Bacterial genetics Flashcards
Define the prokaryotic genome.
The main portion of DNA, along with associated proteins and RNA
Prokaryotic cells are haploid (single chromosome copy)
Describe the typical chromosome in prokaryotes
A typical prokaryotic chromosome is a single, circular, double-stranded molecule of DNA in a nucleoid.
It contains all the genetic information required by a cell.
What is the nucleoid?
DNA is tightly coiled around a protein-dense area called the nucleoid –>
central subcompartment in the cytoplasm where DNA aggregates
What is a plasmid?
Small circular, double-stranded DNA
Stable extra-chromosomal DNA elements that carry nonessential genetic information.
Duplicated and passed on to offspring.
Replicate independently from the chromosome
Plasmids may encode for enzymes responsible for what?
Plasmids may encode for enzymes responsible for antibiotic resistance, production of toxins, and tolerance to toxic metals.
Differentiate between F plasmids and R plasmids.
F plasmids allow genetic material to be transferred from a donor cell to a recipient.
R plasmids carry genes encoding for resistance to antibiotics
Plasmids are used in genetic engineering
because?
they are readily manipulated & transferred from cell to cell
F plasmids function?
F plasmids allow genetic material to be transferred from a donor cell to a recipient.
R plasmids function?
R plasmids carry genes encoding for resistance to antibiotics
What is genetic recombination?
Genetic recombination occurs when an organism acquires and expresses genes that originated in another organism
Genetic information in prokaryotes can be transferred in two ways, what are those ways?
vertically and horizontally
Vertical gene transfer (VGT)
transfer of genetic material from parent cell to daughter cell
Horizontal gene transfer (HGT)
transfer of DNA from a donor cell to a recipient cell
What are the three types of prokaryotes’ genetic recombination?
- Bacterial conjugation
- Transformation
- Transduction
3 means for exogenous genetic recombination in bacteria: same as three types of genetic recombination in prokaryotes
- Conjugation
- Transformation
- Transduction
Transmission of Exogenous Genetic Material in Bacteria
- Conjugation - requires the attachment of two related species & the formation of a bridge that can transport DNA.
- Transformation - transfer of naked DNA
- Transduction - DNA transfer mediated by bacterial virus
Describe DNA replication in prokaryotes.
Initiation:
A) Chromosome is a double-stranded molecule of DNA. The origin of replication exists at one point on the DNA loop.
Elongation:
B) The enzymes open the DNA molecule at the origin of replication and two V-shaped replication forks result.
C) DNA synthesis continues along the two replication forks of the two DNA strands. On both strands, the new DNA lengthens as nucleotides are added to the open ends.
Termination:
D) As synthesis nears completion, the inner chromosome moves to a position outside the outer chromosome and prepares to separate
E) Following separation, two chromosomes now exist. Each chromosome contains an old and new strand of polynucleotides. This is the semi-conservative method of DNA replication.
What is CONJUGATION?
-It is the transfer of a plasmid or chromosomal fragment from a donor cell to a recipient cell via a direct connection.
Gram-negative:
> Cell donor has a fertility plasmid
(F plasmid, F′ factor) which allows the synthesis of a conjugation (sex) pilus
> Recipient cell is a related species or genus without a fertility plasmid
> Donor transfers fertility plasmid to a recipient through a pilus
> F+ and F-
Describe the process of Conjugation. The physical aspect of GRAM negative and positive bacteria.
This is the mechanism for gram-negative bacteria.:
A) The pilus of a donor cell attaches to a receptor on the recipient cell and retracts to draw the two cells together .
This is the mechanism for gram-positive bacteria.:
B) An opening or pore forms between the cell walls, thereby creating a bridge to transmit genetic material. This is presumably how gram-positive bacteria conjugate.
What is TRANSFORMATION?
Chromosome fragments from a lysed cell are accepted by a recipient cell. (free/naked DNA transfer to a recipient)
> Genetic code of DNA fragment is acquired by recipient.
> Donor and recipient cells can be unrelated.
> Useful tool in recombinant DNA technology
What is TRANSDUCTION?
DNA is transferred from one bacterium to another by a virus.
> Bacteriophages
- A virus that infects bacteria.
- Consists of an outer protein capsid enclosing genetic material.
- Serves as a carrier of DNA from a donor cell to a recipient cell.
What are other ways the genetics of an organism can change?
- Transposons
2. Mutations
What are transposons?
Special DNA segments that have the capability of moving from one location in the genome to another
“jumping genes”
Can move from
one chromosome site to another
chromosome to a plasmid
plasmid to a chromosome
May be beneficial or harmful
Changes in traits
Replacement of damaged DNA
Transfer of drug resistance
Transposons can move from?
- one chromosome site to another
- chromosome to a plasmid
- plasmid to a chromosome
