Introduction to virology

Question 1

• What is a virus?

Answer 1

A virus is an infectious, obligate intracellular parasite comprising genetic material (DNA or RNA) surrounded by a protein coat and/or a membrane

Question 2

Why is a virus described as a parasite?

Answer 2

A virus is a described as a parasite as it relies on host cells to replicate and also because it enters a cell and utilizes it for its benefit

Question 3

What makes a virus infectious?

Answer 3

A virus is infectious because it travels from cell to another

Question 4

Why is a virus obligate intracellular?

Answer 4

A virus is obligate intracellular because it requires a cell in order to replicate – as it doesn’t have enough machinery to operate on its own

Question 5

The difference and similarity between viruses

Answer 5

Viruses may differ in size and shape but they all contain a genome in the middle that is protected by a protein

Question 6

What do the proteins that stick out of the surface of the virus enable?

Answer 6

The proteins that stick out of the surface of the virus enables the virus to interact with the host cell it wants to infect

Question 7

What does the envelop embed?

Answer 7

The envelop embeds proteins

Question 8

What is a virus?

Answer 8

“A virus is a piece of bad news wrapped in protein”

Peter Medawar

Question 9

A virus is an organism with 2 phases:

Answer 9

1. Virion phase
   The virus is free floating
2. Infected cell phase
   The virus has engaged with the host cell and has started its replication cycle before its liberation as a free virion

Question 10

What is a virion?

Answer 10

A virion is a complete, mature, infectious viral particle

Question 11

• Briefly describe the process of infection

Answer 11

When a virion infects a host cell, it is disassembled

The infected host cell then makes building blocks for new virions

The virus exits the cell and enters a new cell to start another round of replication

Viruses infect all living things

Question 12

What is used when viewing ribosomes, proteins and small molecules?

Answer 12

Magnetic resonance and X – ray crystallography is used when viewing ribosomes, proteins and small molecules

Question 13

What does NMR stand for?

Answer 13

NMR stands for nanometre range

Question 14

How many viruses can fit on the head of a pin?

Answer 14

2mm = 2000 microns

About 500 million rhinoviruses can fit on the head of a pin

Question 15

What does Rhinovirus cause?

Answer 15

Rhinovirus causes the common cold

Question 16

Properties of viruses: Viruses are smaller than bacteria

Answer 16

• Almost all viruses are sub microscopic i.e., they can only be visualised by electron microscopy
• Diameter: 10 – 1000 nm (most 20 – 300 nm)
• Larger viruses can be viewed using a light microscope

Question 17

What type of genome do viruses contain?

Answer 17

• Viruses contain only one type of nucleic acid, either DNA or RNA, but never both

Question 18

What is the nucleic acid surrounded by?

Answer 18

• The nucleic acid is surrounded by a protein coat

Question 19

What do some viruses have?

Answer 19

• Some viruses have an additional lipoprotein envelope

Question 20

How do viruses replicate?

Answer 20

• Viruses replicate by “tricking” cells into making multiple copies of viral nucleic acid and protein, which then self – assemble to form new virus particles

Question 21

Which organelles are missing in viruses?

Answer 21

• Viruses don’t have organelles, such as mitochondria and ribosomes

Question 22

Viruses can’t replicate…

Answer 22

outside living cells

Question 23

Viruses don’t undergo…

Answer 23

binary fission like bacterial pathogens - Viruses don’t grow

Question 24

Viruses don’t have mitochondria. What does the mean?

Answer 24

Viruses can’t generate their own energy/metabolism

Question 25

Viruses don’t move on their own, i.e.

Answer 25

Movement is passive as they don’t have a flagellum

Question 26

What are differences between viruses and unicellular microorganism?

Answer 26

Size
unicellular microorganisms are microscopic i.e., a light microscope is used; viruses are sub - microscopic i.e., a electron microscope is used.

Grow in non - living media
Unicellular microorganisms grow in non - living media. Example: Agar; Viruses don’t grow in non - living media

Binary fission [subdivide and replicate themselves]
Unicellular microorganisms undergo binary fission; viruses don’t

Contain both DNA and RNA
Microorganisms contain a DNA genome and utilized RNA to fulfil transcription and translation; Viruses contain only one genome

Infectious nucleic acid
Microorganisms don’t contain an infectious; viruses do

Ribosomes
Microorganisms contain ribosomes; viruses don’t

Generate energy
Microorganisms generate energy; viruses don’t

Question 27

What are consequences of having a virus?

Answer 27

• Severe infections +/- hospitalisation
• Chronic infections +/- sequelae such as cancer
• Requirement for long term therapy
• Death

Question 28

When was the 1st written record of virus infection?

Answer 28

approximately 3700 BC (temple priest): clinical signs of Paralytic poliomyelitis seen in hieroglyphics in Memphis

Question 29

What did polio cause and in which years did it spread?

Answer 29

• Polio caused disease in Ancient Egypt and continued spreading well into the mid –1900s and the late 1900s

Question 30

When did the influenza pandemic spread?

Answer 30

• There was an influenza pandemic that spread around the early 1900s – it travelled in waves and it killed millions of people [influenza pneumonia]