Lesson24

Question 1

What is the definition of a virus?

Answer 1

A small, infectious, obligate intracellular parasite that differs from eukaryotic and prokaryotic cells.

Question 2

What are the two main structural types of viruses?

Answer 2

Naked (lower complexity) and Enveloped (higher complexity).

Question 3

Which virus structure primarily infects prokaryotic cells?

Answer 3

Naked viruses.

Question 4

Which virus structure primarily infects eukaryotic cells?

Answer 4

Enveloped viruses.

Question 5

What are the three main types of viral symmetry?

Answer 5

Helical, Icosahedral, and Complex.

Question 6

Give an example of a virus with helical symmetry.

Answer 6

Tobacco Mosaic Virus (300 nm length).

Question 7

Give an example of a virus with icosahedral symmetry.

Answer 7

Adenovirus (100 nm diameter).

Question 8

Give an example of a virus with complex symmetry.

Answer 8

T4 bacteriophage (100 nm ‘head’).

Question 9

What is the basis of the Baltimore Classification System?

Answer 9

The viral genome type (DNA/RNA, single/double stranded, sense) and its replication/mRNA synthesis strategy.

Question 10

How many groups are in the Baltimore Classification System?

Answer 10

Seven groups.

Question 11

What are Class I viruses in the Baltimore system?

Answer 11

Double-stranded DNA viruses.

Question 12

What are Class IV viruses in the Baltimore system?

Answer 12

Positive-sense single-stranded RNA viruses.

Question 13

What are Class VI viruses in the Baltimore system?

Answer 13

Reverse transcribing single-stranded RNA viruses (Retroviruses).

Question 14

What two factors determine which host cells a virus can infect?

Answer 14

Susceptibility (has appropriate receptor) and Permissiveness (can replicate virions).

Question 15

What are the seven stages of the viral replication cycle?

Answer 15

1. Attachment, 2. Penetration, 3. Uncoating, 4. Biosynthesis, 5. Assembly, 6. Maturation, 7. Release.

Question 16

What is viral attachment?

Answer 16

The binding of the virion to specific cell surface receptors on the host cell.

Question 17

What are the two main methods of viral penetration into a host cell?

Answer 17

Injection (direct) and Endocytosis (engulfment).

Question 18

What happens during viral uncoating?

Answer 18

The viral capsid is removed or degraded, releasing the viral genome into the host cell.

Question 19

What occurs during the biosynthesis stage of viral replication?

Answer 19

Replication of the viral genome and synthesis of viral proteins using host machinery.

Question 20

What is the difference between destructive and non-destructive viral release?

Answer 20

Destructive release (lysis) kills the host cell. Non-destructive release (budding) does not immediately kill the cell.

Question 21

What is the ‘burst concept’ in viral replication dynamics?

Answer 21

The rapid production and release of many virions from a single host cell, often leading to cell lysis.

Question 22

What does R₀ (Reproduction Number) represent in epidemiology?

Answer 22

The average number of secondary infections produced by one infected individual in a fully susceptible population.

Question 23

What does an R₀ value greater than 1 indicate?

Answer 23

The outbreak is sustaining and will spread over time.

Question 24

What are the four possible fates of a host cell after viral infection?

Answer 24

Lysis, Latency, Persistence, Transformation.

Question 25

What is viral latency?

Answer 25

The virus remains in the host cell in a dormant state without active replication, but can reactivate later (e.g., Varicella-zoster virus).

Question 26

What is viral persistence?

Answer 26

Progeny virions are released slowly from host cells over time without causing immediate cell death.

Question 27

What is viral transformation?

Answer 27

The viral genome integrates into the host cell genome, altering normal cell functions and potentially leading to cancer (oncogenesis).

Question 28

What is an oncovirus? Give an example.

Answer 28

A virus that can cause cancer. Examples: Human papillomavirus (HPV), Epstein-Barr virus (EBV), Hepatitis B virus (HBV).

Question 29

What is a bacteriophage?

Answer 29

A virus that specifically infects bacterial cells.

Question 30

What are two bacterial defense systems against bacteriophages?

Answer 30

Restriction-Modification systems and the CRISPR-Cas system.

Question 31

What does CRISPR-Cas stand for?

Answer 31

Clustered Regularly Interspaced Short Palindromic Repeats - CRISPR associated system.

Question 32

What is the function of the CRISPR-Cas system in bacteria?

Answer 32

It provides adaptive immunity against bacteriophages by storing genetic memories of past infections to target and destroy matching viral DNA.

Question 33

What are sub-viral agents?

Answer 33

Infectious particles that are not viruses, such as viroids and prions.

Question 34

What are viroids?

Answer 34

Infectious RNA molecules that lack a protein coat, primarily associated with plant diseases.

Question 35

What are prions?

Answer 35

Infectious protein molecules that lack nucleic acids, associated with neurodegenerative diseases in animals (e.g., Mad Cow Disease).

Question 36

What is the role of Viral Attachment Proteins (VAPs)?

Answer 36

They mediate the binding of the virus to specific receptors on the host cell surface.

Question 37

What is a positive-sense (+ve) RNA strand?

Answer 37

An RNA strand that can be directly translated by host ribosomes into viral protein.

Question 38

What is a negative-sense (-ve) RNA strand?

Answer 38

An RNA strand that must first be transcribed into a complementary positive-sense strand before translation can occur.

Question 39

What are 'host-derived membranes' in enveloped viruses?

Answer 39

Lipid bilayers that the virus acquires from the host cell (e.g., plasma membrane) during budding.

Question 40

What is the difference between an acute infection and a latent infection?

Answer 40

Acute infection involves rapid replication and symptoms. Latent infection involves dormancy with possible reactivation.

Question 41

Name a virus that causes both an acute and a latent infection.

Answer 41

Varicella-zoster virus (causes Chickenpox acutely and Shingles upon reactivation).

Question 42

How does the Baltimore system classify Influenza virus?

Answer 42

Class V: Negative-sense single-stranded RNA virus.

Question 43

How does the Baltimore system classify HIV?

Answer 43

Class VI: Reverse transcribing single-stranded RNA virus (Retrovirus).

Question 44

What is a key feature of a 'complex' virus symmetry?

Answer 44

It has a structure that does not fit purely helical or icosahedral symmetry, often with additional components like a tail (e.g., T4 bacteriophage).

Question 45

What happens during the maturation stage of viral replication?

Answer 45

Newly assembled virus particles undergo structural changes to become infectious virions.

Question 46

What is a prophage?

Answer 46

The genetic material of a bacteriophage that is integrated into the genome of its bacterial host during lysogeny.

Question 47

What is lysogeny?

Answer 47

A state where a bacteriophage's genome is integrated into the host bacterium's genome and replicates with it without causing lysis (a type of latency).

Question 48

What is the lytic cycle?

Answer 48

A viral replication cycle that ends with the lysis (destruction) of the host cell to release new virions.