Transcript Wednesday, September 5

18.1
1.
Compare the effect on the host cell
of a lytic (virulent) phage and a
lysogenic (temperate) phage.
Lytic
•Can only carry
out lysis of
host cell
Lysogenic
•Can integrate
into host
chromosome
•Later, can exit
chromosome and
initiate lytic
cycle
18.1
2.
How do some viruses reproduce
without possessing or ever
synthesizing DNA?
18.1
2.
•Genetic material is RNA
•Viral RNA serves as mRNA
•Virus codes for enzymes that
replicate RNA
18.1
3.
Why is HIV called a retrovirus?
18.1
3.
Because it synthesized DNA from
its RNA genome
18.2
1.
Describe two ways a preexisting
virus can become an emerging
virus.
18.2
1.
There are three ways:
1. Mutation
2. Jumping to a new host species
3. Spreading beyond a previously
isolated population
18.2
2.
Contrast vertical and horizontal
transmission of viruses in plants.
18.2
2.
Horizontal
plant is infected
from external
source
Vertical
plant inherits
virus from a
parent
18.2
3.
Why does the long incubation
period of prions increase their
danger as a cause of human
disease?
18.2
3.
Beef may be distributed from an
infected herd for years before
any symptoms appear.
18.3
1.
Distinguish between the three
mechanisms of transferring DNA
from one bacterial cell to another.
18.3
1.
•Transformation: bacteria uptake
naked, foreign DNA
•Transduction: phage viruses
carry bacterial genes from one to
another
•Conjugation: bacteria “mate” and
exchange DNA across a pilus
18.3
2.
What are the similarities and
differences between lysogenic
phage DNA and a plasmid?
similarities
differences
•Both are
•Virus can leave
episomes (can
the cell in a
exists as part of protein coat
chromosome or
•Viruses are
independently)
harmful while
plasmids are
beneficial
18.3
3.
Explain why the process of
conjugation can lead to genetic
recombination of chromosomal DNA
in an Hrf x F- mating, but not in an
F+ x F- mating.
Hrf x F-
•Bacterial genes
are transferred,
because the Ffactor is
integrated into
the chromosome
•Transferred
genes can then
recombind with
recipent’s genes
F+ x F•Only plasmid
genes are
transferred
18.4
1.
A certain mutation in E. coli
changes the lac operator so that the
active repressor cannot bind. How
would this affect the cell’s
production of β-galactosidase?
18.4
1.
•The cell would continuously
produce β-galactosidase (and the
two other enzymes for lactose
utilization) even without any
lactose around
•Wastes cell resources
18.4
2.
How does the binding of the trp
corepressor and the lac inducer to
their respective repressor proteins
alter repressor function and
transcription in each case?
18.4
2.
trp corepressor
•Binds to
repressor
•Activates
repressor
•Shuts off genes
lac inducer
•Binds to
repressor
•Inactivates
repressor
•Turns on genes