L2 - Bacterial cells - basic components Flashcards
How can bacteria shape be influenced by?
- an be influenced by certain factor from the environment
- if environment is poor - higher SA to absorb nutrients
3 main types of bacteria shapes:
- coccus (sphere)
- bacillus (rod)
- spirochete (spiral)
What are the 2 types of bacterial arrangement in coccus
strepto(coccus) = chain
staphylo(coccus) = cluster
What does the bacterial envelope include from inner to outer?
cytoplasmic membrane, cell wall, capsule
3 main functions of cytoplasmic membrane?
- permeability barrier
- protein anchor
- energy conservation
Describe the cytoplasmic membrane’s function as a permeability barrier in detail.
- selectively permeable to prevent leakage of cytoplasmic content (sugar + salt)
- gateway of nutrient and waste
- prevents passive diffusion in/out
- water (polar/charged) diffuses freely but other substances need transport proteins
- allows cells to accumulate solutes within cytoplasm against high conc (crucial for metabolism)
Describe the cytoplasmic membrane’s function as a protein anchor in detail.
- diff types of proteins associated with membrane
- e.g. integral (embedded into membrane) - often transporters
- e.g. peripheral (loosely interacting in the membrane) - enzymes
- membrane is fluid so integral proteins flow around
Describe the cytoplasmic membrane’s function as a energy conservation in detail.
- charged on each side of the membrane serves as energy source
- protons and hydroxyl ions separated by membrane
- create ‘proton motive force’
- drives many energy-requiring functions (transport reactions, motility, synthesis of ATP, etc.)
Describe the difference in cell wall composition gram + vs gram -
gram positive bacteria = cell wall is mainly composed of peptidoglycan, takes up most of the cell wall
gram negative bacteria = thin layer between middle and outer (peptidoglycan)
- periplasmic space = thin layer of peptidogylcan between outer and inner membrane
What is peptidoglycan
- cross link polymer of sugars and amino acids
- very rigid = gives strength to bacterial cell wall
What are the steps in gram staining and what reagents are used
- fixation = drop cellular suspension and fix on glass slide (heat or methanol) - attatch cell to glass slide
-
crystal violet (primary stain) - stains peptidoglycans (periplasm)
- ions penetrates cell walls (gram positive = stains purple)
- trapping agent is needed (iodine) to interact with crystal violet to form large complexes that forms with peptidoglycan
- decolorisation using alcohol - gram positive washes away complexes so only gram negative is visible
- counter stain (safranin) - stains both + and - but pink only visible on gram -
Are most bacteria positive or negative?
gram negative
What is the function of the additional outer membrane on gram negative bacteria?
survival, major clinical significance (antibiotics endotoxin) impact on import/export from cell (permeability
What is on the gram -ve envelope for flowing of molecules? What does it do?
porins, protein channels necessary for passive transport, comes in diff sizes
When bacteria has less porins is it more or less resistant to antibiotics?
more resistant because they are more selective
What is lipopolysaccharides?
- LPS = across all membrane
- decorates outer membrane- integrity of cell, protects cell against antibiotics
- endotoxin - induce strong immune response
What is the capsule? What are its functions?
slime layer loosely associated capsule made of polysaccharides made and secreted from the cell.
- protects cell from desiccation when tight
- double up food in poor areas
- helps evade immune system
- attachment
Why do cells lose their capsule when in labs?
within generations it loses because not required for its functions
What are the 3 external appendages on bactera cells?
pili, fimbriae, flagella
What are pili and fimbriae? functions of each?
filamentous protein structures
long pili = facilitate conjugation and genetic exchange
short pili/fimbriae = surface attachment, sticky feet, movement
What is a flagellum? Function?
long hollow tube made of protein
- helps in motility (swimming)
- allows further dispersal and environment interaction
- allows bacteria to move away or towards stimulus
What is locomotion in terms of flagellum attachment to cell membrane?
- attached to cell membrane via basal body
- hook (secondary structure required) rotates → allows filament to rotate and propels cell forwards
What are the 4 flagellar patterns from least to most number of flagella?
monotrichous = one
amphitrichous = two
lophotrichous - lots stemmed from one location
peritrichous = lots in random spots
How does peritrichous bacteria work?
when bacteria have many flagella → rotate in same direction so they come together in a bundle of flagella with high strength and propels cell forwards
What is cytoplasm and what does it contain?
- cytoplasm is full of macromolecules - small organic molecles, ions, vacuoles, vesicles, carbohydrates, proteins
- interacting molecules (instead of ‘floating’)
- drives reactions due to close interactions
Describe the genome in bacteria (nucleotide)
nucleoid
- double stranded DNA
- main genetic element
- tightly packed into nucleiod
- not membrane bound
- no nucleus
Describe the genome in bacteria (circular)
- supercoiling - another level of coiling on top of helical coiling
- allows chromosome to be compact
- contains essential genes for cell function and survival
What are plasmids?
- small circular ddDNA
- easily transmitted through conjugation using sex pillus
- plasmids confer selective advantage but are not necessary
- if the plasmid contains genes that are extremely useful for survival it may get pushed into its genome chromosome
How does ribosomes work?
associate or dissociate to form ribosome (30s and 50s)
What is significant about the central dogma in bacteria?
- happens in the same place simultaneously
- coupled translation and transcription
- what makes bacteria really excellent at producing proteins
What is the use of polyribosome and how is bacteria so efficient in making protein?
- different RNA polymerases across the strand
- further RNA polymerase = longer strand of mRNA
- as soon as mRNA is produces ribosome attaches
- each ribosome produces proteins (polyribosome)
