Lecture 11

Question 1

Virion

Answer 1

an individual virus

Question 2

Virus

Answer 2

non-living? acellular
metabolically inert
- no energy generation or biosynthesis
- when outside cells not generating ATP
extracellular and intracellular forms

Question 3

virus genomes

Answer 3

RNA or DNA
single or double-stranded
very small, few genes (use host genes)

Question 4

capsid

Answer 4

protein shell
surrounds and protects genome
- arranged in a precise, repetitive pattern
- single or multiple protein types
- capsomeres (dictate symmetry)

Question 5

Icosahedral symmetry

Answer 5

= spherical virus

Question 6

helical symmetry

Answer 6

= rod shaped virus

Question 7

complex virus

Answer 7

icosahedral head and helical tail
- bacteriophage

Question 8

naked viruses

Answer 8

genome + capsid
- bacteriophages (mostly)

Question 9

enveloped

Answer 9

contain an additional membrane
- surrounds the nucleocapsid
- composed of a lipid bilayer and proteins
- common in viruses that infect animals (use membrane to get in/out of host cells)

Question 10

viral enzymes

Answer 10

for functions not provided by host cell enzymes
- an invasion of the host cell (lysozyme– to get through peptidoglycan layer)
- viral replication of RNA (reverse transcriptase– RNA to DNA)

Question 11

viral diversity

Answer 11

infects all forms of life
sputnik virophage example

Question 12

viral shunt

Answer 12

role of viruses in global nutrient cycles
- movement of elements in ocean example

Question 13

plaque assay

Answer 13

used in lab to quantify viruses
plaques = clear areas around lysed host cells
count the plaque forming units PFUs

Question 14

viral replication steps

Answer 14

1. attachment
2. penetration
3. synthesis
4. assembly
5. release (lysis)

Question 15

Attachment

Answer 15

proteins on virion capsid or membrane
- bind to surface receptors of host cells
determines the specificity of the virus
- no receptor = no attachment
- among hosts and within multicellular hosts (ex flu virus only in upper respiratory tract)

Question 16

Penetration

Answer 16

bacterial viruses (bacteriophage)
- tail fibers (attaches to the outer membrane and retracts)
- tail core (contacts cell wall and releases lysozyme)
- viral DNA (enters the cell through cell wall whole)

Question 17

Synthesis

Answer 17

two steps:
1) replicate the viral genome
2) synthesize proteins
Speed depends on the type of viral genome
- Baltimore classification scheme

Question 18

Baltimore classification scheme

Answer 18

seven classes of viruses
based on the viral genome

Question 19

DNA viruses

Answer 19

dsDNA -> mRNA -> protein
ssDNA -> dsDNA -> mRNA -> protein

Question 20

RNA viruses

Answer 20

ssRNA (+) = mRNA -> protein
ssRNA (-) = mRNA -> protein
* need to bring enzymes with them

Question 21

RNA retroviruses

Answer 21

ssRNA (+) -> dsDNA -> mRNA -> protein
* need to bring enzymes with them

Question 22

RNA-dependent RNA polymerase

Answer 22

“RNA replicase”
RNA replication (RNA -> RNA)

Question 23

reverse transcriptase

Answer 23

RNA -> DNA

Question 24

Synthesis and viral proteins

Answer 24

early proteins: aid replication of viral genomes
late proteins: aid construction of viral capsid

Question 25

Assembly

Answer 25

nucleocapsids formed by self-assembly

Question 26

Release

Answer 26

depends on the viral life cycle - lytic (virulent) mode -- host cells lysed and killed - lysogenic (temperate) mode -- host cells remain intact

Question 27

Lytic pathway

Answer 27

viral replication cell lysis -> virions released

Question 28

Lysogenic pathway

Answer 28

viral DNA -> host DNA replicates with host cell

Question 29

bacteriophage lambda

Answer 29

prophage - virus genome in the host chromosome lysogen - bacterial cell with the viral genome ecological significance - new genetic properties - immunity to related viruses

Question 30

Animal viruses

Answer 30

entire virion enters the host cell virion must enter the nucleus of the host cell virion can exit without cell lysis ("budding") - virulent, persistent, and latent infections

Question 31

virulent infections

Answer 31

viral replication - cell lysis -> all virions released

Question 32

persistent infections

Answer 32

viral replication - no cell lysis -> some virions bud

Question 33

latent infections

Answer 33

no viral replication - no cell lysis -> no virions released

Question 34

antiviral mechanisms

Answer 34

attachment and penetration - nearly impossible to prevent - viruses attached to surface receptors of host cells need for normal cell functioning synthesis is the actual antiviral target

Question 35

synthesis antiviral mechanism

Answer 35

target and destroy viral genome - restriction endonucleases (enzymes that cut/break DNA) RNA-based defense systems - CRISPR (prokaryotes) - interference RNA (eukaryotes)

Question 36

Restriction endonucleases

Answer 36

only in prokaryotes recognize and digest foreign DNA cut DNA at specific nucleotide sites high degree of specificity, important to not harm own DNA

Question 37

Restriction modification system

Answer 37

methylate own DNA as protection prevents digestion of self DNA

Question 38

CRISPR

Answer 38

clustered regularly interspaced short palindromic repeats (viral sequence "archive" library of previous infections

Question 39

RNA interference (RNAi)

Answer 39

CAS proteins - identifies dsRNA (= viral infection) - cuts dsRNA into pieces - uses pieces to target and destroy viral mRNA

Question 40

Dicer

Answer 40

cleaves dsRNA into shorter segments

Question 41

RISC

Answer 41

binds siRNA and separates the strands finds messenger RNA complementary to siRNA cleaves mRNA RNA fragments degraded by exonuclease