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Biology IB > Viruses (HL) > Flashcards

Viruses (HL) Flashcards

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1
Q

Why are viruses not living things?

A

No cells, dependent on host cells, no growth, can’t replicate independently, no independent metabolism

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2
Q

Define obligate intracellular parasites

A

Viruses are struct molecular parasites — they must be infect cells in order to reproduce

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3
Q

Define virion

A

Outside the host

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4
Q

Differentiate virions, viruses and viroids

A

Virions:
- outside the host; infectious; nucleic acid and protein coat

Viroid:
- smaller virus; only RNA; plant cells only

Virus:
- inside the host; nucleic acid and protein coat

(general: viruses)

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5
Q

How do viruses vary

A
  • size
  • shape
  • genetic material type
  • genes present
  • enveloping
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6
Q

What are the characteristics of those descended from luca

A

proteins, nucleic acids

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7
Q

Give the multiple possible evolutionary origins of viruses

A

regressive hypo, progressive, and virus-first

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8
Q

What are the common structures ampong all viruses

A
  • nucleic acid
  • capsid: protein coat
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9
Q

What are the features common to all viruses? [7]

A
  • intracellular parasites
  • small
  • fixed in size
  • nucleic acid
  • capsid
  • no cytoplasm
  • no or few enzymes
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10
Q

Viruses vary in…

A
  • size
  • shape
  • genetic material
  • genes present
  • enveloping
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11
Q

How are viruses’ genetic material (?) classified?

A

1.) RNA or DNA

2.) single or dble stranded

3.) linear or circular

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12
Q

Define zoonosis

A

Disease of animals to humans

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13
Q

Define convergent evolution

A

Evolving from different ancestors acquire similarities between one another

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14
Q

Why are viruses said to go through convergent evolution?

A

Because they are highly diverse

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15
Q

Why do we say that viruses may not be part of LUCA?

A

Convergent evolution

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16
Q

Outline the missions of viral genomes

A

1.) Make more virus nucleic acid
2.) More virus proteins
3.) Assemble new virus molecules

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17
Q

Define viral genome

A

composed of DNA or RNA in a virus

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18
Q

Outline the three types of viral nucleic acids

A

1.) Positive sense
2.) Negative sense
3.) Retrovirus

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19
Q

Describe positive sense RNA

A

Viral RNA -> protein

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20
Q

Describe negative sense DNA

A

DNA -> RNA -> protein

(transcription first then translation)

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21
Q

Describe retroviruses RNA

A
  • “retro”: going back
  • RNA -> DNA [reverse transcriptase]
  • Viral DNA injected into cell’s DNA
  • Carries out the functions of the viral genome
  • WBCs cannot detect because of the cell DNA
  • can attack WBC (HIV)
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22
Q

Outline the three possible structures of capsids

A

1.) Helical

2.) Polyhedral/Icosahedral

3.) Complex

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23
Q

Describe virus envelopes or “enveloping”

A
  • Lipid bilayer
  • from the host cell due to “budding” (exocytosis)
  • provides additional protection
  • round things: spikes;
  • spikes used to know which receptor proteins are compatible.
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24
Q

Do all viruses have enveloping?

A

No
- some say it might be hereditary if the envelope is in the genetic material (??)

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25
Q

How do viruses without an envelope exit the host cell?

A
  • BY lysis
  • they make the cell burst sp they could exit
  • therefore, more resistant to extreme pH, dryness and disinfectants
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26
Q

Describe the example virus of bacteriophage lambda

A
  • due to feces consumption
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27
Q

How do viruses infect host cells?

A
  • They attach to compatible recepor proteins of the host cell
  • inject their nucleic acids
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28
Q

Describe SARS-CoV 2

A
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29
Q

Describe HIV

A

Due to excessive amt of sexual partners (?)

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30
Q

Briefly define the process of lysogenic cycle

A
  • Virus assimilates (‘fits in’) with the host cell genome [retroviruses]
  • Doesn’t kill the host
31
Q

Define the lytic cycle

A

Virus reproduces and does lysis out of the cell
- kills the cell

32
Q

Outline the lytic acid cycle

A
  1. also known as “spread”
33
Q

Describe the phage attachment to the host cell (Lytic cycle)

A
  • virus attached to receptor protein;
  • occurs via random collisions
34
Q

Describe the phage nucleic acid entry into host cell (Lytic cycle)

A
  • phage’s genetic material injected into cell
  • phage tails wildly vary
  • but usually a tube
  • tail contracts like a coiled spring that drives the genetic material in the cell
35
Q

Describe phage DNA replication (Lytic cycle)

A
  • cloning of phage DNA via rolling circle replication
  • one strand is nicked
  • enzymes extend the free 3’ end
  • complimentary strand is made around the circular DNA: the 5’ end is peeled off
36
Q

Describe protein synthesis in viruses

A
  • transcription of phage DNA into phage RNA via cell’s polymerase (HC’s “machinery”)
  • translates phage RNA -> phage proteins
37
Q

Describe the assembly of new phage viruses (lytic cycle)

A
  • phage proteins -> phage viruses (assembling)
  • empty heads into which condensed phage is packed
  • tails made independently
  • last step: heads + tails
38
Q

Describe how lysis happens in bacteria due to viruses

A
  • enzymes produced by the phage gradually weaken the bacterial cell wall
  • bacteria cells lyse
  • releases 100-200 phage progeny (“children”)
39
Q

Describe the step of spread (lytic cycle)

A
  • new virus particles infect new cells
  • actively infecting viruses: “virulent” viruses
40
Q

Outline the steps in the lysogenic cycle

A

1.) phage attachment to host cell
2.) phage DNA entry
3.) Phage DNA integrated into hist genome
5.) cell dovision

41
Q

Describe Phage DNA integration (lysogenic chcle)

A
  • circularization: linear phage DNA -> circular after infection
  • has an attachment site
  • prophage: when the virus exists as part of HC genome
42
Q

Describe DNA replication (lysogenic cycle)

A
  • prophage genome DNA replication
  • passively replicates: so small, bacterial hosts unharmed
  • WBCs can’t detect
43
Q

describe cell division (lysogenic cycle)

A
  • cell divides
  • 2 daughter cells with the prophage
  • “temperate”: prophage virus that doesn’t kill or infect bac cells, “dormant”
44
Q

describe return to lytic cycle (lysogenic cycle)

A
  • Under exterme conditions:UV light, low nutrient conditions, chemicals
  • induction: entry into lytic cycle
45
Q

Describe the virus-first hypothesis

A
  • Viruses existed before the LUCA (main claim)
  • HOWEVER, viruses are obligate parasites
46
Q

Describe the progressive hypothesis

A
  • Viruses came from modified cell parts
  • Viruses escaped from LUCA and evolved
  • HOWEVER, virus structures not aligned with cell structures (?)
  • HOWEVER, viruses are very diverse
47
Q

Describe regressive hypothesis

A
  • Similar to endosymbiosis
  • Viruses were other cells that entered the host cell
  • became highly dependent
  • lost all cell components
  • (now just the capsid and the nucleic acid)
  • HOWEVER, no cellular counterparts
  • HOWEVER, no resemblance to ___
  • HOWEVER, unique genetic make up
48
Q

How fast do viruses evolve?

A
  • very fast
  • This means we are “delayed” with our vaccines
49
Q

Define evolution

A

a cumulative (slow and gradual) change in inheritable traits in a population

50
Q

Define generation time

A

Average time between consecutive generations

51
Q

Define natural seleciton

A

When nature selects the traits that allow survival via environmental conditions
- e.g. predators

52
Q

What is the generation time for humans

A

20-30 years (average age for reproduction)

53
Q

What is the relationship between generation time and rate of natural selection

A

Inverse relationship
- less time to pass on traits

54
Q

Outline the characteristics of viruses (regarding reproduction and natural selection)

A
  • small generation time
  • each virion; many offspring
  • high rates of mutations
55
Q

Define eclipse period

A

the time of maturation of a virus
- inside the host

56
Q

What is the generation time of SARS-COV

A

10 hours

57
Q

What is needed in order for natural selection to happen [3]

A

1.) Variation in a population
- to get the best traits
2.) Production of viruses (VIRUS SPECIFIC)
- competition in host cell
- determines the ones who can survive
3.) Passing of trait to the next generation
- the “best” virion reproduce

58
Q

What is the phrase “survival of the fittest” really about

A

The traits that could allow populations to survive in an env. condition

59
Q

Define viral burst size

A
  • how many virion can go out of a cell
  • e.g. HIV = 6,000 virions
  • SARS-Cov = 103 virions
60
Q

Define mutations

A
  • change of intergenetic sequence
  • the difference between original and new sequence
61
Q

Define DNA polymerase III

A
  • adds and pairs nucleotides during replication
62
Q

Why are the VIRUSES with RNA more susceptible to mutations?

A

RNA polymerase has no proofreading abillity
- ^ chance for “incorrect” pairings -> diff types of amino acids

63
Q

Why do viruses with DNa less suceptible to mutattions?

A
  • DNA polymerase has a proff-reading ability
64
Q

Describe the D6-14G mutation of Sars-COV

A
  • GAT -> CGT
  • different amino acid -> changed the shape of the spike protein
  • more infectious bc of ^
  • made very dangerous alongside high reproduction rates
65
Q

How would natural selection affect the amount of beneficial mutations in a population?

A

Increases it because the ones with more beneficial traits survive

66
Q

Why does HIV (>) have the highest mutation rate?

A
  • because they attack the white blood cells
  • some of them are more resistant to drugs
  • they reproduce over time
67
Q

Is the independent variable x-axis or y-axis?

A

x-axis

68
Q

Outline the two different strands of viruses:

A

1.) anti-genic drift

2.) anti-genic shift

69
Q

Define antigens

A

The surface protein of the viruses

70
Q

Describe anti-genic drift

A
  • cumulative small changes of antigens
  • over time
  • (influenza): can make people have the flu again due to changes
  • changes a lot -> need for annual vaccines (?)
71
Q

Describe antigenic shifts

A
  • abrupt and major changes to the antigen
  • antigens combined
  • e.g. the swines (to infect humans)
72
Q

Define temperate

A

Does not cause cell death

73
Q

Define passive

A

Does not assemble viruses

74
Q

Define induction

A

lysogenic cycle -> lytic cycle

Biology IB (32 decks)

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