Chapter 7 - Genetic Transfer and Mapping in Bacteria Flashcards
Are bacteria usually haploid or diploid?
Haploid
Bacteria reproduce asexually through this method
Binary fission
In this process, a segment of bacterial DNA is transferred from one bacterium to another
Genetic transfer (or horizontal genetic transfer)
These are viruses that infect bacteria
Bacteriophages
Do bacteriophages contain their own genetic material?
Yes
Like sexual reproduction in eukaryotes, genetic transfer in bacteria enhances this
Genetic diversity
What are three ways in which genetic material can transfer from one bacterium to another?
Conjugation, transduction, transformation
This method of genetic transfer involves direct physical contact between bacteria
Conjugation
This method of genetic transfer involves bacteriophages
Transduction
This method of bacterial genetic transfer involves uptake from the environment
Transformation
In conjugation, this circular segment of DNA is transferred to a recipient cell
Plasmid
In transformation, is the donor cell alive or dead?
Dead
Genetic transfer in bacteria was discovered in 1946 by these two scientists
Joshua Lederberg and Edward Tatum
What are the two different strains of E. coli that Joshua Lederberg and Edward Tatum studied?
Auxotrophs and prototrophs
This strain of E. coli cannot synthesize a particular nutrient and therefore need it in their growth medium
Auxotrophs
This strain of E. coli make all their nutrients from components in their growth medium
Prototrophs
This scientist showed that bacterial strains must make physical contact for transfer of genetic material to occur
Bernard Davis
Bernard Davis used this apparatus to show that bacteria must make physical contact to transfer genetic material
U-tube
This apparatus has a filter at the bottom with pores that are large enough to allow the passage of genetic material but small enough to prevent the passage of bacterial cells
U-tube
Can all species of bacteria conjugate?
No
Can only certain strains of bacteria act as donor cells in conjugation?
Yes
Certain donor strains of E. coli contain this small circular piece of DNA
F factor (fertility factor)
Bacteria strains containing an F factor are designated this
F+
Bacteria strains lacking an F factor are designated this
F-
Genes that play a role in DNA transfer are named either of these two prefixes
tra or trb followed by a capital letter
What initiates conjugation between bacteria cells?
Contact between donor and recipient cells
These act as attachment sites for F- minus bacteria onto F+ bacteria
Sex pili (or F pili)
Once contact is made and the pili shorten, donor and recipient bacteria cells are drawn together and this forms between the two cells
Conjugation bridge
During conjugation, this recognizes the origin of transfer (DNA sequence) and makes a cut in the DNA
Relaxosome
This protein remains bound to the end of the T-DNA after most accessory proteins of the relaxosome are released
Relaxase
This is a complex of 10 to 15 proteins encoded by the F factor that span both inner and outer membranes and pumps DNA/relaxase into the recipient cell
Exporter
This is the general term used to describe extra-chromosomal DNA
Plasmid
Do plasmids replicate independent of bacterial chromosomes?
Yes
Plasmids can exist as a single copy or up to 100 copies per cell, depending on this
Strength of origin
Are plasmids usually required for survival?
No
Plasmids can provide these to bacteria
Growth advantages
What are the five different categories of plasmids?
- Fertility plasmids; 2. Resistance plasmids; 3. Degradative plasmids; 4. Col-plasmids; 5. Virulence plasmids
This category of plasmids allows conjugation
Fertility plasmids
This category of plasmids contain genes conferring resistance to antibiotics
Resistance plasmids
This is another term for resistance plasmids
R factors
This category of plasmids carries genes allowing digestion of unusual substances
Degradative plasmids
This category of plasmids contain genes that kill other bacteria
Col-plasmids
This category of plasmid carries genes that turn bacterium into pathogenic strains
Virulence plasmids
In the 1950s, this scientist discovered a strain of E. coli that was very efficient at transferring chromosomal genes
Luca Cavalli-Sforza
Luca Cavalli-Sforza discovered a strain of E. coli that was very efficient at transferring chromosomal genes and he designated it this
Hfr (high frequency of recombination)
F factors that were excised imprecisely and carry genes that were found on the bacterial chromosome are called this
F’ factors (F prime factors)
This scientist demonstrated that conjugation between an Hfr and an F- strain involves the transfer of a portion of the Hfr bacterial chromosome
William Hayes
How long does it take for the entire Hfr chromosome to be passed into the F- cell during conjugation?
1.5 - 2 hours
Do most conjugations take less than the full 1.5-2 hours?
Yes
Because most conjugations take less than the full 1.5-2 hours, only a portion of this chromosome gets into the F- cell
Hfr chromosome
Chromosomal material from Hfr cell can recombine with this in the recipient cell
Homologous region on chromosome of recipient cell
This technique to map chromosomes was developed by Elie Wollman and Francois Jacob in the 1950s
Interrupted conjugation technique
These two scientists developed the interrupted conjugation technique in the 1950s
Elie Wollman and Francois Jacob
What is the rationale behind the interrupted conjugation technique?
The time it takes genes to enter the recipient cell is directly related to their order along the bacterial chromosome
In the interrupted conjugation technique, the order of genes along the chromosome can be deduced by determining this
The length of time it takes to transfer certain genes
How long is the E. coli genetic map?
100 minutes
This is a virus that specifically infects bacterial cells
Bacteriophage
A bacteriophage is composed of genetic material surrounded by this
Protein coat
Bacteriophages may follow one or both of these two different cycles
Lytic and lysogenic
This scientist discovered bacterial transformation in 1928 while working with strains of Streptococcus pneumoniae
Frederick Griffith
What are the two types of bacterial transformation?
Natural and artificial
Bacterial cells that are able to take up DNA are termed this
Competent cells
Competent bacterial cells carry genes that encode these proteins
Competence factors
Competence factors are proteins that facilitate this
Binding/uptake/incorporation of DNA into bacterial chromosome
This enzyme cuts extracellular environmental DNA into smaller fragments
Endonuclease
Are both extracellular DNA strands cut by endonuclease transported into the recipient cell?
No (one is degraded and the other enters cell)
This is a region of mismatch caused by sequence differences between two alleles during transformation
Heteroduplex
If the transformed DNA is homologous to a region in the bacterial chromosome, it can be incorporated through this process
Homologous recombination
If the transformed DNA is not homologous to any genes on the chromosome, it may be incorporated at a random site on the chromosome through this process
Nonhomologous recombination
Streptococcus pneumoniae secretes this, which leads to competence only when many cells of the same species are nearby
Competence-stimulating peptide
Some species use these to preferentially take up DNA
DNA uptake signal sequences
How many base pairs long are DNA uptake signal sequences?
9 or 10 bp
How many times are DNA uptake signal sequences repeated throughout a bacterial genome?
1,000 - 2,000 times
This is a common method to artificially induce bacterial transformation
Treat with calcium chloride and high temperature shock to make cells permeable to small DNA molecules
This artificial transformation method makes cells permeable with an external electrical field
Electroporation
Horizontal gene transfer has dramatically contributed to this
Acquired antibiotic resistance
Some strains of this bacterial species are resistant to methicillin and all penicillins
Staphylococcus aureus
