Prokaryote and Extra-chromosomal Genetics Flashcards
How is a prokaryotic chromosome stored within the cell?
As a nucleoid (non-compartmentalised).
How many chromosomes do prokaryotes typically have?
One.
How do prokaryotic chromosomes compare in terms of size?
Much smaller.
Describe the shape of prokaryotic chromosomes.
Circular.
How are aggregates of cells produced?
Via binary fission.
Define the term prokaryotic genetics.
Constant segregation and assortment of genetic information via cellular level gene transfer.
Define the term plasmid.
An extra-chromosomal circle of DNA containing non-essential genes.
What genetic information is stored on plasmids?
Genes allowing replication/segregation of the plasmid.
Genes that confer auxiliary metabolic pathways.
How many origins of replication do prokaryotic chromosomes have?
Usually one.
Define the term conjugate plasmid.
A plasmid containing genes that allow the plasmid to transfer a copy of itself to another cell.
What is the name given to genes that allow conjugation?
Transfer genes.
What are plasmid - strains?
Cells lacking a specific conjugative plasmid.
What are plasmid + strains?
Cells possessing a specific conjugative plasmid.
What do tra genes encode?
Proteins called pilins that extrude from the cell to form pili.
Where are tra genes found?
On plasmids.
How do pili function?
They recognise and adhere to the plasmid to form a channel between cells.
What are transposable elements?
Mobile DNA sequences that are able to jump from one location to another within a cell.
What are inverted repeats?
Flanking identical short DNA sequences.
What do transposase enzymes recognise?
Inverted repeats.
What do transposase enzymes do?
Catalyse transposition.
What are the simplest transposable elements?
Insertion sequences.
What genes do insertion sequences contain?
tnp genes which encode for transposases.
Define the process of replicative transposition.
Creating a new copy of the transposable element.
Define the process of non-replicative transposition.
A transposable element jumping from one position to another.
How are transposable elements “selfish gene” parasites?
They proliferate throughout the genome by jumping between/within chromosomal and plasmid locations.
How is a transposon formed?
Two insertion sequences flank a gene which disrupts the normal function of transposases.
Define the term transposon.
A transposable element carrying extra genes.
How do transposons get transferred between chromosomes and plasmids?
Transposases have no specific DNA target.
How can genes on a chromosome be transferred between cells?
The genes could become part of a transposon and then become incorporated into the plasmid. This plasmid can then be transferred to other cells via conjugation.
What happens when there is no selection for a plasmid?
A mixed population will be formed: some cells will have the plasmid, some won’t.
What happens when selection for a plasmid occurs?
Those with the advantageous plasmid survive and spread the plasmid within the population.
What is meant when a pilus is described as promiscuous?
It means that it has the potential for conjugation between species.
What is a reciprocal strand exchange?
Homologous recombination between a chromosome and plasmid as a result of the two aligning because of identical genes.
What is sometimes formed from reciprocal strand exchange?
A co-integrated molecule (the chromosome and plasmid combine).
What is meant by plasmid excision?
The plasmid separating from the co-integrated molecule. Opposite of reciprocal strand exchange.
Define the term episomal plasmid.
A plasmid with sequences homologous to a host cell
chromosome, capable of reversible integration and excision.
Define the process of transduction.
The transfer of genes via viral transfer as a result of incorporating sections of the host genome.
Define the process of transformation.
The deliberate uptake of DNA from the external environment and its incorporation into the host cell chromosome.
What is the term given to the ability to take up DNA?
Competence.
Eukaryotic gene transmission is vertical. How do prokaryotes compare?
Gene transmission in prokaryotes can be both vertical and horizontal.
Define vertical gene transmission (VGT).
Transfer of genetic information down a lineage (generation to generation)
Define horizontal gene transmission (HGT).
Transfer of genetic information between lineages (between living cells).
What processes allow horizontal gene transmission (HGT) in prokaryotes?
Conjugation, transduction and transformation.
Define the mobilome.
The genetic material that can actively move within a genome and between individuals.
What could be classed as part of the mobilome?
Plasmids, transposons, DNA transduced by viruses and DNA in the environment.
How is horizontal gene transfer restricted (HGT)?
Conjugation is generally limited to one species.
Cells have mechanisms to select DNA.
Prokaryotes have immune systems to destroy foreign DNA.
What is quorum sensing?
A form of HGT prevention. The cell only becomes competent when it senses other similar cells growing nearby.
Why do prokaryotes often contain restriction endonucleases?
They cleave foreign DNA in order to prevent the cell being harmed.
How is host cell DNA protected from restriction endonucleases?
Host DNA is modified by DNA methylase so isn’t recognised.
Where do the organelles and cytoplasm originate from in a eukaryotic cell?
From the maternal gamete.
What shape are mitochondrial chromosomes?
Circular.
What shape are chloroplast chromosomes?
Circular.
What are the evolutionary origins of mitochondria and chloroplasts?
They were originally bacteria that entered into
a symbiotic relationship with archaeal-like cells.
Why do maternally-inherited organelle traits show phenotypic variability?
Variability in the number of mitochondrial chromosomes in each mitochondrion.
What is one technique that can be used to avoid maternally inherited diseases?
“3 parent” IVF combined with transplant of healthy mitochondria.
What is Wolbachia?
An alpha-proteobacteria that is an endosymbiont in
arthropod and nematode cells.
How are Wolbachia cells transmitted?
Maternally via egg cell cytoplasm.
How does Wolbachia proliferate?
It increases the proportion of females as it is passed on maternally.
