MCB 229 Spring 2000 Study Guide 16 Prof.
Terry
Covers Lecture for April 6
This study guide is intended for you to use while you are
doing the assigned text reading. Quiz questions will be made with reference to
topics in this study guide. Quiz #16, based on questions from this study guide,
must be completed by midnight before the class on Thursday, April 6. You will
need to create your "myWebCT" account and visit the MCB 229 WebCT page in order
to access this quiz.
Chapter 16. Viruses: general principles.
- Who deserves credit for discovering the principle of immunization against
viral disease: Lady Wortley Montagu or Edward Jenner?
- What is a virus? How
does a virus differ from a virion? What biomolecules are found in
virions?
- What assay systems are commonly used to study animal viruses? What
components must be added to a petri plate to view phage plaques? What assay
systems are used to study plant viruses?
- Skim the section on "Viruse
Purification and assays", pp. 339-341.
- How can the concentration of viruses
in a sample be counted by direct or indirect methods? What is meant by PFU? Does
this measure the number of virus particles in a sample? Why or why not?
- The
section "The Structure of Viruses" (pp. 342-352) has lots of detail and many
photographs. I don't expect you to remember all these details, except as noted
below. Do read figure captions as you look at the figures, though.
- What do
the following terms mean? Capsid, nucleocapsid, icosahedron, protomer, spikes?
What are the common shapes of virions? What do the terms "enveloped virus" and
"complex virus" imply?
- What type(s) of nucleic acid are found in virions?
How many strands are present? Do any virions contain both DNA and RNA? What is
meant by "+" and "-" RNA? Are viral nucleic acids linear or circular? Is it
possible for a linear viral chromosome to become circularized? If so,
how?
- What is meant by a "segmented genome"? Are there any viruses in which
individual virions are insufficient to cause infection? If so, how many virions
are needed? Why?
- Read box 16.2, "The origin of viruses". What are the two
major speculations about viral origins?
- How does the classification of
viruses compare to the classification of bacteria (remember Bergey's manual?)
What characters are used in classifying
viruses?
Chapter 17. Bacteriophages.
- What is meant by a lytic cycle? How does this cycle end?
- What is
"one-step growth experiment"? What is meant by the terms: latent period,
eclipse, burst size, rise period?
- What sorts of materials serve as receptors
for phages?
- We will concentrate on the study of 3 E. coli phages
(aka coliphages) to demonstrate the variety of mechanisms involved: T4, MS2, and
Lambda.
- Phage T4: Examine Figs. 17.5-7 and related text. Note that
phages T2, 4 and 6 (T-even phages) are very similar. How does T4 attach to host
cells? How does the DNA enter? Which enzymes are "early enzymes? How do they
differ from "late" enzymes and other proteins? Are early and late genes encoded
on the same strand of DNA? What do restiction enzymes do (see pp. 311—312
and Fig. 15.2)? How does phage T4 avoid damage by restiction enzymes? What are
concatemers, and how are they involved in T4 DNA replication? How does the
promoter for late T4 genes differ from the early promoter? How are new T4
virions assembled? What is a typical burst size for T4? When and how does the
host cell lyse?
- Phage MS2: What is the nucleic acid for this phage?
How many enzymes are encoded? Is the virion RNA + or -? What enzyme is needed to
replicate copies of this phage nucleic acid? How does MS2 attach to host cells?
- Phage Lambda: What form of nucleic acid is in the virion? Does the
virion contain linear or circular nucleic acid? What happens to this NA when it
enters the cell? Note that lambda can undergo either a lytic or a lysogenic
stage, depending on early events following infection. What is meant by the
following terms: lysogeny, temperate phage; prophage; induction; lysogenic
conversion? What environmental conditions favor lysogeny over lytic infection?
- Early events in the lambda phage life cycle that determine whether lytic or
lysogenic modes will be active are complex, and are described on pp. 367-369 and
Fig. 17.18. Note that there is a race between two proteins: cro protein
and lambda repressor. What does each of these proteins do? What is the
function of the integrase enzyme? What situations can trigger induction?