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Flashcards in Viruses Deck (19):
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Are antibiotics helpful for a virus or bacteria?

Bacterial infections

1

What is a virus?

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

2

What do viruses infect

Every type of living organism
-plant animal bacteria archaebacteria

3

Virus structure

Nucleic acid encased in a protein capsid
-enveloped or nonenveloped

4

Virus genome

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

5

Virus size

Much smaller then prok or euk cells

6

Virus that infects bacteria

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

7

Virus that infects animal cells

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

8

Bacteriophage life cycles
LYTIC CYCLE

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

9

Disadvantage of the lytic cycle

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

10

Bacteriophage life cycle
LYSOGENIC CYCLE

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

11

Animal cell virus life cycles

-have very similiar cycles to the lytic and lysogenic

12

How do eukaryotes enter and exit the host cell

Enter: endocytosis
Exit: budding out of the host cell

13

Advantage of animal virus

Doesnt kill the host cell

14

Bacteria's defense against a virus

-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

15

Three common typs of viruses

[+] RNA viruses
[-] RNA virus
Retroviruses

Distinguished by what their genome is made up of

16

[+] RNA virus

-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

17

[-] RNA viruses

-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

18

Retroviruses

[+] 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