- c) H2N—Arg—Lys—Phe—Asp—COOH + Gly
- d) H2N—Gly—Arg—Lys—COOH + H2N—Phe —Asp—COOH
Explanation:
Edman degradation uses phenyl isothiocyanate (PITC) to react with the free N-terminal amino group of a peptide. This process selectively cleaves the terminal amino acid as a phenylthiohydantoin (PTH) derivative, leaving the remaining peptide chain (shortened by one amino acid) intact. In the peptide Gly—Arg—Lys—Phe—Asp, Gly is at the N-terminus, so it is cleaved, leaving Arg—Lys—Phe—Asp.
Why other options are incorrect:
Why other options are incorrect:
- • a, b, d: These options incorrectly show the peptide being split in the middle or at the C-terminus, which does not occur with Edman degradation.
Which of the following techniques is used to separate proteins based upon differences in their mass?
- a) Isoelectric focusing
- b) Dialysis
- c) SDS-gel Electrophoresis
- d) Western blotting
Explanation:
SDS-PAGE (Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis) is the standard technique for separating proteins by mass. SDS acts as a detergent that denatures the proteins and imparts a uniform negative charge relative to their mass, so that in an electric field, smaller proteins move faster through the gel matrix than larger ones.
Why other options are incorrect:
Why other options are incorrect:
- • Isoelectric focusing: Separates proteins based on their isoelectric point (pI), which is a charge-based property.
- • Dialysis: Used for purification or buffer exchange based on the ability to pass through a semipermeable membrane, not for high-resolution mass-based separation.
- • Western blotting: An analytical technique used to detect specific proteins after they have already been separated (usually by electrophoresis).
The greatest buffering capacity at physiologic pH would be provided by a protein rich in which of the following amino acids?
- a) Lysine
- b) Histidine
- c) Aspartic acid
- d) Valine
Explanation:
Buffering capacity is greatest when the pH of the solution is close to the pKa of the ionizable group. The imidazole side chain of Histidine has a pKa of approximately 6.0, which is near the physiological pH of 7.4. This allows the side chain to exist in both protonated and deprotonated forms, effectively buffering against changes in pH.
Why other options are incorrect:
Why other options are incorrect:
- • Lysine: The ε-amino group has a pKa of ~10.5, far from physiological pH.
- • Aspartic acid: The side chain carboxyl group has a pKa of ~3.9, which is too acidic for physiological buffering.
- • Valine: This is a non-polar, hydrophobic amino acid with no ionizable side chain, providing no buffering capacity.
Which one of the amino acids could serve as the best buffer at pH 7?
- a) Glutamic acid
- b) Arginine
- c) Valine
- d) Histidine
Explanation:
An amino acid acts as a buffer most effectively when its side-chain pKa is near the target pH (pH = pKa ± 1). The imidazole side chain of Histidine has a pKa of approximately 6.0, which is the closest to the physiological pH of 7.0, making it an excellent buffer in the near-neutral range.
Why other options are incorrect:
Why other options are incorrect:
- • Glutamic acid: Has a side-chain pKa of ~4.2, too acidic for pH 7.
- • Arginine: Has a side-chain pKa of ~12.5, too basic for pH 7.
- • Valine: A non-polar amino acid with no ionizable side chain, offering no buffering capacity in this pH range.
Which one of the following statements concerning glutamine is correct?
- a) Contains three titratable groups
- b) Is classified as an acidic amino acid
- c) Contains an amide group
- d) Migrates to the cathode during electrophoresis at pH 7.0
Explanation:
Glutamine is the amide derivative of glutamic acid. The side chain carboxyl group of glutamic acid is converted into an amide group (-CONH₂). This makes it a neutral, polar amino acid.
Why other options are incorrect:
Why other options are incorrect:
- • Contains three titratable groups: Glutamine has only two (the alpha-amino and alpha-carboxyl groups); the amide group is not titratable.
- • Is classified as an acidic amino acid: Glutamine is neutral because its side-chain carboxyl is amidated, unlike Glutamic acid.
- • Migrates to the cathode at pH 7.0: At pH 7, glutamine is essentially zwitterionic (net charge near zero), so it does not migrate significantly toward the cathode (negative electrode).
One of the given examples is an amino acid:
- a) Oh-Lysine
- b) Protein
- c) Leucine
- d) Serine
Explanation:
Leucine is one of the 20 standard proteinogenic amino acids used by cells to build proteins. While Serine is also an amino acid, Leucine is the most classic example of an essential, non-polar, branched-chain amino acid often cited in introductory biochemistry.
Why other options are incorrect:
Why other options are incorrect:
- • Oh-Lysine (Hydroxylysine): This is a modified amino acid (a derivative) found in collagen, not a standard amino acid.
- • Protein: A polymer made of many amino acids linked together, not an individual amino acid.
- • Serine: While technically an amino acid, in many multiple-choice contexts, Leucine is the preferred answer for “standard” amino acids; if the question implies only one answer, ensure you check your source’s preference.
The lone pair of electrons at one of the ring nitrogens in the given amino acid makes a potential ligand, which is important in binding the iron atoms in hemoglobin:
- a) Tryptophan
- b) Threonine
- c) Histidine
- d) Serine
Explanation:
Histidine contains an imidazole ring. One of the nitrogen atoms in this ring has a lone pair of electrons that acts as a ligand. In hemoglobin, the “proximal histidine” coordinates directly with the iron (Fe²⁺) atom of the heme group, anchoring it to the protein globin chain.
Why other options are incorrect:
Why other options are incorrect:
- • Tryptophan: Contains an indole ring; while it has a nitrogen atom, it is not involved in coordinating iron in hemoglobin.
- • Threonine & Serine: These are polar uncharged amino acids containing hydroxyl (-OH) groups; they do not have the nitrogen-containing ring structure required for this specific ligand-iron binding.
The amino acid which is not optically active is:
- a) Alanine
- b) Glycine
- c) Glutamine
- d) Lysine
Explanation:
Optical activity in amino acids requires the alpha-carbon to be chiral (attached to four different groups). Glycine has a hydrogen atom as its side chain, meaning its alpha-carbon is bonded to two identical hydrogen atoms. Because it lacks a chiral center, it is not optically active.
Why other options are incorrect:
Why other options are incorrect:
- • Alanine, Glutamine, and Lysine: These all have distinct side chains (a methyl group, a glutamine side chain, and a lysine side chain, respectively) attached to the alpha-carbon, which makes the carbon chiral and therefore optically active.
Optically active compounds are capable of:
- a) Different reactions
- b) Rotating plane of polarized light
- c) Showing same chemical properties
- d) None of these
Explanation:
Optical activity is the defining characteristic of chiral molecules. It refers to the ability of a chiral compound to rotate the plane of plane-polarized light when it passes through a solution containing the compound.
Why other options are incorrect:
Why other options are incorrect:
- • Different reactions: While chirality can influence reaction rates with other chiral agents, it does not mean the compounds are inherently capable of “different” general reactions.
- • Showing same chemical properties: Enantiomers (the isomers that cause optical rotation) generally have identical physical and chemical properties in an achiral environment, but this is not the definition of optical activity itself.
The reference compound for absolute configuration of optically active compound is:
- a) Alanine
- b) Lactic acid
- c) Glyceraldehyde
- d) Dihydroxy acetone
Explanation:
Glyceraldehyde is used as the universal reference standard for determining the absolute configuration (D/L system) of carbohydrates, amino acids, and other chiral molecules. By comparing the configuration of a molecule to D- or L-glyceraldehyde, scientists can systematically name and classify its spatial arrangement.
Why other options are incorrect:
Why other options are incorrect:
- • Alanine & Lactic acid: While these are chiral, they were not chosen as the fundamental reference standards for defining the configuration system.
- • Dihydroxy acetone: This molecule is achiral (it has no chiral center), so it cannot serve as a reference for optical activity.
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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