Viruses

Question 0

What is a virus?

Answer 0

Non-living
Parasitic
Infectious agent that can only replicate within a host cell

Question 1

Are antibiotics helpful for a virus or bacteria?

Answer 1

Bacterial infections

Question 2

What do viruses infect

Answer 2

Every type of living organism

-plant animal bacteria archaebacteria

Question 3

Virus structure

Answer 3

Nucleic acid encased in a protein capsid

-enveloped or nonenveloped

Question 4

Virus genome

Answer 4

• can be linear or circular
• can be either dsDNA, ssDNA, dsRNA or ssRNA
• small genomes that can be read in different reading frames

Question 5

Virus size

Answer 5

Much smaller then prok or euk cells

Question 6

Virus that infects bacteria

Answer 6

Bacteriophage

• consists of a head and a tail
• protein coating on the head and a genome inside the head
• tail portion binds onto the bacteria cell and injects its DNA through the tail into the bacteria

Question 7

Virus that infects animal cells

Answer 7

Animal virus

• gets in a cell through endocytosis
• gets its cell membrane from the host cell
• some have an outer envelope

Question 8

Bacteriophage life cycles

LYTIC CYCLE

Answer 8

1. Adsorption-bind cell surface via tail
2. Penetration- puncture cell wall and membrane and inject genome into the host cell
3. Hydrolase (a viral gene product) is produced and degrades the host’s genome.. Now the cell is destined to die
4. Replication of the viral genome (many copies) and syntheis of much capsid protein
5. Assembly of new virus particles
6. Production of lysozyme to degrade the cell wall resulting in cell lysis and release of virus particles

Question 9

Disadvantage of the lytic cycle

Answer 9

• it kills the host cell

- if you kill all the host cells, as a virus you are done

Question 10

Bacteriophage life cycle

LYSOGENIC CYCLE

Answer 10

1. Adsorption-bind cell surface via tail
2. Penetration- puncture cell wall and membrane and inject genome into the host cell
3. Integation of the phage genome into the host genome
4. Dormancy- viral genes not expressed by viral genome is transmitted to all progeny during cell division
5. Sctivation- excision of viral DNA and entrance into the lytic cycle

Question 11

Animal cell virus life cycles

Answer 11

-have very similiar cycles to the lytic and lysogenic

Question 12

How do eukaryotes enter and exit the host cell

Answer 12

Enter: endocytosis
Exit: budding out of the host cell

Question 13

Advantage of animal virus

Answer 13

Doesnt kill the host cell

Question 14

Bacteria’s defense against a virus

Answer 14

• restriction enzymes
• the host cell contains restriction enzymes that degrade the viral DNA
• bacteria methylate their own DNA to distinguish it from the foreign DNA

Question 15

Three common typs of viruses

Answer 15

[+] RNA viruses
[-] RNA virus
Retroviruses

Distinguished by what their genome is made up of

Question 16

[+] RNA virus

Answer 16

• viral genome is ssRNA which can also serve directly as mRNA
• uses the cells translation machinary to start making his own genome
• must code for an RNA-dependent RNA polymerase for viral replication because the cell doesnt have one for translation
• the RNA itsels if th sense strand

Question 17

[-] RNA viruses

Answer 17

• viral genome is ssRNA which is anti-sense and therefore (doesnt code for a protein) complementary to the mRNA coding for viral genes
• must code for RNA-dependent polymerase and include this polymerase in its capsid to be infectious

Question 18

Retroviruses

Answer 18

[+] RNA (codes for proteins) viruses that convert their genomes into dsDNA for incorporation into the host’s genome
-must encode an RNA-dependent polymerase (reserve transcriptase)

Example: HIV