Question
Which of the following statements about inclusion bodies is incorrect? [NEET (Sep.) 2020]
(a) These are involved in ingestion of food particles
(b) They lie free in the cytoplasm
(c) These represent reserve material in cytoplasm
(d) They are not bound by any membrane
Answer/Explanation
Ans. (a)
Option (b),(c) and (d) are correct whereas option (a) is incorrect because Inclusion bodies are nuclear or cytoplasmic aggregates of proteins. They represent sites of viral multiplication in a bacterium or a eukaryotic cell and usually consist of viral capsid proteins. These are not involved in ingestion of food particles.
Question
Which of the following statements is incorrect? [NEET (National) 2019]
(a) Viruses are obligate parasites
(b) Infective constituent in viruses is the protein coat
(c) Prions consist of abnormally folded proteins
(d) Viroids lack a protein coat
Answer/Explanation
Ans. (b)
The statement “infective constituent in viruses is protein coat” is incorrect. The correct information about the statement is as follows. Viruses infect their host organisms through their genetic material, i.e either DNA or RNA and not protein. They take over the biosynthetic machinery of the host cell and produce chemicals required for their own multiplication. Rest statements are correct.
Question
Viroids differ from viruses in having [NEET 2017]
(a) DNA molecules with protein coat
(b) DNA molecules without protein coat
(c) RNA molecules with protein coat
(d) RNA molecules without protein coat
Answer/Explanation
Ans. (d)
Viroids differ from viruses in having RNA molecules without protein coat. Viruses on the other hand posses DNA or RNA with a protein coat as their genetic material.
Viruses can infect a wide range of organisms including plants, animals or bacteria, while viroids infect only plants.
Question
112 Which of the following statements is wrong for viroids? [NEET 2016 Phase I]
(a) They are smaller than viruses
(b) They cause infections
(c) Their RNA is of high molecular weight
(d) They lack a protein coat
Answer/Explanation
Ans. (c)
Viroids are infectious, non-proteincoding, highly structured with small circular RNA’s, which have the ability to replicate autonomously. These contain RNA of low molecular weight and induce diseases in higher plants.
Question
Select wrong statement. [CBSE AIPMT 2015]
(a) The viroids were discovered by DJ Ivanowski
(b) WM Stanley showed that viruses could be crystallised
(c) The term ‘Contagium vivum fluidum’ was coined by MW Beijerinek
(d) Mosaic disease in tobacco and AIDS in human being are caused by viruses
Answer/Explanation
Ans. (a)
All statements are correct except the statement(a), which can be corrected as Viroids were discovered by TO Diener in 1971 as a new infectious agent that was smaller than virus.
Question
Which of the following shows coiled RNA strand and capsomeres? [CBSE AIPMT 2014]
(a) Polio virus
(b) Tobacco mosaic virus
(c) Measles virus
(d) Retrovirus
Answer/Explanation
Ans. (b)
In TMV RNA is single stranded (ss) helically coiled structure containing about 2130 capsomeres, which is a basic subunit of capsid (an outer covering of protein that protects the genetic material of a virus).
There are about 16 capsomeres present in each helical turn.
Question
Which statement is wrong for viruses? [CBSE AIPMT 2012]
(a) All are parasites
(b) All of them have helical symmetry
(c) They have ability to synthesise nucleic acids and proteins
(d) Antibiotics have no effect on them
Answer/Explanation
Ans. (b)
The nucleocapsids of viruses are constructed in highly symmetric ways. Two types of symmetry are recognised in viruses, which correspond to the two primary shapes, rod and spherical. Rod-shaped viruses have hellical symmetry and spherical viruses have icosahedral symmetry.
Question
Virus envelope is known as [CBSE AIPMT 2010]
(a)capsid
(b) virion
(c) nucleoprotein
(d) core
Answer/Explanation
Ans. (a)
Structurally viruses are very diverse varying widely in size, shape and chemical composition. The nucleic acid of virus is always located within the virion particle and surrounded by a protein shell called capsid.
The protein coat is composed of a number of individual protein molecules called structural subunits. The complete complex of nucleic acid and proteins, packaged in the virion is called the virus nucleocapsid.
Question
117 TO Diener discovered a [CBSE AIPMT 2009]
(a) free infectious RNA
(b) free infectious DNA
(c) infectious protein
(d) bacteriophage
Answer/Explanation
Ans. (a)
Viroids are small, circular, single stranded free infectious RNA molecules that are the smallest known pathogens. The extracellular form of the viroid is naked RNA, i.e. there is no protein capsid of any kind.
These RNA molecule contains no protein encoding genes and therefore, the viroid is totally dependent on host for its replication. No viroid diseases of animals are known and the precise mechanisms by which viroids cause plant diseases remain unclear.
Question
Viruses that infect bacteria, multiply and cause their lysis are called [CBSE AIPMT 2004]
(a) lysozymes
(b) lytic
(c) lipolytic
(d) lysogenic
Answer/Explanation
Ans. (b)
When bacteriophage infects a bacterium, it entirely depends on the host for its multiplication. It utilises the host machinery for replication and produce a large number of progeny (phage particles). The bacterium cell undergoes lysis and dies to liberate a large number of these phage particles which are ready to start another cycle by infecting new bacterial cell. This cycle is known as lytic cycle.
Question
Which of the following statements is not true for retroviruses? [CBSE AIPMT 2004]
(a) DNA is not present at any stage in the life cycle of retroviruses
(b) Retroviruses carry gene for RNA dependent DNA polymerase
(c) The genetic material in mature retroviruses is RNA
(d) Retroviruses are causative agents for certain kinds of cancer in man
Answer/Explanation
Ans. (a)
Retroviruses are so, named because they contain enzyme reverse transcriptase or RNA dependent DNA polymerase. The genetic material of these viruses is RNA, e.g. Rous Sarcoma Virus.
Question
Viruses are no more ‘alive’ than isolated chromosomes because [CBSE AIPMT 2003]
(a) both require the environment of a cell to replicate
(b) they require both RNA and DNA
(c) they both need food molecules
(d) they both require oxygen for respiration
Answer/Explanation
Ans. (a)
Viruses are non-cellular obligate parasite. In the free state they are just like the particles. They do not have their own metabolic machinery and use host’s machinery for multiplication.
Question
Which one of the following statements about viruses is correct? [CBSE AIPMT 2003]
(a) Nucleic acid of viruses is known as capsid
(b) Viruses possess their own metabolic system
(c) All viruses contain both RNA and DNA
(d) Viruses are obligate parasites
Answer/Explanation
Ans. (d)
Viruses are non-cellular, obligate parasites. They have DNA or RNA as genetic material(never both). Genetic material of virus is covered in protein coat, known as capsid. Viruses do not contain their own metabolic system instead they occupy host’s metabolic system after entrance in them.
Question
Tobacco mosaic virus is a tubular filament of size [CBSE AIPMT 2003]
(a) $700 \times 30 \mathrm{~nm}$
(b) $300 \times 10 \mathrm{~nm}$
(c) $300 \times 5 \mathrm{~nm}$
(d) $300 \times 18 \mathrm{~nm}$
Answer/Explanation
Ans. (d)
TMV is elongated rod-like, $3000 \AA$ $(300 \mathrm{~nm})$ long and $180 \AA \AA(18 \mathrm{~nm})$ in diameter.
Question
Interferons are synthesised in response to [CBSE AIPMT 2001]
(a) Mycoplasma
(b) bacteria
(c) viruses
(d) fungi
Answer/Explanation
Ans. (c)
Cells infected by virus produce interferon which is an antiviral protein. It spreads to neighbouring cells and makes them resistant to virus infections by inhibiting viral growth.
Question
Cauliflower mosaic virus contains [CBSE AIPMT 2001]
(a) ssRNA
(b) dsRNA
(c) dsDNA
(d) SSDNA
Answer/Explanation
Ans. (c)
Caulimovirus (Cauliflower Mosaic Virus) contains double stranded (ds) DNA.
Influenza virus contains single stranded RNA(ssRNA).
Parvovirus contains single stranded DNA(SsDNA).
Question
Which one of the following statements about viruses is correct? [CBSE AIPMT 1997]
(a) Viruses possess their own metabolic system
(b) Viruses contain either DNA or RNA
(c) Viruses are facultative parasites
(d) Viruses are readily killed by antibiotics
Answer/Explanation
Ans. (b)
Viruses contain only one type of nucleic acid DNA or RNA. These are obligate parasites; do not possess metabolic machinery and are not readily killed by antibiotics.
Question
Influenza virus has [CBSE AIPMT 1996]
(a) DNA
(b) RNA
(c) Both (a) and (b)
(d) Only proteins and no nucleic acids
Answer/Explanation
Ans. (b)
Influenza virus is single (-) stranded RNA virus, which cannot serve directly as mRNA but rather as templates for mRNA synthesis via a viral transcriptase. Influenza virus (orthomyxo virus) infects the respiratory tract and cause influenza.
Question
Tobacco Mosaic Virus (TMV) genes are [CBSE AIPMT 1994]
(a) double stranded RNA
(b) single stranded RNA
(c) polyribonucleotides
(d) proteinaceous
Answer/Explanation
Ans. (b)
Tobacco Mosaic Virus (TMV) is
elongated, rod shaped, most thoroughly studied plant virus, with $95 \%$ protein and $5 \%$ RNA by weight. RNA is genomic, i.e. genetic material which is single stranded, linear, helically coiled, $5 \mathrm{m \mu}$ in length with 6500 nucleotides long.