5101 to 5150 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 5101 to 5150
All the following statements about albinism are correct except:
- a) Tyrosine hydroxylase (tyrosinase) is absent or deficient in melanocytes
- b) Skin is hypopigmented
- c) It results in mental retardation
- d) Eyes are hypopigmented
Explanation:
Albinism is a group of inherited disorders characterized by little or no production of the pigment melanin. Unlike Phenylketonuria (PKU), albinism does not cause mental retardation; it primarily affects the skin, hair, and eyes.
Why the other statements are correct:
Why the other statements are correct:
- • Tyrosinase Deficiency: Most forms of albinism result from a biological deficiency or total absence of the tyrosinase enzyme, which is needed to convert tyrosine into melanin.
- • Skin Hypopigmentation: A lack of melanin results in very light skin and hair, making individuals highly sensitive to UV radiation.
- • Eyes Hypopigmented: Reduced pigment in the iris and retina leads to light-colored eyes and is often associated with vision problems and photophobia.
Glycine is not required for the formation of
- a) Taurocholic acid
- b) Creatine
- c) Purines
- d) Pyrimidines
Explanation:
Glycine is required for the synthesis of creatine and purine nucleotides.
However, taurocholic acid is formed by conjugation of bile acid with taurine,
which is derived from cysteine; glycine is not involved.
Why other options are incorrect:
Why other options are incorrect:
- • Creatine: Glycine is one of the amino acids used in creatine synthesis.
- • Purines: Glycine contributes carbon and nitrogen atoms to the purine ring.
- • Pyrimidines: Glycine is not a major direct precursor of the pyrimidine ring, but the best answer here is Taurocholic acid because it specifically uses taurine rather than glycine.
Histamine is formed from histidine by:
- a) Deamination
- b) Dehydrogenation
- c) Decarboxylation
- d) Carboxylation
Explanation:
Histamine is synthesized via the decarboxylation of the amino acid L-histidine. This reaction is catalyzed by the enzyme histidine decarboxylase and requires Vitamin B6 (Pyridoxal Phosphate) as a cofactor.
Why other options are incorrect:
Why other options are incorrect:
- • Deamination: This involves the removal of an amino group, which would result in an alpha-keto acid, not histamine.
- • Dehydrogenation: This is an oxidation process involving the removal of hydrogen atoms, typically seen in redox reactions.
- • Carboxylation: This is the addition of a carbon dioxide group, which is the opposite of the process required to form histamine.
DOPA is an intermediate in the synthesis of
- a) Thyroid hormones
- b) Catecholamines
- c) Melanin
- d) Catecholamines and melanin
Explanation:
L-DOPA (3,4-dihydroxyphenylalanine) is an important intermediate in
the synthesis of both catecholamines and melanin. It is converted
to dopamine in catecholamine synthesis and to dopaquinone in melanin synthesis.
Why other options are incorrect:
Why other options are incorrect:
- • Thyroid hormones: Their synthesis involves iodination and coupling of tyrosine residues in thyroglobulin, not DOPA.
- • Catecholamines: Correct, but incomplete because DOPA is also an intermediate in melanin synthesis.
- • Melanin: Correct, but incomplete because DOPA is also an intermediate in catecholamine synthesis.
All the following statements about pepsin are correct except:
- a) It is smaller than pepsinogen
- b) It is formed by the action of HCl on its precursor
- c) Its optimum pH is 1.0–2.0
- d) It hydrolyses the C-terminal and N-terminal peptide bonds of proteins
Explanation:
Pepsin is an endopeptidase, meaning it hydrolyzes internal peptide bonds within a protein chain (specifically those involving aromatic amino acids). It does not remove amino acids from the ends (terminals) of the protein; that is the job of exopeptidases like carboxypeptidase or aminopeptidease.
Why the other statements are correct:
Why the other statements are correct:
- • Smaller than pepsinogen: Pepsinogen (the inactive zymogen) is converted to pepsin by losing a 44-amino acid peptide, making the active enzyme smaller.
- • Action of HCl: Hydrochloric acid in the stomach provides the low pH required to trigger the self-cleavage (autocatalysis) of pepsinogen into pepsin.
- • Optimum pH: Pepsin is highly specialized for the stomach’s acidic environment, functioning best at a pH of 1.0 to 2.0.
Pancreatic juice contains the precursors of all of the following except
- a) Trypsin
- b) Chymotrypsin
- c) Carboxypeptidase
- d) Aminopeptidase
Explanation:
Pancreatic juice contains inactive zymogens of several proteolytic enzymes,
including trypsinogen, chymotrypsinogen, and procarboxypeptidase. Aminopeptidase
is primarily a brush-border enzyme of the intestinal mucosa and is not secreted
by the pancreas as a precursor.
Why other options are incorrect:
Why other options are incorrect:
- • Trypsin: Secreted by the pancreas as inactive trypsinogen.
- • Chymotrypsin: Secreted as inactive chymotrypsinogen.
- • Carboxypeptidase: Secreted as inactive procarboxypeptidase.
The only correct statement about chymotrypsin is
- a) It is formed from trypsin
- b) Carboxypeptidase converts trypsin into chymotrypsin
- c) Its optimum pH is around 7
- d) It hydrolyses peptide bonds involving basic amino acids
Explanation:
Chymotrypsin is a pancreatic proteolytic enzyme that is secreted as
the inactive zymogen chymotrypsinogen. Its optimum pH is approximately
7.8, which is around neutral pH.
Why other options are incorrect:
Why other options are incorrect:
- • It is formed from trypsin: Incorrect. Trypsin activates chymotrypsinogen to form chymotrypsin.
- • Carboxypeptidase converts trypsin into chymotrypsin: Incorrect. Trypsin itself is formed from trypsinogen and activates other pancreatic zymogens.
- • Basic amino acids: Incorrect. Chymotrypsin preferentially hydrolyses peptide bonds involving aromatic amino acids such as phenylalanine, tyrosine, and tryptophan.
The portion of the antigen molecule which is recognized by antibody is known as:
- a) Hapten
- b) Epitope
- c) Complement
- d) Variable region
Explanation:
An Epitope (also known as an antigenic determinant) is the specific chemical group or molecular configuration on the surface of an antigen that is recognized by and binds to a specific antibody.
Why the other options are incorrect:
Why the other options are incorrect:
- • Hapten: A small molecule that is not antigenic by itself but can become so when conjugated to a larger carrier protein.
- • Complement: A system of plasma proteins that helps (complements) the ability of antibodies to clear pathogens; it is not part of the antigen.
- • Variable region: This is a part of the antibody molecule (the paratope) that binds to the antigen, not a part of the antigen itself.
All the following statements about haptens are true except
- a) They have high molecular weights
- b) They cannot elicit an immune response by themselves
- c) When combined with some other large molecule, they can elicit an immune response
- d) Once an immune response develops, the free hapten can be recognized by the antibody
Explanation:
Haptens are small, low-molecular-weight molecules that are antigenic but not
immunogenic by themselves. They can induce an immune response when attached
to a larger carrier molecule. Once antibodies are produced, the free hapten
can bind to and be recognized by those antibodies.
Why other options are incorrect:
Why other options are incorrect:
- • They cannot elicit an immune response by themselves: This is a characteristic feature of haptens.
- • When combined with some other large molecule: A hapten can become immunogenic when attached to a carrier protein.
- • Free hapten can be recognized by the antibody: Antibodies generated against the hapten-carrier complex can recognize and bind the free hapten.
Antigens and haptens have the following similarity:
- a) They have high molecular weights
- b) They can elicit immune response by themselves
- c) They can elicit an immune response only in association with some other large molecule
- d) Once an immune response develops, free antigen and free hapten can be recognized by the antibody
Explanation:
Both antigens and haptens can be recognized by antibodies. A hapten is a small molecule
that cannot independently induce an immune response but can react with antibodies once
an immune response has been generated against the hapten-carrier complex.
Why other options are incorrect:
Why other options are incorrect:
- • High molecular weights: Haptens are typically small, low-molecular-weight molecules.
- • Elicit immune response by themselves: Haptens cannot induce an immune response without being attached to a carrier.
- • Require association with another molecule: This applies to haptens, not to complete antigens, which can be immunogenic on their own.
The minimum number of polypeptide chains in an immunoglobulin is
- a) Two
- b) Four
- c) Five
- d) Six
Explanation:
A typical immunoglobulin molecule consists of four polypeptide chains:
two identical heavy chains and two identical light chains, linked by
disulfide bonds.
Why other options are incorrect:
Why other options are incorrect:
- • Two: An immunoglobulin requires both heavy and light chains, making four chains in the basic structure.
- • Five: This exceeds the number of chains in the basic immunoglobulin structure.
- • Six: This is not the minimum number of polypeptide chains in an immunoglobulin.
Light chains of immunoglobulins are of following types:
- a) Alpha and kappa
- b) Alpha and gamma
- c) Lambda and delta
- d) Kappa and lambda
Explanation:
Immunoglobulin molecules are composed of two identical heavy chains and two identical light chains. In humans, there are only two types of light chains: Kappa (κ) and Lambda (λ).
Why other options are incorrect:
Why other options are incorrect:
- • Alpha (α): This is a type of heavy chain found in IgA antibodies.
- • Gamma (γ): This is a type of heavy chain found in IgG antibodies.
- • Delta (δ): This is a type of heavy chain found in IgD antibodies.
- Note: While an antibody can have either Kappa or Lambda light chains, it cannot have both at the same time.
Immunoglobulins are classified on the basis of:
- a) Type of light chains
- b) Type of heavy chains
- c) Types of light and heavy chains
- d) Molecular weight
Explanation:
Immunoglobulins are classified into five main classes (isotypes) based on the differences in the amino acid sequences in the constant region of their heavy chains. These are Gamma (IgG), Alpha (IgA), Mu (IgM), Delta (IgD), and Epsilon (IgE).
Why other options are incorrect:
Why other options are incorrect:
- • Type of light chains: Light chains (Kappa or Lambda) determine the “type” of the immunoglobulin, but not its “class” or “isotype.”
- • Types of light and heavy chains: While both make up the structure, the primary classification into IgG, IgA, etc., is determined solely by the heavy chain.
- • Molecular weight: Molecular weight varies between classes (e.g., IgM is much heavier as a pentamer), but it is a characteristic of the class, not the basis for the classification system itself.
The molecular weight of light chains is:
- a) 10,000–15,000
- b) 20,000–25,000
- c) 25,000–50,000
- d) 50,000–75,000
Explanation:
The light chains (L-chains) of an immunoglobulin molecule consist of approximately 214 amino acids and have a molecular weight of roughly 22,000 to 25,000 Daltons (Da).
Why other options are incorrect:
Why other options are incorrect:
- • 10,000–15,000: This range is too small for a light chain, which must contain two immunoglobulin domains (one variable and one constant).
- • 25,000–50,000: While the upper end of this range might catch some larger proteins, the specific light chain weight is consistently cited around 25 kDa.
- • 50,000–75,000: This range corresponds to the molecular weight of the heavy chains (H-chains) of immunoglobulins, which are much larger than light chains.
The molecular weight of heavy chains is:
- a) 20,000–25,000
- b) 25,000–50,000
- c) 50,000–70,000
- d) 70,000–1,00,000
Explanation:
The heavy chains (H-chains) of immunoglobulins are larger than light chains and contain more amino acids (about 440–550). Their molecular weight typically ranges between 50,000 and 70,000 Daltons, depending on the class (e.g., IgG is ~50 kDa, while IgM is ~70 kDa).
Why other options are incorrect:
Why other options are incorrect:
- • 20,000–25,000: This is the molecular weight range for light chains.
- • 25,000–50,000: This range is too high for light chains but generally too low for the standard heavy chains found in human immunoglobulins.
- • 70,000–1,00,000: This is higher than the standard heavy chain monomer, though the total molecular weight of a full antibody molecule (2 heavy + 2 light) is much higher (~150,000 Da).
Secretory component is present in:
- a) IgA
- b) IgG
- c) IgM
- d) All of these
Explanation:
The secretory component is a glycoprotein found in Secretory IgA (sIgA). It is produced by epithelial cells and helps transport IgA across the epithelium into secretions (like saliva, milk, and mucus), while also protecting the antibody from digestion by proteolytic enzymes.
Why other options are incorrect:
Why other options are incorrect:
- • IgG: This is the most abundant antibody in the blood and does not typically contain a secretory component or form dimers for mucosal secretion.
- • IgM: Although IgM is a polymer (pentamer) and contains a J-chain, the “secretory component” is specifically the characteristic feature of secretory IgA.
- • All of these: Only IgA (and rarely IgM in specific deficient states) utilizes the secretory component for mucosal transport.
The variable region of light chains is the:
- a) N-terminal quarter
- b) N-terminal half
- c) C-terminal quarter
- d) C-terminal half
Explanation:
Immunoglobulin light chains consist of approximately 214 amino acids divided into two domains of equal length. The N-terminal half (the first ~107 amino acids) is the Variable (V) region, while the C-terminal half is the Constant (C) region.
Why other options are incorrect:
Why other options are incorrect:
- • N-terminal quarter: In heavy chains, the variable region represents only the N-terminal quarter (since heavy chains have 4-5 domains), but in light chains, it is exactly half.
- • C-terminal quarter: This does not represent a standard functional division in light chain terminology.
- • C-terminal half: This part of the light chain is the Constant region (CL), which remains relatively similar within the same type of light chain (Kappa or Lambda).
The variable region of light chains has
- a) One hypervariable region
- b) Two hypervariable regions
- c) Three hypervariable regions
- d) Four hypervariable regions
Explanation:
The variable region of an immunoglobulin light chain contains
three hypervariable regions, also called complementarity-determining
regions (CDRs). These regions participate directly in antigen binding.
Why other options are incorrect:
Why other options are incorrect:
- • One: The light-chain variable region contains three CDRs, not one.
- • Two: There are three hypervariable regions in the light-chain variable domain.
- • Four: The standard light-chain variable region contains three hypervariable regions.
The variable region of heavy chains has
- a) One hypervariable region
- b) Two hypervariable regions
- c) Three hypervariable regions
- d) Four hypervariable regions
Explanation:
The variable region of an immunoglobulin heavy chain contains
three hypervariable regions, also known as complementarity-determining
regions (CDRs). These CDRs contribute to the antigen-binding site.
Why other options are incorrect:
Why other options are incorrect:
- • One: The heavy-chain variable region contains three CDRs, not one.
- • Two: The heavy-chain variable region contains three hypervariable regions.
- • Four: The standard variable region contains three hypervariable regions.
The most abundant immunoglobulin in plasma is:
- a) IgA
- b) IgG
- c) IgM
- d) IgD
Explanation:
IgG is the most abundant class of immunoglobulin in the plasma (serum), constituting approximately 75% to 80% of the total circulating antibodies in a healthy adult.
Why other options are incorrect:
Why other options are incorrect:
- • IgA: The second most abundant (about 10–15%), but it is the primary antibody found in secretions like mucus, tears, and breast milk.
- • IgM: Makes up about 5–10% of serum antibodies; it is the first antibody produced during an initial immune response.
- • IgD: Found in very small amounts in the serum (less than 1%); it mainly acts as a receptor on the surface of B cells.
The largest immunoglobulin is
- a) IgA
- b) IgG
- c) IgM
- d) IgD
Explanation:
IgM is the largest immunoglobulin. It is usually present as a pentamer
in the circulation, consisting of five antibody units linked together
by a J chain. It has a high molecular weight of approximately 900 kDa.
Why other options are incorrect:
Why other options are incorrect:
- • IgA: It is mainly a dimer in secretions and is smaller than pentameric IgM.
- • IgG: It is a monomer and is considerably smaller than IgM.
- • IgD: It is a monomer and is present in very low concentrations in serum.
The plasma concentration of IgA is:
- a) 1–5 mg/dl
- b) 40–200 mg/dl
- c) 60–500 mg/dl
- d) 700–1,500 mg/dl
Explanation:
IgA is the second most abundant immunoglobulin in human serum after IgG. Its normal plasma concentration typically ranges from 60 to 400 or 500 mg/dl (depending on the laboratory reference range).
Why other options are incorrect:
Why other options are incorrect:
- • 1–5 mg/dl: This is a very low concentration, more characteristic of IgD.
- • 40–200 mg/dl: This range is more typical for IgM plasma levels.
- • 700–1,500 mg/dl: This is the concentration range for IgG, which is the most abundant immunoglobulin in the blood.
An immunoglobulin found in exocrine secretions is:
- a) IgA
- b) IgG
- c) IgM
- d) IgE
Explanation:
IgA is the predominant immunoglobulin in exocrine secretions such as saliva, tears, breast milk (colostrum), sweat, and gastrointestinal/respiratory mucus. In these fluids, it exists as “Secretory IgA,” providing the first line of defense against pathogens at mucosal surfaces.
Why other options are incorrect:
Why other options are incorrect:
- • IgG: Mainly found in the blood and interstitial fluid; it can cross the placenta but is not the primary secretory antibody.
- • IgM: Primarily found in the intravascular compartment (blood) due to its large size. While it can be secreted in small amounts, IgA is the major secretory class.
- • IgE: Found in very low concentrations in the blood; it is primarily involved in allergic reactions and defense against parasites, bound to mast cells.
Allergic reactions are mediated by:
- a) IgA
- b) IgG
- c) IgD
- d) IgE
Explanation:
IgE is the immunoglobulin primarily responsible for Type I hypersensitivity (allergic) reactions. It binds to high-affinity receptors on the surface of mast cells and basophils. When an allergen cross-links these bound IgE molecules, it triggers the release of inflammatory mediators like histamine.
Why other options are incorrect:
Why other options are incorrect:
- • IgA: Primarily involved in mucosal immunity and found in secretions like saliva and tears.
- • IgG: Responsible for long-term immunity, neutralizing toxins, and crossing the placenta; it does not mediate immediate allergic reactions.
- • IgD: Mainly serves as an antigen receptor on the surface of mature B-lymphocytes and its systemic function is less well-defined.
An immunoglobulin which can cross the placental barrier is:
- a) IgA
- b) IgM
- c) IgD
- d) None of these
Explanation:
The only immunoglobulin capable of crossing the placental barrier is IgG. It possesses a specific Fc portion that binds to neonatal Fc receptors (FcRn) in the placenta, allowing it to pass from the mother to the fetus to provide passive immunity.
Why other options are incorrect:
Why other options are incorrect:
- • IgA: Does not cross the placenta; however, it is provided to the infant after birth through breast milk.
- • IgM: Because of its large pentameric size and lack of specific transport receptors, it cannot cross the placenta.
- • IgD: This immunoglobulin is not transported across the placental barrier.
- Note: Since IgG is not listed among options a, b, or c, the correct choice is “None of these.”
The immunoglobulin having the longest half-life is:
- a) IgA
- b) IgG
- c) IgM
- d) IgE
Explanation:
IgG has the longest serum half-life of all immunoglobulins, lasting approximately 21 to 23 days. This longevity is due to the neonatal Fc receptor (FcRn), which binds to IgG and protects it from degradation by recycling it back into the circulation.
Why other options are incorrect:
Why other options are incorrect:
- • IgA: Has a half-life of about 6 days.
- • IgM: Has a half-life of about 5 days.
- • IgE: Has the shortest half-life in the serum, lasting only about 2 days (though it remains stable for much longer when bound to mast cells).
The half-life of IgG is:
- a) 2–3 days
- b) 5–6 days
- c) 8–10 days
- d) 20–25 days
Explanation:
The biological half-life of IgG is the longest of all immunoglobulin classes, typically cited as approximately 23 days (falling within the 20–25 day range). This is made possible by the neonatal Fc receptor (FcRn), which protects IgG from lysosomal degradation.
Why other options are incorrect:
Why other options are incorrect:
- • 2–3 days: This is the characteristic half-life of IgE in the serum.
- • 5–6 days: This is the approximate half-life range for both IgM (5 days) and IgA (6 days).
- • 8–10 days: This does not correspond to the standard half-life of any major immunoglobulin class in humans.
Recognition of antigen is the function of:
- a) Variable region of light chains
- b) Variable regions of light and heavy chains
- c) Constant region of heavy chains
- d) Constant regions of light and heavy chains
Explanation:
The antigen-binding site (also known as the paratope) is formed by the interaction of the variable regions of both the light (VL) and heavy (VH) chains. These regions contain the hypervariable loops that determine the specificity for a particular antigen.
Why other options are incorrect:
Why other options are incorrect:
- • Variable region of light chains: While involved, it cannot recognize an antigen effectively on its own; it must work in tandem with the heavy chain’s variable region.
- • Constant region of heavy chains: This region (the Fc portion) is responsible for effector functions, such as complement activation and binding to Fc receptors on immune cells.
- • Constant regions of light and heavy chains: These regions provide structural support and stability to the antibody but do not participate in binding to the antigen.
The effector function of antibody is performed by:
- a) Variable region of light chains
- b) Constant region of heavy chains
- c) Variable regions of light and heavy chains
- d) Constant regions of light and heavy chains
Explanation:
The constant region of the heavy chains (which forms the Fc fragment) is responsible for the biological effector functions of an antibody. This includes activities such as complement activation, placental transfer, and binding to Fc receptors on phagocytes, mast cells, and NK cells.
Why other options are incorrect:
Why other options are incorrect:
- • Variable regions (a & c): The variable regions (both light and heavy) are responsible for antigen recognition and binding, not effector functions.
- • Constant regions of light chains: While light chains have a constant region, it serves primarily as a structural link and does not mediate major effector functions like the heavy chain does.
- Note: The heavy chain constant region determines the antibody “class” (IgG, IgM, etc.), which in turn determines which specific effector functions the antibody can perform.
Complement system can be activated by binding of antigen to:
- a) IgA
- b) IgD
- c) IgE
- d) IgM
Explanation:
The classical pathway of the complement system is activated when IgM or IgG binds to an antigen. IgM is the most efficient activator of complement because its pentameric structure allows a single molecule to bind to the C1q component of the complement cascade.
Why other options are incorrect:
Why other options are incorrect:
- • IgA: Does not activate the classical pathway, though it can activate the alternative pathway in aggregated form.
- • IgD: This immunoglobulin does not have the capacity to activate the complement system.
- • IgE: Primarily involved in allergic reactions and histamine release; it does not activate the complement system.
- Note: Among all immunoglobulins, IgM and certain subclasses of IgG (IgG1, IgG2, and IgG3) are the only ones that activate the classical complement pathway.
C1 component of classical complement pathway is made up of
- a) Complements 1q and 1r
- b) Complements 1q and 1s
- c) Complements 1r and 1s
- d) Complements 1q, 1r and 1s
Explanation:
The C1 component of the classical complement pathway is composed of
three subcomponents: C1q, C1r, and C1s. C1q recognizes the Fc portion
of antigen-bound antibodies, while C1r and C1s are serine proteases
involved in activation of the complement cascade.
Why other options are incorrect:
Why other options are incorrect:
- • C1q and C1r: Incomplete because C1s is also an essential component of C1.
- • C1q and C1s: Incomplete because C1r is also present in the C1 complex.
- • C1r and C1s: Incomplete because C1q is responsible for recognition of antibody-bound antigen.
The components of the complement system are activated by:
- a) Microsomal hydroxylation
- b) Phosphorylation
- c) Glycosylation
- d) Proteolysis
Explanation:
The complement system consists of plasma proteins that circulate as inactive precursors (zymogens). They are activated through a cascade of Proteolysis, where one active enzyme cleaves the next protein in the series into two or more fragments, thereby activating it.
Why other options are incorrect:
Why other options are incorrect:
- • Microsomal hydroxylation: This is a metabolic process usually involved in the detoxification of drugs in the liver.
- • Phosphorylation: This involves adding a phosphate group to a molecule, commonly used in intracellular signaling but not the primary mechanism of the complement cascade.
- • Glycosylation: This is the attachment of sugar chains to proteins (often during post-translational modification) and does not trigger the rapid activation cascade of the complement system.
The complement system forms a membrane attack complex (MAC) made up of:
- a) Complements 1q, 1r and 1s
- b) Complements 1, 2, 3 and 4
- c) Complements 5b, 6, 7 and 8
- d) Factors B and D
Explanation:
The Membrane Attack Complex (MAC) is the end product of the complement activation cascade. It is composed of the terminal complement components: C5b, C6, C7, C8, and multiple C9 molecules. This complex forms a pore in the target cell membrane, leading to cell lysis.
Why other options are incorrect:
Why other options are incorrect:
- • Complements 1q, 1r and 1s: These form the C1 complex, which is the initiator of the classical pathway, not the attack complex.
- • Complements 1, 2, 3 and 4: These are early-stage components involved in the formation of C3 and C5 convertases.
- • Factors B and D: These are specialized proteins belonging to the Alternative Pathway of complement activation.
Factors B and D are required in:
- a) The classical pathway of complement fixation
- b) The alternate complement pathway
- c) Both (a) and (b)
- d) None of these
Explanation:
Factors B and D (along with Properdin) are unique proteins required for the Alternative Complement Pathway. In this pathway, Factor B binds to C3b, and Factor D then cleaves Factor B to form the C3 convertase (C3bBb).
Why other options are incorrect:
Why other options are incorrect:
- • The classical pathway: This pathway uses different components, specifically C1, C4, and C2, to initiate the cascade and form its C3 convertase (C4b2a).
- • Both: Factors B and D are strictly specific to the alternative pathway loop and do not participate in the classical or lectin pathways.
- • Key Difference: The alternative pathway can be activated directly by microbial surfaces without the need for antibodies, unlike the classical pathway.
The alternate complement pathway doesn’t involve:
- a) Antigen-antibody complex
- b) Complement 3
- c) Factors B and D
- d) Membrane attack unit
Explanation:
The Alternative pathway is an antibody-independent component of the innate immune system. Unlike the Classical pathway, it is triggered by foreign surface molecules (like bacterial LPS) and does not require an Antigen-antibody complex to initiate the cascade.
Why other options are incorrect:
Why other options are incorrect:
- • Complement 3: C3 is a central component common to all three pathways (Classical, Lectin, and Alternative).
- • Factors B and D: These are specific proteins required for the Alternative pathway to form the C3 convertase (C3bBb).
- • Membrane attack unit: All pathways eventually lead to the formation of the Membrane Attack Complex (MAC/C5b-9) to lyse the target cell.
Antibody diversity arises from:
- a) Gene amplification
- b) Gene re-arrangement
- c) Alternative splicing
- d) All of these
Explanation:
The primary mechanism for generating the vast diversity of antibodies is Gene re-arrangement (also known as V(D)J recombination). During B-cell development, various gene segments are randomly shuffled and joined together to create unique antigen-binding sites.
Why other options are incorrect:
Why other options are incorrect:
- • Gene amplification: This involves increasing the number of copies of a gene, which is common in drug resistance or cancer, but it does not create the structural diversity needed for antibodies.
- • Alternative splicing: While alternative splicing is used to determine if an antibody is membrane-bound or secreted (and to switch between IgM and IgD), it is not the primary source of the billions of different antigen-specificities.
- • All of these: Since gene amplification is not a mechanism for antibody diversity, this option is incorrect.
A light chain gene is constructed from the following segments:
- a) Variable and constant segments
- b) Variable, joining and constant segments
- c) Variable, diversity and constant segments
- d) Variable, joining, diversity and constant segments
Explanation:
The light chain of an antibody (either Kappa or Lambda) is encoded by three types of gene segments: Variable (V), Joining (J), and Constant (C). During B-cell development, one V segment and one J segment rearrange to form the functional variable region.
Why other options are incorrect:
Why other options are incorrect:
- • Variable and constant segments: This is incomplete because it omits the J (Joining) segment, which is essential for connecting the V and C regions.
- • Variable, diversity and constant segments: Diversity (D) segments are not found in light chains; they are specific to heavy chains.
- • Variable, joining, diversity and constant segments: This describes the Heavy chain gene construction (V-D-J-C). Light chains lack the D (Diversity) segment.
In metabolic point of view, amino acids are classified as
- a) Glycogenic
- b) Ketogenic
- c) Glycogenic or Ketogenic
- d) All of these
Explanation:
Metabolically, amino acids are classified as glycogenic, ketogenic, or both
glycogenic and ketogenic, depending on the metabolic products formed from
their carbon skeletons.
Why other options are correct:
Why other options are correct:
- • Glycogenic: These amino acids can give rise to glucose through gluconeogenesis.
- • Ketogenic: These amino acids produce acetyl-CoA or acetoacetate, which can contribute to ketone body formation.
- • Glycogenic or Ketogenic: Some amino acids can be exclusively glycogenic, exclusively ketogenic, or both.
Diversity segments are present in:
- a) Light chain genes
- b) Heavy chain genes
- c) Light and heavy chain genes
- d) None of these
Explanation:
Diversity (D) segments are specific gene segments found only in the Heavy chain genes of immunoglobulins (and TCR beta/delta chains). The heavy chain variable region is formed by the recombination of V (Variable), D (Diversity), and J (Joining) segments, whereas the light chain lacks the D segment.
Why other options are incorrect:
Why other options are incorrect:
- • Light chain genes: These are constructed using only V (Variable) and J (Joining) segments (V-J recombination).
- • Light and heavy chain genes: This is incorrect because, while both have V and J segments, only the heavy chain contains the D segment.
- • None of these: This is incorrect because D segments are a fundamental part of the heavy chain gene architecture.
Constant segments of heavy chains are of:
- a) Five types
- b) Six types
- c) Seven types
- d) Eight types
Explanation:
The constant region of the heavy chain determines the isotype (class) of the antibody. In humans, there are five types of heavy chains, designated by Greek letters:
Why other options are incorrect:
- μ (Mu) – creates IgM
- δ (Delta) – creates IgD
- γ (Gamma) – creates IgG
- ε (Epsilon) – creates IgE
- α (Alpha) – creates IgA
Why other options are incorrect:
- • Six, Seven, or Eight: These do not correspond to the standard classification of human immunoglobulin classes. While there are subclasses (like IgG1, IgG2, etc.), the primary constant segment types remain five.
Gamma heavy chains are of:
- a) Two types
- b) Three types
- c) Four types
- d) Five types
Explanation:
The Gamma ($\gamma$) heavy chain, which characterizes the IgG class of antibodies, exists in four distinct subclasses in humans: IgG1, IgG2, IgG3, and IgG4. These subclasses differ in their hinge regions and the number of disulfide bonds.
Why other options are incorrect:
Why other options are incorrect:
- • Two types: This applies to the light chains (Kappa and Lambda), not the Gamma heavy chain.
- • Three types: No major human antibody class is divided into exactly three subclasses.
- • Five types: This is the total number of primary heavy chain classes ($\mu, \delta, \gamma, \epsilon, \alpha$), not the number of subclasses within the Gamma group.
Gamma heavy chains are present in:
- a) IgA
- b) IgG
- c) IgM
- d) IgD
Explanation:
The classification of antibodies (Immunoglobulins) is based on the type of heavy chain they possess. IgG is the class of antibody that contains Gamma ($\gamma$) heavy chains.
Why other options are incorrect:
Why other options are incorrect:
- • IgA: This class contains Alpha ($\alpha$) heavy chains.
- • IgM: This class contains Mu ($\mu$) heavy chains.
- • IgD: This class contains Delta ($\delta$) heavy chains.
- • Note: IgE contains Epsilon ($\epsilon$) heavy chains.
Heavy chains in IgD are of following type:
- a) Alpha
- b) Gamma
- c) Delta
- d) Epsilon
Explanation:
The heavy chain type determines the class of the immunoglobulin. For IgD, the heavy chain is designated by the Greek letter Delta (δ). These are primarily found on the surface of B cells where they serve as antigen receptors.
Why other options are incorrect:
Why other options are incorrect:
- • Alpha: This heavy chain type is found in IgA.
- • Gamma: This heavy chain type is found in IgG.
- • Epsilon: This heavy chain type is found in IgE.
On exposure to any antigen, the first antibody to be formed is of the following class:
- a) IgA
- b) IgG
- c) IgM
- d) IgE
Explanation:
IgM is the first immunoglobulin class produced during a primary immune response to an antigen. Because secreted IgM is a pentamer (containing 10 antigen-binding sites), it is highly efficient at neutralizing pathogens and activating the complement system early in an infection.
Why other options are incorrect:
Why other options are incorrect:
- • IgA: Primarily associated with mucosal immunity (tears, saliva, colostrum) and is usually not the first isotype produced systemically.
- • IgG: This is the most abundant antibody in long-term immunity, but it typically appears after IgM during the primary response or rapidly during a secondary (memory) response.
- • IgE: Primarily involved in allergic reactions and defense against parasitic worms, not as a general first-responder to all antigens.
Cell-mediated immunity is the function of:
- a) B lymphocytes
- b) T lymphocytes
- c) Plasma cells
- d) Basophils
Explanation:
Cell-mediated immunity (CMI) is an immune response that does not involve antibodies. It is primarily driven by T lymphocytes (T cells). These cells can directly kill infected host cells (Cytotoxic T cells) or release cytokines to activate other immune cells (Helper T cells).
Why other options are incorrect:
Why other options are incorrect:
- • B lymphocytes: These are responsible for Humoral immunity, which involves the production of antibodies.
- • Plasma cells: These are fully differentiated B cells that secrete large volumes of antibodies; they are the effector cells of the humoral response.
- • Basophils: These are a type of granulocyte involved in inflammatory and allergic responses, not the primary mediators of cell-mediated immunity.
The most abundant T cells are:
- a) Cytotoxic T cells
- b) Helper T cells
- c) Suppressor T cells
- d) Memory T cells
Explanation:
Helper T cells (CD4+) are the most numerous type of T lymphocyte, typically making up about 60-70% of the total T cell population in the blood. They play a central role in the immune system by secreting cytokines that “help” or coordinate the activities of other immune cells.
Why other options are incorrect:
Why other options are incorrect:
- • Cytotoxic T cells: These (CD8+) are the second most abundant, generally maintaining a 2:1 ratio (CD4:CD8) in healthy individuals.
- • Suppressor T cells: Also known as Regulatory T cells (Tregs), these make up a much smaller percentage (roughly 5-10%) of the T cell pool.
- • Memory T cells: These are a specialized subset that forms after an initial infection; while significant, they do not outnumber the primary Helper T cell population.
T cells can recognise:
- a) Free antigens
- b) Antigens bound to cells
- c) Antigens bound to antibodies
- d) Antigens bound to MHC proteins
Explanation:
Unlike B cells, T cells cannot recognize antigens in their native or “free” form. They can only recognize protein fragments (peptides) that have been processed and displayed on the surface of other cells in association with Major Histocompatibility Complex (MHC) proteins. This requirement is known as MHC restriction.
Why other options are incorrect:
Why other options are incorrect:
- • Free antigens: These are recognized directly by the B-cell receptor (BCR) or antibodies, not the T-cell receptor (TCR).
- • Antigens bound to cells: While T cells do interact with cells, they specifically require the MHC molecule to “present” the antigen; they don’t just recognize any antigen stuck to a cell surface.
- • Antigens bound to antibodies: These form immune complexes that are typically cleared by phagocytes (like macrophages) or activate the complement system, rather than being the target of direct T-cell recognition.
MHC proteins are unique to:
- a) Each cell
- b) Each organ
- c) Each individual
- d) Each species
Explanation:
MHC (Major Histocompatibility Complex) proteins are highly polymorphic, meaning there are many different versions of these genes within the population. Except for identical twins, the specific set of MHC molecules is unique to each individual, acting as a biological “fingerprint” that allows the immune system to distinguish “self” from “non-self.”
Why other options are incorrect:
Why other options are incorrect:
- • Each cell: All nucleated cells within a single person’s body express the same set of MHC Class I molecules.
- • Each organ: Different organs in the same body share the same MHC markers.
- • Each species: While a species shares the same naming system (e.g., HLA in humans), the specific proteins vary significantly between different members of that species.
MHC class I proteins are present on the surface of:
- a) B cells only
- b) T cells only
- c) Macrophages only
- d) All cells
Explanation:
MHC Class I proteins are expressed on the surface of almost all nucleated cells in the body. Their primary function is to present endogenous antigens (like viral or tumor proteins) to CD8+ Cytotoxic T cells, allowing the immune system to monitor the health of every cell.
Why other options are incorrect:
Why other options are incorrect:
- • B cells, T cells, and Macrophages: While all these cells do have MHC Class I (because they are nucleated), the proteins are not restricted “only” to these specific types.
- • Exception: Non-nucleated cells, such as red blood cells, do not express MHC Class I proteins.
- • MHC Class II: Unlike Class I, MHC Class II is found only on specialized “professional” antigen-presenting cells (like B cells, macrophages, and dendritic cells).
MHC class I proteins, in conjunction with antigens are recognised by:
- a) Cytotoxic T cells
- b) Helper T cells
- c) Suppressor T cells
- d) Memory T cells
Explanation:
MHC Class I molecules present endogenous antigens (like viral peptides) to Cytotoxic T cells (CD8+ T cells). This interaction allows the Cytotoxic T cell to identify and kill infected or abnormal “self” cells.
Why other options are incorrect:
Why other options are incorrect:
- • Helper T cells: These are CD4+ cells and specifically recognize antigens presented by MHC Class II molecules.
- • Suppressor T cells: Also known as Regulatory T cells (Tregs), they are generally CD4+ and focus on dampening the immune response rather than direct MHC I-mediated killing.
- • Memory T cells: While some memory cells are CD8+ and do recognize MHC I, the functional class defined by the recognition of MHC I in the context of cell-mediated killing is the Cytotoxic T cell.
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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