Download 26 microbial genetics

Microbial genetics
- Bacteria
gene regulation
genetic exchange
- Viruses
diversity
- Viroids
- Prions
Refer to chapter 13.1 and 20.1 in text
E. coli has genes for one pathway regulated together. (Not seen in eukaryotes)
↑ NB
(tryptophan is an amino acid)
If there is plenty of trp,
it binds as a corepressor,
and blocks expression
of the trp-making genes:
Repressible enzymes
If there is no lactose, these genes aren’t expressed:
Inducible enzymes
↓catabolite activator protein
←allosteric regulatory protein
- Bacterial genetic exchange
1. Transformation: uptake of naked DNA from the surroundings.
- could be fragments from ruptured cells
(classic Griffith experiment, below)
- could be free-floating plasmids
(You will do this in a future lab.)
Some bacteria have genes to enable this among related strains,
E. coli can be artificially made competent for uptake.
- Bacterial genetic exchange (cont.)
2. Transduction: transfer of bacterial DNA incident to viral infection.
- could be generalized
(host DNA accidentally, randomly packaged in capsid)
- could be specialized
(takes genes adjacent to a viral insertion site).
- Bacterial genetic exchange (cont.)
3. Conjugation: transfer of DNA through a sex pilus.
- coded for by F factor
(could be in genome or on a plasmid)
- R plasmids (for drug resistance)
may also have conjugation genes.
from text ↑
Viruses
- Hosts might be bacteria, plants, animals, protists or fungi
(In other words, anything living)
but there is generally high specificity for a given host.
-Viruses are made of a protein capsid (case),
nucleic acids,
and sometimes an envelope derived from the host (few phages do).
Viral nucleic acid might be the familiar double-stranded DNA,
or single-stranded DNA,
or single-, or double-stranded RNA.
↓ Two possible cycles for bacteriophages:
(Temperate phages do both).
I doubt either test will ask for these details.
I include this because it is a wonderful
example of the variety of biological (?)
systems,
and of the range of diseases
caused by viruses.
← NB strategies for ssRNA virus takeover!
←(reverse transcriptase here)
HIV cycle
smallpox
Other viral diseases
measles
influenza
polio
- Viroids
Like viruses, only less.
Small segments of RNA only (no capsid!) that infect plants,
interfering with gene regulation,
causing growth problems.
Some are responsible for the streaky color in tulips.
- Prions
Like viruses, only even more less.
Small segments of protein only (no nucleic acid!) that infect animals,
interfering with brain function.
- scrapie in sheep
- mad cow disease… in cows
(bovine spongiform encephalopathy)
- Creutzfeldt-Jakob and Kuru in people
s.a. fatal familial insomnia, (S.A. 10/15)
normal↓
Seems like a misfolding of a protein that causes other
normal proteins to follow suit.
Very slow acting, so hard to track down
abnormal ↓
Explain the processes of inducible and repressible genes.
Compare lytic and lysogenic cycles.
How do prokaryotes exchange DNA?
What is a viroid?
What is a bacteriophage?
In which processes did bacteria and viruses participate together?
What is a prion?
What is a Prius?
What is a temperate phage?
repressible enzymes
inducible enzymes
repressor
operator
transformation
competent
transduction
generalized
specialized
conjugation
sex pilus
F factor
virus
capsid
envelope
bacteriophage
temperate phage
lytic cycle
lysogenic cycle
prophage
reverse transcriptase
viroid
prion