3. Explanation
Virus capsids are predominantly one of two shapes, helical
(protein subunits and the nucleic acid are arranged in a helix)
or icosahedral (protein subunits assemble into a symmetric
shell that covers the nucleic acid-containing core) although a
few viruses have a complex architecture (eg: bacteriophages,
poxviruses)
5. Explanation
The capsid, or core, is a protein shell surrounding the viral genome and
is usually composed of single or multiple protein subunits called
capsomeres. The capsomere is a subunit of the capsid. Capsomeres
self-assemble to form the capsid. Subunits called protomers aggregate
to form capsomeres. The capsid serves to protect and introduce the
genome into host cells.
Some viruses consist of no more than a genome surrounded by a capsid
and are called nucleocapsid.
Attachment proteins project out from the capsid and bind the virus to
susceptible host cells. The genome of a virus may consist of DNA or
RNA, which may be single stranded (ss) or double stranded (ds), linear
or circular.
7. Explanation
The lytic cycle, which is commonly referred to as the "reproductive
cycle" of the bacteriophage. Lytic cycle involves the lysis and the
destruction of the cell.
In the lytic cycle, sometimes referred to as virulent infection, the
infecting phage ultimately kill the host cell to produce many of their
own progeny. Bacteriophages that only use the lytic cycle are called
virulent phages.
9. Explanation
Lysogeny or the lysogenic cycle is characterized by integration of
the bacteriophage nucleic acid into the host bacterium's genome. In
this condition the bacterium continues to live and reproduce normally,
while the bacteriophage lies in a dormant state in the host cell. The
genetic material of the bacteriophage, called a prophage.
12. Bacteriophages, also known as phages, are viruses that
infect and replicate only in bacterial cells.
Phages are simple organisms that consist of a core of
genetic material (nucleic acid) surrounded by a
protein capsid. The nucleic acid may be either DNA or
RNA and may be double-stranded or single-stranded.
Some phages can only reproduce via a lytic lifecycle, in
which they burst and kill their host cells. Other phages
can alternate between a lytic lifecycle and a lysogenic
lifecycle, in which they don't kill the host cell (and are
instead copied along with the host DNA each time the
cell divides).
16. Explanation
Viruses are infectious agents that replicate inside the body
of a host.
A fully assembled infectious virus is called a virion.
The process of virus assembly involves protein-protein
interactions between viral structural and nonstructural
proteins and the coordinated action of host factors.
A virus is an infectious microbe consisting of a segment of
nucleic acid (either DNA or RNA) surrounded by a protein
coat.
Viroids are infectious pathogens that affect only plants,
therefore are also called plant pathogens. Structurally,
viroids are smaller than viruses and possess circular strands
of ribonucleic acids (RNAs) with no protein coating. These
are among the smallest known agents causing infectious
disease.
18. Explanation
Tobacco mosaic virus was the first virus to be
crystallized. It was achieved by Wendell Meredith
Stanley in 1935.
TMV crystalization also showed that TMV remains
active even after crystallization. He found that the
crystal was made of proteins.
For his work, he was awarded the Nobel Prize in
Chemistry in 1946.
20. Explanation
Heteroploid cultures /Continuous cell lines are derived
from cancer cell lines. They can be serially cultured
indefinitely so named as continuous cell lines.
They can be maintained either by serial subculture or
by storing in deep freezer at -70°C.
Due to derivation from cancer cells they are not useful;
for vaccine production.
Examples: HeLa (Human carcinoma of cervix cell
line), HEP-2 (Human Epithelioma of Larynx cell line),
Vero kidney cell lines, BHK-21 (Baby Hamster Kidney
Cell line).
22. Explanation
A lysogen or lysogenic bacterium is a bacterial cell which can
produce and transfer the ability to produce a phage. A prophage
is either integrated into the host bacteria's chromosome or more
rarely exists as a stable plasmid within the host cell.
The lambda virus is an example of a lysogenic bacteriophage.
Lysogeny is characterized by integration of
the bacteriophage nucleic acid into the host bacterium's genome
or formation of a circular replicon in the bacterial cytoplasm. In
this condition the bacterium continues to live and reproduce
normally, while the bacteriophage lies in a dormant state in the
host cell.
The genetic material of the bacteriophage, called a prophage, can
be transmitted to daughter cells at each subsequent cell division,
and later events (such as UV radiation or the presence of certain
chemicals) can release it, causing proliferation of new phages via
the lytic cycle
24. Explanation
The growth of viruses in cell culture can be monitored
by a number of biochemical procedures indicative of
the intracellular increase in viral macromolecules and
virions.
The growth of virus in cell culture can be monitored by
Cytopathic effects, Hemagglutination and
Hemadsorption, Immunofluorescence etc.
26. Explanation
Tobacco mosaic virus (TMV) is a positive-sense
single-stranded RNA virus species in the
genus Tobamovirus that infects a wide range of plants,
especially tobacco and other members of the
family Solanaceae.
TMV was the first virus to be discovered.
The virus was crystallised by Wendell Meredith
Stanley.
32. Explanation
Primary cell culture are normal cells derived from
animal or human cells.
They are able to grow only for limited time and cannot
be maintained in serial culture.
They are used for the primary isolation of viruses and
production of vaccine.
Examples: Monkey kidney cell culture, Human
amnion cell culture.
34. Explanation
Bacteriophages that cause bacterial cell lysis are called
virulent phages. They are also called lytic phages. They
lack the ability to lysogenize.
38. Explanation
TMV affects a wide range of plants including, tobacco,
tomato and other members of the solanaceous plants.
The namesake symptom of TMV is the mosaic patterns
of discolouration on the leaves. Mottling, yellowing
tissue and leaf curling are also common. Symptoms
can vary depending on the species and background of
the host plant, the environmental conditions and the
strain of the virus.
Discolouration and symptoms that affect leaves limit a
plant's ability to photosynthesise.
Tobacco mosaic disease leads to secondary symptoms
like stunted growth and necrosis.
40. Explanation
TMV capsids are composed of 2130 identical protein
subunits, which assemble around the viral ssRNA to
form a helical structure, with a hollow central cavity of
4 nm diameter.
46. Explanation
Some viruses have viral envelopes which covers
capsids. A peplomer is a glycoprotein spike which are
the subunits of viral envelope.
The term "peplomer" refers to an individual spike from
the viral surface; collectively the layer of material at
the outer surface of the virion has been referred to as
the "peplos“.
These peplomeres will only bind to certain receptors
on the host cell. They are essential for both host
specificity and viral infectivity.
48. Explanation
The simplest virions consist of two basic
components: nucleic acid (single- or double-stranded
RNA or DNA) and a protein coat, the capsid, which
functions as a shell to protect the viral genome from
nucleases and which during infection attaches the
virion to specific receptors exposed on the prospective
host cell.
50. Explanation
The capsomere is a subunit of the capsid, an outer covering
of protein that protects the genetic material of a virus.
Capsomeres self-assemble to form the capsid. Subunits
called protomers aggregate to form capsomeres. Various
arrangements of capsomeres are: 1 Icosahedral, 2 Helical,
and 3 Complex.
Capsomere
52. Explanation
Bacteriophages were first discovered in 1915 by William
Twort, and in 1917 by Felix d'Herelle realized that they
had the potential to kill bacteria.
D'Hérelle coined the term bacteriophage, meaning
“bacteria eater,” to describe the agent's bacteriocidal
ability.
