Viruses and Prions || 100% Error-free Answers.
Describe the general structure of a virus. correct answers Nucleic acid (DNA or RNA)
surrounded by a protein coat called a capsid. Virus may be naked or enveloped.
What is a complete viral particle (nucleic acid + capsid + envelope if present) called? correct
answers Virion
Why are viruses considered obligate intracellular parasites? correct answers Can only
reproduce/replicate if inside a host cell.
Why are viruses considered living? correct answers ➢ they evolve by natural selection
➢ they direct their own reproduction (they have the plan for replication in their nucleic acid)
and they spontaneously assemble
Why aren't viruses considered living? correct answers ➢ they have no cellular structure: no
cytoplasm or plasma membrane
➢ they have DNA or RNA, unlike prokaryotic and eukaryotic cells, which have both.
➢ they lack a metabolism of their own; for example, they cannot produce their own energy
(ATP) from glucose
➢ they do not contain all 4 groups of organic molecules (they lack carbs and lipids - these
molecules are present in the viral envelope, but envelopes really belong to the host cells)
➢ they can only replicate with the help of a host cell; the host cell actually replicates the viral
nucleic acid and makes the capsid proteins
Describe the different variations on the viral nucleic acid. correct answers double stranded or
single stranded RNA or DNA, single or multiple segments, linear or circular
Describe the 3 basic shapes of capsids correct answers 1) polyhedral (capsomeres organized
into equilateral triangles, which are assembled into dome-shaped structure)
2) helical (capsomeres fit together as a helix that forms a rod-shaped structure)
3) complex (polyhedral head + helical tail)
Explain how a virus acquires an envelope. correct answers The virus pushes out of the cell
membrane, forming a bud that encloses the virus - then the bud pinches off behind, resealing
the cell - as a result, the host cell is not lysed.
Where are glycoprotein spikes found? correct answers Glycoprotein spikes are found in the
viral envelope. Viral glycoprotein "spikes" are coded for on the viral nucleic acid and are
inserted into the host cell's plasma membrane prior to budding.
Viruses that lack envelopes are called? correct answers Naked
, How does the presence of an envelope increase a virus's disease causing capacity? (2-ways)
correct answers 1.) Makes it difficult for the host's immune system to recognize the foreign
virus.
2.) Makes it easy for the enveloped virus to enter another cell (membrane fusion: cell
membranes fuse, dumping the virus into the new host cell)
What determines host range/viral specificity? correct answers Viral specificity is determined
by whether or not a virus can attach to a cell. Attachment depends on the presence specific
receptor sites on the surface of host cell and on specific attachment structures on the viral
capsid or envelope. Examples of receptor sites are proteins, LPS's, glycolipids, or
glycoproteins.
What are viruses that infect bacteria? correct answers Bacteriophages
List the 6 major steps of the lytic cycle. correct answers 1. Attachment - the virion attaches
itself to a specific receptor site on the surface of the host cell
2. Penetration - viral nucleic acid enters host cell (3 different ways depending on whether
virus is naked or enveloped)
3. Uncoating - removal of the capsid & envelope; only occurs if virus is enveloped.
4. Biosynthesis - viral components (nucleic acids & proteins for capsids) are synthesized by
the host cell.
5. Assembly/Maturation - components are assembled into new viruses (nucleic acids are
inserted into capsids)
6. Release - hundreds of intact virions exit host cell (2 different ways lysis or budding)
Penetration: How do enveloped virions enter the host cell? (2 ways) correct answers 1.
Membrane Fusion: the viral envelope fuses with host cell membrane, emptying the rest of the
virion inside the cell
2. Receptor Mediated Endocytosis: the enveloped virus is phagocytized by a host cell
Penetration: How do most naked animal virions penetrate the host cell? correct answers Most
naked animal viruses enter the host cell when the viral capsid adsorbs (attaches) to the host
cell surface & only the viral nucleic acid enters cell; the capsid is left on the outside
Penetration: How do bacteriophages penetrate the host cell? correct answers The
bacteriophage is a naked virus. The tail pins penetrate the thick bacterial cell envelope,
injecting only the viral nucleic acid; the capsid stays on the outside of the cell and
disintegrates.
What are 2 ways virions released from a host cell? correct answers 1. Burst/Lyses - If the
virus is the naked type, an encoded protein, lysozyme, dissolves the cell membrane &/or cell
wall of the host cell, causing the cell to lyse & releasing the hundreds of viruses inside it
Describe the general structure of a virus. correct answers Nucleic acid (DNA or RNA)
surrounded by a protein coat called a capsid. Virus may be naked or enveloped.
What is a complete viral particle (nucleic acid + capsid + envelope if present) called? correct
answers Virion
Why are viruses considered obligate intracellular parasites? correct answers Can only
reproduce/replicate if inside a host cell.
Why are viruses considered living? correct answers ➢ they evolve by natural selection
➢ they direct their own reproduction (they have the plan for replication in their nucleic acid)
and they spontaneously assemble
Why aren't viruses considered living? correct answers ➢ they have no cellular structure: no
cytoplasm or plasma membrane
➢ they have DNA or RNA, unlike prokaryotic and eukaryotic cells, which have both.
➢ they lack a metabolism of their own; for example, they cannot produce their own energy
(ATP) from glucose
➢ they do not contain all 4 groups of organic molecules (they lack carbs and lipids - these
molecules are present in the viral envelope, but envelopes really belong to the host cells)
➢ they can only replicate with the help of a host cell; the host cell actually replicates the viral
nucleic acid and makes the capsid proteins
Describe the different variations on the viral nucleic acid. correct answers double stranded or
single stranded RNA or DNA, single or multiple segments, linear or circular
Describe the 3 basic shapes of capsids correct answers 1) polyhedral (capsomeres organized
into equilateral triangles, which are assembled into dome-shaped structure)
2) helical (capsomeres fit together as a helix that forms a rod-shaped structure)
3) complex (polyhedral head + helical tail)
Explain how a virus acquires an envelope. correct answers The virus pushes out of the cell
membrane, forming a bud that encloses the virus - then the bud pinches off behind, resealing
the cell - as a result, the host cell is not lysed.
Where are glycoprotein spikes found? correct answers Glycoprotein spikes are found in the
viral envelope. Viral glycoprotein "spikes" are coded for on the viral nucleic acid and are
inserted into the host cell's plasma membrane prior to budding.
Viruses that lack envelopes are called? correct answers Naked
, How does the presence of an envelope increase a virus's disease causing capacity? (2-ways)
correct answers 1.) Makes it difficult for the host's immune system to recognize the foreign
virus.
2.) Makes it easy for the enveloped virus to enter another cell (membrane fusion: cell
membranes fuse, dumping the virus into the new host cell)
What determines host range/viral specificity? correct answers Viral specificity is determined
by whether or not a virus can attach to a cell. Attachment depends on the presence specific
receptor sites on the surface of host cell and on specific attachment structures on the viral
capsid or envelope. Examples of receptor sites are proteins, LPS's, glycolipids, or
glycoproteins.
What are viruses that infect bacteria? correct answers Bacteriophages
List the 6 major steps of the lytic cycle. correct answers 1. Attachment - the virion attaches
itself to a specific receptor site on the surface of the host cell
2. Penetration - viral nucleic acid enters host cell (3 different ways depending on whether
virus is naked or enveloped)
3. Uncoating - removal of the capsid & envelope; only occurs if virus is enveloped.
4. Biosynthesis - viral components (nucleic acids & proteins for capsids) are synthesized by
the host cell.
5. Assembly/Maturation - components are assembled into new viruses (nucleic acids are
inserted into capsids)
6. Release - hundreds of intact virions exit host cell (2 different ways lysis or budding)
Penetration: How do enveloped virions enter the host cell? (2 ways) correct answers 1.
Membrane Fusion: the viral envelope fuses with host cell membrane, emptying the rest of the
virion inside the cell
2. Receptor Mediated Endocytosis: the enveloped virus is phagocytized by a host cell
Penetration: How do most naked animal virions penetrate the host cell? correct answers Most
naked animal viruses enter the host cell when the viral capsid adsorbs (attaches) to the host
cell surface & only the viral nucleic acid enters cell; the capsid is left on the outside
Penetration: How do bacteriophages penetrate the host cell? correct answers The
bacteriophage is a naked virus. The tail pins penetrate the thick bacterial cell envelope,
injecting only the viral nucleic acid; the capsid stays on the outside of the cell and
disintegrates.
What are 2 ways virions released from a host cell? correct answers 1. Burst/Lyses - If the
virus is the naked type, an encoded protein, lysozyme, dissolves the cell membrane &/or cell
wall of the host cell, causing the cell to lyse & releasing the hundreds of viruses inside it
