Viruses Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

What is a bacteriophage?

A

These are viruses that can infect and take over bacteria.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why is E. coli and its viruses referred to as a model system by researchers?

A

They are used by researchers to reveal broad biological principles.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are bacteria classified as? Are they smaller than eukaryotes? How do viruses stack up to bacteria?

A

Bacteria are prokaryotes, that are much smaller and simpler than eukaryotes.

Viruses are even small and even simpler than prokaryotes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Did scientists indirectly discover viruses before they could see them?

A

YES

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How did Beijerinck initially indirectly discover the existence of viruses?

A

Tobacco mosaic disease of tobacco plants was used.

Sap was extracted from infected plant and sent through a filter known to trap bacteria, ruling out that possibility.

The filtered sap was introduced to a new plant and the plant eventually became infected.

This step was repeated and the plants continued to show infection. This rules out the possibility of the infection being caused by a toxin because eventually the toxin would decrease in concentration enough to now affect the plant.

THIS MEANS THAT IT MUST BE SOMETHING MUCH SMALLER THAN A BACTERIA THAT CAN REPLICATE.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Who and how was Beijerincks proposal confirmed?

A

By wendell Stanley by crystallizing the infectious particle that is now known as tobacco mosaic virus.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Are viruses cells?

A

NO

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is a virus? What does a virus consist of?

A

A virus is a very small infectiour particle that consists of nucleic acids enclosed in a protein coat (capsid). Some of them have a membraneous envelope covering the protein coat.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What makes up the capsid?

A

Small protein subunits called capsomeres, usually their is very little variety of the proteins that make up the capsid.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are two shapes that the capsid can take on in a virus described in the book?

A

Helical - Capsomere forms alpha helix that is compressed into rod shape.

Icosahedral - polyhedral shape with 20 facets.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Capsid structure?

A

Helical

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Capsid structure?

A

Icosahedral

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the two types of genomes a virus consists of? Can they be either single or double stranded?

A

DNA or RNA

Yes both can either be single stranded or double stranded

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

So if a virus has DNA it is a DNA virus and if it has RNA it is an RNA virus?

A

YES

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How many genes do the smallest viruses have? What about the largest?

A

3

several hundred to a thousand

NUMBER OF GENES VARIES.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is a capsid?

A

This is a protein shell that encloses the viral genome that consists of protein subunits called a capsomere.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Do some viruses have a membraneous (Viral) envelope? What are they derived from?

A

YES

They are derived from the host cell membrane, and consist of both viral and host cell molecules.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the purpose of the membraneous (viral) envelope?

A

These help the virus infect the host.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What virus has the most complex capsid? Describe them.

A

Bacteriophages.

They have an elongated capsid head (icosahedral) that encloses DNA, and a protein tailpiece that attaches to host and allows for the insertion of the phages DNA genome into the host.

20
Q

What is meant by the statement that viruses are OBLIGATE intracellular parasites?

A

They can only reproduce within a host cell.

21
Q

Does a virus have a limited number of hosts that are viable for them to infect and reproduce in?

A

YES

22
Q

Do viruses have the supplies needed to replicate? So what do they do?

A

NO

They must use the enzymes, ribosomes, and small host molecules to synthesize progeny viruses.

23
Q

Describe a simple replicative cycle of a plant or animal virus in 4 steps.

A
  1. Virus enters the cell and sheds its capsid coat, releasing viral DNA genome and capsid proteins.
  2. Hosts enzymes replicate viral genome.
  3. Host enzymes transcribe viral genome into RNA, then host ribosomes make more capsid proteins with this RNA.
  4. Viral genomes and capsid proteins self-assemble into new viral particles that exit the cell.
24
Q

Which viruses do we understand the best?

A

Phages

25
Q

What are the two reproductive cycles of a phage?

A

Lytic

Lysogenic

26
Q

Describe the 5 steps of the lytic cycle.

A
  1. Attachment: Phage binds to surface protein of cell using tail fibers.
  2. Entry of phage DNA and degradation of host DNA: Sheath of tail contracts and injects phage DNA into cell, empty capsid is left outside. Cells DNA is hydrloyzed during this step.
  3. Synthesis of viral genomes and proteins: Phage DNA directs production og phage proteins and copies of phage genomeby host and viral enzymes, using components within the cell.
  4. Self-assembly: Three separate sets of proteins self-assemble to form phage heads, tails, and tial fibers. The phage genome is inside the capsid as the head forms.
  5. Release: Phage directs production of enzyme that damages bacterial cell wall allowing fluid to enter, the cell swells and bursts releasing 100-200 phages.
27
Q

How does the lysogenic cycle of a phage work?

A

This is the replication of the phage genome by incorporating it into the hosts genome and allowing the host to replicate naturally. This allows the hosts genome to replicate without destroying the host cell.

28
Q

How does the Lytic cycle differ from the lysogenic cycle?

A

Lytic - New phages are produced and hosts cell wall is digested, destroying the host cell.

Lysogenic cycle - replicated the phage genome without destroying the host cell.

29
Q

What is the difference between a virulent phage and a temperate phage?

A

Virulent - Replicated only by the lytic cycle.

Temperate - Can use both the lytic and the lysogenic cycle.

30
Q

Why might a temperate phage choose to switch between the lytic or lysogenic cycle?

A

Lytic vs. lysogenic – temperate virus may choose between the two based on the population of the host cell. Lysogenic if population is too low so host cells can replicate and recover population.

31
Q

In the lysogenic cycle, what is the integrated viral DNA known as?

A

A prophage

32
Q

What are the two key variables involved in classifying an animal virus?

A

Genome: DNA or RNA

Strand #: Single-stranded or Double-stranded

33
Q

Look at table 19.1 on page 404 and become familiar with how to navigate it.

A

DO IT.

34
Q

Do many animal viruses have a viral (membraneous) envelope?

A

YES

35
Q

What do viral envelopes have that help them to infect their host?

A

They have glycoproteins on their surface that help them bind to specific receptor proteins on the host cell surface.

36
Q

Do most viruses with an RNA genome have a viral envelope?

A

YES

37
Q

What is the difference between a positive sense RNA strand and a negative sense RNA strand in regards to viral replication?

A

Positive sense - similar to mRNA and can immediately be translated

Negative sense - complementary to mRNA (NOT mRNA) and must be converted to positive sense before translation can occur.

38
Q

What do retroviruses contain inside their capsid other than RNA?

A

Reverse transcriptase

39
Q

What is the function of reverse transcriptase?

A

Copies their RNA genome into double-stranded DNA

40
Q

What retrovirus are we very familiar with?

A

HIV

41
Q

Understand the structure of the retrovirus by looking at this picture.

A

DO IT.

42
Q

What is a provirus? How does this differ from a prophage?

A

A provirus is the reverse transcripted DNA of a provirus that is integrated into the host genome.

A prophage is only part of the host cells genome for a finite period, while a provirus remains a permanent resident of the host cells genome.

43
Q

In the reproduction of HIV, once reverse transcriptase transcibes the viral RNA into DNA and it is integrated into the host genome (provirus), what happens next?

A

The hosts RNA polymerase transcribes the viral DNA into RNA.

This RNA functions as mRNA for both viral proteins and viral genomes for new virus particles to be released for the cell.

44
Q

What defines an emerging virus? What 3 processes are known to contribute to the rise of a previously unknown viral disease?

A

These are viruses that appear suddenly or come to the attention of scientists.

  1. Mutation of existing virus
  2. Dissemination from a small isolated human population contributing to spread to greater population
  3. Spread of existing virus from OTHER ANIMALS
45
Q

What agent causes SARS?

A

A type of coronavirus.

46
Q

What are viroids and what are prions?

A

Viroids - circular RNA molecules that infect plants and disrupt their growth.

Prions - SLOW ACTING, INDESTRUCTABLE, infectious proteins that cause brain disease in mammals.

47
Q

How do prions replicate?

A

They convert normal proteins into infectious proteins.