Microbiology & Infectious Diseases

Microbiology & Infectious Diseases

On a ribosome, the mRNA is read from………….and the polypeptide chain is synthesized from:

Ribosomes translocate 5' to 3' along mRNA decoding codons in that direction. Polypeptide synthesis proceeds amino to carboxyl as peptidyl transferase adds incoming aminoacyl-tRNA at C-terminus. Thus nascent chain grows N to C while message is read 5' to 3'.

Ref: Alberts, Molecular Biology of the Cell, 6th Edition, Chapter 6 on Translation and Genetic Code, explains ribosome reads mRNA 5' to 3' while polypeptide synthesized amino terminus to carboxyl terminus with peptidyl transferase elongation, published by Garland Science.

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Microbiology & Infectious Diseases

DNA and RNA polymerase differ in ALL of the following, EXCEPT:

Both DNA and RNA polymerases catalyze identical nucleophilic attack of 3'-OH on alpha-phosphate of incoming NTP, forming phosphodiester bonds. They diverge in substrates (dNTPs vs NTPs), proofreading and error rates, processivity, and requirement for primer versus de novo initiation.

Ref: Lehninger Principles of Biochemistry, Nelson and Cox, 8th Edition, Chapter 26 on RNA Metabolism and Chapter 25 on DNA Replication, discusses polymerases catalyze same phosphodiester bond formation but differ in substrates, error rates and processivity mechanisms, published by Macmillan Learning.

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Microbiology & Infectious Diseases

The core of the spliceosome complex is formed by:

Spliceosome is a dynamic complex of five small nuclear ribonucleoproteins U1, U2, U4, U5, U6 snRNAs plus over 150 proteins. snRNAs provide catalytic RNA core recognizing splice sites and branch point, mediating two transesterification reactions that excise introns from pre-mRNA.

Ref: Alberts, Molecular Biology of the Cell, 6th Edition, Chapter 6 on RNA Processing and Splicing, describes spliceosome core formed by small nuclear RNAs U1, U2, U4, U5, U6 snRNPs catalytic machinery for intron excision, published by Garland Science.

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Microbiology & Infectious Diseases

What type of amplification takes place in sequencing by synthesis technique?

Illumina sequencing by synthesis employs bridge amplification on flow cell to clonally amplify fragments into clusters. Single-stranded DNA bends forming bridges with adjacent oligos, extended by polymerase. This generates dense clusters of identical templates enabling fluorescence-based detection of incorporated reversible terminators.

Ref: Alberts, Molecular Biology of the Cell, 6th Edition, Chapter 8 on Genomics and Sequencing Technologies, and Metzker Nature Reviews Genetics 2010, explain bridge amplification for clonal cluster generation in sequencing by synthesis workflow on Illumina flow cells, published by Garland Science.

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Microbiology & Infectious Diseases

What does HGVS stands for?

HGVS denotes Human Genome Variation Society that maintains standardized nomenclature for describing sequence variants at DNA, RNA, and protein levels. Its guidelines ensure unambiguous reporting of mutations in clinical genetics, databases like ClinVar, and publications, facilitating international data sharing.

Ref: Strachan and Read, Human Molecular Genetics, 5th Edition, Chapter 18 on Genetic Testing and Bioinformatics, describes Human Genome Variation Society HGVS nomenclature standards for human variant description and clinical reporting guidelines, published by Garland Science.

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Microbiology & Infectious Diseases

Which of the following is wrongly paired?

Nucleic acids are polymers linked by 3'-5' phosphodiester bonds, not hydrogen bonds. Hydrogen bonds stabilize complementary base pairing between strands. Polysaccharides use glycosidic, proteins peptide, and phospholipids ester phosphate linkages correctly, making nucleic acid-hydrogen pairing erroneous.

Ref: Lehninger Principles of Biochemistry, Nelson and Cox, 8th Edition, Chapter 8 on Nucleic Acid Chemistry, details phosphodiester bonds forming nucleic acid backbone and hydrogen bonds stabilizing base pairs, not backbone linkage, published by Macmillan Learning.

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Microbiology & Infectious Diseases

A single nucleotide substitution (C has been replaced by A) has taken place in a gene, but the protein sequence is not a

Genetic code is degenerate, with multiple codons encoding same amino acid. A C to A change causing same residue preserves protein sequence, termed synonymous or silent variant. It may still influence splicing or translation kinetics despite unchanged primary structure.

Ref: Griffiths, Introduction to Genetic Analysis, 12th Edition, Chapter 9 on Gene Expression and Mutation, defines synonymous silent variant where nucleotide substitution does not alter amino acid due to degenerate genetic code and codon redundancy, published by Macmillan Learning.

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Microbiology & Infectious Diseases

How many DNA duplexes are obtained from one DNA duplex after 10 cycles of PCR?

PCR amplification is exponential because each cycle doubles duplexes when efficiency is 100 percent. Starting from one molecule, after n cycles yield equals 2 to power n. After ten cycles, 2^10 equals 1024 duplexes, mostly newly synthesized short amplicons flanked by primers.

Ref: Alberts, Molecular Biology of the Cell, 6th Edition, Chapter 8 on Molecular Genetic Techniques, explains polymerase chain reaction exponential amplification where one duplex yields 2 to the power n copies after n cycles, published by Garland Science.

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Microbiology & Infectious Diseases

If the total amount of adenine and thymine in a double-stranded DNA is 45%, the amount of guanine in this DNA will be:

According to Chargaff, A pairs with T and G pairs with C equally in duplex DNA. If A+T equals 45 percent, then G+C equals 55 percent. Since G equals C proportion, guanine equals 27.5 percent, maintaining base composition parity.

Ref: Lehninger Principles of Biochemistry, Nelson and Cox, 8th Edition, Chapter 8 on Nucleotides and Nucleic Acids, describes Chargaff parity rules A equals T and G equals C, calculation of guanine content from adenine plus thymine percentage, published by Macmillan Learning.

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Microbiology & Infectious Diseases

Single step large mutation leading to speciation is also called:

Saltation proposes abrupt origin of new species via macromutation in single generation, contrasting gradual Darwinian divergence. Hugo de Vries and Goldschmidt championed this, suggesting hopeful monsters instantly reproductively isolated, now related to polyploidy and regulatory gene mutations causing punctuated evolution.

Ref: Futuyma's Evolutionary Biology, Douglas Futuyma, 3rd Edition, Chapter 17 on Speciation, discusses saltation or macromutational speciation single large mutation concept by de Vries and Goldschmidt contrasting gradual natural selection models, published by Sinauer Associates.

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Microbiology & Infectious Diseases

Kinetoplast is made up of copies of:

Kinetoplast is a specialized mitochondrial region in kinetoplastids like Trypanosoma and Leishmania, containing concatenated network of circular DNAs: many minicircles and ~20-50 maxicircles. Maxicircles encode mitochondrial respiratory proteins, while minicircles guide RNA editing of those transcripts.

Ref: Paniker's Textbook of Medical Parasitology, 8th Edition, Chapter 3 on Protozoa and Kinetoplastida, explains kinetoplast as network of mitochondrial DNA with maxicircles and minicircles guiding RNA editing of respiratory genes, published by Jaypee Brothers Medical Publishers.

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Microbiology & Infectious Diseases

The hormone involved in rhythmic activities, such as day/night and seasonal changes is:

Melatonin secreted by pineal gland transduces photoperiodic information, peaking in darkness. It regulates circadian rhythm, sleep-wake cycle, and seasonal reproduction via SCN signaling. Suprachiasmatic nucleus entraining through melatonin receptors maintains day-night physiological oscillations.

Ref: Guyton and Hall Textbook of Medical Physiology, 14th Edition, Chapter 77 on Pituitary and Pineal hormones, describes melatonin role in circadian rhythm regulation, day-night cycles and seasonal changes via suprachiasmatic nucleus pathways, published by Elsevier.

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