Biochemistry & Structural Biology

Biochemistry & Structural Biology

T lymphocytes in a lymph node are concentrated in which of the following anatomical locations?

Lymph node architecture segregates lymphocytes functionally. B cells populate follicles, germinal centers, and mantle zones, while T cells localize predominantly in deep cortex paracortex surrounding high endothelial venules adjacent to follicles, where dendritic cells present antigen entering via afferent lymph.

Ref: Abbas AK et al., Cellular and Molecular Immunology, 10th Edition, Chapter 2 Cells and Tissues of Immune System, section on lymph node anatomy describing paracortex as T-cell zone adjacent to B-cell follicles containing high endothelial venules, published by Elsevier Saunders.

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Biochemistry & Structural Biology

Which of the following autoantibodies is characteristically associated with limited scleroderma?

Limited cutaneous systemic sclerosis, formerly CREST syndrome, shows strong association with anti-centromere antibodies targeting kinetochore centromere proteins A-C. These antibodies produce discrete speckled immunofluorescence pattern, predicting limited skin involvement, pulmonary hypertension, and better prognosis than diffuse topoisomerase-positive disease.

Ref: Kumar V et al., Robbins and Cotran Pathologic Basis of Disease, 10th Edition, Chapter 6 Diseases of Immune System, section on systemic sclerosis autoantibodies describing anti-centromere specificity for limited scleroderma CREST variant, published by Elsevier Saunders.

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Biochemistry & Structural Biology

Natural killer (NK) cells recognize target cells for a cytotoxic response by which of the following mechanisms?

NK cells employ missing-self recognition, detecting loss of inhibitory signals. Normal cells expressing self MHC class I engage KIRs and CD94/NKG2A inhibiting killing. Tumor or virus-infected cells downregulating MHC I escape T-cell recognition but become susceptible to NK cytotoxicity through reduced inhibition.

Ref: Abbas AK et al., Cellular and Molecular Immunology, 10th Edition, Chapter 4 Innate Immunity, section on NK cell recognition and missing-self hypothesis where absence of MHC Class I molecules triggers cytotoxic response via inhibitory receptors, published by Elsevier Saunders.

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Biochemistry & Structural Biology

CD40L, an early activation marker is predominantly expressed on which of the following lymphocyte subset?

Activated CD4 helper T cells rapidly upregulate CD40 ligand CD154 upon TCR engagement, interacting with CD40 on B cells and dendritic cells to promote germinal center formation, class switching, and co-stimulation. Expression is transient activation marker, predominantly restricted to CD4 T-cell subset.

Ref: Abbas AK et al., Cellular and Molecular Immunology, 10th Edition, Chapter 7 Lymphocyte Activation, section on CD40 ligand CD154 expression on activated helper T lymphocytes and CD40-CD40L co-stimulatory pathway for B cell activation, published by Elsevier Saunders.

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Biochemistry & Structural Biology

When an alkali metal is dissolved in NH3 , it forms a blue coloured solution. The colour is due to:

Liquid ammonia solvates alkali metals releasing electrons trapped in solvent cavities surrounded by ammonia molecules. These solvated or ammoniated electrons absorb strongly in visible range producing characteristic deep blue color, exhibiting paramagnetism and high electrical conductivity at dilute concentrations.

Ref: Lee JD, Concise Inorganic Chemistry, 5th Edition, Chapter on Alkali Metals, section on solutions of alkali metals in liquid ammonia describing formation of ammoniated or solvated electrons responsible for blue color and conductivity, published by Wiley-Blackwell.

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Biochemistry & Structural Biology

Microtubule and microfilament are composed of which type of protein?

Cytoskeletal organization depends on distinct polymers: microtubules formed by alpha-beta tubulin heterodimer assembly mediating mitotic spindle and vesicular transport, while microfilaments comprise filamentous actin providing contractility, cell shape, and motility through polymerization driven treadmilling and myosin interactions.

Ref: Alberts B et al., Molecular Biology of the Cell, 6th Edition, Chapter 16 The Cytoskeleton, sections on microtubules composed of tubulin dimers and microfilaments composed of actin filaments, their structure and functions, published by Garland Science.

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Biochemistry & Structural Biology

A few chromosomes having a small fragment called the satellite, have:

SAT chromosomes possess secondary constrictions separate from centromere that appear non-staining due to tandem rRNA gene repeats organizing nucleolus. These NOR regions occur at constant positions on short arms of acrocentric chromosomes, yielding satellite segment distal to constriction.

Ref: Gardner EJ et al., Principles of Genetics, 8th Edition, Chapter 7 Chromosome Structure, section on satellite chromosomes and non-staining secondary constrictions at constant locations harboring nucleolar organizer regions, published by John Wiley and Sons.

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Biochemistry & Structural Biology

In eukaryotic cell transcription, RNA splicing and RNA capping take place inside?

In eukaryotes, transcription by RNA polymerase II, 5' capping with 7-methylguanosine, and intron removal by spliceosome all occur co-transcriptionally inside nucleus. Pre-mRNA processing completes before export through nuclear pores, unlike ribosomal translation which occurs cytoplasmically after maturation.

Ref: Alberts B et al., Molecular Biology of the Cell, 6th Edition, Chapter 6 From DNA to RNA, section on eukaryotic transcription and co-transcriptional RNA processing including capping and splicing occurring in the nucleus, published by Garland Science Taylor and Francis Group.

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Biochemistry & Structural Biology

A sample of DNA is found to have the base composition (mole ratio) of A = 40, T = 22, G = 21 and C = 17. This suggests:

According to Chargaff's rules, double-stranded DNA exhibits A=T and G=C equimolarity. The given composition shows A 40 ≠ T 22 and G 21 ≠ C 17, violating parity. Such imbalance indicates single-stranded DNA where base pairing does not constrain composition, often seen in some viral genomes.

Ref: Watson JD et al., Molecular Biology of the Gene, 7th Edition, Chapter 6 Structure of DNA, section discussing Chargaff's rules of base parity in double-stranded DNA and deviation indicating single-stranded nature, published by Pearson and Cold Spring Harbor Laboratory Press.

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Biochemistry & Structural Biology

The computational methodology that tries to find the best matching between two molecules, a receptor and ligand is calle

Ligand-receptor binding prediction relies on sampling conformational space and scoring binding energy. Molecular docking computationally predicts preferred orientation, affinity, and interactions within active sites, essential for structure-based drug design, virtual screening, and identifying inhibitors before experimental validation.

Ref: Baxevanis AD and Ouellette BFF, Bioinformatics A Practical Guide to Analysis of Genes and Proteins, 3rd Edition, Chapter 14 Protein Structure Prediction and Chapter on molecular docking predicting receptor-ligand interactions for drug discovery, published by John Wiley and Sons.

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Biochemistry & Structural Biology

The major donor of carbon atoms of the one-carbon pool is:

One-carbon metabolism transfers formyl, methylene, and methyl groups via tetrahydrofolate for purine and thymidylate synthesis. Serine, through serine hydroxymethyltransferase, donates its beta-carbon to THF generating 5,10-methylene-THF, providing the primary source contributing majority of one-carbon units.

Ref: Nelson DL and Cox MM, Lehninger Principles of Biochemistry, 7th Edition, Chapter 22 Amino Acid Oxidation and Production of Urea, section on one-carbon metabolism and role of serine as major donor generating 5,10-methylene tetrahydrofolate, published by W H Freeman and Company.

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Biochemistry & Structural Biology

Which of the following is NOT used as a vector in Molecular cloning?

Plasmids, cosmids, and artificial chromosomes replicate autonomously and carry selective markers, ideal for cloning foreign DNA. Haptens are small immunogenic incomplete antigens requiring carrier conjugation to elicit antibody response, lacking replication origin, thus completely unrelated to molecular cloning vector systems.

Ref: Green MR and Sambrook J, Molecular Cloning A Laboratory Manual, 4th Edition, Chapter 4 Plasmids and Their Usefulness in Molecular Cloning and Chapter 7 discussing cosmid and artificial chromosome vectors versus haptens which are immunological molecules, published by Cold Spring Harbor Laboratory Press.

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