MLT GlobeVirology: General virology & lab methods – page 2
76 Virology MCQs on General virology & lab methods with answers and explanations.
Which virus is NOT transmitted by the respiratory route?
HPV spreads by direct skin or mucosal contact, including sexual contact. Adenovirus, measles and VZV are spread by respiratory droplets or aerosols.
How do cytotoxic CD8 T lymphocytes mainly contribute to recovery from viral infection?
CTLs recognise viral peptides on MHC class I and kill infected cells with perforin, granzymes and Fas ligand. Antibodies, not CTLs, neutralise free virus.
Plant viruses usually need wounds or insect vectors to enter host cells. Which plant cell structure is the main barrier?
The rigid cellulose wall blocks direct entry, so plant viruses enter through mechanical damage or insect feeding and then spread via plasmodesmata.
Virus-host interactions are classified as acute, persistent, latent and so on. Which feature is NOT used for this classification?
Virus-host interactions are classed by duration, clinical outcome and whether progeny virus is produced. Virion size is a structural property, not an interaction type.
Which virus has NO known teratogenic effect on the fetus?
Rhinoviruses cause only local upper-respiratory infection with no viraemia reaching the fetus. CMV, rubella and VZV can all cause congenital malformations.
What is the term for viral DNA that has become integrated into the host cell chromosome?
A provirus is the integrated form, as with HIV DNA inserted by integrase. Viroids are naked RNA, prions are proteins, and VLPs are empty capsids.
Which statement best describes the cytopathic effect (CPE) of viruses in cell culture?
CPE includes rounding, syncytia, inclusions and detachment, seen with an ordinary inverted microscope. Patterns suggest but do not prove a virus; confirmation needs specific tests.
Viruses must use host cells to make their proteins mainly because they lack:
Viruses have no ribosomes and no energy-generating system, so viral proteins are translated on host ribosomes. They do carry a genome and structural proteins.
Which disinfectant is recommended to decontaminate a laboratory blood spill that may contain HBV or HIV?
Hypochlorite is a broad, high-level virucide used for blood spills. Chlorhexidine, quaternary ammonium compounds and hexachlorophene are low-level agents with poor activity against many viruses.
Which of these is NOT a role of the viral capsid?
The capsid protects the genome, provides attachment sites in naked viruses and is antigenic. Viruses have no energy metabolism, so the capsid does not make ATP.
When a temperate phage integrates its genome into the bacterial chromosome, the integrated phage DNA is called:
Integrated phage DNA is a prophage, and the host is lysogenic. Provirus is the equivalent term for animal viruses such as HIV.
The glycoprotein spikes that project from the surface of enveloped viruses such as influenza are called:
Peplomers are glycoprotein spikes such as haemagglutinin and neuraminidase. Capsomeres are the protein subunits of the capsid.
A phage that always multiplies and bursts its host cell, producing clear plaques, is called a:
Virulent phages follow only the lytic cycle and give clear plaques. Temperate phages can enter lysogeny and give turbid plaques.
Coliphage T2, like T4, contains which type of genome?
T-even phages have large linear dsDNA genomes. ssDNA phages include phiX174, and ssRNA phages include MS2.
Enterobacteria phage lambda belongs to which group of viruses?
Viruses that infect bacteria are bacteriophages; lambda infects E. coli. Virophages parasitise giant viruses, and arboviruses are carried by arthropods.
Under the electron microscope, tobacco mosaic virus looks like:
TMV has helical symmetry, forming a rigid rod about 300 nm long. Brick shape is typical of poxviruses, and head-tail is typical of phages.
In a virion, the protein shell that directly surrounds and protects the nucleic acid is called the:
The capsid is the protein coat around the genome, built from capsomeres. The envelope is a host-derived lipid membrane outside the capsid in some viruses.
What type of genome can a virus have?
A virion contains only one type of nucleic acid, DNA or RNA, which may be single- or double-stranded, linear or circular.
Which virus shows complex symmetry, with an icosahedral head attached to a helical tail?
T4 has an icosahedral head and a helical contractile tail, which is complex symmetry. Adenovirus and poliovirus are icosahedral, and influenza has helical nucleocapsids.
A capsomere is:
Capsomeres are protein units visible by EM that assemble into the capsid. Polymerases are separate enzymes.