4901 to 4950 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 4901 to 4950
In mammalian tissues, serine can be a biosynthetic precursor of:
- a) Methionine
- b) Glycine
- c) Tryptophan
- d) Phenylalanine
Explanation:
Serine is converted to Glycine by the enzyme serine hydroxymethyltransferase. This reaction is reversible and requires pyridoxal phosphate (PLP) and tetrahydrofolate (THF) as cofactors.
Why other options are incorrect:
Why other options are incorrect:
- • Methionine: This is an essential amino acid that mammals cannot synthesize de novo; it is not directly produced from serine.
- • Tryptophan: This is an essential aromatic amino acid that must be obtained through the diet.
- • Phenylalanine: This is an essential amino acid. While it can be converted into Tyrosine, it cannot be synthesized from serine in mammalian tissues.
A vasodilating compound is produced by the decarboxylation of the amino acid:
- a) Arginine
- b) Aspartic acid
- c) Glutamine
- d) Histidine
Explanation:
The decarboxylation of the amino acid Histidine produces Histamine, a potent vasodilator and mediator of inflammatory and allergic reactions. This reaction is catalyzed by the enzyme histidine decarboxylase.
Why other options are incorrect:
Why other options are incorrect:
- • Arginine: While it is a precursor for Nitric Oxide (a vasodilator), it forms it via oxidation by NO synthase, not by decarboxylation. Decarboxylation of arginine produces agmatine.
- • Aspartic acid: Decarboxylation of aspartic acid primarily produces beta-alanine, which is not a primary vasodilator.
- • Glutamine: Glutamine is usually converted to glutamate; the decarboxylation of glutamate produces GABA, an inhibitory neurotransmitter.
Biuret reaction is specific for
- a) –CONH– linkages
- b) –CSNH2 group
- c) (NH)NH2 group
- d) All of these
Explanation:
The Biuret reaction is specific for peptide bonds (–CONH– linkages). It gives a violet or purple colour when proteins or peptides containing peptide bonds react with copper ions in an alkaline medium.
Why other options are incorrect:
Why other options are incorrect:
- • –CSNH2 group: This is not the functional group responsible for the Biuret reaction.
- • (NH)NH2 group: This group is not specific for the Biuret reaction.
- • All of these: Incorrect because the Biuret reaction is primarily associated with peptide (–CONH–) linkages.
Sakaguchi’s reaction is specific for:
- a) Tyrosine
- b) Proline
- c) Arginine
- d) Cysteine
Explanation:
The Sakaguchi reaction is a specific chemical test used to detect the presence of Arginine. It works by reacting with the guanidino group of arginine using α-naphthol and sodium hypobromite, producing a characteristic red-colored complex.
Why other options are incorrect:
Why other options are incorrect:
- • Tyrosine: This is typically detected using Millon’s test or the Xanthoproteic test due to its phenolic group.
- • Proline: Being an imino acid, it reacts with Ninhydrin to give a yellow color instead of the usual purple/Ruhemann’s purple.
- • Cysteine: This sulfur-containing amino acid is identified using the Lead Acetate test or the Nitroprusside test because of its sulfhydryl (-SH) group.
Millon-Nasse’s reaction is specific for the amino acid:
- a) Tryptophan
- b) Tyrosine
- c) Phenylalanine
- d) Arginine
Explanation:
The Millon-Nasse reaction (commonly known as Millon’s test) is specific for the phenolic group. Among the standard amino acids, only Tyrosine contains a phenol ring, which reacts with Millon’s reagent (mercuric nitrate in nitric acid) to form a brick-red precipitate.
Why other options are incorrect:
Why other options are incorrect:
- • Tryptophan: It contains an indole ring and is typically identified using the Hopkins-Cole test.
- • Phenylalanine: Although it is an aromatic amino acid, it lacks the hydroxyl (-OH) group on its ring that is required to react with Millon’s reagent.
- • Arginine: As noted previously, this amino acid is identified by Sakaguchi’s reaction due to its guanidino group.
Ninhydrin with evolution of CO2 forms a blue complex with:
- a) Peptide bond
- b) α-Amino acids
- c) Serotonin
- d) Histamine
Explanation:
The Ninhydrin reaction is a powerful tool for detecting amino acids. When α-amino acids react with ninhydrin, they undergo oxidative deamination and decarboxylation (releasing CO2 and Ammonia). The ammonia then reacts with another molecule of ninhydrin to form a deep blue/purple complex known as Ruhemann’s purple.
Why other options are incorrect:
Why other options are incorrect:
- • Peptide bond: The Biuret test is the specific test for peptide bonds. While proteins react with Ninhydrin because of their terminal amino groups, the specific evolution of CO2 is the hallmark of free amino acids.
- • Serotonin: This is a biogenic amine. While it may react with ninhydrin to produce color, it lacks the α-carboxyl group required for the characteristic evolution of CO2.
- • Histamine: Like serotonin, histamine is an amine but not an α-amino acid; it does not follow the decarboxylation pathway of this specific test.
The most of the ultraviolet absorption of proteins above 240 nm is due to their content of:
- a) Tryptophan
- b) Aspartate
- c) Glutamate
- d) Alanine
Explanation:
Proteins show a strong ultraviolet absorption maximum at 280 nm. This is primarily due to the aromatic rings of the amino acids Tryptophan and Tyrosine (and to a smaller extent, Phenylalanine). Tryptophan has the highest molar extinction coefficient, making it the dominant contributor to UV absorption in this range.
Why other options are incorrect:
Why other options are incorrect:
- • Aspartate & Glutamate: These are acidic amino acids with no aromatic ring structure; they do not absorb light significantly at 280 nm.
- • Alanine: This is a simple aliphatic amino acid. Like other non-aromatic amino acids, its absorption is restricted to much lower wavelengths (below 220 nm).
Which of the following is a dipeptide?
- a) Anserine
- b) Glutathione
- c) Glucagon
- d) β-Lipoprotein
Explanation:
Anserine (beta-alanyl-N-methylhistidine) is a dipeptide consisting of beta-alanine and 1-methylhistidine. It is found in the skeletal muscle and brain of mammals and birds.
Why other options are incorrect:
Why other options are incorrect:
- • Glutathione: This is a tripeptide (gamma-glutamyl-cysteinyl-glycine) important for preventing damage to important cellular components.
- • Glucagon: This is a polypeptide hormone consisting of a chain of 29 amino acids.
- • β-Lipoprotein: This is a large macromolecular complex (low-density lipoprotein) composed of proteins and lipids, not a simple dipeptide.
Which of the following is a tripeptide?
- a) Anserine
- b) Oxytocin
- c) Glutathione
- d) Kallidin
Explanation:
Glutathione is a tripeptide composed of three amino acids: Glutamate, Cysteine, and Glycine (specifically γ-glutamyl-cysteinyl-glycine). it plays a vital role as an antioxidant in cells.
Why other options are incorrect:
Why other options are incorrect:
- • Anserine: This is a dipeptide (beta-alanyl-N-methylhistidine) found in muscle tissue.
- • Oxytocin: This is a nonapeptide, meaning it consists of a chain of 9 amino acids.
- • Kallidin: This is a decapeptide (10 amino acids) that acts as a potent vasodilator.
A peptide which acts as potent smooth muscle hypotensive agent is:
- a) Glutathione
- b) Bradykinin
- c) Tyrocidine
- d) Gramicidin-s
Explanation:
Bradykinin is a physiologically and pharmacologically active peptide (a nonapeptide). It is an extremely potent vasodilator that causes the relaxation of vascular smooth muscle, leading to a significant drop in blood pressure (hypotensive effect).
Why other options are incorrect:
Why other options are incorrect:
- • Glutathione: This is a tripeptide involved in redox reactions and antioxidant defense, not in blood pressure regulation.
- • Tyrocidine: This is a cyclic decapeptide produced by bacteria that acts as an antibiotic, not a human hypotensive agent.
- • Gramicidin-s: Similar to tyrocidine, this is a cyclic peptide antibiotic that disrupts bacterial membranes; it is not used as a hypotensive agent.
A tripeptide functioning as an important reducing agent in the tissues is:
- a) Bradykinin
- b) Kallidin
- c) Tyrocidin
- d) Glutathione
Explanation:
Glutathione (GSH) is a tripeptide composed of glutamate, cysteine, and glycine. It serves as a crucial reducing agent and antioxidant in cells. The sulfhydryl (-SH) group of the cysteine residue can donate electrons to neutralize reactive oxygen species (free radicals), becoming oxidized to GSSG in the process.
Why other options are incorrect:
Why other options are incorrect:
- • Bradykinin: A nonapeptide (9 amino acids) that primarily functions as a vasodilator to lower blood pressure.
- • Kallidin: A decapeptide (10 amino acids) involved in the kinin-kallikrein system, acting similarly to bradykinin as a vasodilator.
- • Tyrocidin: A cyclic decapeptide that acts as an antibiotic by disrupting bacterial cell membranes; it does not function as a tissue reducing agent.
An example of metalloprotein is:
- a) Casein
- b) Ceruloplasmin
- c) Gelatin
- d) Salmine
Explanation:
Ceruloplasmin is a classic example of a metalloprotein. It is the major copper-carrying protein in the blood and also plays a vital role as an enzyme (ferroxidase) that oxidizes ferrous iron to ferric iron.
Why other options are incorrect:
Why other options are incorrect:
- • Casein: This is a phosphoprotein found in milk, meaning it is conjugated with phosphoric acid rather than a metal ion.
- • Gelatin: This is a derived protein produced by the partial hydrolysis of collagen; it is not a metalloprotein.
- • Salmine: This is a simple protein (specifically a protamine) found in the sperm of salmon fish, characterized by a high arginine content.
Carbonic anhydrase is an example of:
- a) Lipoprotein
- b) Phosphoprotein
- c) Metalloprotein
- d) Chromoprotein
Explanation:
Carbonic anhydrase is a metalloprotein because it contains a tightly bound Zinc (Zn²⁺) ion at its active site. This metal ion is essential for the enzyme’s ability to catalyze the rapid interconversion of carbon dioxide and water into bicarbonate and protons.
Why other options are incorrect:
Why other options are incorrect:
- • Lipoprotein: These are conjugated proteins consisting of a protein combined with a lipid (e.g., HDL or LDL).
- • Phosphoprotein: These are proteins that are chemically bonded to a substance containing phosphoric acid (e.g., Casein).
- • Chromoprotein: These are proteins combined with a colored prosthetic group (e.g., Hemoglobin with heme). While many metalloproteins are colored, Carbonic anhydrase is defined specifically by its functional metal cofactor.
An example of chromoprotein is:
- a) Hemoglobin
- b) Sturine
- c) Nuclein
- d) Gliadin
Explanation:
Hemoglobin is a chromoprotein, which is a conjugated protein containing a pigmented prosthetic group. In hemoglobin, the protein (globin) is combined with heme, an iron-containing porphyrin that gives blood its characteristic red color.
Why other options are incorrect:
Why other options are incorrect:
- • Sturine: This is a protamine (a simple protein) found in the sperm of sturgeon; it is not conjugated with a colored group.
- • Nuclein: This is an older term for nucleoproteins, which are proteins conjugated with nucleic acids, not pigments.
- • Gliadin: This is a prolamin (a simple protein) found in wheat gluten; it is not a conjugated chromoprotein.
An example of scleroprotein is:
- a) Zein
- b) Keratin
- c) Glutenin
- d) Ovoglobulin
Explanation:
Scleroproteins (also known as fibrous proteins) are tough, insoluble, and provide structural support. Keratin is the primary scleroprotein found in hair, nails, skin, feathers, and horns.
Why other options are incorrect:
Why other options are incorrect:
- • Zein: This is a prolamin, a simple protein found in maize (corn).
- • Glutenin: This is a glutelin, a simple protein found in wheat.
- • Ovoglobulin: This is a globulin, a simple globular protein found in egg white.
Casein, the milk protein is:
- a) Nucleoprotein
- b) Chromoprotein
- c) Phosphoprotein
- d) Glycoprotein
Explanation:
Casein is a phosphoprotein. It contains phosphoric acid residues esterified to the hydroxyl groups of the amino acids serine and threonine. In milk, it exists as a calcium salt (calcium caseinate), which is vital for carrying calcium and phosphorus to the infant.
Why other options are incorrect:
Why other options are incorrect:
- • Nucleoprotein: These are proteins conjugated with nucleic acids (DNA or RNA), such as histones or ribosomes.
- • Chromoprotein: These are proteins combined with a colored prosthetic group, like hemoglobin or myoglobin.
- • Glycoprotein: These are proteins that contain oligosaccharide chains (carbohydrates) covalently attached to amino acid side-chains.
An example of phosphoprotein present in egg yolk is:
- a) Ovoalbumin
- b) Ovoglobulin
- c) Ovovitellin
- d) Avidin
Explanation:
Ovovitellin is the principal phosphoprotein found in egg yolk. It contains significant amounts of phosphorus linked to its amino acid structure and exists as a complex with lipids (lipovitellin).
Why other options are incorrect:
Why other options are incorrect:
- • Ovoalbumin: This is the main protein found in egg white (albumen), not the yolk, and it is a glycoprotein.
- • Ovoglobulin: This is a simple globulin protein found in egg white.
- • Avidin: This is a glycoprotein found in egg white known for its extremely high affinity for biotin (Vitamin B7).
A simple protein found in the nucleoproteins of the sperm is:
- a) Prolamine
- b) Protamine
- c) Glutelin
- d) Globulin
Explanation:
Protamines are small, arginine-rich, nuclear proteins that replace histones late in the haploid phase of spermatogenesis. They are essential for the high-level condensation of DNA in the sperm head. Examples include salmine (from salmon) and sturine (from sturgeon).
Why other options are incorrect:
Why other options are incorrect:
- • Prolamine: These are a group of plant storage proteins found in the seeds of cereal grains (e.g., gliadin in wheat, zein in maize).
- • Glutelin: These are also plant storage proteins, soluble in dilute acids or bases, found in grains like rice and wheat.
- • Globulin: These are a general class of globular proteins (like serum globulin or egg ovoglobulin) that are soluble in dilute salt solutions but insoluble in pure water.
Histones are:
- a) Identical to protamine
- b) Proteins rich in lysine and arginine
- c) Proteins with high molecular weight
- d) Insoluble in water and very dilute acids
Explanation:
Histones are highly alkaline proteins found in eukaryotic cell nuclei. They are rich in lysine and arginine, which gives them a positive charge. This allows them to bind tightly to the negatively charged phosphate backbone of DNA to form nucleosomes.
Why other options are incorrect:
Why other options are incorrect:
- • Identical to protamine: While both are basic proteins that bind DNA, protamines are much smaller than histones and specifically replace histones during the final stages of sperm formation.
- • Proteins with high molecular weight: Histones are relatively small proteins (low molecular weight), typically ranging from 11 to 22 kDa.
- • Insoluble in water and very dilute acids: Histones are actually soluble in water and notably soluble in dilute acids (which is why they are often extracted using HCl or H2SO4).
The protein present in hair is:
- a) Keratin
- b) Elastin
- c) Myosin
- d) Tropocollagen
Explanation:
The protein found in hair is Keratin (specifically alpha-keratin). It is a fibrous structural protein (scleroprotein) that is rich in sulfur-containing amino acids like cysteine, which form disulfide bridges to provide strength and insolubility to hair, nails, and the outer layer of skin.
Why other options are incorrect:
Why other options are incorrect:
- • Elastin: This is a highly elastic protein found in connective tissues that allows many tissues in the body to resume their shape after stretching or contracting (e.g., in arteries and lungs).
- • Myosin: This is a motor protein found in muscle fibers that interacts with actin to cause muscle contraction.
- • Tropocollagen: This is the basic structural unit of collagen, found primarily in connective tissues like tendons, ligaments, and bones, rather than hair.
The amino acid from which synthesis of the protein of hair keratin takes place is:
- a) Alanine
- b) Methionine
- c) Proline
- d) Hydroxyproline
Explanation:
Hair keratin is highly characterized by its high content of sulfur-containing amino acids (specifically Cysteine). Since Methionine is an essential sulfur-containing amino acid, it serves as the primary precursor for the synthesis of cysteine via the transsulfuration pathway, which is then incorporated into keratin.
Why other options are incorrect:
Why other options are incorrect:
- • Alanine: While present in most proteins, it does not provide the sulfur groups necessary for the disulfide bridges that give keratin its strength.
- • Proline: Although found in many structural proteins, it is much more characteristic of collagen than the specific chemical properties of hair keratin.
- • Hydroxyproline: This amino acid is almost exclusively associated with Collagen (where it stabilizes the triple helix) and is virtually absent in keratin.
In one molecule of albumin the number of amino acids is
- a) 510
- b) 590
- c) 610
- d) 650
Explanation:
Human serum albumin is a protein consisting of approximately 585 amino acid residues. Among the given options, 590 is the closest standard value.
Why other options are incorrect:
Why other options are incorrect:
- • 510: Lower than the approximate number of amino acid residues in albumin.
- • 610: Higher than the standard value of approximately 585 residues.
- • 650: Significantly higher than the standard value.
Plasma proteins which contain more than 4% hexosamine are classified as:
- a) Microglobulins
- b) Glycoproteins
- c) Mucoproteins
- d) Orosomucoids
Explanation:
Plasma proteins conjugated with carbohydrates are classified based on their carbohydrate content. Mucoproteins (also known as seromucoids) are those that contain more than 4% hexosamine (carbohydrate).
Why other options are incorrect:
Why other options are incorrect:
- • Glycoproteins: While they also contain carbohydrates, the term is generally used for proteins containing less than 4% hexosamine.
- • Microglobulins: These are small globular proteins (like $\beta_2$-microglobulin) defined by their size, not specifically by a high hexosamine percentage.
- • Orosomucoids: This is a specific example of a mucoprotein ($\alpha_1$-acid glycoprotein), but the question asks for the general class of proteins meeting the 4% criteria.
After releasing O2 at the tissues, hemoglobin transports:
- a) CO2 and protons to the lungs
- b) O2 to the lungs
- c) CO2 and protons to the tissue
- d) Nutrients
Explanation:
After unloading oxygen at the tissues, hemoglobin helps transport metabolic waste products. It binds to protons (H+) and Carbon Dioxide (CO2) (forming carbaminohemoglobin) to carry them back to the lungs, where they are eventually expelled. This process is closely related to the Bohr Effect and the Haldane Effect.
Why other options are incorrect:
Why other options are incorrect:
- • O2 to the lungs: Hemoglobin carries O2 from the lungs to the tissues, not the other way around.
- • CO2 and protons to the tissue: CO2 and protons are generated at the tissues; hemoglobin picks them up there to take them away.
- • Nutrients: Nutrients like glucose and fatty acids are primarily transported dissolved in the plasma or by specific carrier proteins (like albumin), not by hemoglobin.
Ehlers-Danlos syndrome characterized by hypermobile joints and skin abnormalities is due to:
- a) Abnormality in gene for procollagen
- b) Deficiency of lysyl oxidase
- c) Deficiency of prolyl hydroxylase
- d) Deficiency of lysyl hydroxylase
Explanation:
Ehlers-Danlos syndrome (EDS) is a group of inherited connective tissue disorders. The most common forms (Classic EDS) are caused by an abnormality in the genes for procollagen (specifically Type V and Type I/III collagen). This leads to defects in the structure, production, or processing of collagen, resulting in skin hyperextensibility and joint hypermobility.
Why other options are incorrect:
Why other options are incorrect:
- • Deficiency of lysyl oxidase: This deficiency is associated with Menkes syndrome (due to copper deficiency) or Lathyrism, affecting the cross-linking of collagen, but is not the primary cause of EDS.
- • Deficiency of prolyl hydroxylase: This enzyme requires Vitamin C; its deficiency leads to Scurvy, where collagen fibers are weak due to lack of hydroxylation.
- • Deficiency of lysyl hydroxylase: While a deficiency in this enzyme causes EDS Type VI (Kyphoscoliotic type), the general symptoms of hypermobile joints and skin abnormalities in the majority of cases are linked to mutations in the procollagen genes themselves.
Proteins are soluble in:
- a) Anhydrous acetone
- b) Aqueous alcohol
- c) Anhydrous alcohol
- d) Benzene
Explanation:
While most proteins are soluble in water or dilute salt solutions, a specific class of simple proteins called Prolamines (such as gliadin from wheat and zein from maize) are characteristically soluble in 70–80% aqueous alcohol.
Why other options are incorrect:
Why other options are incorrect:
- • Anhydrous acetone/alcohol: These are non-polar organic solvents that remove the hydration shell from protein molecules, causing them to denature and precipitate rather than dissolve.
- • Benzene: This is a completely non-polar solvent. Proteins, which have many polar and charged groups, are generally insoluble in non-polar hydrocarbons like benzene.
A cereal protein soluble in 70% alcohol but insoluble in water or salt solution is:
- a) Glutelin
- b) Protamine
- c) Albumin
- d) Gliadin
Explanation:
Gliadin belongs to the Prolamine group of proteins. Prolamines are characteristic cereal proteins that are specifically soluble in 70-80% ethyl alcohol but remain insoluble in water or neutral salt solutions.
Why other options are incorrect:
Why other options are incorrect:
- • Glutelin: These proteins (like Glutenin in wheat) are soluble in dilute acids or bases, not alcohol.
- • Protamine: These are small, arginine-rich, highly basic proteins usually associated with DNA in sperm cells, not typical cereal storage proteins.
- • Albumin: These are globular proteins that are readily soluble in pure water.
Many globular proteins are stable in solution inspite they lack in:
- a) Disulphide bonds
- b) Hydrogen bonds
- c) Salt bonds
- d) Non polar bonds
Explanation:
While Disulphide bonds (covalent cross-links) provide significant structural reinforcement, many globular proteins achieve stability primarily through non-covalent interactions such as the hydrophobic effect, hydrogen bonding, and ionic interactions. Many intracellular proteins do not contain disulfide bonds at all.
Why other options are incorrect:
Why other options are incorrect:
- • Hydrogen bonds: Essential for stabilizing alpha-helices and beta-sheets; almost all globular proteins rely on them.
- • Salt bonds (Ionic bonds): These help stabilize the protein structure by forming bridges between oppositely charged side chains.
- • Non polar bonds (Hydrophobic interactions): These are the primary driving force behind the folding and stability of globular proteins in an aqueous environment.
The hydrogen bonds between peptide linkages of a protein molecules are interfered by:
- a) Guanidine
- b) Uric acid
- c) Oxalic acid
- d) Salicylic acid
Explanation:
Guanidine (specifically Guanidine hydrochloride) is a powerful denaturant and chaotropic agent. It interferes with the internal hydrogen bonds between peptide linkages and destabilizes the hydrophobic effect, causing the protein to unfold or denature.
Why other options are incorrect:
Why other options are incorrect:
- • Uric acid: A metabolic byproduct of purine metabolism; it does not act as a general denaturant for protein hydrogen bonds.
- • Oxalic acid: An organic acid that can chelate minerals, but it is not used to disrupt the secondary or tertiary structure of proteins via hydrogen bond interference.
- • Salicylic acid: While it can interact with proteins, it is not a standard biochemical reagent used for the systematic disruption of peptide hydrogen bonds like Guanidine or Urea.
Globular proteins have completely folded, coiled polypeptide chains, and the axial ratio (ratio of length to breadth) is:
- a) Less than 10 and generally not greater than 3–4
- b) Generally 10
- c) Greater than 10 and generally 20
- d) Greater than 10
Explanation:
Globular proteins are characterized by their spherical or ellipsoidal shape. Because they are tightly folded into a compact structure, their length-to-breadth ratio (axial ratio) is very low, usually less than 10 and most commonly between 3 and 4.
Why other options are incorrect:
Why other options are incorrect:
- • Greater than 10: This describes Fibrous proteins (like collagen or keratin), which are long, thread-like molecules with high axial ratios.
- • Generally 10 / Greater than 10 and generally 20: These values represent elongated structural proteins rather than the compact, soluble globular proteins.
Fibrous proteins have an axial ratio of:
- a) Less than 10
- b) Less than 10 and generally greater than 3-4
- c) Generally 10
- d) Greater than 10
Explanation:
Fibrous proteins (such as keratin, collagen, and elastin) are elongated, thread-like molecules that serve structural roles. Because of their long, rod-like shape, their axial ratio (length:breadth) is greater than 10.
Why other options are incorrect:
Why other options are incorrect:
- • Less than 10 / 3–4: These ratios are characteristic of globular proteins, which are folded into compact, nearly spherical shapes.
- • Generally 10: While some proteins may fall near this borderline, the defining characteristic of fibrous proteins in biochemistry is that they significantly exceed this ratio due to their extended secondary structures.
Each turn of α-helix contains the amino acid residues (number):
- a) 3.6
- b) 3.0
- c) 4.2
- d) 4.5
Explanation:
Each turn of an α-helix contains approximately 3.6 amino acid residues. The helix has a pitch of about 0.54 nm per turn.
Why other options are incorrect:
Why other options are incorrect:
- • 3.0: Fewer than the standard 3.6 residues per turn.
- • 4.2: More than the standard number of residues per turn.
- • 4.5: More than the standard number of residues per turn.
Distance traveled per turn of α−helix in nm is
- a) 0.53
- b) 0.54
- c) 0.44
- d) 0.48
Explanation:
One complete turn of an α-helix advances approximately 0.54 nm along the helix axis. This distance is known as the pitch of the α-helix.
Why other options are incorrect:
Why other options are incorrect:
- • 0.53: Close to the correct value but not the standard pitch of an α-helix.
- • 0.44: Does not represent the distance traveled per turn of an α-helix.
- • 0.48: Does not represent the standard pitch of an α-helix.
Along the α-helix each amino acid residue advances in nm by
- a) 0.15
- b) 0.10
- c) 0.12
- d) 0.20
Explanation:
In an α-helix, each amino acid residue advances approximately 0.15 nm along the axis of the helix. The α-helix has about 3.6 amino acid residues per turn, with a pitch of approximately 0.54 nm.
Why other options are incorrect:
Why other options are incorrect:
- • 0.10 nm: This is less than the characteristic axial rise per residue in an α-helix.
- • 0.12 nm: This does not represent the standard axial rise per amino acid residue.
- • 0.20 nm: This is greater than the standard axial rise per residue.
The number of helices present in a collagen molecule is:
- a) 1
- b) 2
- c) 3
- d) 4
Explanation:
A collagen molecule consists of three polypeptide chains (called alpha chains) that wrap around each other to form a characteristic triple helix (also known as a tropocollagen unit).
Why other options are incorrect:
Why other options are incorrect:
- • 1: While each individual chain is a left-handed helix, the molecule itself is a complex of three.
- • 2: This describes the double helix structure of DNA, not collagen.
- • 4: Some proteins like Hemoglobin consist of four subunits, but the structural unit of collagen is strictly a triple helix.
In proteins, the α-helix and β-pleated sheet are examples of:
- a) Primary structure
- b) Secondary structure
- c) Tertiary structure
- d) Quaternary structure
Explanation:
Secondary structure refers to the local folding of the polypeptide backbone into regular, repeating patterns. These structures, primarily the α-helix and β-pleated sheet, are stabilized by hydrogen bonds between the carbonyl oxygen and the amide hydrogen of the peptide backbone.
Why other options are incorrect:
Why other options are incorrect:
- • Primary structure: This is simply the linear sequence of amino acids linked by covalent peptide bonds.
- • Tertiary structure: This is the overall three-dimensional shape of a single polypeptide chain, formed by interactions between R-groups (side chains).
- • Quaternary structure: This refers to the spatial arrangement and interaction of multiple polypeptide chains (subunits) in a multi-subunit protein.
The α-helix of proteins is:
- a) A pleated structure
- b) Made periodic by disulphide bridges
- c) A non-periodic structure
- d) Stabilised by hydrogen bonds between NH and CO groups of the main chain
Explanation:
The α-helix is a highly regular (periodic) secondary structure. It is held together and stabilized by hydrogen bonds formed between the Oxygen atom of the Carbonyl group (C=O) of one amino acid and the Hydrogen atom of the Amino group (N-H) of the amino acid four residues further down the chain.
Why other options are incorrect:
Why other options are incorrect:
- • A pleated structure: This describes β-pleated sheets, not the spiral α-helix.
- • Made periodic by disulphide bridges: Periodicity in the helix is established by hydrogen bonding. Disulphide bridges (S-S bonds) are covalent bonds that typically stabilize tertiary or quaternary structures.
- • A non-periodic structure: The α-helix is a periodic structure because it repeats its geometric pattern (3.6 residues per turn) consistently.
At the lowest energy level, the α-helix of a polypeptide chain is stabilised:
- a) By hydrogen bonds formed between the H of peptide N and the carbonyl O of the residue
- b) Disulphide bonds
- c) Non polar bonds
- d) Ester bonds
Explanation:
The α-helix is the most common secondary structure in proteins because it represents a low-energy, stable conformation. This stability is achieved through a regular pattern of hydrogen bonds between the peptide nitrogen’s hydrogen (N-H) and the carbonyl oxygen (C=O) of the fourth amino acid residue behind it in the sequence.
Why other options are incorrect:
Why other options are incorrect:
- • Disulphide bonds: These are covalent bonds between Cysteine residues that stabilize tertiary or quaternary structures, not the fundamental α-helix coil.
- • Non polar bonds: While hydrophobic interactions (non-polar) drive the overall folding of a protein, the specific geometry of the α-helix is defined by backbone hydrogen bonding.
- • Ester bonds: Proteins are made of amino acids linked by peptide (amide) bonds; ester bonds are not a standard feature of the protein backbone or helical stabilization.
Both α-helix and β-pleated sheet conformation of proteins were proposed by:
- a) Watson and Crick
- b) Pauling and Corey
- c) Waugh and King
- d) Y.S. Rao
Explanation:
The fundamental secondary structures of proteins—the α-helix and the β-pleated sheet—were first described by Linus Pauling and Robert Corey (along with Herman Branson) in 1951. Their models were based on the understanding of the planar nature of the peptide bond and the importance of hydrogen bonding.
Why other options are incorrect:
Why other options are incorrect:
- • Watson and Crick: They are famous for discovering the double helix structure of DNA in 1953, not protein secondary structures.
- • Waugh and King / Y.S. Rao: These researchers are not associated with the original mathematical and physical proposal of protein α-helices and β-sheets.
The primary structure of fibroin, the principal protein of silk worm fibres, consists almost entirely of:
- a) Glycine
- b) Aspartate
- c) Keratin
- d) Tryptophan
Explanation:
Fibroin is the insoluble protein found in silk. Its primary structure is highly repetitive, consisting largely of the sequence (Gly-Ser-Gly-Ala-Gly-Ala). Glycine accounts for nearly 50% of the total amino acid content, allowing the beta-sheets to pack tightly together.
Why other options are incorrect:
Why other options are incorrect:
- • Aspartate: This is a polar, charged amino acid found in much smaller quantities in silk; it would disrupt the tight packing of the fibroin sheets.
- • Keratin: This is a different class of fibrous protein found in hair, nails, and horns, not an amino acid component of fibroin.
- • Tryptophan: Silk fibroin is notably deficient in bulky amino acids like Tryptophan, which would interfere with its crystalline structure.
Tertiary structure of a protein describes:
- a) The order of amino acids
- b) Location of disulphide bonds
- c) Loop regions of proteins
- d) The ways of protein folding
Explanation:
The tertiary structure refers to the overall three-dimensional arrangement or folding of a single polypeptide chain. It describes how the secondary structural elements (helices, sheets, loops) collapse into a compact unit, driven primarily by interactions between the amino acid side chains (R-groups).
Why other options are incorrect:
Why other options are incorrect:
- • The order of amino acids: This is the primary structure, which is the linear sequence of amino acids.
- • Location of disulphide bonds: While disulfide bonds are a key feature that stabilizes tertiary structure, they do not define the entire structural level itself.
- • Loop regions of proteins: Loops are specific components of secondary and tertiary structures, but the term “Tertiary structure” encompasses the entire folded molecule.
In a protein molecule the disulphide bond is not broken by
- a) Reduction
- b) Oxidation
- c) Denaturation
- d) X-ray diffraction
Explanation:
Disulphide bonds are covalent bonds formed between two cysteine residues. They can be cleaved by reducing agents and may also be affected by strong oxidative conditions. Denaturation generally disrupts non-covalent interactions but does not necessarily break disulphide bonds. X-ray diffraction is an analytical technique used to determine molecular or crystal structure and does not break disulphide bonds.
Why other options are incorrect:
Why other options are incorrect:
- • Reduction: Reducing agents such as β-mercaptoethanol can break disulphide bonds.
- • Oxidation: Oxidative conditions can alter cysteine/disulphide chemistry.
- • Denaturation: Denaturation can disrupt protein structure, although disulphide bonds are relatively resistant to ordinary denaturation.
The technique for purification of proteins that can be made specific for a given protein is:
- a) Gel filtration chromatography
- b) Ion exchange chromatography
- c) Electrophoresis
- d) Affinity chromatography
Explanation:
Affinity chromatography is the most specific purification technique. It exploits the unique biological binding of a protein to a specific ligand (such as an antibody, substrate, or receptor) immobilized on a stationary phase. Only the specific protein that recognizes that ligand will bind, while others are washed away.
Why other options are incorrect:
Why other options are incorrect:
- • Gel filtration: Separates proteins based on their size and molecular weight, not biological specificity.
- • Ion exchange: Separates proteins based on their net surface charge; many different proteins can have similar charges.
- • Electrophoresis: Primarily an analytical tool that separates proteins based on charge-to-mass ratio in an electric field.
Denaturation of proteins results in:
- a) Disruption of primary structure
- b) Breakdown of peptide bonds
- c) Destruction of hydrogen bonds
- d) Irreversible changes in the molecule
Explanation:
Denaturation is the process where a protein loses its native 3D shape (secondary, tertiary, and quaternary structures). This occurs because the weak non-covalent interactions, primarily hydrogen bonds, hydrophobic interactions, and salt bridges, are disrupted by heat, pH changes, or chemicals.
Why other options are incorrect:
Why other options are incorrect:
- • Disruption of primary structure / Breakdown of peptide bonds: Denaturation does not break the covalent peptide bonds that form the primary sequence. The sequence of amino acids remains intact.
- • Irreversible changes: While many proteins (like egg whites) denature irreversibly, some proteins can undergo renaturation (refolding) if the denaturing agent is removed slowly under the right conditions. Therefore, “irreversible” is not a universal rule for denaturation.
Ceruloplasmin is:
- a) α1-globulin
- b) α2-globulin
- c) β-globulin
- d) None of these
Explanation:
Ceruloplasmin is a copper-carrying protein synthesized in the liver and is classified as an α2-globulin. It plays a vital role as a ferroxidase enzyme, helping in the metabolism of iron.
Why other options are incorrect:
Why other options are incorrect:
- • α1-globulin: This group includes proteins like α1-antitrypsin and Orosomucoid, but not ceruloplasmin.
- • β-globulin: Proteins like transferrin and LDL (Low-Density Lipoprotein) belong to this category.
- • None of these: This is incorrect because Ceruloplasmin is a well-defined α2-globulin.
The lipoprotein with the fastest electrophoretic mobility and the lowest triglyceride content is:
- a) Chylomicron
- b) VLDL
- c) IDL
- d) HDL
Explanation:
HDL (High-Density Lipoprotein) has the highest protein-to-lipid ratio, making it the smallest and densest lipoprotein. Due to its high net charge and small size, it migrates the fastest toward the anode (α-region) in electrophoresis. It also contains the lowest amount of triglycerides (approx. 5%).
Why other options are incorrect:
Why other options are incorrect:
- • Chylomicron: These are the largest and least dense, usually remaining at the origin during electrophoresis. They have the highest triglyceride content (~90%).
- • VLDL: These have “Pre-beta” mobility and contain a significantly higher triglyceride content (~55-65%) than HDL.
- • IDL: These are intermediate in both mobility and triglyceride content, sitting between VLDL and LDL.
The lipoprotein associated with activation of LCAT is:
- a) HDL
- b) LDL
- c) VLDL
- d) IDL
Explanation:
HDL (High-Density Lipoprotein) contains Apolipoprotein A-I (Apo A-I), which is the primary activator of the enzyme LCAT (Lecithin-Cholesterol Acyltransferase). This enzyme is crucial for converting free cholesterol into cholesterol esters, allowing HDL to sequester cholesterol from peripheral tissues.
Why other options are incorrect:
Why other options are incorrect:
- • LDL: Primarily contains Apo B-100 and functions to deliver cholesterol to peripheral tissues; it does not activate LCAT.
- • VLDL: Primarily transports endogenous triglycerides from the liver and is not the site of LCAT activation.
- • IDL: Formed during the degradation of VLDL; while it contains some cholesterol, it is not the functional partner for LCAT activation.
The apolipoprotein which acts as activator of LCAT is:
- a) A-I
- b) A-IV
- c) C-II
- d) D
Explanation:
Apolipoprotein A-I (Apo A-I) is the major structural protein in HDL and is the primary physiological activator of LCAT (Lecithin-Cholesterol Acyltransferase). This activation is essential for the maturation of HDL particles during reverse cholesterol transport.
Why other options are incorrect:
Why other options are incorrect:
- • A-IV: While it may have some minor stimulatory effect on LCAT in vitro, its primary roles are related to chylomicron metabolism and satiety signaling.
- • C-II: This apolipoprotein is the essential activator of Lipoprotein Lipase (LPL), which breaks down triglycerides in chylomicrons and VLDL.
- • D: Apo D is associated with HDL but its primary function is likely related to the transport of small hydrophobic molecules like bilirubin or steroids, not LCAT activation.
The apolipoprotein which acts as activator of extrahepatic lipoprotein lipase is:
- a) Apo-A
- b) Apo-B
- c) Apo-C
- d) Apo-D
Explanation:
Apo-C (specifically Apo C-II) is the essential cofactor and activator for Lipoprotein Lipase (LPL). LPL is located on the walls of blood capillaries in extrahepatic tissues (such as adipose tissue, heart, and muscle) where it hydrolyzes triglycerides into free fatty acids and glycerol.
Why other options are incorrect:
Why other options are incorrect:
- • Apo-A: Specifically Apo A-I is an activator of LCAT (Lecithin-Cholesterol Acyltransferase), not LPL.
- • Apo-B: This is a structural protein (B-100 in VLDL/LDL and B-48 in chylomicrons) and acts as a ligand for the LDL receptor.
- • Apo-D: It is a minor protein in HDL and is thought to be involved in the transport of small hydrophobic molecules.
The apolipoprotein which forms the integral component of chylomicron is:
- a) B-100
- b) B-48
- c) C
- d) D
Explanation:
Apolipoprotein B-48 (Apo B-48) is the essential structural protein required for the assembly and secretion of chylomicrons from the small intestine. It is called B-48 because it represents the N-terminal 48% of the Apo B-100 protein, produced via mRNA editing in intestinal cells.
Why other options are incorrect:
Why other options are incorrect:
- • B-100: This is the integral protein for lipoproteins of hepatic origin, specifically VLDL, IDL, and LDL.
- • C: Apolipoproteins of the C-family (C-I, C-II, C-III) are peripheral proteins that are exchanged between lipoproteins; they are not the primary structural “integral” component.
- • D: Apo D is a minor apolipoprotein associated with HDL and is not a structural component of chylomicrons.
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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