A2.3 Viruses - revision quiz HL
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The hepatitis B virus has 3.2 kbp, the smallest genome size of all DNA viruses that infect humans. What does this mean?
Genome size is measured in bp (base pairs of DNA). 3.2 kbp is 3200 base pairs. K=kilo x1000.
Viruses have only one DNA strand. (Some viruses have RNA)
A single vaccine injection and a later booster vaccine is sufficient to provide protection against the polio virus.
In contrast annual injections are recommended for the influenza virus.
Which of the following causes, make annual vaccinations necessary?
I The long persistence of memory cells in humans.
II High mutation rates in the flu virus.
III High effectiveness of immunisation against new variants of a virus.
IV High mutation rates in B-lymphocytes.
Virus generation times are very rapid as are rates of mutation of some viruses producing new variants which may need regular booster inoculations. Memory cells may persist for a lifetime (e.g. polio, smallpox) or for a short time period (e.g. influenza virus). Host mutation rates are not a factor as the host is inoculated during their lifetime.
Why are viruses considered to be non-living?
Viruses do evolve but do not, independently, carry out the functions of living organisms.
Which two of the following apply to viruses?
Viruses are obligate parasites as they can only function in a host cell, and evolve by mutation. They cannot metabolise and can have RNA or DNA as their genetic material.
Which two of the following features are shared by all viruses?
Viurses do not have cytoplasm. Some viruses, but not all have one or more proteins that function as enzymes.
Which of the following occur in the lysogenic cycle of viral infection but not in the lytic cycle?
In the lysogenic cycle, the viral DNA is incorporated into host DNA. In the lytic cycle the DNA or RNA is used in the cytoplasm.
The image shows a bacteriophage virus particle about to infect a prokaryote cell.
Which of the following points lists the steps of the events which occur, in the correct order?
In both the lytic and the lysogenic cycles, bacteriophage viruses, attach to the host cell, insert their genome into the cell.
Which two of the following may be a reason for the diversity of structure of viruses?
The diversity of morphology of viruses suggests several evolutionary pathways and they also can evolve rapidly.
Most viruses have less than 200 genes. Why can viruses exist with very few genes?
The use of host cell metabolism for production of viral components means that they do not need genes for these enzymes of cell metabolism.
Which two of the following are the same in both viruses and prokaryotic cells?
Viruses have a protein capsid which has a specific function, just as prokaryote cells have proteins with specfic functions, e.g. enzymes. The genetic code is universal.
In which ways do different types of viruses differ from each other?
Each type of virus has a fixed size but different types have different sizes, from 5nm to 300nm.
Types of virus have different genomes, some have RNA as the genetic material others DNA.
The shape of a virus is causedby the protein capsid proteins.
Viruses rarely have enzymes, and don't have metabolism, as cells do.