the microbial cell part 2 Flashcards
what are the two main intracellular structures of prokaryotes
1) the nuceloid
2) cytoplasm
what is a nucleoid
a structure in which compacted DNA within the cytoplasm is kept allowing the prokaryotes to couple transcription and translation
how is DNA organised in prokaryotes
- organised into chromosomes
- chromosomes are usually circular
most bacteria have a single chromosomes
outline the structure of prokayotes DNA
a double helix in the circular chromosome folded by DNA binding proteins into supercoil loops
what is a negative supercoil
when DNA is twisted in opposite directions to the double helix
what is a positive super coil
when DNA is twisted in the same direction as the double helix
what are the three challenges faced in DNA replication in prokaryotes
1) unwinding the DNA helix
2) replicating each DNA strand at the same time
3) sperating the two daughter chromosomes
outline the process of unwinding the double helix in DNA replication
1) after binding of DnaA two strands are seperated
2) DnaB helicase is responsible for seperating two parental strands
3) the strands are kept apart by a ssDNA binding protein
4) seperating and relaxing the two DNA strands tightens the double helix in the unopen region inducing the formation of positve supercoils which can block DNA replication
how is the formation of a positve supercoil relaxed during DNA replication
DNA gyrase eases the tension fomred by rapid unwinding of helix carried out by DnaB
outline the process of replicating each DNA strand at the same time
1) DNA primase synthesises the RNA primer
2) the leading strand is synthesised continuously
3) the lagging strand is synthesed discontinously and produces okazaki fragments
3) these are ligated and primers are removed
outline how the two daughter chromosomes are seperated
1) after DNA replication the two chromosomes are interlocked
2) DNA gyrase decatenates the two daughter chromosomes
what is the role of DNA gyrase in replication
1) release the tension of subercoiling
2) decatenates two daughter chromosomes by cutting double helix
where does transcription in prokaryotes occur
the nucleoid-cytoplasm interface
outline coupled transcription/translation
1) as soon as the prokaryote gene beings being transcribed into mRNA the ribosome lacthes onto the transcript and translates the info into protein
2) many ribosomes can translate the same mRNA transcript
3) this allows proteins to be made faster than in eukaryotes
outline the inititation of transcription
1) RNA polyermase has associated with a protein subunit called the sigma factor
2)the sigma subunit of RNA polyermase allows recognition and binding to a specific promoter sequence
3) there are different sigma factors each recognises the consensus sequence
outline elongation of transcription
1) once the rNAP clears the promotor region the sigma factor is released
2) NusA protein associated with the RNAP to assist the hairpins in growing RNA strand which can interupt transcription
outline termination of transcription
1) can be rho-independant
2) can be rho-dependant
outline rho-independant termination
occurs when RNAP reaches a termination signal a GC rich region followed by a string of A residues which forms a hairpin thereby stalling RNAP
outline rho-dependant termination
rho factor binds specific sequences within the newly formed mRNA moving towards the 3’
rho catches up with RNAP helping to release mRNA from the DNA template and RNAP
what does gene regulation ensure
that cells resources are not wasted making proteins which the cell doesnt need
what is an operon
signle transcriptional unit which corresponds to multiple genes whose expression is also controlled by a single promoter and terminator
what is a regulatory region
includes the promoter and the region surrounding the promoter to which a regulatory gene will bind
what is a regulatory gene
a gene which encodes for a protein that controls transcription by binding to a particular site of the DNA aka transcription factors
what are cis-acting factors
mechanisms that affect gene expression in the vicinity of the gene
