What are viruses?

Question 1

Importance of Koch and Pasteur in virology

Answer 1

Developed porcelain-based filter

Contaminated liquids that passed through = no longer infectious

Viruses could pass through - turning point for virology

Question 2

Importance of Dmitri Ivanovski in virology

Answer 2

Investigates the tobacco mosaic virus

Infected leaves had patched appearance - light sections = dead

Mashed infected leaves into extract and ran through filter

Still caused disease -> transmissable entity could not be filtered away

Question 3

Importance of Martinus Beijerinck in virology

Answer 3

Investigated tobacco mosaic virus

Agent causing disease could only multiply on living plants

So replicating agent = not a toxin

Thought it was a poisonous living fluid

Came up with name virus

Question 4

Importance of Loeffler and Frosch in virology

Answer 4

Same filter observation

But with human virus

Foot and mouth virus

Question 5

Importance of Walter Reed in virology

Answer 5

Described the yellow fever virus

Was the first human virus

Question 6

What are the 3 basic characteristics of viruses?

Answer 6

Small - can be filtered

Dependent on host - different from all other organisms

Transmissible - key to viral survival

Question 7

What is the importance of transmission in viruses?

Answer 7

Key to viral survival

Everything about virus biology is focused on securing transmission to a new host

Question 8

What is another way of describing viruses?

Answer 8

By what they don’t do compared to other biological entities

Question 9

What do viruses not do compared to other biological entities?

Answer 9

Grow

Respond to stimuli

Consume energy

Undertake homeostasis - same environment inside as outside the virus

Reproduce

Question 10

What happens to viruses without a host?

Answer 10

Becomes inert

No biological characteristics

Question 11

Average size of viruses?

Answer 11

20 - 300 nm

Question 12

What are the two key components of viruses needed for them to transmit from one host to another?

Answer 12

Genome

Container for the genome

Question 13

What is a viral genome?

Answer 13

Encodes information to direct the host cell to generate new viruses

Can be made of DNA or RNA

Question 14

What is the container of a viral genome?

Answer 14

Necessary to get the genome from one host to another

Called capsid - protein shell that protects the genome

Question 15

What is a capsid?

Answer 15

Container for viral genome

Made of protein

Question 16

What is a virion?

Answer 16

Complete infectious virus particle

Question 17

Structure of a virus

Answer 17

Genome -> Capsid -> Matrix/ Tegument -> Envelope

Question 18

What is the matrix/ tegument?

Answer 18

Layer between the capsid and the envelope

Question 19

What is a nucleocapsid?

Answer 19

Name given to the capsid of a virus with the enclosed nucleic acid

Question 20

Do all viruses contain matrix/tegument?

Answer 20

No

Question 21

Do all viruses contain an envelope?

Answer 21

No

Most human viruses contain one

Plant viruses don’t

Question 22

What is a viral envelope?

Answer 22

Phospholipid bilayer

Made by host cell

Encloses nucleocapsid

Contains viral glycoproteins

Is always spherical, even if the capsid inside is helical or icosahedral

Question 23

What are the 2 possible shapes of viruses?

Answer 23

Icosahedral

Helical

Question 24

Structure of icosahedral viruses

Answer 24

Platonic solids - spheroid structure made of 20 triangular phases

Symmetrical

Efficient way of enclosing space

Question 25

Viruses with icosahedral structures

Answer 25

Adenovirus Polio Herpes

Question 26

Structure of helical viruses

Answer 26

Genomes are helical and curl Assembly of structure follows coils of DNA Thin, long, circular structure

Question 27

Which viruses have helical strucures?

Answer 27

Single stranded RNA viruses DNA viruses

Question 28

Why are virus structures simple?

Answer 28

Building a structure with few parts increases the genetic economy Have to code for less proteins Reduces the genome for the virus, which is beneficial

Question 29

What are the 5 theories describing the origin of viruses?

Answer 29

Progressive Regressive Virus first None of the above All of the above

Question 30

What does the progressive hypothesis of origin of viruses describe?

Answer 30

Viruses evolved from bits of DNA or RNA Like plasmids and transposons Plasmids - molecules of DNA that can move between cells Transposons - molecules of DNA that can replicate and move to different positions within a cell Retroposons - Transposons that move to a new place via RNA intermediate Viruses are replicating nucleic acids - independent transposions or retroposons

Question 31

What does the regressive hypothesis of origin of viruses describe?

Answer 31

Small cells used to parasitise larger cells Lack of genetic economy Abandoned the genes required to survive outside the cell Complex progenitor cell shed functions and became more dependent

Question 32

What does the virus first hypothesis of origin of viruses describe?

Answer 32

Viruses prefate cells Self-replicating, catalytic molecules that led to life

Question 33

Origin of HIV

Answer 33

Can be traced via phylogenetic tree Zoonotic infection - simian HIV is a primate virus Came from transfer of monkeys -> human