Banfield lecture two - viral structure

Question 1

what is a Virion

Answer 1

The mature infectious viral particle

Question 2

What is the capsid

Answer 2

The protein shell that encloses and protects the viral nucleic acid

Question 3

what is a capsomere

Answer 3

the structural unit of the icosahedral capsid

Question 4

what is the core

Answer 4

the internal part of the viral particle that contains the nucleic acid and closely associated proteins.

Question 5

what is the nucleocapsid

Answer 5

the structure composing of the capsid and the viral nucleic acid or core
capsid –> encloses genetic info / core
nucleocapsid –> capsid + enclosed genetic info/core

Question 6

what is the envelope

Answer 6

viral lipid-bilayer consisting of internal spike proteins

Question 7

what are spike proteins?

Answer 7

viral glycoproteins the project outward from the viral envelope

Question 8

Briefly explain the adenovirus (structure + viral infection)

Answer 8

causes pinkeye
has no envelope
icosahedral structure

Question 9

Briefly explain the rhabdovirus (structure + viral infection)

Answer 9

causes rabies
enveloped
helical capsid

Question 10

Briefly explain the coronavirus (structure + viral infection)

Answer 10

often causes common cold

spike proteins cause the corona fusion shape

Question 11

Briefly explain the papovirus (structure + viral infection)

Answer 11

causes warts
no envelope
many capsomers forming a circular nucleocapsid

Question 12

what are the two common capsids in viruses

Answer 12

helical capsids

icosahedral capsids

Question 13

what is a naked virus?

Answer 13

a virus with no envelope

Question 14

true or false, helical animal viruses are naked

Answer 14

false, no helical animal viruses are naked

Question 15

What organisms commonly have helical capsids?

Answer 15

plant viruses and bacteriophages

Question 16

enveloped animal viruses with helical capsids contain what kind of nucleic acid?

Answer 16

helical capsid animal viruses will ALWAYS HAVE RNA and never have DNA

Question 17

True or false, many RNA viruses build nucleocapsids using helical symmetry

Answer 17

true

Question 18

If an animal virus contains a helical capsid it contains what nucleic acid? is this animal virus enveloped or not?

Answer 18

naked helical viruses do not exist, therefore it has to be enveloped. Additionally, no helical animal viruses contain DNA. therefore the nucleic acid must be RNA

Question 19

true or false, helical capsids are closed structures

Answer 19

false, they are open ended rods

Question 20

What is one well studied helical capsid virus

Answer 20

TMV –> tobacco mosaic virus

Question 21

what are the two types of helical capsids?

Answer 21

flexible helical capsids

rigid helical capsids

Question 22

Rhabdovirus is an example of what capsid?

Answer 22

a rigid helical capsid

rhabdovirus causes rabies

Question 23

Paramyxovirus is an example of what capsid? what does it cause?

Answer 23

a helical flexible capsid.

Paramyxovirus causes measles

Question 24

why are there no naked helical capsid animal viruses?

Answer 24

no envelope inhibits the diversity of the virus and allows the immune system to easily defeat the naked helical virus. Glycoproteins in an envelope increase immune evasion

Question 25

explain the icosahedral capsid

Answer 25

icosahedral capsids are twenty-sided structures that from a sphere. Each building block of the icosahedron is a triangle. Science world is an example of this.

Question 26

what are the different axises of the icosahedron? explain this genetic economy?

Answer 26

2-fold 3-fold 5-fold this is an example of genetic economy since the icosahedron uses many triangle subunits to produce one larger triangle

Question 27

what kind of capsid does herpes simplex have?

Answer 27

spherical icosahedral capsid

Question 28

HIV is an example of what kind of virus? what capsid does it have?

Answer 28

HIV is a retrovirus | it has an "unusual" capsid in which is contains hex and pent units

Question 29

why do some viruses have envelopes and others do not?

Answer 29

Viruses that are enveloped will exits the cell they infect after budding through some extra - cytoplasmic membrane. Non-enveloped viruses leave the cell they infect through cell lysis which is terminal.

Question 30

true or false, envelope viruses must kill their host

Answer 30

false, envelope viruses bud with cellular membranes which permits them to leave without lysing the cell.

Question 31

what are three general functions of glycoproteins on the envelope?

Answer 31

- entry and host range determination - assembly and egress (exit) - evasion of immune response

Question 32

What form of viruses often bud out of cells and do not lyse them?

Answer 32

retro viruses

Question 33

Breifly explain the budding mechanism of retro viruses?

Answer 33

1. proteins are expressed by the virus RNA genome 2. these proteins interact with RNA thats been exported out of the nucleus 3. the proteins bind the plasma membrane an begin exocytosis while DNA gets packed into the leaving molecule 4. once the full virus has left the intermolecular proteins form the capsid.

Question 34

explain the general process of non-envelope viruses

Answer 34

1. the virus binds and enters 2. transport via microtubules to ER 3. incorporated into nucleus where modifications occur and virus transcription occurs. 4. transcripts become translated 5. proteins help assemble virus within the nucleus which then finally causes cell lysis.

Question 35

true or false, the viral genome can consist of RNA, DNA, or both.

Answer 35

false, it can contain one or the other, never both.

Question 36

what type of strand (+/-) is mRNA

Answer 36

always designated + strand since its info is directly translated

Question 37

what type of strand is the coding strand

Answer 37

the coding strand has the same polarity as the mRNA strand and therefore is also a + strand

Question 38

complementary strands to the RNA or coding DNA are?

Answer 38

- strands

Question 39

how would you synthesize a - strand?

Answer 39

by using a + strand as a template

Question 40

explain the characteristics / possibilities of viral DNA

Answer 40

- can be linear or circular - can be ds or ss ss DNA can be either + or - polarity - in some cases it can partially double stranded and circular (hepatitis B)

Question 41

explain the characteristics / possibilities of viral RNA

Answer 41

- can only be linear - ss or ds - can be + or - or ambisense (both polarities) - mono-partite (single piece of RNA) or multipartite (multiple genome segments)

Question 42

What type of genome does the common Flu virus have?

Answer 42

it has a multipartite RNA virus which all code for different proteins that assemble into a single protein.

Question 43

where do most DNA and RNA viruses replicate

Answer 43

DNA - nucleus | RNA - cytoplasm

Question 44

what exceptions are there to the location of replication for DNA and RNA viruses?

Answer 44

the flu virus is an RNA virus that replicates within the nucleus . Pox virus is a DNA virus that replicates in the nucleosome

Question 45

Pox virus has a ___ genome which replicates in the ___. Due to this it provides its own ___

Answer 45

DNA genome cytoplasm DNA polymerase