Chapter 11:Viruses, Viroids and prions

What are viruses?

-acellular
-obligate intracellular parasites
-no ATP generating system
-no ribosomes of protein synthesis

What are the 6 characteristics of life?

1. Made of cells
2. Grow and maintain structure by metabolizing chemicals from the environment
3. Respond to the external environmental stimuli
4. Reproduce and pass on their genes to the offspring
5. Evolve and adapt to their environment
6. Possess both DNA and RNA

Why are viruses not considered to be alive?

Viruses do not respond to external environmental stimuli
Viruses do not pass genes to their offspring (they reproduce differently)
Viruses have either DNA or RNA, but never both

Name the different parts of a virus

Nucleic acid: can be DNA or RNA(never both
capsid: (protein coat)
envelope: sometimes

binding proteins:on capsid or envolope, allows virus to interact with host cell

How big is a virus?

0.02 µm-14 µm

How is the viral host range determined?

by the viruses ability to interact with the host cell by binding to its surface on it's receptor sites (receptors and receptor sites have to match for infection to happen)

What are the 4 viral morphologies?

Helical Virus - rod of helical capsomeres
Polyhedral Virus - many sided
Enveloped virus - surrounds the capsid
complex virus - anything that doesn’t fit under other categories

How are viruses classified using the Baltimore classification strategy?

7 groups of genome replication:
Group 1: dsDNA
Group 2: ssDNA
Group 3: dsRNA
Group 4: ssRNA+
Group 5: ssDNA-
Group 6: ssRNA-RT
Group 7: dsDNA-RT

Where did viruses originate from?

They have no common ancestor, they seem to have risen many times during evolution.

what is the ICTV classification

International Committee on Taxonomy of Viruses
viruses that are related can be classified similarly to living things: Order, family, subfamily, genus, species

What are oncogenic viruses?

viruses that cause cancer

Give an example of oncogenic viruses?

Hepatitis B, human herpesvirus 4, Human papillomavirus, etc.

What are oncolytic viruses?

viruses that infect and kill cancer cells

Give an example of an oncolytic virus

strains of adenovirus, reovirus, measles virus, poliovirus, human herpesvirus

How do you grow bacteriophages?

Start with a lawn of bacteria on a spread plate
add the phage
infection results in clear plaques where bacteria have been killed by the phage

How can animal viruses be grown?

1. In living animals
2. Chicken embryos
3. Cell cultures

How can plant viruses be grown?

1. In living plants

2. In cell cultures(protoplasts)

What are viroids?

small rings of naked RNA with no capsid
300-400 nucleotides long
closed folded 3D shape
plant pathogens

What is a Prion?

proteins that have lost their normal shape that can cause disease

What disease do Viroids cause

Potato spindle tuber viroid, apple viroid disease, Coconut Cadang-cadang viroid

What diseases to prions cause?

- Bovine Spongiform Encephalopathy
- Kuru
- Creutzfeldt-Jakob's disease

List the steps of the lytic cycle

1. Attachment - binding sites must match receptor sites
2. Penetration - viral DNA is injected into bacterial cell
3. Biosynthesis
a. genome replication
b. transcription and translation to make proteins
4. Assembly - viral particles are assembled
5. Release by lysis
- bacterial cell is filled up and it bursts
- bursting time: 20-40 min
- burst size: 50-200 new viruses

List the steps of the lysogenic cycle

1. Attachment
2. Penetration
3. Integration: virus inserts its genes into the host cell genome, prophage: virus is latent, bacterial cell replicates its genome and the viral genome, virus gets turned on
4. Biosynthesis, virus takes over the host cell for genome replication & transcription and translation
5. Assembly
6. Release by lysis

What is lysogenic conversion?

when the infecting phage changes something in the host bacterium's life style

List the steps of non-enveloped animal virus replication

1. attachment
2. penetration by endocytosis or phagocytosis
3. uncoating: separating capsid from the viral genome
4. biosynthesis: genome replication, transcription and translation
5. Assembly
6. release by lysis

List the steps of enveloped virus replication

1. Attachment
2. penetration by fusion of viral envelope and cell membrane
3. uncoating
4. biosynthesis: genome replication, transcription and translation
5. Assembly
6. release by budding: virus pinches out through the host cell membrane, the part of the membrane becomes the envelop

What are cell lines

cell cultures categorized by origin and lifespan

Primary cell line-die out after a few generations

Diploid cell lines- greater reproductive potential, derived from human embryos, maintained up to 100 generations

Continuous cell lines- immortal under the right conditions

What cell lines are mainly used for growing viruses and what was the first cell line developed

Continuous cell Lines(cancerous cells)

HeLa cells