Lecture 10 Virology Flashcards Preview

BIO 425: Microbiology > Lecture 10 Virology > Flashcards

Flashcards in Lecture 10 Virology Deck (40)
Loading flashcards...
1

What is a virion?

an individual virus
-non living, acellular, and metabolically inert

2

How do viruses differ from plasmids?

Plasmids have extracellular and intracellular forms
-viruses only have intracellular form

3

What composes virus structure?

Genome
-RNA or DNA
-Very small genome b/c it relies on host DNA

Capsid
-protein shell protects genome

4

What kind of structure do viral capsids have?

Composed of protein molecules in repetitive pattern
-single or multiple protein types = capsomere
-the protein arrangement determines shape

Icosahedral symmetry = spherical virus
Helical symmetry = rod shaped virus

5

What are complex viruses?

virus with several parts with different symmetry
-eg. helical tail and icosahedral head = bacteriophage

6

What is the difference between naked and enveloped viruses?

naked = genome+capsid

Enveloped = contain an additional membrane
-surrounds nucleocapsid
-common in animal viruses

7

Why would some virions contain enzymes?

For functions not provided by host cells
-lysozymes for invasion of host cell
-viral replication of RNA = reverse transcriptase

8

What forms of life can viruses infect?

Prokaryotes
-bacteriophage
-archaeal viruses

Eukaryotes

Other viruses
-virophages

9

What is a sputnik virophage?

virus that infects other viruses in order to get into host cell

10

What role do viruses play in global ecology?

Viral shunt
-Phagocytosed by macrophages
-cause cell lysis
-food chain

11

How do we study viruses in the lab?

Plaque assay
-used to quantify viruses

the plate completely covered with bacterial colony
-the number of holes that form = number of viruses
-the virus lyses bacterial cells forming 'plaques'

12

What are the steps of viral replication?

1. Attachment
2. Penetration
3. Synthesis
4. Assembly
5. Release (lysis)

13

What is the viral replication step attachment?

Proteins on virion capsid bind surface receptors on host cell

If the host doesn't have right receptors then virion can't bind = specificity

14

What is the viral replication step Penetration?

Bacterial Viruses (Bacteriophage)
·∙
Tail Fibers
-­‐ (a) Attaches to Outer Membrane
-­‐ (b) Retracts
·∙
Tail Core
-­‐ (c) Contacts Cell Wall
-­‐ (c) Releases Lysozyme
·∙
Viral DNA
-­‐ (c) Enters Cell through Cell Wall Hole

15

What is the viral replication step Synthesis?

Two Steps:
·∙
1) Replicate the Viral Genome
2) Synthesize Proteins

16

What is the baltimore classification scheme?

Synthesis classification depends on type of viral genome
-DNA or RNA
-Double stranded or single stranded

17

How does synthesis differ for DNA viruses, RNA viruses, RNA retroviruses?

DNA Viruses
-dsDNA to mRNA to Protein
-ssDNA to dsDNA to mRNA to Protein

RNA Viruses
-ssRNA (+) = mRNA to Protein
-ssRNA (–) to mRNA to Protein

RNA Retroviruses
-ssRNA (+) to dsDNA to mRNA to Protein

18

What is RNA-dependent RNA Polymerase and what is Reverse transcriptase?

Part of the synthesis step to replicate viral genome

RNA-dependent RNA Polymerase
-RNA Replicase
-RNA to RNA

Reverse Transcriptase
-RNA to DNA

19

What types of proteins do viruses synthesize in the synthesis step of viral replication?

·∙Early Proteins
– Aid Replication of Viral Genomes
·∙
Late Proteins
– Aid Construction of Viral Capsid

20

What is the viral replication step Assembly?

Nucleocapsids Formed By Self-­‐Assembly

21

What is the viral replication step Release?

Depends on Viral Life Cycle
·∙
Lytic (Virulent) Mode
-­‐ Host cells lysed and killed
·∙
Lysogenic (Temperate) Mode
-­‐ Host cells remain intact

22

What is the bacteriophage lambda?

Two pathways of viral replication in bacteria

Lytic Pathway
-Viral Replication
-Cell Lysis = Virions Released

Lysogenic Pathway
-Viral DNA to Host DNA
-Replicates with Host Cell

When jump from lysogenic to lytic pathway called induction

23

In the lysogenic pathway, what is a prophage and what is a lysogen?

Prophage
-virus genome in the host chromosome

Lysogen
-bacterial cell with viral genome

24

What is the ecological significance of lysogenic pathway?

New genetic properties

immunity to related viruses

25

What kinds of viruses infect bacteria and what kind infect animals?

Naked viruses = bacteriophages

Enveloped viruses = animals

26

What are the key differences of animal viruses from bacterophages?

Entire Virion Enters the Host Cell
·∙
Virion Must Enter the Nucleus
·∙
Virion Can Exit without Cell Lysis (“Budding”)

27

What are the types of animal viruses?

Virulent Infections
-Viral Replication
-Cell Lysis = All Virions Released

Persistent Infections
-Viral Replication
-No Cell Lysis = Some Virions Bud

Latent Infections
-No Viral Replication
-No Cell Lysis = No Virions Released

28

What steps of viral replication are targeted in ANTI-VIRAL mechanisms?

Attachment
Penetration
Synthesis

If it gets to Assembly or Release then its too late

29

What are the mechanisms of anti-viral defense for attachment?

NEARLY Impossible to Prevent
-Viruses Attached to Surface Receptors of Host Cells
-Same Receptors Needed for Normal Cell Functioning

30

What are the mechanisms of anti-viral defense for synthesis?

Target and Destroy Viral Genome
-Restriction Endonucleases
-RNA-­‐Based Defense Systems
·∙
CRISPR (prokaryotes)
-Interference RNA (eukaryotes)