Bacteria Flashcards
What are found in the internal structure of bacteria
Bacterial chromosome, Nucleoid, 70S ribosomes, Storage granules, Plasmids
What are bacterial cell wall made of?
Peptidoglycan
What is binary fission?
Binary fission is the asexual means by which bacterial cells produce offspring
How does bacterial chromosome replicate?
DNA replication begins at origin of replication (ori), double helix seperates to form a replication bubble. As chromosome replicates, 2 newly formed ori move to opposite poles of the cell and binds to cell membrane. Toipoisomerase is used to cut, separate and reseal the 2 DNA molecules.
State the method(s) that give rise to genetic variation in bacteria genomes.
Transformation, Tranduction and Conjugation
Describe the process of transformation
During transformation, naked and foreign DNA fragments form surrounding environments are taken into cell via cell-surface proteins that allows for binding and transport of DNA into cell. Foreign DNA incorporated into bacterial chromosome by crossing over at homologous regions, process is known as homologous recombination. Cell is now known as recombinant cell. If alleles of genes were changed, there will be a permanant change in organism phenotype as new allele is expressed.
Describe the process of transduction
During transduction, DNA from another bacterial cell is injected into another bacterium as phage is defective. During assembly of phage genome, host cell’s degraded DNA is packaged instead of phage’s genetic material. Hence, foreign injected bacterial DNA will replace the homologous region of recipient cell’s chromosome by crossing over. Recipient cell is now known as recombinant cell and will express new alleles resulting in new phenotypes.
How is general transduction different from specialised transduction?
Any random portion of host bacterial DNA may be transferred during general transduction but only adjacent DNA can be transferred during specialised transduction.
Describe the process of conjugation
Conjugation occurs when sex pilus on surface of F+ cell contacts F- cell. After sex pilus attaches, it retracts and pulls both cells closer, forming a temporary mating bridge. One of the 2 strands of the plasmid DNA passes through the bridge via rolling circle DNA replication. Single strand plasmid DNA recircularises and acts as template. Now both cells are F+.
Describe the process of rolling circle DNA replication
One strand of the double stranded F plasmid is nicked by nuclease, free 3’ OH end of nick is extended by DNA polymerase for synthesis of new complementary strand using intact strand as the template. Newly synthesized strand displaces nicked strand at the 5’ end and transferred across mating bridge.
What does the lac Operon do?
Hydrolyses lactose into glucose
What does the DNA of lac operon code for?
Beta-galactosidase, Permease and Transacetylase
What does beta-galactosidase do?
It converts lactose into allolactose
What does permease do in the lac operon?
It increases cell permeability to lactose.
What happens to the lac operon in the presence of lactose but absence of glucose?
Activator protein has a DNA-binding and allosteric site. Activator protein is Catabolite Activator Protein (CAP). DNA binding site allows for binding to CAP-binding site within promoter and allosteric site is specific for binding of cyclic AMP (cAMP). In absence of glucose, cAMP levels increases, forming more CAP-cAMP complex, activating CAP. Activated CAP increases affinity of promoter region of for RNA polymerase, increasing rate of transcriptional initiation.
