Block A - Microbial Genomes and Evolution Flashcards
What type of microbe is this describing and fill in the gaps.
The Chromosome need to be ______ packed to fit inside the cell. It needs to be ________ by more than 1,000 times. (3 marks)
Bacteria. tightly. compacted
Bacterial DNA needs to be organised in a way to make it compatible with what process? Give 3 examples (3 marks)
essential cellular processes, ensuring proper function and regulation such as replication, transcription, segregation during cell division
How do we get from a relaxed nicked circular DNA to a supercoiled circular DNA. (1 mark)
break one strand and rotate one end of broken strand around helix and seal
What are 2 characteristics of positive supercoiling? (2 marks)
-increases chromosomal DNA interactions and tightens interaction with histone
-can hinder transcription and gene expression
What is a characteristic of negative supercoiling? (1 mark)
-favours local unwinding of the DNA, enhancing processes such as transcription DNA replication and recombination
What’s the role of Topoisomerase I in terms of supercoiling? (1 marks)
relaxes negatively supercoiled DNA
What’s the role of DNA gyrase in terms of supercoiling? (1 marks)
compacts DNA by introducing supercoils
Which enzyme relaxes supercoiled DNA?
Topoisomerase I
Which enzyme compacts DNA into supercoils?
DNA gyrase
Bacteria divide through a process called ____ _____
binary fission
Cell division and replication need to be ______
synchronised
What’s terminus segregation? (2 marks)
a process by which the terminus region of a bacterial chromosome moves to the centre of a cell during replication
In E.coli which protein plays the biggest role in chromosome segregation
FtsK
What is chromosome segregation? (2 marks)
the process by which chromosomes are separated and distributed equally between daughter cells
What’s the role of Topoisomerase IV?
Its also involved in cell division
Describe the process of bacterial cell division (5 marks)
-FtsZ positions SLmA and MatP on the nucleoid and MinC-MinD-MinE oscilating between the cell poles, to
ensure FtsZ only assembles into a Z ring at the midcell
-replicated daughter nucleoids seperate, a Z ring assembles at midcell from the FtsZ protein, MinCDE moves to poles
-Z ring recruits other septum-synthesis proteins which result in the formation of the divisome
-divisome synthesizes the septum
-nutrient depletion induces a quiescent state in which FtsZ depolymerizes from its Z ring structure and transitions into a punctate structure which acts as a FtsK reservior, this allows FtsK to quickly repolymerize upon favourable nutrient conditions reforming the Z ringt
Describe the process of transformation in horizontal gene transfer. (1 mark)
where a bacterium absorbs genetic material or naked DNA from a dead bacterium from its environment or from another bacterium.
For transformation, the bacterium must be in a state of ______.
competance
Describe how we can chemically induce competance of a bacteria in lab? (3 marks)
we can treat the cells with a divalent cation, such as calcium chloride or lithium chloride to increase the efficiency of DNA entering the bacterium through pores in the cell wall
Aside from chemically induction, how else would we induce competence into bacteria? (2 marks)
We can use electroporation, which uses electricity or we can expose the cells to a heat shock treatment at 42C for 2 mins
Describe natural transformation? (1 mark)
naturally competant bacteria actively pull DNA fragments from their environment into their cells
What is transfection? (1 mark)
It is a laboratory technique that introduces foreign nucleic acid from a bacterial virus into eukaryotic cells
What is Transduction?
it involves the transfer of a DNA fragment from one bacterium to another by a bacteriophage
What is a bacteriophage
a bacterial virus
what is phage conversion
phage alters the phenotype of a bacterial host after infecting it
what is the difference between generalized transduction and specialized transduction?
the difference is that with generalized transduction, a bacteriophage can package any random fragment of bacterial DNA while in specialized it can only package specific parts of the bacterial DNA adjacent to the prophage insertion site.
What is conjuction/ bacterial sex
when DNA is transferred from a donor to a reciepient bacterium by direct contact
What is essential in conjuction?
that the donor cell has a sex pilus
In conjugation, what is a F+ cell
cells that have a nonintegrated F plasmid and act as donors during conjugation
In conjugation, what is a F- cell
cells that lack the F plasmid and act a recIepient during conjugation
What is the importance of conjugation in the field today?
its a major way bacteria exchange antibiotic resistance genes
What are the 2 key factors that determine the dynamics of conjugation
the rate of gene transfer and the growth rate
Define silent mutation?
does not affect amino acid sequence
Define missense mutation?
amino acid changed, polypepetide altered
Define nonsense mutation?
codon becomes stop codon: polypeptide is incomplete
Define frameshift mutation?
deletion/ insertion resulting in a shift in the reading frame. usually results in complete loss of gene function
Name 3 factors that can induce mutations more rapidly?
-chemical mutagens
-ionising radiation (uv radiation, x-rays)
-biological mutagens
Describe 3 ways DNA repair itself from mutations
-direct reversal: where the mutated base is directly restored to its original base without the need for DNA excision or synthesis
-repair of single strand damage: where damaged DNA is removed and repaired using opposite strand as template
-repair of double strand damage: a break in the DNA requires more error prone repair mechanisms
Whats an ames test
makes practical use of bacterial mutations to detect for potentially hazardous chemicals
