Objectives: describe the basic structural characteristics of viruses, compare the lytic and lysogenic replication cycles of bacteriophages, outline the replication cycles of mammalian cell viruses(naked and enveloped), describe the term viral latency in relation to the replication of bacterial and mammalian viruses.
Viruses can multiply only by using a dividing host cell's machinery.
Viruses are ubiquitous.
Virus particles are called virions.
There is estimated to be around 2000 viruses which affect humans.
Question 2
Question
Which statements BEST describes viruses?
Answer
Viruses are a diverse group of acellular or 'sub-cellular' particles with no metabolic activity of their own, which rely on the biomachinery of their hosts to reproduce.
Viruses are very small non-living cells which hijack living cells in order to reproduce copies of themselves.
Viruses are ubiquitous 'sub-cellular' particles which rely on their hosts to reproduce.
Question 3
Question
The independent particles of viruses are called [blank_start]virions[blank_end], whose genetic material can be [blank_start]single[blank_end] or double stranded DNA or [blank_start]RNA[blank_end]. This is protected by a protein coat known as a [blank_start]capsid[blank_end].
Viruses with only a capsid are 'naked'. Viruses with an [blank_start]envelope of lipids[blank_end] around this protein coat are 'enveloped'. This envelope of lipids can sometimes have [blank_start]glycoprotein spikes[blank_end].
Answer
virions
single
RNA
capsid
envelope of lipids
glycoprotein spikes
Question 4
Question
Select the statements about viral capsids which are CORRECT.
Answer
Viral capsids are always symmetrical and made of repetitive structures.
Capsomers and protomers are the sub-units of capsids.
Protomers are made up of capsomers.
Capsids can be helical, icosahedral, or complex in shape.
Question 5
Question
Which order of the steps of the viral life cycle is CORRECT?
Answer
entry, attachment, synthesis, assembly, release
attachment, entry, assembly, synthesis, release
attachment, entry, synthesis, assembly, release
Question 6
Question
Lytic=virulent and lysogenic=latent.
Answer
True
False
Question 7
Question
Bacteriophages are the virions which have a capsid specialised to infect bacterial cells.
Answer
True
False
Question 8
Question
Which statement about bacteriophage replication types is INCORRECT?
Answer
Lysogenic cycles are temperate e.g. can kill the cell or live within it.
The lytic cycle ends in cell lysing.
The lytic cycle releases 10-20 virions.
Lytic and lysogenic cells both inject their DNA into the host cell in order to reproduce.
Question 9
Question
Which statement BEST describes a prophage?
Answer
A prophage is the phage genome of the bacteriophage, either integrated with the DNA of the Lysogen (bacterium) or floating free in its cytoplasm, able to produce a lytic phage.
A prophage is the inserted DNA from the bacteriophage which lives inside the host cell, known as the Lysogen.
The prophage lives in the Lysogen and can become a lytic phage.
Question 10
Question
Which statement is true?
Answer
Lytic insertion is followed by immediate degradation of host DNA while the lysogenic genome only becomes virulent when induction (environmental stress, UV irradiation) occurs.
Lytic insertion does not harm the host DNA until the final stage of the lytic cycle.
Question 11
Question
Retroviruses must use the host cell's machinery, and their own enzyme Reverse Transcriptase, to make DNA from their RNA. An example is HIV.
Answer
True
False
Question 12
Question
Naked viruses enter the cell via receptors (endocytosis). Enveloped viruses fuse their viral envelope with the host's membrane.
Answer
True
False
Question 13
Question
The provirus (DNA of enveloped virus in host genome) is virulent.