N org and control of PROK Flashcards
prok vs euk cells
- circular DNA vs linear DNA
- 70S ribosomes vs 80S ribosomes
- no true nucleus (no nuclear envelope and nucleolus) vs has a true nucleus
what happens to the genome during binary fission?
Before the bacterial cell divides, semi-conservative replication of parental DNA begins at the origin of replication to give rise to TWO origins. As the chromosome continues to replicate, each origin moves rapidly toward the opposite end of the cell and adhere to the cell membrane. While the chromosome is replicating, the cell elongates. Elongation of the cell also separates the two identical copies of the chromosomes.
lac operon (inducible) vs trp operon (repressible)
- both consists of a promoter, operator and a cluster of genes that encode enzymes in a metabolic pathway
- both operon will transcribe their structural genes to form a polycistronic mRNA
- usually turned off vs turned on
- synthesises enzymes in a catabolic vs anabolic pathway
- less structural genes (Lac Z,Y,A) vs more (Trp E, D, C, B, A)
- transcription of structural genes can be turned on when inducer ie allolactose binds allosterically to the repressor vs can be turned off when corepressor ie tryptophan binds to the repressor
what does structural gene mean?
it is a region of DNA that codes for a protein or RNA molecule that forms part of a structure or has an enzymatic function
what does regulatory gene mean?
it codes for a specific protein product that inhibits the expression of the structural genes
how does the presence of lactose induce a bacterium to use lactose as a respiratory substrate?
In the presence of lactose, allolactose binds to the repressor, resulting in a conformational change of the repressor thus the inactive repressor is unable to bind to the operator site and RNA polymerase is able to transcribe the structural genes, synthesising enzymes that break down lactose. Beta-galactosidase catalyse the hydrolysis of lactose to glucose and galactose, which are used in respiration.
prok vs euk genes
- In euk, each gene is under the control of single promoter whereas in prok, CLUSTER of genes like lac Z, Y, A genes under the control of a promoter called an operon
- In euk, expression of gene can be controlled by silencer vs in prok, expression regulated by operator
- In euk, presence of introns within the genes vs in prok, no introns present
structure of prok cell
pilus, flagellum, capsule (protein slime layer) -> peptidoglycan cell wall -> plasma membrane -> cytoplasm incluing ribosomes, food granules, chromosome, plasmid (DNA)
negative control using lac repressor - absence of lactose
- without allolactose bound, the lac repressor is active
- the DNA binding site of the active lac repressor is complementary in 3D conformation to the operator binding and binds to it
- RNA polymerase cannot bind to the promoter and transcribe lac operon genes, switching operon off
- B-galactosidase cannot be synthesised and lactose cannot be hydrolysed into galactose and glucose
negative control using lac repressor - presence of lactose
- allolactose acts as an inducer by binding to the allosteric site of the lac repressor, triggering a conformational change to turn it INACTIVE
- DNA binding site of the inactive lac repressor is no longer complementary in 3D conformation to the operator and cannot bind
- RNA polymerase can bind to the promoter and transcription can occur, switching on the operon
- B-galactosidase can be synthesised and lactose can be hydrolyse into galactose and glucose
positive control using CAP - absence of glucose
- cAMP conc increases -> cAMP binds to CAP to activate it
- DNA binding site of CAP is complementary in 3D shape to the CAP binding site, allowing it to bind
- enhanced binding of RNA polymerase to promoter, enabling higher rate of transcription of lac operon to occur
- operon switched on, B-galactosidase enzyme can be synthesised, lactose can be hydrolysed to produce glucose and lactose
positive control using CAP - presence of glucose
- cAMP conc decreases -> cAMP does not bind to CAP, CAP remains inactive
- DNA binding site of CAP is now complementary in 3D shape to the CAP binding site and cannot bind
- RNA polymerase may still be able to bind but transcription occurs at BASAL rate
- lactose hydrolysis proceeds at a low rate
bacterial transformation
naked, foreign DNA released from lysed bacteria into the surrounding environment is taken up by bacteria using specific cell surface proteins -> foreign DNA incorporated into the genome by homologous recombination
bacterial conjugation
a sex pilus of the F+ bacterial cell attach to the F- bacterial cell and the pilus then retracts tissue to form a temporary cytoplasmic mating bridge between both cells -> one strand of F plasmid’s DNA is cut at the origin of transfer and then the DNA strand travels through the cytoplasmic mating bridge from donor cell into recipient cell
generalised transduction
bacteria genes are transferred randomly from one bacterial cell to another one by a temperate -> error in the phage lytic cycle may result in small piece of host cell’s degraded DNA to be accidentally packaged within a phage capsid in place of the phage genome -> the phage can attach to another bacterium. and inject the piece of bacterial DNA which is then incorporated in the recipient cell’s DNA by homologous recombination
