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Why are viruses not considered living organisms?
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Why are viruses not considered living organisms?
Viruses lack cellular structures, metabolism, and the ability to grow or reproduce independently, so they are not classified as living organisms.
What is the function of the capsid in viruses?
The capsid is a protein coat that surrounds the viral genome and contains attachment proteins, allowing the virus to bind to and enter host cells.
How do viruses reproduce?
Viruses are parasitic and can only reproduce by infecting a host cell and using the host's ribosomes and energy to create new viral particles.
What are common structural features found in all viruses?
All viruses have a small, fixed size, genetic material (either DNA or RNA), a protein capsid, attachment proteins, few or no enzymes, and lack cytoplasm.
True or False?
Genetic material in viruses is only RNA.
False.
Genetic material may be RNA or DNA, which can be either single- or double-stranded.
What is the genetic material of bacteriophage lambda, and what organism does it infect?
Bacteriophage lambda has a double-stranded DNA genome and infects the bacterial species Escherichia coli (E. coli).
Describe the structure of coronaviruses.
Coronaviruses have a single-stranded RNA genome, a spherical shape, and an envelope with projecting glycoproteins.
What enzyme does HIV contain, and what role does it play?
HIV contains reverse transcriptase, an enzyme that enables the production of DNA from its RNA, making HIV a retrovirus.
How is HIV transmitted between individuals?
HIV is transmitted through the exchange of body fluids, including during sexual contact, blood transfusions, needle sharing, and from mother to child during pregnancy and breastfeeding.
True or False?
All viruses are enveloped in host cell membranes.
False.
Some viruses are enveloped in host cell membranes, whilst others are not.
True or False?
Viruses can reproduce on their own without infecting a host cell.
False.
Viruses are parasitic and require a host cell to reproduce.
What is the primary purpose of the lytic cycle in viral replication?
The lytic cycle's primary purpose is to replicate viruses within a host cell and then release the new viral particles by causing the host cell to burst (lyse).
During the lytic cycle, an enzyme called causes the host cell to burst, releasing new virus particles.
During the lytic cycle, an enzyme called lysozyme causes the host cell to burst, releasing new virus particles.
Why does a virus inject its nucleic acid into the host cell during the lytic cycle?
A virus injects its nucleic acid so that it can use the host cell’s protein synthesis machinery to produce viral proteins and assemble new virus particles.
How does the lysogenic pathway differ from the lytic pathway in terms of disease progression?
In the lysogenic pathway, the virus does not immediately cause disease or release new particles. Instead, the viral DNA integrates into the host genome and remains dormant until triggered to enter the lytic cycle.
True or False?
In the lysogenic pathway, viral nucleic acids become part of the host cell's DNA and can be passed on to future generations of the host cell.
True.
In the lysogenic pathway, viral nucleic acids become part of the host cell's DNA and can be passed on to future generations of the host cell.
What triggers a dormant virus in the lysogenic pathway to enter the lytic cycle?
Environmental changes such as exposure to UV rays or certain chemicals can trigger the virus to leave the lysogenic pathway and enter the lytic cycle.
In the lytic cycle, new virus particles are called once they are fully assembled.
In the lytic cycle, new virus particles are called virions once they are fully assembled.
What processes does a virus rely on from a host cell?
Viruses rely on a host cell for energy supply, nutrition, protein synthesis.
What happens to the host cell during the lysogenic pathway?
In the lysogenic pathway, the viral nucleic acid integrates into the host cell’s DNA and remains inactive, allowing the host cell to function normally and replicate, passing the viral DNA to its daughter cells until a trigger prompts the virus to enter the lytic cycle.
What characteristics allow viruses like influenza and HIV to evolve quickly?
High mutation rates, large population sizes, and short generation times allow these viruses to adapt and evolve rapidly.
Why are vaccines often less effective against viruses that undergo rapid evolution?
Rapid evolution causes rapid, unpredictable genetic changes, making it hard for vaccines to match the new viral forms.
Why might viruses be considered to have undergone convergent evolution?
Viruses share an extreme form of obligate parasitism as a mode of existence, so the structural features that they have in common could be regarded as convergent evolution.
Define obligate parasitism.
Obligate parasitism is a parasitic relationship where an organism, called an obligate parasite, can't complete its life cycle without using a host.