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IB Biology - Theme A : Unity and Diversity > A2.3 Viruses (HL) > Flashcards

A2.3 Viruses (HL) Flashcards

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1
Q

What are some characteristics common to all viruses?

A

Small, fixed size
Contain nucleic acid (RNA or DNA)
Enclosed by a protein capsid
Lack cytoplasm inside the capsid
Possess few, if any, enzymes

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2
Q

Why are viruses not considered alive?

A

Viruses don’t perform all life functions, relying on infected cells for reproduction.

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3
Q

How do viruses infect host cells?

A

They attach to specific host cells using specialized sites on their capsid.

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4
Q

What determines a virus’s ability to infect a host cell?

A

The unique composition and structure of its capsid.

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5
Q

What is the role of an envelope in some viruses?

A

it aids in host cell recognition and attachment.

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6
Q

What occupies the space inside a virus capsid?

A

Nucleic acid and sometimes enzymes.

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7
Q

How do viruses replicate?

A

They can’t replicate on their own and rely on host cells for reproduction.

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8
Q

What’s the range of sizes for most viruses?

A

10-400 nm, comparable to large protein macromolecules.

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9
Q

What tools are needed to study virus structure due to their size?

A

Electron microscope.

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10
Q

uniqueness and variation in shapes of viruses

A

polyhedral
spherical
Helical
Complex

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11
Q

example of uniqueness and variation in shapes of viruses

A

polyhedral (adenovirus)
spherical (influenza)
Helical (tobacco mosaic virus)
Complex (bacteriophage)

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12
Q

Three specific viruses and their shapes (that i need to know)

A

bacteriophage lambda
coronaviruses
human immunodeficiency virus (HIV)

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13
Q

Important features of bacteriophage lambda are:

A
  • a capsid head that protects the double-stranded DNA core
  • tail fibres that attach the virus to the host cell
  • a tail sheath that consists of proteins that contract to drive the tail tube through the host cell’s outer membrane
  • DNA that is injected through the tail into the host cell.
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14
Q

Important features of coronaviruses are:

A
  • a spherical shape
  • single-stranded RNA as its genetic material
  • an envelope outside the capsid
  • numerous projections of spike proteins on the envelope, creating a “corona”.
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15
Q

Important features of HIV are:

A
  • it has an envelope outside the capsid
  • two identical single strands of RNA, protected by the capsid
  • within the viral RNA, reverse transcriptase is encoded, which allows the production of DNA using the viral RNA as a model
  • it is known as a retrovirus because it makes a DNA copy of its RNA code
  • the envelope spikes of HIV are made of protein and carbohydrate.
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16
Q

What defines viruses as obligatory intracellular parasites?

A

They rely on living host cells for multiplication and metabolic functions.

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17
Q

How do viruses determine the cells they infect?

A

Specific attachment points on the virus correspond with host cells.

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18
Q

Why do viruses show specificity towards certain host cells?

A

Certain properties in host cells are necessary for the virus to carry out its functions.

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19
Q

What dictates a virus’s choice of host cell?

A

Attachment points and properties required in the host cell for virus functions.

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20
Q

What are some host cells targeted by specific viruses?

A

-White blood cells (CD4 cells) by HIV
-Spinal nerve cells by Poliovirus
-Liver cells by Hepatitis virus
-Cells of the intestinal system by Norovirus

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21
Q

What is the medical challenge in treating viral infections?

A

Controlling the virus without disrupting normal host cell function.

22
Q

What steps are involved in the reproduction of all viruses?

A
  1. Attach to a specific host cell site.
  2. Incorporate genetic material into the host cell’s cytoplasm.
  3. Utilize host cell processes to produce virus components.
  4. Assemble viral components into new virus entities.
  5. Release the new viruses into the host cell’s environment.
23
Q

What distinguishes bacteriophages?

A

They infect bacteria and exhibit unique reproductive cycles.

24
Q

What is the lytic cycle?

A

A viral replication cycle involving five stages: attachment, penetration, biosynthesis, maturation, and release.

25
Q

Describe the stages of the lytic cycle. Attachment

A

Phage attaches to the host cell.

26
Q

Describe the stages of the lytic cycle. Penetration:

A

Phage injects its DNA into the host cell.

27
Q

Describe the stages of the lytic cycle. Biosynthesis:

A

Phage DNA directs the host cell to produce viral components.

28
Q

Describe the stages of the lytic cycle. Maturation:

A

Viral components assemble into new virions.

29
Q

Describe the stages of the lytic cycle. Release:

A

Host cell lyses, releasing new virions.

30
Q

Why is it called the lytic cycle?

A

Viruses are released through cell lysis caused by an enzyme called lysozyme, coded for by bacteriophage DNA.

31
Q

How does the lysogenic cycle differ from the lytic cycle?

A

The lysogenic cycle does not immediately release new viruses; instead, bacteriophage DNA integrates with bacterial DNA to form a prophage.

32
Q

What happens when the viral DNA integrates into the bacterial DNA?

A

It becomes a prophage, remaining inactive and replicated along with bacterial DNA during cell replication.

33
Q

What triggers the transition from lysogenic to lytic cycle?

A

The separation of the prophage from bacterial DNA can initiate a lytic cycle.

34
Q

How does the prophage affect the bacterial cell’s replication?

A

It’s replicated along with the bacterial DNA, carried into subsequent generations.

35
Q

What are the stages of the lysogenic cycle?

A
  1. Phage attaches to host cell and injects DNA.
  2. Phage DNA integrates within bacterial chromosome, becoming a prophage.
  3. Lysogenic bacterium reproduces normally.
  4. As bacterial DNA replicates, the viral DNA is also replicated.
  5. Occasionally, the prophage may excise from the bacterial chromosome, initiating a lytic cycle.
36
Q

what are the three leading hypotheses on the origin of viruses?

A

Virus first hypothesis
Regressive hypothesis
Escape hypothesis

37
Q

what are the three leading hypotheses on the origin of viruses explanation?

A
  1. Virus first hypothesis: Viruses originated before cells, possibly providing materials for cell development.
  2. Regressive hypothesis: Viruses were once small cells that became parasites and shed unnecessary structures.
  3. Escape hypothesis: Genetic material escaped from larger organisms and developed an outer boundary.
38
Q

What features suggest evidence of convergent evolution in viruses?

A
  • Obligate parasites unable to replicate or function independently.
  • Possess a protein outer boundary (capsid) without cytoplasm.
  • Genetic material (DNA or RNA) inside the capsid, sharing code with Earth’s organisms.
39
Q

What factors contribute to the rapid evolution of viruses like influenza and HIV?

A

Large population sizes
Short generation times
High mutation rates

40
Q

How do influenza and HIV differ in terms of genetic material and mutation rates?

A

Both have single-stranded RNA, which, during replication, must produce DNA, increasing mutation chances. DNA-containing viruses usually have lower mutation rates.

41
Q

How do viruses generate variation within their populations?

A

Through mutations, changes in the genetic code.

42
Q

What is antigenic drift?

A
  • Produces gradual changes in viral genetic material over longer periods.
  • Leads to slow variation in surface proteins, eventually evading immune recognition.
  • HIV undergoes rapid antigenic drift, challenging immune control even within individuals.
43
Q

Describe antigenic shift.

A
  • Occurs when different viral strains or viruses infect the same cell, recombining genetic material.
  • Results in significant, rapid changes in viral surface proteins, creating a new virus.
  • Creates potential for pandemics as the immune system doesn’t recognize the new strain.
44
Q

How does antigenic drift affect vaccine effectiveness?

A
  • In influenza, vaccine adjustments are made yearly to counter small, gradual changes.
  • Antigenic drift-related changes are manageable but require yearly vaccine adjustments.
45
Q

Why is it challenging to develop a vaccine against HIV?

A

HIV undergoes rapid antigenic drift, making vaccine development difficult.

46
Q

What contributes to the difficulty in treating diseases caused by rapidly evolving viruses like influenza and HIV?

A
  • High mutation rates and genetic recombination result in varied virus populations.
  • Variants resistant to treatment may emerge, leading to continued infections.
47
Q

Why are antibiotics ineffective against viruses?

A

Antibiotics work against living organisms, not viruses, making them ineffective in viral infections.

48
Q

The genome of adenoviruses is composed of

A

DNA
deoxyribonucleic acid

49
Q

the genome of retroviruses is composed of

A

RNA
ribonucleic acid

50
Q
A
51
Q
A

IB Biology - Theme A : Unity and Diversity (12 decks)

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