Microbial Genetics #7 Flashcards
- Name two general mechanisms by which change occurs in the genetic code.
1: Mutation
2: Recombination
- Describe the processes of conjugation, transduction, and transformation.
Conjugation: exchange of genetic material through plasmid
Transduction: transfer of DNA via a virus (phage)
Transformation: Uptake of DNA from the virus
- Generalized Transduction
Generalized Transduction:
1: A phage invades
2: breaks down the bacterial genome (with an enzyme
3: As nucleocapsids form some form around bacterial DNA
4: cell lysis, bacterial DNA them brought to a new bacteria
5: Recombination may insert viral carried bacterial DNA into the chromosome
Specialized Transduction:
Specialized Transduction:
1: Virus enters and integrates into the host chromosomal DNA.
2: When phage cuts itself out of the genome, sometimes it takes a few genes next to where it integrated
3: those are replicated with the viral DNA (viral DNA is missing a few genes)
4: Phage lyses cell, virus invades new cell, viral DNA minus a few viral genes plus a few bacterial genes integrates into the bacterial chromosome.
5: called specialized because it will only take genes near where the virus integrated in the original host chromosome
- Describe the factors that determine whether a bacterial strain will be “competent.”
Genetic Factors:
- Low # of endonucleases
- DNA binding proteins: single stranded DNA binding proteins which recruit new DNA
Environmental Factors:
- Cells will weight until they are at a certain density (quorum sense)
- Depends on phase of stage growth (often best in early log phase)
- Ca2+ makes cells more competent
- Cold shock increases competency
- Describe two potential outcomes of conjugation involving an Hfr strain.
1: Origin of transfer is located after the genes encoding for the F pillus. This will lead to transfer of a few F plasmid genes and a few host chromosome genes. The F- cell remains F- after the transfer
2: the origin of transfer occurs before the genes encoding for the F pillus. During conjugation, transfer of a few F plasmid genes (including F pillus genes), and a few host DNA genes will occur. Creating an F+ cell out of an F- cell.
- Describe the role and function of restriction endonucleases.
These are restriction enzymes (restriction endonucleases). They recognize specific sequences and perform a sticky ended cut on them.
Often used to destroy viral DNA upon entry.
- Describe a series of four independently replicating genetic units that may represent the evolutionary sequence leading to viruses.
1: Insertion Sequence:
- Can move, carries a gene for its own replication and movement
2: Transposon:
- what IS do + can carry a few more genes
3: F plasmid:
- Transposon + circular DNA, can replicate, can leave the cell through conjugation
4: virus:
- Oh… you know what viruses do.
F plasmid:
encodes for the F pillus (which forms conjugation bridge) can use rolling circle replication to send itself through into a new cell
Has origin of transfer, which is where it is nicked for replication.
Hfr strain:
High Frequence Replication strain:
- F plasmid has crossed over with host chromosome (integrated within it)
- Can transfer a few genes after the origin of transfer to a F- strain, without turning it into an F- strain.
F+
F-
F+ : capable of forming an F pillus and transfering DNA, generally an F plasmid unless it is an Hfr strain
F- : does not form an F pillus
- Describe two types of transposable elements.
Insertion Sequence (simple transposon): contains inverted repeats with a transposase gene within it.
AATTCG-transposaseGene-GCTTAA
Transposon (complex transposon): Has two insertion sequences flanking ~1-3 other genes. Moves all as a collective unit.
IS1–Genes–IS2
