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Biology > A2.3 > Flashcards

A2.3 Flashcards

Viruses

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1
Q

Are viruses obligate parasites?

A

yes

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2
Q

What is an obligate parasite?

A

An organism that requires other living host cells to reproduce

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3
Q

What are the features all viruses have in common?

A
  1. extremely small with a fixed size range of 20-400nm in diameter
  2. have nucleic acid (DNA or RNA) as their genetic material
    3.a capsid made of protein surrounds the nucleic acid
    4.no cytoplasm
  3. few or no enzymes
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3
Q

What is a virus?

A

a non-cellular parasite of animals, plants and bacteria that consists of nucleic acid surrounded by a protein coat (a capsid)

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3
Q

What is a bacteriophage?

A

a virus that infects bacteria

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4
Q

What is adenovirus?

A

a DNA virus that causes an eye disease

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5
Q

Where can the nucleic acid be replicated in RNA viruses?

A

either in the cytoplasm e.g. SARS-CoV-2 or in the nucleus e.g. influenza

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5
Q

What are some RNA viruses?

A

coronavirus or HIV

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6
Q

What is positive sense RNA?

A

Viral RNA that has the same base sequence as mRNA, this allows it to function as a template for protein synthesis during virus replication

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7
Q

What is a capsid?

A

the protein coat enclosing the viral genome. Comes in a variety of shapes such as helical, conical, and polyhedral

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7
Q

What is negative sense RNA?

A

viral RNA that is complementary to mRNA and so it cannot be directly encoded for potein synthesis but it must be converted to positive sense by RNA polymerase before translation

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8
Q

Is the nucleic acid single or double stranded in viruses?

A

some viruses have single stranded nucleic acid such as hepatitis E and some have double stranded nucleic acid such as HIV and SV-40

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9
Q

What is the viral envelope?

A

Some viruses can be classified as enveloped and others non-enveloped, the viral envelope encloses the nucleocapsids of many viruses that infect animals.

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9
Q

What is a capsomere?

A

one of the individual proteins that make up a capsid

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9
Q

What are the capsids of the bactereophages like?

A

they have elogenated icosahedral heads which are made of equilateral triangles fused together in a spherical shape forming a 20 sided structure

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10
Q

What is a nucleocapsid?

A

the capsid of a virus with an envelope

11
Q

What is a virion?

A

an isolated but infectious virus particle found inside the host cell

12
Q

What are the stages of viral reproduction?

A

attachment
entry
replication of viral genome
transcription of mRNA and protein synthesis using host cell ribosomes
maturation and assembly of viruses and release from host cell

13
Q

Can viruses carry out life processes independently?

A

no they cannot, they rely on their host cell for energy supply, nutrition, protein synthesis and other life functions

14
Q

What is the lytic life cycle?

A

a phage life cycle where it attaches to a host, injects its DNA which undergoes replication to form new virions which then lyse the cell

15
Q

What does lysis mean?

A

breakdown, typically of cells

15
Q

What is the lysogenic life cycle

A

a phage life cycle where it attaches to a host, injects its genome and becomes resident within the cell where it replicates alongside it

16
Q

What is a prophage?

A

a bacteriophage in an inactive state in which the genome is typically integrated into the chromosome of the host

17
Q

Do viruses have one common ancestor?

A

it is highly unlikely that viruses have a common ancestor

18
Q

What does polyphyletic mean?

A

means the virus has a few independent origins

19
Q

What is the virus-first theory?

A

suggests that viruses evolved before or co-evolved with their current host cells

19
Q

What is the escaped genes theory?

A

suggests that viruses arose from genetic elements that gained the ability to move between cells.

19
Q

What is the regressive theory?

A

suggests that viruses are remnants of cellular organisms

20
Q

Why do viruses evolve so fast?

A

due to mutations which are a natural by-product of viral replication

21
Q

What does antigenic drift mean?

A

small changes caused by mutations in viral genes that can lead to changes in the surface proteins of a virus

22
Q

What does antigenic shift mean?

A

an abrupt, major change in a virus maybe resulting in a new influenza A subtype

23
Q

What is a retrovirus?

A

a virus that has RNA as its nucleic acid and uses the enzyme reverse transcriptase to copy its genome into the DNA of the host cells chromosome

24
Q

What is reverse transcriptase?

A

an enzyme found in HIV and other retroviruses that is used to convert RNA into viral DNA in a process called reverse transcription

25
Q

What is a provirus?

A

a virus that has integrated into a host’s genome and is replicated when the cell replicates its DNA

Biology (13 decks)

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