ch11 micro - 1 What is meant by early and late genes of...

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1. What is meant by early and late genes of phage t4? What do they encode? early genes are transcribed by host RNA polymerase. Early genes o Phage genes expressed early in the infection cycle o Products include proteins needed to cleave host DNA o Phage t4 is synthesized w/in the host cell by rolling-circle replication Late genes o are induced to produce the capsid and tail proteins that assemble on the membrane. - A late gene encodes lysozyme, which lyses the cell, releasing the mature phages. 2. What is a conditional lethal mutant? Give examples of two classes of conditional lethal mutants produced in T4 to demonstrate its assembly. o Mutations that cause a lethal defect under one growth condition but permit growth under a second condition o Temp. sensitive mutants o Mutants that are temp. sensitive can grow at one temp. but fail to grow at another o Nonsense mutations countered by suppressor tRNA o A mutant that contains a nonsense codon in the middle of a gene prematurely terminates translation of protein 3. Why are capsids of icosahedral symmetry so common among viruses? o Is a 20-sided capsid. Each triangle can be composed of 3 identical protein units o Each triangular face of the capsid is determined by the same genes encoding the same protein subunits 4. Why is it difficult to visualize the hepatitis C virus (HCV), even by transmission electron microscopy (TEM) and scanning electron microscopy (SEM)?
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