4 The Genetics of Bacteria Flashcards
How does the bacterial chromosome differ from that of eukaryotes?
Bacterial DNA:
- Circular, double-stranded
- One per cell
Eu. DNA:
- Linear
- > 1 per cell
What’re the two conformations of bacterial DNA, and what’re the enzymes responsible for their formation?
- Supercoiled (gyrase > causes supercoiling)
2. Relaxed (topoisomerase I > removes supercoils)
What happens to a bacterium if its DNA is prevented from supercoiling (by the use of an antibiotic, for example)?
It dies.
What’re plasmids?
A second, separate form of DNA carried by SOME bacteria
T or F: Plasmids are often larger than chromosomes.
F
Plasmids are smaller than chromosomes
About how many genes does an average bacterial chromosome contain?
3000-4000
About how many genes does an average bacterial plasmid contain?
5-100
T or F: A bacterial cell is only able to contain one plasmid.
F
They can have multiple copies per cell
Plasmids usually carry “accessory” genes. What does this mean?
These genes are NOT required for survival, but they make bacteria better adapted to their envir.
Name 4 differences b/w eukaryotic and bacterial cells in terms of how genetic info is converted into fn’al proteins.
- Eukaryotes export mRNA from nucleus into cytoplasm prior to translation. There’s no export in prokaryotes - mRNA is translated as soon as it’s synthesized (i.e. transcription and translation are COUPLED)
- Eukaryotic genes have introns. Prokaryotic genes do not have introns.
- Eukaryotic and prokaryotic ribosomes are structurally different.
- Rate of protein synthesis is HIGHER in prokaryotes (350 AAs/min) compared to eukaryotes (50 AAs/min)
List 3 reasons prokaryotic cells grow much more rapidly compared to eukaryotic cells.
- HIGHER surface:volume ratio.
- Transcription and translation are COUPLED
- Protein synthesis is FASTER
What genetic mechanisms are used to generate genetic diversity among bacteria?
- MUTATION of bases in DNA
2. EXCHANGE of partial or complete genes b/w bacteria
Define mutation (in terms of genetics)
A physical change in DNA sequence > change in mRNA > change in protein
What type of mutation occurs via random errors introduced during DNA replication?
Spontaneous mutation
What type of mutation occurs due to external agents (chemical, radiation, etc.)?
Induced mutation
Mutations can be:
- ____ (no effect on cell)
- ____ (kills cell)
- ____ (gives growth advantage to cell)
- Neutral
- Lethal
- Beneficial
What determines whether a mutation will be neutral or beneficial?
the ENVIRONMENT
What is the Ames Test?
A biological assay that uses bacteria to test the mutagenic potential of new chemicals and drugs.
What’s the purpose of the Ames Test?
Rapidly pre-screen a chemical’s ability to cause genetic mutations (in bacterial cells)
What genetic mechanisms are used to generate genetic diversity among bacteria?
- MUTATION of bases in DNA
2. EXCHANGE of partial or complete genes b/w bacteria
List three ways bacteria can “swap” genes?
- Transformation
- Transduction
- Conjugation
What is transformation (method of genetic exchange)?
When a bacterial cell takes up and incorporates DNA fragments of another bacterial cell that has died into its own chromosome.
Is mutation or exchange faster in generating genetic diversity in bacteria?
Exchange
What is transduction (method of genetic exchange)?
DNA transfer from bacterium to bacterium via bacteriophages
What’re two probs w/ using bacteriophages as anti-bacterial agents?
- No such thing as “broad-spectrum” phage
2. Phage must be purified away from bacterial debris, such as LPS, that can cause fever and other immune rxns
What is conjugation (method of genetic exchange)?
The transfer of plasmids by direct cell-to-cell contact b/w two bacterial cells
What’s the name of the initial structure that attaches a bacterial cell to another for the purpose of transferring plasmids?
Sex pilus
This method of genetic exchange involves bacteria taking up genetic material of dead bacterial cells.
Transformation
This method of genetic exchange involves bacteriophages.
Transduction
This method of genetic exchange is a very efficient process for transferring large blocks of genetic info (i.e. entire plasmids)
Conjugation
