Microbiology - MCQ Practice Questions

Bacillus subtilis is a gram-positive, rod-shaped bacterium capable of forming endospores. E. coli is gram-negative, V. cholerae is gram-negative curved rod, and P. aeruginosa is gram-negative.

Peptidoglycan is the major structural component of bacterial cell walls, forming a rigid framework. It contains N-acetylglucosamine and N-acetylmuramic acid linked by peptide bridges.

SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) is the virus responsible for the COVID-19 pandemic that emerged in late 2019. SARS-CoV-1 caused the 2003 outbreak.

Mycobacterium tuberculosis is the causative agent of tuberculosis (TB). M. leprae causes leprosy, C. diphtheriae causes diphtheria, and S. aureus causes various infections.

Bacteriophages replicate through either the lytic cycle (destroying the host cell) or lysogenic cycle (integrating DNA into host chromosome). Binary fission is bacterial reproduction.

Flagella are whip-like appendages that enable bacterial motility. Pili are used for attachment and DNA transfer, capsule provides protection, and mesosomes are infoldings of cell membrane.

Influenza viruses (types A, B, and C) belong to the family Orthomyxoviridae. They are enveloped, negative-sense RNA viruses with segmented genomes.

Viruses lack their own metabolic machinery and depend on host cell machinery for replication. Options A, C, and D are all characteristics of viruses.

Flagella enable bacterial movement in response to chemical gradients (chemotaxis). Chemoreceptors detect signals, but flagella provide the locomotion. The other options are not functions of flagella.

Penicillin inhibits peptidoglycan cross-linking in bacterial cell walls. Streptomycin targets ribosomes, tetracycline inhibits protein synthesis, and chloramphenicol inhibits 70S ribosomes.

Enveloped viruses acquire their envelope from host cell membranes (plasma membrane, nuclear envelope, or ER) during viral release. The envelope contains both host and viral proteins.

HIV is a retrovirus that carries reverse transcriptase enzyme to convert RNA to DNA. It causes acquired immunodeficiency syndrome (AIDS). Hepatitis B is a hepadnavirus, HSV is a herpesvirus.

The F (fertility) plasmid encodes the sex pilus (F pilus) that forms a bridge between F+ and F- cells for DNA transfer. This is bacterial conjugation, a horizontal gene transfer mechanism.

Varicella-zoster virus (VZV) causes varicella (chickenpox) in primary infection. The virus remains dormant in nerve tissue and reactivates as herpes zoster (shingles) later in life.

Streptococcus mutans is the primary causative agent of dental caries (cavities). It produces lactic acid from carbohydrate fermentation, demineralizing tooth enamel. Other listed bacteria cause different infections.

Antibiotic resistance develops through natural selection. When antibiotics kill susceptible bacteria, resistant strains (with pre-existing mutations or acquired resistance genes) survive and proliferate.

Prions are infectious agents composed solely of misfolded proteins (PrPsc) without any nucleic acids. They cause diseases like Creutzfeldt-Jakob disease (CJD). Viruses require nucleic acids for replication.

RFLP uses restriction endonucleases to cut DNA at specific recognition sequences, creating fragments of variable lengths used for genetic analysis and bacterial strain identification.

Prokaryotes (bacteria and archaea) lack a membrane-bound nucleus and organelles, with circular DNA. Eukaryotes (animals, plants, fungi) have a true nucleus and membrane-bound organelles with linear chromosomes.

Antigenic drift involves gradual accumulation of point mutations in viral genes (especially surface proteins), causing slight changes in viral characteristics. This is distinct from antigenic shift (reassortment in segmented viruses like influenza).