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Viruses
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Which of the following shows coiled RNA strand and capsomeres?Tobacco mosaic virus is rod-shaped, with a single coiled RNA strand surrounded by protein subunits called capsomeres arranged helically.
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Viruses have:A virus is a nucleoprotein: its genetic material is enclosed in a protein coat (capsid). It has either DNA or RNA, never both, and no nucleus.
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Which statement is wrong for viruses?Viruses are obligate parasites, are not affected by antibiotics, and direct the host machinery to make their nucleic acids and proteins.
Their capsids may be helical (e.g. TMV), polyhedral (e.g. adenovirus) or complex (e.g. bacteriophage).
So the statement that all of them have helical symmetry is wrong. -
Given below is the diagram of a bacteriophage. In which one of the options are all the four parts A, B, C and D correct?
[add image]A bacteriophage (e.g., T-even phage) has a polyhedral head, a short collar, a tail with a contractile sheath, a basal plate and tail fibres.
A is the polyhedral structure at the top that encloses the nucleic acid (DNA): the head.
C is the narrow ring-like region just below the head, joining it to the tail: the collar.
B is the long cylindrical, contractile covering of the tail: the sheath.
D is the set of long thread-like leg structures arising from the base plate, with which the phage attaches to the bacterium: the tail fibres.
Hence A – head, B – sheath, C – collar, D – tail fibres. -
Virus envelope is known asA virus is a nucleoprotein particle: it has genetic material (DNA or RNA) surrounded by a protein coat.
The protein coat that envelops and protects the nucleic acid is called the capsid; it is made of small subunits called capsomeres arranged in helical or polyhedral forms.
The core is the central nucleic acid, the virion is the complete infectious virus particle outside the host, and nucleoprotein refers to the nucleic acid together with its protein.
Hence the covering (envelope) of the virus is known as the capsid.