Bacteria Flashcards
(43 cards)
What is the function of bac chromosome?
1 circular, dsDNA in nucleoid region⇒ contains genes essential for survival (genes code for… )
What is the function of plasmids?
autonomously replicating, extrachromosomal circular DNA⇒ containing genes that confer advantages to bacteria living in stressful environments e.g. antibiotic resistance (/use new substrates for energy)
What is the function of 70S ribosomes?
synthesise proteins
What is the function of storage granules in cytoplasm?
containing nutrients and chemical reserves
What is the function of plasma membrane?
membranes chpt + where ETCs & ATP synthase embed to produce ATP in photosynthesis/ respiration
What is the function of peptidoglycan cell wall?
Protects cell from osmotic lysis
What is the function of capsule/slime layer?
Ensure phagocytes unable to recognise bac–> protect bac from being taken in by them
Enables bac to adhere to one another/surfaces→ biofilm
Prevent desiccation of bacteria as it contains water
Protection from antibiotics
What is the function of fimbriae?
attachment to sf or other bacteria/organisms
What is the function of pili?
for conjugation and motility
What is the function of the flagella?
for motility/propulsion by rotation
What are the advantages of asexual reproduction via binary fission?
+: selective advantage in stable, unchanging, favourable environment as it allows genotypes to rapidly reproduce and colonise a habitat (all adapted for the area)
+ fast reproduction
-: change in environment→ whole colony can’t survive
Describe the process of binary fission
- Semi-conservative DNA replication begins at Ori:
> DNA is unzipped by helicase by breaking hydrogen bonds between bases of the 2 strands. Ds separates→ replication bubble
> Each parental strand serves as a template for synthesis of daughter strands
> Free deoxyribonucleotides cbp with bases on template strand→ DNA polymerase forms phosphodiester bonds between adj dNTPs
> Leading strand + lagging strand - As chromosome replicates, 2 newly formed Ori move to opposite poles of the cell & attach to plasma membrane
- Cell concurrently elongates to prepare for division
- Interlocking struc made up of 2 daughter DNA molecules formed with the completion of replication, as DNA is circular w no free ends→ Topoisomerase cuts, separate and reseal 2 DNA molecules
- Cell budding off: Plasma membrane invaginates, new cell wall deposited→ parent cell divided into 2 daughter cells, each inheriting a complete genome
Compare mitosis and binary fission
End pdt Amt of DNA DNA replication Behaviour of chromosomes - Attach to plasma membrane? - Form tangled rings? - Chromosome condensation? - Specific positioning of chromosomes? Spindle fibre Type of division
Describe transformation
Fragments of foreign naked DNA (from lysed bac) in the surrounding medium are taken up by competent bac cell via surface proteins→ foreign DNA incorporated into bac chromosome via homologous recombination/ crossing over at homologous regions→ foreign DNA contains a different allele that is now expressed, bac cell transformed
What is meant by a competent bacterial cell?
natural ability to readily take up foreign DNA
How can bac become artificially competent?
immerse in a cold culture medium w high [CaCl2] + heat shock treatment
Describe generalised transduction
- Phage infects bac, injecting its viral genome into the host cell
- Bac DNA degraded into small fragments, one may be randomly packaged into a capsid head during assembly
- cell lysis–> defective phage infects another bac by injecting bac DNA from prev host cell into new bac
- Homologous recombination: foreign bac DNA replaces homologous region of recipient cell chromosome→ (possibly) expression of a different allele
Describe specialised transduction
- Temperate phage infects bac, injecting its viral genome into the host cell
- Viral DNA integrates into bac chromosome, forming prophage, which may be improperly excised to include adj segments of bac DNA during an induction event.
- phage-host DNA hybrid packaged into capsid head during assembly
- cell lysis–> defective phage infects another bac by injecting bac DNA from prev host cell into new bac
- Homologous recombination: foreign bac DNA replaces homologous region of recipient cell chromosome→ (possibly) expression of a different allele
In what ways are F plasmids different from bac chromosome?
Smaller
Has non-essential genes coding for advantageous traits e.g. antibiotic resistance
Explain why conjugation can only be initiated by an F+ cell with an F plasmid / Role of plasmid
F+ cells possess F plasmid, which has an F factor that carries genes coding for proteins needed to form sex pili & subsequent cytoplasmic mating bridge
→ allow for conjugation & transfer of bac genes between bac
Describe conjugation
- Sex pilus of F+ cell makes contact w F- cell & retracts→ bring F- cell closer, mating bridge forms
- Rolling circle DNA replication
- One of the 2 strands of plasmid DNA is nicked & transferred from F+ to F– cell. Phosphodiester bond is broken.
- Free 3’ OH end of the nick is used for strand elongation by DNA polymerase using intact strand as a template→ synthesis of new complementary strand
- Elongation process is facilitated by the displacement of the 5’ end of nicked strand and is transferred to the recipient bacterium via the mating bridge
- Completion of a unit length of plasmid DNA→ another nick releases original strand, which re-circularises
- Recipient cell: ss F plasmid DNA re-circularises and serves as template for the synthesis of a new complementary daughter strand→ ds F plasmid→ F- cell becomes F+ cell
Benefits of conjugation for recipient bac?
- Gains new alleles that, when expressed, allow survival in a diff environment e.g antibiotic resistance
- Use of a new metabolites/resources eg new C source by producing the relevant enzymes
Compare transformation, generalised and specialised transduction, conjugation
Source of DNA/ Types of donor cell
Agent mediating transfer
Type of DNA transferred
Homologous recombination needed for permanent expression of foriegn gene?
Define an operon
An operon is a cluster of genes with related functions, under the control of the same promoter, allowing for functionally related proteins to be synthesised as a unit