Chapter 10.1 Viruses

Question 1

What is pathology?

Answer 1

The study of specific diseases caused by microorganisms and the strategies used to combat them.

Question 2

What is a pathogen?

Answer 2

Foreign invaders that cause disease

Question 3

What are 4 examples of pathogens?

Answer 3

1. Viruses
2. Bacteria
3. Fungi
4. Protists (parasites)

Question 4

What is a virus?

Answer 4

1. The smallest of the infectious agents - 18-300nm in diameter
2. Considered biologically inert - somewhere between simple biomolecules (ie: proteins, DNA) and living organisms (bacteria)
3. Cannot be seen with light microscopes
4. Estimated to be 100 families with 2,800 species of viruses (this number rises every year)
5. Not all viruses infect humans

Question 5

Why are viruses not considered to be alive?

Answer 5

They do not meet the basic criteria scientists use to characterize life

1. They DO NOT perform metabolism
2. They have no capacity to reproduce (by itself)
3. DO NOT respond to stimuli
4. No cellular composition (acellular)
5. No complex growth

Question 6

When and how were viruses discovered?

Answer 6

Discovered in the late 19th century

Scientists were studying sap from plants and the sap would transmit disease, but no bacteria present in the plant. Sap was filtered to remove all bacteria, but still transmitting disease!

Scientists concluded the agent must be way smaller than simpler bacteria but couldn’t be cultured in lab

Question 7

What are the components of the structure of a virus?

Answer 7

Genetic material (DNA or RNA) inside a protein casing.

Envelope protein
Envelope
Viral genome
Capsid
Viral tegument

NO membranes, organelles, nucleus or cytoskeleton

Question 8

What is a capsid?

Answer 8

The protein shell that encloses the genetic material

Question 9

What are capsomeres?

Answer 9

Smaller pieces that make up the capsid

Question 10

What are some common viral structures?

Answer 10

1. Rod-shaped or helical
2. Icosahedral - solid with 20 faces
3. Membranous envelope covered in spikes
4. Bacteriophage - rod and icosahedral mixture, comples structure that looks like weird, little spiders

Question 11

What is an example of rod shaped or helical virus?

Answer 11

Tobacco mosaic virus

Question 12

What is an example of a icosahedral virus?

Answer 12

Adenovirus

Question 13

What is an example of a membranous envelope shaped virus?

Answer 13

Influenza, coronavirus

Question 14

What do viruses need to replicate?

Answer 14

Because they don’t have ribosomes to express genes, they need a cell to do it for them!

Question 15

What are the steps in replication?

Answer 15

1. Recognition
2. Injection
3. Transcription and translation
4. Reassembly

Question 16

What is necessary for recognition?

Answer 16

1. A virus must be recognized by a specific type of cell in order to enter that cell
2. Usually contains specificity for a small group of species or one specific species

Question 17

What happens during injection?

Answer 17

The virus injects its genetic material OR is brought into the cell, completely intact through endocytosis

Question 18

What happens during transcription and translation?

Answer 18

The virus disassembles and the viral DNA is transcribed and translated by the host cell

Question 19

What happens during reassembly?

Answer 19

Once there are many copies of the viral DNA, the capsid protein re-assembles and releases new viral particles.
Sometimes this destroys the cell.

Question 20

What is the lytic cycle?

Answer 20

The host cell is terminated at the end of the replicated cycle.
It happens once many viruses have been generated.
The cell lyses and releases viral particles.

Question 21

What is the lysogenic cycle?

Answer 21

The host cell is not destroyed when the viral DNA enters the cell
Rather than hijacking the cell, the virus inserts its viral DNA into the host’s genome creating a prophage.
The cell continues to replicate, where the DNA remains silent.
An environmental signal causes a switch to the lytic cycle, causing all infected cells to lyse.

Question 22

What is lysis?

Answer 22

The disintegration of a cell by rupture of the cell wall or membrane

Question 23

What is endocytosis?

Answer 23

Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material.

Question 24

What is a prophage?

Answer 24

Viral DNA that is embedded in the host’s DNA during lysogenic infection

Question 25

What is important about membrane and surface receptors?

Answer 25

It is important for the virus to be recognized by the surface cell receptors.
The receptors allow the virus to enter and exit WITHOUT damaging the cell.

Question 26

What is a retrovirus?

Answer 26

It contains an enzyme called reverse transcriptase, which makes RNA into DNA.

Question 27

What is an example of a retrovirus?

Answer 27

HIV

Question 28

What are viroids?

Answer 28

Even smaller infectious agents

Naked, circular RNA molecules that disrupt regulatory systems in plants

Question 29

What are prions?

Answer 29

Contain no genome.

Infectious protein particles that cause other protein particles to aggregate and bring on disease symptoms.

Question 30

What are examples of prions?

Answer 30

Alzheimer’s and Parkinsons’s