Lesson 1: Introduction to the study of viruses

Question 1

are the
smallest viruses (20nm)

Answer 1

picornavirus

Question 2

are the largest viruses
(300nm)

Answer 2

poxviruses

Question 3

Viruses cannot be seen by light microscope because of their small size except?

Answer 3

poxviruses

Question 4

General description of Virus

Answer 4

• Filterable agents
• seen only by the aid of electron microscope
• No cellular organization and do not have organelles
• Composed of nucleic acid surrounded by a protein coat
• Contain only one type of nucleic acid, either DNA or RNA
• viable host
cells are required for replication
• Viruses are unaffected by antibiotics
• Viruses multiply by a complex process involving protein synthesis and nucleic
acid production

Question 5

Three categories;

Answer 5

✓ DNA viruses
✓ RNA viruses
✓ Viruses that utilize both DNA
and RNA for replication

Question 6

the viruses that infect bacteria

Answer 6

Bacteriophages or phages

Question 7

an infectious extracellular virus particle consists of nucleic acid (DNA or
RNA) that is covered by a protein coat called CAPSID.

Answer 7

Virion

Question 8

a shell of subunits of proteins called CAPSOMERE that encloses the
genome of vertebrate viruses

Answer 8

Capsid

Question 9

a shell of subunits of proteins called CAPSOMERE that encloses the
genome of vertebrate viruses

Answer 9

Capsid

Question 10

capsid functions

Answer 10

• offers protection for the nucleic acid against adverse conditions
• it facilitates attachment and entry of the virus into host cell
• it
possesses antigens used for virus identification in serological tests
• it
determines the symmetry of the virus

Question 11

two types of capsid symmetry
described in viruses;

Answer 11

Icosahedral and helical symmetries

Question 12

large viruses with large genome have
complicated symmetry which is neither icosahedral nor helical such as?

Answer 12

Poxviruses

Question 13

used to refer to the combined nucleic acid and capsid
which can either be naked or covered with a membrane termed an envelope

Answer 13

nucleocapsid

Question 14

The viral
genome also codes for important enzymes called _______________
required for viral replication but are not incorporated in the virion.

Answer 14

non-structural proteins

Question 15

proteins that make up the subunit of capsid

Answer 15

structural proteins

Question 16

generally assembled in the host cell prior to
incorporation of the viral nucleic acid

Answer 16

icosahedral capsid

Question 17

formed by the insertion of protein units between each turn of
the nucleic acid helix, incorporating the RNA in the tubular package

Answer 17

Helical capsids

Question 18

lipid bilayer and associated glycoproteins that cover a nucleocapsid

Answer 18

envelope

Question 19

acquired when the nucleocapsid buds through a cellular membrane,
endoplasmic reticulum, the Golgi apparatus or the nuclear membrane

Answer 19

envelope

Question 20

are usually susceptible to detergent and are rendered noninfectious following damage to the envelope

Answer 20

enveloped viruses

Question 21

the proteins encoded by viral nucleic acid for binding to
receptors on host cells, membrane fusion, uncoating of the virion and destruction
of receptors on host cells

Answer 21

glycoproteins

Question 22

are knob-like projections from the envelope formed from
the oligomers of glycoproteins.

Answer 22

peplomers/spikes

Question 23

Peplomers/spikes are present in certain viruses including;

Answer 23

coronaviruses, retroviruses, orthomyxoviruses, rhabdoviruses and
paramyxoviruses

Question 24

a layer of protein present between the nucleocapsid and the
envelope in some enveloped viruses that provides additional rigidity to the virion

Answer 24

matrix protein

Question 25

Some viruses are named according to the type of disease they cause (creeping lesion) Examples;

Answer 25

poxviruses herpesviruses

Question 26

viruses named based on acronyms of disease example

Answer 26

picornavirus and papovavirus

Question 27

Viruses are also named based on morphology as revealed by electron microscopy example;

Answer 27

coronavirus, togavirus, rhabdovirus, and calicivirus

Question 28

viruses are named after individual discoverer

Answer 28

Epstein-bar viruses

Question 29

developed and expanded the universal scheme in which characteristics of virions are used to assign them to five hierarchical levels (order, family, subfamily, genus and species).

Answer 29

International Committee on Taxonomy of Viruses (ICTV) 1973

Question 30

The hierarchical levels are denoted with the following suffixes:

Answer 30

Order: -virale Family: -viridae Genus: virus Species: virus

Question 31

Four orders containing viruses of animals are so far recognized:

Answer 31

• mononegavirale • herpesvirales • picornavirales • nidovirales

Question 32

are infectious particles, which can transmit a disease, composed mainly of a protein without any detectable nucleic acid.

Answer 32

Prions

Question 33

___________ causative agents of slow viral infections such as ___________

Answer 33

Prions Subacute spongiform encelophathy

Question 34

After long incubation period of years, Prions produce a progressive disease that causes damage to the central nervous system, leading to

Answer 34

subacute spongiform encephalopathy

Question 35

Susceptibility to Physical and Chemical Agents

Answer 35

• Disinfectants • Temperature • pH • lipid solvents • radiations

Question 36

initial stage of virus replication whereby the infecting virus loses its physical identity and most or all of its infectivity

Answer 36

eclipse phase

Question 37

stage as new viral particles are formed and released from the cell wherein the number of viral particles increases exponentially.

Answer 37

productive stage

Question 38

Steps in Virus Replication

Answer 38

Attachment Entry Uncoating Biosynthesis or Replication of nucleic acid Maturation/Assembly of virus

Question 39

enveloped viruses enter the cell by an alternate method called ___________, in which the viral envelope fuses with the plasma membrane and releases the capsid into the cell cytoplasm.

Answer 39

Fusion

Question 40

naked viruses or non-enveloped viruses undergo a receptor-based endocytosis also known?

Answer 40

viropexis

Question 41

process of separation of viral nucleic acid from its protein core for transcription to take place

Answer 41

uncoating

Question 42

in certain viruses, transcription may proceed without complete release of the viral genome

Answer 42

reovirus

Question 43

Replication of DNA viruses

Answer 43

DNA viruses replicate their DNA in the nucleus of the host cell by using viral enzymes.

Question 44

Replication of RNA viruses

Answer 44

RNA viruses replicate in the cytoplasm except orthomyxoviruses and Borna disease virus which require host DNA transcription inside the nucleus, paramyxoviruses which have a non-obligatory nuclear phase of replication and retroviruses which replicate via a DNA intermediate (provirus)

Question 45

Abnormal replicative cycles may occur in four ways:

Answer 45

incomplete viruses pseudovirions abortive infections defective viruses

Question 46

Due to defect during assembly of viral components, some of the daughter virions that are produced may not be infective

Answer 46

incomplete viruses

Question 47

viruses that occasionally enclose host cell nucleic acid instead of viral nucleic acid, therefore, are non infective and lack the capability to replicate.

Answer 47

pseudovirions

Question 48

type of infection, the virus components may be synthesized but the maturation is defective maybe due to infection of the wrong host cells by the virus.

Answer 48

abortive infections

Question 49

are viruses that produce fully mature virions only in the presence of helper viruses which supplement the genetic deficiency in the defective viruses

Answer 49

Defective viruses

Question 50

Example of defective virus

Answer 50

Hepatitis D virus, replicate only in the presence of Hepatitis B virus (helper virus)

Question 51

Spontaneous and random errors in the copying of viral nucleic acid

Answer 51

mutations

Question 52

can occur during the replication of viruses. It is the most important mechanism by which a virus can be genetically modified which results in production of new viral strains showing properties different from parental or wild-type virus such as inactivation of viruses, altered antigenicity and pathogenicity of the virus, and induce drug resistance in viruses

Answer 52

mutations

Question 53

resulting from single nucleotide substitutions, are the most common type of mutation

Answer 53

point of mutations

Question 54

a new area of antiviral research wherein those RNA viruses with inherently high mutation rates are administered with mutagenic agents to drive viral extinction through violation of the error threshold and error catastrophe.

Answer 54

lethal mutagenesis

Question 55

is the extinction of an organism as a result of excessive mutations

Answer 55

error catastrophe