MID 2 - Lecture 9

Question 1

Virus

Answer 1

Small, Infectious agent
Can only replicate within host organism, cannot reproduce (> 1 molecule)

Question 2

Bacteriophages

Answer 2

bacterial viruses, many infect euk hosts, classified into families based on genome struc, life cycle, etc)

Question 3

Virion

Answer 3

Virus particle, size 10-400 nm, contain nucleocapsid, can be non-enveloped, or enveloped

Question 4

Capsids

Answer 4

Large, protect viral genetic material, helps with transport, made of promoters

Question 5

Helical capsids

Answer 5

Hollow tubes with protein walls, self assemble, size is function of nucleic acid

Question 6

Icosahedral capsid

Answer 6

Many viruses have, regular polyhedron (20 faces)

Question 7

Capsid with complex symmetry

Answer 7

Don’t fit category (poxviruses, large bacteriophages)

Question 8

Viral envelopes

Answer 8

Many viruses bound by envelope

Question 9

Viral envelope proteins

Answer 9

Spikes, used for identification of virus, viral attachment, enzymatic/other activity, role in nucleic acid replication

Question 10

Virulent phage

Answer 10

one reproductive choice (multiples immediately upon entry, lyses bacterial host cell) LYTIC ONLY

Question 11

Temperate phage

Answer 11

2 reproductive options (lytically, or remain within host cell without destroying it)
LYTIC OR LYSOGENIC

Question 12

Lytic cycle and lysogenic cycle

Answer 12

look at picture

Question 13

Viral genome

Answer 13

diverse array of genomes, virus may have single/double stranded DNA or RNA, length of nucleic acid varies (4000, 2 mill bps), linear, circular or segmented

Question 14

Virus classification (OG)

Answer 14

Nucleic acid type, presence or absence of envelope, capsid symmetry, dimensions of virion and capsid

Question 15

Alternative classification scheme

Answer 15

7 groups
1. dsDNA 2. ssDNA 3. dsRNA 4. + strand ssRNA 5. - strand ssRNA 6. retroviruses 7. reverse-transcribing DNA viruses

Question 16

dsDNA viruses

Answer 16

largest, most bacteriophages have, important vertebrate viruses, rely on host’s DNA/RNA polymerase

Question 17

Bacteriophage T4 (3 steps)

Answer 17

Virulent dsDNA phage
steps:
1. adsoprtion to receptor on E.coli outer membrane
2. Tail sheath lysosome/central tube pierce the cell wall
3. Viral nucleic acid is injected into host cell through tube

Question 18

Life cycle of bacteriophage T4

Answer 18

Early mRNA transcrip, host DNA degrad, Phage DNA repl, late RNA transc, head and tails synthe, genome packing, virion assembly, host cell lysis

Question 19

Bacteriophage lambda

Answer 19

Phage lambda can enter either the lytic or lysogenic cycle upon infection of e.coli (lyso- dsDNA become prophage)

Question 20

Reproduction of RNA phages

Answer 20

RNA genome don’t rely on host cell enzymes for replication/ mRNA synthesis
RNA- dependent RNA polymerase completes life cycle

Question 21

Plus strand RNA viruses

Answer 21

Used for protein synthesis, replicate in cytoplasm, synthesize RNA depen- RNA polymerase (SARS-CoV-2)

Question 22

Negative strand RNA viruses

Answer 22

preformed RNA-dependent RNA polymerase, new plus strand intermediates synthesized, new + strand serves as template for genome synthesis

Question 23

Retroviruses

Answer 23

convert ssRNA into dsDNA using reverse transcriptase dsDNA integrates into host cell genome, HIV

Question 24

Viral multiplication

Answer 24

attachement, entry and uncoating of genome, synthesis, assembly, virion release

Question 25

Viral entry (3 methods)

Answer 25

1. Fusion of viral envelope with host membrane
2. Endocytosis in vesicle
3. Injection of nucleic acid
   Naked - Endocytosis, inject nucleic acid
   Enveloped virus - attachement to receptors with spikes, fusion or endocytosis

Question 26

Animal virus entry mechanisms

Answer 26

a) enveloped virus: fusion with plasma membrane
b) enveloped virus: endocytosis (escape into cytoplasm)
c) naked virus: endocytosis - nucleic acid extruded

Question 27

Virion release (influenza)

Answer 27

budding, viral proteins in host membrane, nucleocapsid may bind to viral proteins, envelope derived from host cell membrane

Question 28

Infection in eukaryotic cells

Answer 28

cytocidal infection = cell death through lysis
Cytopathic effects = degenerative changes, abnormalities