Biochemistry & Cell Biology

Biochemistry & Cell Biology

The following constitutes approximately 75% of total immunoglobulins in humans:

IgG dominates humoral immunity, constituting about 75% of serum immunoglobulins with four subclasses providing systemic long-lived defense. Small monomeric structure allows extravascular distribution and placental transfer. High affinity, complement activation and opsonization underlie its protective role, while predominance makes total immunoglobulin levels largely reflect IgG concentrations.

Ref: Abbas A.K., Lichtman A.H., Pillai S., Cellular and Molecular Immunology, 10th Edition, Chapter 10 Antibodies Structure and Functions, states IgG is most abundant immunoglobulin comprising approximately seventy-five percent of total serum immunoglobulins providing systemic long-term immunity, published by Elsevier Saunders.

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Biochemistry & Cell Biology

Phagocytosis enhanced by coating the surface of antigen is called:

Opsonization coats microbial surfaces with opsonins such as IgG and complement fragment C3b, enhancing recognition by phagocyte Fc and complement receptors. This coating bridges pathogen to phagocyte, promoting adhesion, ingestion and respiratory burst killing. Deficiency in opsonization explains recurrent infections with encapsulated bacteria lacking effective phagocytic clearance.

Ref: Owen J.A., Punt J., Stranford S.A., Kuby Immunology, 7th Edition, Chapter 6 Phagocytosis and Opsonization, explains opsonization as coating antigens with IgG and C3b enhancing phagocytosis via enhanced Fc and complement receptor binding promoting ingestion and killing, published by W.H. Freeman.

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Biochemistry & Cell Biology

Which one of the following is an example of artificial passive immunization?

Pooled human gamma globulin administration provides ready-made IgG antibodies for immediate short-term protection, exemplifying artificial passive immunization. Unlike active vaccination inducing memory, protection wanes as antibodies catabolize. This approach treats immunodeficiency, envenomation and post-exposure prophylaxis, whereas transplacental antibody transfer represents natural passive immunity mechanism.

Ref: Owen J.A., Punt J., Stranford S.A., Kuby Immunology, 7th Edition, Chapter 17 Passive and Active Immunization, distinguishes artificial passive immunization using pooled human gamma globulin injection providing immediate IgG protection versus natural transplacental antibody transfer, published by W.H. Freeman.

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Biochemistry & Cell Biology

In SDS-PAGE the movement of proteins is from:

SDS PAGE separates proteins by molecular weight after denaturing SDS binds uniformly imparting negative charge proportional to length. Under electric field, SDS-protein complexes migrate from negative cathode toward positive anode through polyacrylamide matrix, smaller proteins traveling farther. Migration distance inversely correlates with log molecular weight for estimation.

Ref: Wilson K. and Walker J., Principles and Techniques of Biochemistry and Molecular Biology, 8th Edition, Chapter 15 SDS-PAGE Principles, explains SDS-protein complexes acquiring uniform negative charge migrating from cathode to anode separating by molecular weight in polyacrylamide gel, published by Cambridge University Press.

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Biochemistry & Cell Biology

RNAs that catalyse biological reactions such as self-splicing introns, are known as

Ribozymes are catalytically active RNA molecules capable of cleaving and ligating phosphodiester bonds without protein enzymes, exemplified by self-splicing group I introns in Tetrahymena. Their discovery demonstrated RNA can store information and catalyze reactions, supporting RNA world hypothesis and providing tools for gene manipulation and therapeutic intervention.

Ref: Cech T.R. and Zaug A.J., Cell Journal Article, Discovery of Catalytic RNA Ribozymes, and Alberts et al Molecular Biology of the Cell 6th Edition Chapter 6 RNA Catalysis, describes ribozymes as catalytic RNAs including self-splicing introns catalyzing phosphodiester bond reactions, published by Elsevier Cell Press.

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Biochemistry & Cell Biology

An object that cannot be superimposed on its mirror image is known as:

Chirality describes molecules or objects non-superimposable on their mirror images due to lack of symmetry plane, common with asymmetric carbon centers. Chiral compounds exist as enantiomers with distinct optical activity and biological interactions. Understanding chirality explains drug stereoselectivity, as enantiomers often exhibit different pharmacologic potencies.

Ref: Clayden J., Greeves N., Warren S., Organic Chemistry, 2nd Edition, Chapter 4 Chirality and Stereochemistry, defines chiral objects as non-superimposable on mirror images due to stereogenic centers and explains enantiomers optical activity and biological significance, published by Oxford University Press.

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Biochemistry & Cell Biology

Which of the following is not used as a vector in molecular cloning?

Hapten is a small molecule requiring carrier protein to evoke immune response and never serves as molecular cloning vehicle. Vectors like plasmid, cosmid, BAC replicate foreign DNA inside host cells, providing origin of replication, selectable marker and cloning sites. Haptens belong to immunology, not recombinant DNA technology.

Ref: Green M.R. and Sambrook J., Molecular Cloning A Laboratory Manual, 4th Edition, Chapter 1 Plasmid and Cloning Vectors, outlines plasmids cosmids and bacterial artificial chromosomes as cloning vectors, clarifying hapten as immunological antigen not cloning vector, published by Cold Spring Harbor Laboratory Press.

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Biochemistry & Cell Biology

Which of the following is also called "suicide enzyme"?

O6-methylguanine-DNA methyltransferase removes alkyl adducts from O6 position of guanine by transferring methyl group to its own cysteine residue, irreversibly inactivating itself. Each enzyme molecule acts only once, hence designated suicide enzyme. This direct repair mechanism protects genome without excision and prevents mutagenic G to A transitions.

Ref: Friedberg E.C., Walker G.C., Siede W., Wood R.D., Schultz R.A., Ellenberger T., DNA Repair and Mutagenesis, 2nd Edition, Chapter 4 Direct Reversal Repair, describes O6-alkylguanine-DNA alkyltransferase as suicide enzyme transferring alkyl group to self cysteine causing irreversible inactivation, published by ASM Press.

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Biochemistry & Cell Biology

In hybridoma technology, B cells are fused with:

Hybridoma technology fuses antibody-producing B lymphocytes with immortal myeloma cells to generate continuous hybrid lines secreting monoclonal antibody. Polyethylene glycol mediated fusion, followed by HAT medium selection, eliminates unfused parents. Resultant hybridomas combine specific antibody specificity with perpetual growth, revolutionizing therapeutic and diagnostic antibody production.

Ref: Owen J.A., Punt J., Stranford S.A., Kuby Immunology, 8th Edition, Chapter 20 Monoclonal Antibodies and Hybridoma Technology, describes fusing B lymphocytes with myeloma cells using polyethylene glycol and HAT selection to produce monoclonal antibody secreting hybridomas, published by Macmillan.

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Biochemistry & Cell Biology

BLAST uses a________to find matching words, whereas FASTA identifies identical matching words using the______.

BLAST accelerates similarity searches using scoring substitution matrices like BLOSUM62 to identify high-scoring word matches allowing mismatches, extending seeds into local alignments. FASTA traditionally relies on exact ktup word hashing to find identical matches before joining diagonals. This difference influences sensitivity and speed between algorithms.

Ref: Mount D.W., Bioinformatics Sequence and Genome Analysis, 2nd Edition, Chapter 3 Pairwise Sequence Alignment and BLAST FASTA Algorithms, explains BLAST using substitution matrices for word matching while FASTA uses ktup hashing to find identical words, published by Cold Spring Harbor Laboratory Press.

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Biochemistry & Cell Biology

Frame shift mutation results from:

Frameshift mutations arise when insertion or deletion of bases not divisible by three alters downstream reading frame. Deleting a single nucleotide shifts all subsequent codons, typically producing premature termination and nonfunctional protein. Substituting three bases or whole codon deletions preserve frame, causing in-frame alterations rather than frameshift.

Ref: Alberts B., Johnson A., Lewis J., Raff M., Roberts K., Walter P., Molecular Biology of the Cell, 6th Edition, Chapter 5 DNA Mutation, Frameshift Mutations, explains single base deletion shifting reading frame causing premature termination and altered downstream amino acids, published by Garland Science.

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Biochemistry & Cell Biology

Which of the following is a nucleotide sequence data base?

EMBL Nucleotide Sequence Database at European Bioinformatics Institute archives primary nucleotide sequences and annotations from genome projects worldwide. It collaborates in International Nucleotide Sequence Database Collaboration with GenBank and DDBJ. SWISS-PROT, PROSITE and TrEMBL instead curate protein sequences or motifs, separating nucleotide versus protein resources.

Ref: Mount D.W., Bioinformatics Sequence and Genome Analysis, 2nd Edition, Chapter 2 Databases, EMBL Nucleotide Database as primary member of International Nucleotide Sequence Database Collaboration archiving nucleotide sequences and annotations, contrasting protein databases, published by Cold Spring Harbor Laboratory Press.

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