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Exam3 2010 SAQ KEY - SHORT ANSWER QUESTIONS W 2010 ANSWER...

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1 SHORT ANSWER QUESTIONS W 2010 ANSWER KEY SA1 . Parts A through C pertain to the biology of viruses;10 pts total. A) Compare and contrast the structure of a virus and the structure of a bacterial cell. How are they similar (2) and how are they different (2)? Similarities: Any one of the following: both have genetic material both have proteins on surface Differences: Any two of the following: Viruses are acellular (=non-cellular) whereas bacteria have a cell and all its components Viruses are not alive, whereas bacteria have all the properties of life Viruses can make copies of their genome and make viral proteins ONLY BY getting inside the correct host cell and taking over the cellular machinery of the host whereas bacteria can do this because they have a cell and all cellular components Viral genomes can be DNA or RNA whereas bacteria have DNA genome Viruses do not have a cell wall or plasma membrane or ribosomes whereas bacteria have all these cellular structures ; however, enveloped viruses have phospholipid bilayer derived from host cell B) Why is it difficult to develop an effective flu vaccine and why do we have to develop a new one every year? List two reasons (1) and explain each briefly (2) Any two of the following 3 reasons with explanations (one of the bullet points) : High mutation rate: each time the viral RNA genome is copied, there is an opportunity for one or more bases to be changed (called antigenic drift) RNA polymerases have a higher error rate than DNA polymerases do Reassortment: If two strains of flu virus infect the SAME HOST CELL, then RNA segments from the two strains can be combined into new virus particles this can cause large genetic changes in the flu virus and if the two strains are from different host species, we consider this antigenic shift High Replication rate: the high replication rate of influenza virus provides more opportunities for mutations to occur each time the viral RNA genome is copied, there is an opportunity for one or more bases to be changed C) Current AIDS drugs target 3 different HIV enzymes in an attempt to block the virus in key parts of its replication cycle. Name two of these HIV enzymes (1) and explain what they do (2). Any two of the following with explanations : reverse transcriptase: takes viral RNA and makes double-stranded DNA integrase: inserts viral DNA into one of the host’s chromosomes protease: cuts up long viral poplypeptide chain into functional viral proteins; without this enzyme, new virus particles cannot be assembled
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