Biotechnology & Biochemistry

Biotechnology & Biochemistry

Ligand for TLR3 receptor is:

TLR3 is endosomal pattern recognition receptor recognizing double-stranded RNA produced during viral replication. Binding dsRNA recruits TRIF adaptor, activating IRF3 and NF-kB pathways leading to type I interferon production. LPS binds TLR4, lipopeptides TLR2, flagellin TLR5, not TLR3.

Ref: Owen, Punt and Stranford, Kuby Immunology, 7th Edition, Chapter 4, Innate immunity receptors, explains Toll-like receptor 3 ligand specificity for double-stranded RNA and downstream signaling via TRIF adaptor leading to interferon response, published by W.H. Freeman.

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Biotechnology & Biochemistry

Cluster of differentiation (CD) molecules are present on:

CD molecules are surface glycoproteins used as immunophenotypic markers to identify leukocyte lineages, activation status and differentiation stages. Examples CD3 on T cells, CD19 on B cells, CD4 helper identity. Flow cytometry detects these cell-surface antigens, not cytoplasmic or organellar locations.

Ref: Abbas, Lichtman and Pillai, Cellular and Molecular Immunology, 9th Edition, Chapter 2, Cells and Tissues of Immune System, describes CD molecules as cell surface markers for immune cell identification and classification, published by Elsevier.

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Biotechnology & Biochemistry

The process by which normal serum enhances phagocytosis is called:

Opsonization coats pathogens with serum opsonins like IgG antibodies and complement C3b, recognized by Fc and complement receptors on neutrophils and macrophages. This bridging enhances adhesion and engulfment, dramatically increasing phagocytosis efficiency of innate immune clearance and pathogen destruction.

Ref: Owen, Punt and Stranford, Kuby Immunology, 7th Edition, Chapter 3, Innate Immunity, discusses opsonization by complement and antibodies enhancing phagocytosis through Fc and complement receptors on phagocytes, published by W.H. Freeman.

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Biotechnology & Biochemistry

The electrophoretic technique used to separate very large DNA segments is:

Conventional agarose electrophoresis cannot resolve megabase DNA because large fragments co-migrate. Pulsed-field gel electrophoresis periodically changes electric field direction, forcing DNA to reorient. Larger molecules take longer to reorient, thus separating chromosomes up to several megabases for genomic mapping and karyotyping.

Ref: Sambrook and Russell, Molecular Cloning: A Laboratory Manual, 3rd Edition, Chapter 5, Gel Electrophoresis of DNA, describes pulsed-field gel electrophoresis principle for separating very large DNA fragments and chromosomal DNA, published by Cold Spring Harbor Laboratory Press.

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Biotechnology & Biochemistry

Niemann-Pick disease is a:

Niemann-Pick disease results from acid sphingomyelinase deficiency or NPC protein defects, causing lysosomal accumulation of sphingomyelin and cholesterol in macrophages, liver, spleen and brain. This autosomal recessive lipidosis leads to hepatosplenomegaly, neurodegeneration and foam cell formation.

Ref: Scriver et al., The Metabolic and Molecular Bases of Inherited Disease, 8th Edition, Chapter 134, Lysosomal storage disorders, describes Niemann-Pick disease as sphingomyelin lipid storage disorder due to sphingomyelinase deficiency, published by McGraw-Hill.

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Biotechnology & Biochemistry

Hybridomas are immortalized for production of unlimited supply of monoclonal antibodies by which of the following:

Hybridoma technology fuses antibody-producing B lymphocytes with immortal myeloma cells using polyethylene glycol or electrofusion. Resulting hybrid cells retain B-cell immunoglobulin secretion and myeloma immortality, selected in HAT medium, providing continuous unlimited monoclonal antibody production for research and therapy.

Ref: Owen, Punt and Stranford, Kuby Immunology, 7th Edition, Chapter 20, Monoclonal antibody production, explains hybridoma generation by cell fusion of B cells with myeloma cells to achieve immortalized antibody-secreting lines, published by W.H. Freeman.

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Biotechnology & Biochemistry

What are the Yamanaka factors used for iPSCs reprogramming?

Shinya Yamanaka demonstrated somatic cells reprogram to pluripotent stem cells by overexpressing four transcription factors: Oct3/4, Sox2, Klf4 and c-Myc. These induce endogenous pluripotency network, silencing differentiation genes, enabling generation of induced pluripotent stem cells for regenerative medicine and disease modeling.

Ref: Lanza and Atala, Essentials of Stem Cell Biology, 3rd Edition, Chapter 18, Induced pluripotent stem cells, discusses Yamanaka factors Oct4, Sox2, Klf4 and c-Myc reprogramming mechanism and applications, published by Academic Press.

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Biotechnology & Biochemistry

COVID-19 caused by:

SARS-CoV-2 causing COVID-19 is an enveloped betacoronavirus containing positive-sense single-stranded RNA genome of about 30 kb. Its genomic RNA directly serves as mRNA for translation of replicase polyproteins, enabling rapid cytoplasmic replication via RNA-dependent RNA polymerase without DNA intermediate.

Ref: Knipe and Howley, Fields Virology, 6th Edition, Volume 1, Chapter on Coronaviridae, describes SARS-CoV-2 as positive-sense single-stranded RNA virus, its replication strategy and classification, published by Lippincott Williams and Wilkins.

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Biotechnology & Biochemistry

How many unusual bases are observed in a tRNA molecule?

Transfer RNA contains extensively modified nucleosides formed post-transcriptionally, including pseudouridine, dihydrouridine, methylguanosine, inosine, methylinosine and ribothymidine. These unusual bases stabilize cloverleaf structure, enhance anticodon wobble pairing and protect against degradation, with approximately five major types commonly described in textbooks.

Ref: Watson et al., Molecular Biology of the Gene, 7th Edition, Chapter 14, RNA modification, discusses tRNA containing unusual bases such as pseudouridine, dihydrouridine, inosine and methylated bases crucial for function, published by Pearson Education.

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Biotechnology & Biochemistry

Cryo-preservant used for cells consists of:

Dimethyl sulfoxide at ten percent in fetal bovine serum prevents intracellular ice crystal formation by penetrating cells and displacing water, lowering freezing point. This cryoprotectant mixture maintains membrane integrity during slow freezing to -196°C and thawing, ensuring high post-thaw viability of mammalian cell lines.

Ref: Freshney, Culture of Animal Cells: A Manual of Basic Technique, 6th Edition, Chapter 19, Cryopreservation, details standard freezing medium containing 10% DMSO in fetal bovine serum as cryoprotectant for mammalian cell preservation, published by Wiley-Blackwell.

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Biotechnology & Biochemistry

If the purpose is to calculate the probability of one event and a second event, the odds scores for the events are:

The joint probability of two independent events occurring together follows product rule. When calculating probability of event A and event B, their individual probabilities are multiplied, while probabilities for or events are added, reflecting fundamental principles of combinatorial probability and statistical independence.

Ref: Daniel and Cross, Biostatistics: A Foundation for Analysis in the Health Sciences, 10th Edition, Chapter 4, Probability concepts, explains multiplication rule for joint probability of independent events and addition rule for mutually exclusive events, published by Wiley.

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Biotechnology & Biochemistry

In sequence alignment by BLAST, each word from query sequence is typically _______ residues for protein sequences and __

BLAST accelerates alignment using short word seeds to find initial matches. For proteins default word size is three amino acids, balancing sensitivity and speed given 20-letter alphabet. For DNA, longer eleven-nucleotide seeds are used because four-letter alphabet would generate excessive random hits otherwise.

Ref: Mount, Bioinformatics Sequence and Genome Analysis, 2nd Edition, Chapter 6, Sequence Alignment and Database Searching, describes BLAST word size parameters, default three residues for proteins and eleven for DNA sequences, published by Cold Spring Harbor Laboratory Press.

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