7.1 - Chromosome Organization Flashcards
What is the shape of a typical bacterial chromosome?
Circular
Are all bacterial chromosomes circular? Give examples
No some are linear for example:
Borrelia burgdorferi which causes lime disease
Do bacteria only have circular or linear chromsomes?
No some can have both such as Agrobacterium tumefaciens
Which species have the largest genome amongst bacteria?
Streptomyces
When does a plasmid become a chromsome?
The moment when, if lost, the bacteria cannot survive without it
How much of the human genome is coding for genes?
Less than 1%.
There are a lot of repetitive sequences like transposons and introns (spliced out of mRNA).
How much of the bacterial genome is coding DNA
90%.
Introns and repetitive elements are rare in bacteria
What is the most common repeptitive element in bacteria?
The IS (insertion sequence) element which are mobile elements
What does it mean when we say an RNA is monocistronic. What organism has monocistronic RNA?
When 1 mature mRNA makes 1 protein. Eukaryotes have this property
What does it mean when we say an RNA is polycistronic. What organism has polycistronic RNA?
When 1 mature mRNA makes multiple proteins. Eubacteria and archaebacteria have this property
What regulatory system do most bacteria have?
Operons
What is an operon?
A cluster of genes under the control of one promoter. Those genes are often involved in the same metabolic process.
What is a regulon?
A gene whose transcription results in the production of a regulatory protein that regulates the expression of promoter elements
What is the accepted bacterial nomenclature
lacZ = gene LacZ = protein
Any number after the “Z” designates an allele of the gene, or a mutant.
What are nucleoids?
Bacterial chromsomes are compacted into nucleoids.
What is DAPI
A chemical dye that has an affinity to DNA
What happens when bacterial cells are treated with DAPI?
When some bacteria are treated with DAPI, we observe a blue stain at a specific location of the cell. This means that the bacterial cell has a nucleoid that is contained in a specific location/compartment in the cell. When all the cell is stained, this means that there is no nucleoid and the DNA is floating in the whole cytoplasm.
What is a significant difference between bacteria and eukaryotes and archae
Bacteria, unlike the other two, do not have histones or nuclear membranes.
How is DNA compacted in the nucleoid?
DNA is compacted by histone-like anchoring proteins, as well as by supercoiling/twisting to form loops. When histone-like proteins try to twist the DNA, the DNA will respond by trying to untwist itself. Since the DNA can’t untwist itself, it will release the tension due to the twisting by forming what we call a negative supercoil. A nick in a single strand will result in relaxing the supercoiling in the nicked strand. Most bacterial genomes are organized in negative supercoils.
How is negative supercoiling maintained?
With Topoisomerase I and II
What does Topoisomerase do?
Topoisomerase acts to regulate DNA supercoiling by catalyzing the winding and unwinding of DNA strands.
What is the general mode of action of topoisomerases?
o They cut the DNA backbone.
o They pass the DNA strands through one another to coil or relax.
o They ligate the DNA backbone
How does Type I topoisomerase work?
They work by breaking one strand of DNA, twisting the DNA to pass it through the gap and then re-ligating it.
How does Type II topoisomerase work?
They work by breaking both strands of DNA (needs ATP), twisting them and then re-ligating them. (DNA gyrase most typical type II)
