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infectious disease midterm > lecture 1 part 2 > Flashcards

lecture 1 part 2 Flashcards

1
Q

DNA viruses can be ___ or ____

A

enveloped or naked

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2
Q

HERPES is an example of a ___ virus

A

enveloped double strand linear DNA

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3
Q

Adenovirus is an example of a ____ virus

A

naked double strand linear DNA virus

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4
Q

the majority of viruses that infect bacteria are DNA or RNA?

A

DNA

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5
Q

Name the 9 general steps of viral replication

A
  1. recognize target cell
  2. attachment
  3. penetration/fusion
  4. uncoating of virion – exposes nucleic acid
  5. transcription
  6. protein synthesis
  7. replication of nucleic acid – happens for ALL VIRUSES
  8. assembly
  9. release
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6
Q

there are __ mechanisms in which a virus can get into the cell:

A

2:

-straight endocytosis
-receptor mediated endocytosis

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7
Q

viruses can be ___ or ___ and cells can be ___ or ____

A

viruses can be PRODUCTIVE or NON-PRODUCTIVE

cells can be PERMISSIVE or NON-PERMISSIVE

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8
Q

explain the difference between a productive and non-productive virus

A

a productive virus lyses the infected cell (lytic response)

a non-productive virus DOES NOT LYSE THE HOST CELL and can be:

-lysogenic (integration of viral genome into host genome, or the formation of an extrachromosomal plasmid)

-oncogenic – integrate in genome (chromosome) next to growth factor gene. virus gets growth factor gene on it and virus is in control ex: RNA tumor virus

-persistent – latent or chronic. continually buds off infectious particles. does NOT lyse the cell

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9
Q

explain how cells can be permissive or non-permissive in relation to viruses

A

permissive cells allow viral replication or integration

non-permissive cells allow entry but do NOT allow replication. they may be transformative
ABORTIVE = cell does not allow replication, but cell death still results due to the transformation (shape change)

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10
Q

step 1 of viral replication is ________.
explain how the virus accomplishes this

A

step 1 = target recognition and attachment

accomplished through viral attachment proteins (VAPs; spikes), host range, and tissue tropism

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11
Q

the second step of viral replication is ____.
explain how this is accomplished

A

PENETRATION

either through receptor mediated endocytosis or membrane fusion

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12
Q

what is VIROPEXIS

A

receptor-mediated endocytosis of a virus

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13
Q

explain how membrane fusion works

A

if the virus is enveloped, it can fuse with the host cell membrane and release the capsid into the cytoplasm

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14
Q

the 3rd step of viral replication is ____.
explain why this is done and how

A

uncoating

the virus removes it’s coat and the nucleic acid is delivered to the site of replication

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15
Q

in the SYNTHESIS of viruses, what 2 classes of gene products are needed?

A

early gene products — non-structural proteins that are required for REPLICATION

late gene products – structural proteins

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16
Q

true or false

membrane fusion is also known as viropexis

A

FALSE – it’s receptor mediated endocytosis

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17
Q

explain the difference in the process of viropexis vs membrane fusion

A

in membrane fusion, the virus has an envelope derived from the previous host cell. therefore, it fuses with the membrane of the next host cell and releases the nucleocapsid into the cytosol.
the plasma membrane is now continuous with the previous envelope of the virus

in viropexis, the enveloped virus recognizes receptors on the surface of the host and gets phagocytized in in an ENDOSOME with the virus still fully intact (along with the receptors that recognized the virus on the host cell surface).

the endosomal receptors then again recognize the VAPs on the virus within the endosome, which triggers the lowering of pH. the virus takes advantage of this and fuses with the endosomal membrane, and releases its nucleocapsid into the cytosol

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18
Q

which virus recognizes CR2 receptors on our cell surfaces?

A

Epstein-Barr virus

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19
Q

____ are potential viral receptors that are present on just about all of our cells

A

integrins

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20
Q

hepatitis A virus recognizes what receptor?

A

alpha 2 macroglobulin receptor

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21
Q

which 2 viruses recognizes CD4?

A

human herpes 7
HIV

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22
Q

which virus recognizes iCAM-1?

A

rhinoviruses

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23
Q

most DNA viruses generate ___ through ____

A

mRNA through SPLICING

24
Q

TRUE OR FALSE

from the same DNA, MANY different mRNA transcripts are translated into proteins

A

TRUE

25
Q

in a few viruses, the RNA genomes are arranged as….

what enzyme catalyzes this reaction?

A

individual segments. each segment encodes for a different (+)mRNA strand and thus a different protein

catalyzed by RNA dependent RNA polymerase which is ONLY present in viruses. the virus brings this enzyme into the host cell to accomplish (-) RNA genome –> (+)mRNAs

26
Q

which RNA is the CODING STRAND

A

(+) mRNA

27
Q

some viruses have one long genomic RNA strand. what happens with this?

A

this long genome can have multiple promotor regions which results in 3 different mRNAs and 3 different proteisn

28
Q

viral replication can also occur….

A

through a polyprotein

there is a (+) RNA genome that goes through a NEGATIVE RNA INTERMEDIATE and then produces mRNA, to create a polyprotein that is cleaved by a protease to produce 3 mature proteins

29
Q

WHY do viruses sometimes go through a (-) RNA intermediate ?

A

2 reasons:

-serve as a template to make many (+)mRNA strand (messages) to be packaged into the many newly formed viruses

-can make many many more mRNA to make many more viral proteins

30
Q

ALL ROADS LEAD TO THE PRODUCTION OF ____

A

mRNA (+)

31
Q

WHY do all roads lead to the production of mRNA?

A

need mRNA to make viral proteins for a successful infection

32
Q

the synthesis of viral proteins requires what components?

A

host ribosomes
tRNA
post translational machinery (processing in golgi)

33
Q

in regard to viral protein synthesis, what is happening at the host ribosome?

A

a giant, genome spanning polyprotein can produced which gets cleaved

can produce small transcripts that produce individual proteins

-produce smaller polypeptides

34
Q

can human cells produce a polyprotein?

A

NO
this is an adaptation of viruses. they go through a (-) RNA intermediate to accomplish this

for humans, a single gene is a single transcript (mRNA)

35
Q

In viral protein synthesis, they can achieve preferential translation over the host.
explain this

A

they block preexisting mRNAs, degrade host DNA and mRNA (so it has nucleotides to use), and decrease cellular transcription (no competition)

36
Q

explain how viruses are able to assemble their proteins/nucleic acids to form a functional virus

A

they have recognition sequences that allow:

protein-protein
protein-nucleic acid
protein-membrane
interactions to fully form

to bud, viral membrane proteins (like VAPs) are inserted into the plasma membrane – in the region where the capsid will bud off. very convenient.

37
Q

explain the release of newly formed viruses from the host cell

A

when released, the viruses take the membrane from the host so they become enveloped in the host membrane.

they can:

-bud from the plasma membrane
-bug through the ER/golgi (and remain intracellular)
-pass through the ER and be transported to the surface in endosomes
-they can lyse the cell
-form a cell-cell bridge

38
Q

what does a virus make that enables the efficient release of a newly formed virus?

A

matrix protein – in a region with spike proteins on the INNER SURFACE of the plasma membrane

the nucleocapsid comes into that region of the plasma membrane of the host and gets pinched off along with the membrane to form a new enveloped virus

39
Q

DNA viruses use ____ to make mRNA and use ____ to copy DNA

A

use DNA-dependant RNA polymerase to make mRNA

use freshly made DNA dependent DNA polymerase to copy their DNA

40
Q

explain the entire process of DNA virus replication

A

DNA virus gets into the cell (either through viropexis or membrane fusion).

the DNA virus goes to the nucleus where it releases its viral DNA through a nuclear pore.
viral mRNA is then synthesized (using DNA dependant RNA polymerase of the host)

viral mRNA is then made to viral protein on a ribosome.

the proteins being made at this point are IMMEDIATE EARLY PROTEINS (non-structual proteins; required for replication of the virus)

then, EARLY PROTEIN SYNTHESIS and GENOME REPLICATION begins. at this point, DNA dependent DNA polymerase (JUST MADE BY THE VIRUS) is used to copy the viral DNA into multiple strands.
then late protein synthesis occurs (structural proteins)

packaging of DNA and capsid formation then occurs. this DNA containing naked capsid goes through the ER, and golgi.
gets into the golgi and buds off to get its membrane – becomes enveloped. get SPIKE PROTEINS in the golgi.

after leaving the golig, the newly formed active virus is either released and lyses the cell, exocytised and released, or released and directly put onto an adjacent cell

41
Q

in viral DNA replication, where are we starting to package our newly made virus?

A

starts in the nucleus of the host. then moves through ER and golgi

42
Q

explain the entire replication process of (+) RNA viruses

A

has VPg (viral protein gene) that binds to 5’ end of the message that helps to load messages. translation to polyprotein – cleaved – several proteins made right off bat

2 functions of - strand intermediate:

-make (+) mRNA to make more protein
-make (+)mRNA to be packaged into viral proteins

when the (+)mRNA is packaged into the viral proteins, it leaves the cell and lyses it

43
Q

which viruses MUST carry RNA dependent RNA polymerase in order to successfully replicate?

A

(-) strand RNA viruses – they need to make a MESSAGE (+) mRNA

44
Q

explain the process of (-)RNA replication

A

positive strand is made from the (-) RNA through RNA dependent RNA polymerase, brought in by the virus

this positive strand has 2 fates:
-transcribe back into negative strand which is needed for packaging – will meet up with structural proteins to form active virion

-directly used as mRNA to synthesize viral proteins

45
Q

which replicates faster – viruses or bacteria?

A

viruses

46
Q

which is more accurate by far – DNA polymerase or RNA polymerase?

A

DNA polymerase

47
Q

viruses have terrible polymerases.
why is this a bad thing for us?

A

because this means the spike proteins of the virus are continually changing. therefore, the antibodies that we had previously developed against the virus are no longer effective

48
Q

name 6 mutations that can occur in viruses that make it less strong of a virus

A

-lethal mutation
-deletion mutants
-plaque mutants
-host range mutants
-attenuated mutants
-conditional mutants

49
Q

is there more recombination in DNA viruses or RNA viruses?

A

DNA

50
Q

When HSV-1 and HSV-2 coinfect a cell, what happens?

A

recombination. this generates a hybrid molecule.
neither HSV-1 or HSV-2. BRAND NEW VIRUS

51
Q

influenza has 8 separate strands of ssRNA.
if 2 strains infect the same organism, what can happen?

A

random assortment of those chromosomes to generate 2 very different viable viruses.

called ANTIGENIC SHIFT

52
Q

can a virus with a lethal mutation be saved?

A

YES – by a wild type DNA fragment. recombination occurs to produce a viable virus.

this is called MARKER RESCUE

53
Q

explain the process of antigenic DRIFT

A

a point mutation occurs.
as long as not a stop codon, it will only affect a SINGLE amino acid, most likely not a significant change. However, there can be a significant change that affects protein folding.

SLOW ACCUMULATION OF POINT MUTATIONS

54
Q

explain the process of antigenic shift

A

2 strains of a virus infect the same organism and undergo a rapid random reassortment to produce completely unrecognizable viruses in some cases

more dangerous than antigenic drift. its a very fast process

55
Q
A

infectious disease midterm (9 decks)

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