Microbiology & Sterilization Techniques

Microbiology & Sterilization Techniques

How many genes are there is E. coli K-12 genome

E. coli K-12 MG1655 genome sequenced in 1997 revealed approximately 4,377 protein-coding genes within 4.6 Mb. This laboratory strain annotation includes operons, regulatory RNAs and metabolic pathways extensively used as bacterial genetics reference model.

Ref: Blattner et al., Science 1997 and Brown, Genomes, 4th Edition, Chapter 7, Model Genomes, describes complete sequence of Escherichia coli K-12 MG1655 comprising 4,377 genes, genome organization and functional annotation, published by Garland Science.

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Microbiology & Sterilization Techniques

Inhibition of succinic dehydrogenase by malonic acid is

Malonate structurally resembles succinate and competes for active site of succinate dehydrogenase in TCA cycle. It increases apparent Km without affecting Vmax, reversible by excess substrate, classic example of competitive inhibition in mitochondrial complex II.

Ref: Lehninger Principles of Biochemistry, Nelson and Cox, 7th Edition, Chapter 6, Enzyme Inhibition and Regulation, uses succinate dehydrogenase inhibition by malonate as textbook example of competitive inhibition with kinetic parameters, published by W.H. Freeman.

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Microbiology & Sterilization Techniques

Difference between a DNA and RNA

DNA contains deoxyribose sugar and thymine as pyrimidine, while RNA contains ribose with 2'-OH and uracil instead of thymine. Both share purines adenine guanine and phosphate backbone, but sugar and pyrimidine differences confer distinct stability and function.

Ref: Watson et al., Molecular Biology of the Gene, 7th Edition, Chapter 4, DNA and RNA Structure, details differences in sugar moiety, uracil versus thymine, ribose 2'-hydroxyl group and impact on chemical stability, published by Pearson.

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Microbiology & Sterilization Techniques

Alu sequences are

Alu elements are short interspersed nuclear elements about 300 bp, present in over one million copies in human genome. Derived from 7SL RNA, they are SINE retrotransposons mobilized by L1 machinery, contributing to genome evolution and regulation.

Ref: Lewin, Genes XII, 12th Edition, Chapter 15, Repetitive DNA and Transposons, discusses Alu sequences as most abundant SINEs, structure, copy number and role in human genome variation and disease, published by Jones and Bartlett Publishers.

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Microbiology & Sterilization Techniques

Which of the following amino acid found abundantly in collagen protein

Collagen triple helix requires glycine at every third position due to its minimal side chain fitting crowded center. This Gly-X-Y repeat allows tight helical packing, stability via hydroxyproline and proline, making glycine about 33% of collagen composition.

Ref: Lodish et al., Molecular Cell Biology, 8th Edition, Chapter 20, Collagen and Extracellular Matrix, explains Gly-X-Y repeat pattern, requirement of glycine for triple helix formation and abundance of proline and hydroxyproline, published by W.H. Freeman.

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Microbiology & Sterilization Techniques

Which of the following is a non-natural amino acid?

β-alanine is positional isomer of alanine where amino group shifts to beta carbon, not encoded by codons and not found in proteins. Natural amino acids like arginine, proline and tryptophan are 20 canonical proteinogenic L-alpha amino acids incorporated translationally.

Ref: Lehninger Principles of Biochemistry, Nelson and Cox, 7th Edition, Chapter 3, Amino Acids and Peptides, discusses standard versus non-standard amino acids, beta-amino acids, GABA and metabolic intermediates not incorporated into proteins, published by W.H. Freeman and Company.

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Microbiology & Sterilization Techniques

Which of the following is not required for a PCR reaction?

PCR requires Taq polymerase, deoxyribonucleoside triphosphates, primers and template DNA for amplification. Dideoxy-dNTPs lack 3'-OH and terminate chain elongation, used in Sanger sequencing, not PCR where continuous extension via normal dNTPs is essential.

Ref: Brown, Molecular Biology LabFax, and Sambrook and Russell Molecular Cloning, 4th Edition, Chapter 9, Polymerase Chain Reaction, lists essential PCR components and distinguishes dNTPs from ddNTPs used solely for chain-termination sequencing, published by Cold Spring Harbor Laboratory Press.

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Microbiology & Sterilization Techniques

‘RNAi’ stands for which of the following?

RNA interference is conserved gene silencing mechanism mediated by small interfering RNAs and microRNAs. Dicer cleaves dsRNA into siRNAs, loaded into RISC complex, guiding sequence-specific degradation of complementary mRNA, regulating expression.

Ref: Alberts et al., Molecular Biology of the Cell, 6th Edition, Chapter 7, RNA Interference, details discovery of RNAi, Dicer and Argonaute proteins, RISC complex formation and applications in functional genomics and therapeutics, published by Garland Science.

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Microbiology & Sterilization Techniques

Which of the following is a purine?

Adenine is double-ring purine base with structure of fused pyrimidine and imidazole. Purines include adenine and guanine, while pyrimidines are single-ring thymine, uracil and cytosine, differing in nitrogenous base classification in nucleic acids.

Ref: Watson et al., Molecular Biology of the Gene, 7th Edition, Chapter 4, Chemical Structure of Nucleic Acids, describes purine and pyrimidine classification, double-ring versus single-ring bases and Watson-Crick base pairing rules, published by Pearson Cold Spring Harbor.

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Microbiology & Sterilization Techniques

Which of the following does not have phosphate?

Nucleoside comprises nitrogenous base plus pentose sugar linked via N-glycosidic bond without phosphate. Adding phosphate converts nucleoside to nucleotide, building block of DNA and RNA which contain phosphodiester backbone with phosphate groups.

Ref: Lehninger Principles of Biochemistry, Nelson and Cox, 7th Edition, Chapter 8, Nucleotides and Nucleic Acids, defines nucleoside versus nucleotide structure, phosphate ester linkage and role in DNA and RNA polymers, published by W.H. Freeman.

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Microbiology & Sterilization Techniques

The enzyme responsible for the synthesis of RNA primer in eukaryotes

DNA polymerase alpha contains primase subunit that synthesizes short RNA primer 7-12 nucleotides on lagging strand. It initiates DNA replication at origins and Okazaki fragments, then polymerase alpha extends DNA briefly before polymerase delta takes over high-fidelity elongation.

Ref: Alberts et al., Molecular Biology of the Cell, 6th Edition, Chapter 5, DNA Replication, details eukaryotic replicative polymerases, polymerase alpha-primase complex as initiator of RNA primer synthesis and handoff to delta and epsilon, published by Garland Science.

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Microbiology & Sterilization Techniques

The organ with maximum O₂ consumption per minute

Liver exhibits highest total oxygen uptake approximately 20% of resting VO2 due to metabolically active hepatocytes performing gluconeogenesis, urea synthesis and detoxification. Though brain has higher per-gram consumption, absolute per-minute uptake is greatest in liver and skeletal muscle during activity.

Ref: Ganong's Review of Medical Physiology, 26th Edition, Chapter 32, Hepatic Circulation and Metabolism, explains high metabolic rate of liver, oxygen consumption, splanchnic oxygen extraction and comparison with brain, heart and skeletal muscle, published by McGraw Hill.

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