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MCAT-BIOLOGY > Microbiology > Flashcards

Microbiology Flashcards

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1
Q

virus

A

tiny infectious agents

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2
Q

obligate intracellular parasite

A

able (obligated) to reproduce within (intra) cells. an example is a virus

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3
Q

are viruses cells or living organisms?

A

NO

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4
Q

what can a viral genome consist of?

A

DNA or RNA, single or double stranded, circular or linear

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5
Q

for any type of virus, how many nucleic acids can it’s genome carry?

A

only one type present in mature genomes, and only one type of nucleic acid as its genome

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6
Q

bacteriophage

A

a virus that infects bacteria

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7
Q

what is the limiting factor of all viral genomes, regardless of the form of nucleic acid used as a genome?

A

size

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8
Q

why is size the limiting factor for viruses?

A

the exterior protein shell is typically a rigid and fixed structure that cannot expand

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9
Q

what is an adaptation for the small size of viral genomes?

A

each genome can encode more than one protein in a given length by utilizing multiple reading frames

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10
Q

capsid

A

protein coat surrounding the viral nucleic acid gnome

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11
Q

helical capsids

A

rod shaped

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12
Q

polyhedral capsids

A

multiple-sided geometric figure

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13
Q

envelope

A

membrane on the exterior of the virus that surrounds the capsid, is derived from the membrane of the host cell

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14
Q

budding

A

the process through which viruses can acquire an envelope through the host cell membrane

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15
Q

naked viruses

A

viruses which do not have envelopes

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16
Q

which viruses are always naked?

A

all phages and plant viruses

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17
Q

attachment/adsorption

A

first step: virus binds to exterior of a bacterial cell

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18
Q

penetration/eclipse

A

second step: injection of the viral genome into the host cell, capsid remains on the outer surface while genome disappears into the cell, removing infectious virus from the media

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19
Q

what happens to the phage once the viral genome is injected into the host?

A

it can either enter the lytic or lysogenic cycle

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20
Q

hydrolase

A

a hydrolytic enzyme that degrades the entire host genome, an early gene

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21
Q

early gene

A

one of a group of genes that are expressed immediately after infection and which includes any special enzymes required to express viral genes

22
Q

lysozyme

A

destroys the bacterial cell wall, causing cell lysis, a late gene

23
Q

what is the main difference between lytic and lysogenic cycle?

A

host cells are not destroyed in the lysogenic cycle

24
Q

prophage

A

when the phage genome is incorporated into the bacterial genome

25
Q

lysogen

A

refers to the host after the phage genome has been incorporated

26
Q

how are infected cells able to remain dormant in the lysogenic cycle?

A

transcription of phage genes are blocked by a phage-encoded repressor protein that binds to specific DNA phage promoters and operators

27
Q

excision

A

the process whereby the prophage becomes activated and removes itself from the host genome, entering the lytic cell

28
Q

transduction

A

the process whereby a small section of host genome is replicated and packaged with the viral genome, and may be coded to create mutated viruses

29
Q

how do animal viruses enter cells?

A

by endocytosis (host cell engulfs the virus and internalizes it), the viral genome is released from the capsid (uncoated)

30
Q

what possible cycles can an animal virus enter?

A

lytic cycle, lytic-like cycle (productive cycle) or lysogenic cycle

31
Q

productive cycle

A

similar to lytic cycle but does not destroy the host cell because it exits the membrane by budding, becoming coated with membrane in the process

32
Q

provirus

A

refers to the dormant form of the viral genome in the animal virus lysogenic cycle

33
Q

+ RNA viruses

A

must encode RNA-dependent RNA pol (and do not have to carry it: a ssRNA genome, viral genome acts directly as mRNA and is translated by host ribosomes to create viral proteins

34
Q

infective

A

means injecting an isolated genome into the host cell will result in virus production

35
Q
  • RNA virus
A

must carry RNA-dependent RNA pol, - RNA is complementary to the piece of RNA that encodes viral proteins, so -RNA is the template for viral mRNA production

36
Q

how does the -RNA virus propagate the viral life cycle?

A

the enzyme will create a + strand from the - genome, this is what encodes viral proteins

37
Q

retroviruses

A

must encode reverse transcriptase, usually + RNA viruses that undergo lysogeny

38
Q

if an RNA virus undergoes lysogeny, what does this imply about its genome?

A

to be able to integrate into our double-stranded DNA, the viral genome must also be composed of double-stranded DNA (i.e. reverse transcription)

39
Q

reverse transcription

A

to make DNA from an RNA template

40
Q

RNA-dependent DNA polymerase (reverse transcriptase)

A

enzyme that produces DNA from an RNA template

41
Q

what are the three main retroviral genes?

A

gag (codes for viral capsid proteins), pol (polymerase codes for reverse transcriptase) and env (envelope codes for viral envelope proteins)

42
Q

double-stranded DNA viruses

A

often encode enzymes required for dNTP (nucleotide) synthesis and DNA replication: these viruses often have large genomes, this is required because dNTP’s aren’t always available but NTP’s are

43
Q

subviral particles

A

infectious agents that are even smaller and simpler than viruses, ex. prions and viroids

44
Q

prion

A

a subviral particle, a version of a protein that can self-replicate without transcription or translation

45
Q

helper virus

A

one virus which complements another

46
Q

transmissible spongiform encephalopathies (TSEs)

A

caused by prions, a class of diseases in mammals that causes degeneration in the nervous system, especially the brain where characteristic holes develop, and are always fatal

47
Q

what is a characteristic of prion diseases?

A

long incubation periods

48
Q

viroid

A

a subviral particle that consists of a short piece of circular, single-stranded RNA with extensive self-complementarity that allows it to base-pair with itself to create regions of double strandedness

49
Q

do viroids code for proteins?

A

no, they also lack capsids

50
Q

what is the effect of viroids?

A

some are catalytic ribozymes that can silence normal gene expression, or a viroid RNA-dependent RNA polymerase can synthesize a (-) strand that could be used as a template to produce a (+) strand and thus propagate the viroid sequence

MCAT-BIOLOGY (17 decks)

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