L2 - Prokaryotic genomes Flashcards
What are the drawbacks of an RNA genome?
Unstable because single stranded (information encoded in bases is exposed to the environment). Phosphodiester bond is more labile so can be broken by hydrolysis.
Which form of DNA is most common in cells? A, B or Z form?
B form
What is the good and bad thing about the DNA backbone?
It protects from damage but makes the info harder to access.
List properties of DNA thinking about rigidity, charge, direction of winding, direction of strands
Flexible, negatively charged (phosphates), right handed double helix, single strands running antiparallel.
What does the GC content and what does a high GC content mean for the DNA?
The proportion of guanine and cytosine bases in DNA. High GC content means DNA is more stable and protected from chemical damage.
Why does the genome size give an accurate estimation of the number of genes?
Because there is very little ‘junk’ DNA, genome size is readily decreased where possible.
How does packaging compare in eukaryotes and prokaryotes?
More tight and careful in eukaryotes because it must fit into small nucleus. Prokaryotic DNA takes p a smaller proportion of the cell
What is the nucleoid?
Small region of the cell where DNA is packaged by basic proteins and is near the pole of the cell.
3 ways of getting new genes into a genome?
1) Gene duplication and divergent evolution (very slow)
2) Plasmids - can be incorporated into chromosomal DNA be homologous recombination and can remove genes via transposable elements (transposition). They are transient and transfer genetic material between cells.
3) Phages - can insert DNA into chromosome after infection (specialised transduction). Can also pull genes out when they leave
What allows some bacteria to have a broad host range?
The ability to replicate themselves (from oriV)
Several plasmids can be carried provided they are from different _____?
Compatibility groups.
By what means are plasmids acquired?
Conjugation, a random process.
What is a selfish plasmid and why is it maintained?
Produces both a toxin and an antitoxin so cell would die if it got rid of the plasmid.
A composite transposon is flanked by.
Insertion sequences which are each themselves flanked with inverted repeats recognised by a transposase enzyme.
What makes an atypical composite transposon different?
It only needs one insertion sequence (IS) element
