Virology

Question 1

Define what a virus is ?

Answer 1

A virus is a submicroscopic infectious agents composed of nucleic acid enclosed in a protein coat, requiring a host cell to replicate

Question 2

Are viruses considered living organisms ?

Answer 2

No viruses are acellular and non living outside a host. They cannot reproduce or carry out metabolism independently

Question 3

What are the main structural components of a virus ?

Answer 3

Nucleic acid, protein capsid and sometimes a lipid envelope

Question 4

What does obligate intracellular parasite mean ?

Answer 4

It means viruses can only replicate inside the living cells of a host organism

Question 5

How are viruses classified ?

Answer 5

By nucleic acid type, capsid symmetry, envelope presence, replication strategy and host range

Question 6

Why are viruses important in biology and medicine?

Answer 6

They cause diseases, drive genetic evolution, and serve as tools in biotechnology and gene therapy

Question 7

what is the main structural difference between enveloped and non-enveloped viruses ?

Answer 7

Enveloped viruses have a lipid membrane (envelope) surrounding the capsid, non-enveloped viruses lack this envelope and have only the protein capsid

Question 8

How do enveloped viruses typically enter host cells?

Answer 8

By membrane fusion or endocytosis, using their envelope to merge with the host cell membrane.

Question 9

How do non-enveloped viruses typically enter host cells?

Answer 9

Usually via endocytosis followed by capsid penetration or pore formation to release the genome.

Question 10

Which type is more sensitive to environmental factors like heat, desiccation, and detergents?

Answer 10

Enveloped viruses are more fragile due to their lipid membranes.

Question 11

Which type is generally more resistant to harsh environmental conditions?

Answer 11

Non-enveloped viruses, because their protein capsids are more stable.

Question 12

Give two examples of enveloped viruses.

Answer 12

HIV (Human Immunodeficiency Virus), Influenza virus.

Question 13

Give two examples of non-enveloped viruses.

Answer 13

Adenovirus, Norovirus.

Question 14

What is one similarity between enveloped and non-enveloped viruses?

Answer 14

Both contain genetic material (DNA or RNA) and require a host cell for replication.

Question 15

What are the main types of nucleic acid genomes found in viruses?

Answer 15

iruses can have DNA or RNA genomes, and the nucleic acid can be single-stranded (ss) or double-stranded (ds), either linear or circular, and sometimes segmented.

Question 16

What is the Baltimore classification system used for?

Answer 16

It classifies viruses into seven groups based on their genome type and replication strategy, especially how they synthesize mRNA.

Question 17

What is Group I of the Baltimore classification system?

Answer 17

Double-stranded DNA (dsDNA) viruses

Question 18

What is Group II of the Baltimore classification system?

Answer 18

: Single-stranded DNA (ssDNA) viruses

Question 19

What is Group III of the Baltimore classification system?

Answer 19

Double-stranded RNA (dsRNA) viruses

Question 20

What is Group IV of the Baltimore classification system?

Answer 20

Positive-sense single-stranded RNA (+ssRNA) viruses

Question 21

What is Group V of the Baltimore classification system?

Answer 21

Negative-sense single-stranded RNA (−ssRNA) viruses

Question 22

What is Group VI of the Baltimore classification system?

Answer 22

Retroviruses (ssRNA-RT)

Question 23

What is Group VII of the Baltimore classification system?

Answer 23

Double-stranded DNA viruses with reverse transcriptase (dsDNA-RT)
Example: Hepatitis B virus

Question 24

How does understanding viral genome types benefit biotechnology?

Answer 24

Knowledge of viral genome types aids in the development of gene therapies, viral vectors for gene delivery, and vaccine design.

Question 25

What is the first step of the viral life cycle, and what does it involve ?

Answer 25

Attachment - the virus binds to specific receptors on the host cell surface via surface proteins.

Question 26

How do viruses enter host cells ?

Answer 26

Via membrane fusion, endocytosis or direct genome injection

Question 27

What is unceasing in the viral life cycle ?

Answer 27

The process where the viral capsid is removed, releasing the genome into the host cell for replication

Question 28

Where do most DNA and RNA viruses replicate in the host cell ?

Answer 28

DNA viruses - nucleus; RNA viruses: cytoplasm

Question 29

How do enveloped and non-enveloped viruses typically exit the host cell ?

Answer 29

Enveloped viruses: via budding;Non-enveloped viruses: via cell lysis

Question 30

What does a plaque assay measure ?

Answer 30

Number of infectious virus particles, expressed as PFU/ml

Question 31

When is the TCID assay used, and what does it measure ?

Answer 31

For viruses that dont form plaque; measures the dilution at which 50 % of cells show cytopathic effect

Question 32

What is a focus-forming assay, and when is it used ?

Answer 32

Uses immunostaining to detect infected cells ; used when CPE is absent or subtle

Question 33

What is a limitation of qPCR for viral detection ?

Answer 33

It detects viral genomes, not necessarily infectious particles - may overestimate infectivity

Question 34

What is the hemagglutination assay used for ?

Answer 34

Detecting viruses that agglutinate red blood cells - indirect, not a measure of infectivity

Question 35

what does ELISA measure in viral detection ?

Answer 35

Detects viral proteins or host antibodies - useful for diagnostics and vaccine response monitoring

Question 36

What is a lytic infection, and what is its outcome ?

Answer 36

A lytic infection leads to active viral replication, cell lysis, and death of the host cell. Example: Poliovirus

Question 37

What is a persistent (chronic) infection, and what is its outcome?

Answer 37

The virus replicates at low levels over time without killing the host cell, leading to long-term infection. Example: Hepatitis B virus

Question 38

What is a latent infection, and what happens to the virus?

Answer 38

The virus enters a dormant state with no active replication, but can reactivate later. Example: Herpes Simplex Virus (HSV)

Question 39

What is a transforming infection, and what is its outcome?

Answer 39

The virus integrates into the host genome or alters cell regulation, potentially leading to uncontrolled cell growth or cancer. Example: Human Papillomavirus (HPV)

Question 40

What are the two broad categories of viral transmission ?

Answer 40

Horizontal transmission(person to person ) and vertical transmission ( from parent to offspring )

Question 41

What is respiratory transmission? Give examples.

Answer 41

Spread via inhalation of aerosols or droplets from coughing/sneezing. Examples: Influenza virus, SARS-CoV-2

Question 42

What is fecal-oral transmission? Give examples.

Answer 42

Ingestion of virus-contaminated food or water. Examples: Norovirus, Poliovirus, Rotavirus

Question 43

What is bloodborne transmission? Give examples.

Answer 43

Transmission via contact with infected blood, e.g., transfusion, sharing needles. Examples: HIV, Hepatitis B & C

Question 44

What is sexual transmission? Give examples.

Answer 44

Spread through sexual contact and genital secretions. Examples: HIV, Herpes Simplex Virus type 2, HPV

Question 45

What is vertical transmission? Give examples.

Answer 45

Transmission from mother to child during pregnancy, birth, or breastfeeding. Examples: HIV, Zika virus, Rubella

Question 46

What is vector-borne transmission? Give examples.

Answer 46

Transmission via arthropod vectors such as mosquitoes or ticks. Examples: Dengue virus, Zika virus, West Nile virus

Question 47

What is zoonotic transmission? Give examples.

Answer 47

Virus is transmitted from animals to humans. Examples: Rabies virus, SARS-CoV-2, Ebola