Prokaryotic Cell Structure and Function Flashcards
Describe the primary function of the cell membrane
permeability barrier between the cellular contents and the extraenous evironment, preventing leakage
Describe secondary function of the cell membrane
transportation of cellular inputs and outputs, such as nutrients, or toxic metabolic products, respectively
Describe tertiary function of the cell membrane
provides a protein achor, for which proteins can capitalise in order to fufill their repsective transportative, bioenergetic and chemotactic functions
Describe a function of cell membranes specific to unicellular organisms
energy conservation, as the site of generation and dissipation of the proton motive force in respiration
Describe the generalities of unicellular cell wall
composed of peptidoglycan (murein)
Describe peptidoglycan
- aka murein
- glycan tetrapeptide composed of repeating amino suagrs of N-acetylglucosamine and N-acetylmuramic acid, L-alanine, L-lysine, D-glutamic acid, diaminopimelic acid (DAP) and D-alanine
- contains a lysozyme-sensitive glycosidic bond
Describe the characteristics of a Gram positive cell wall in bacteria
- much thicker peptidoglycan layer (taking up to 90% of the cell wall’s composition) arranged in cross-linked cables
- variable glycine interbridge between D-alanine and L-lysine
- various protruding acid components
List some of the protruding acid components of Gram positive cell walls in bacteria
- teichoic acid (glycerol or ribitol-phopsphate)
- lipoteichoic acid
Describe the cell wall of Staphylococcus aureus
- Gram-positive
- interbridge is 5 glycine residues long
Describe the characteristics of a Gram-negative bacterial cell wall
- outer membrane
- peptide crosslinker between DAP and D-Alanine
- components are made up of Lipid A , Core polysaccharide and O-specific polysaccharide segments
- as necessitated by the presence of two membranes, there is periplasm space in between
Describe Lipid A
a non-glycerol-lipid saccharide of glucosamine phosphate
Describe Lipopolysachharides
- endotoxins
- result in sicknesses such as diarrhoea
- eg. Lipid A
Describe the periplasm space
- site for enzyme and protein binding
- contains porins
What are porins (in the periplasm space of Gram negative bacterial cell walls)
protein trimers that form solute pores
Describe cell walls of Methanobacterial archaea
- Pseudomurein compound
Describe Psuedomurein
- lysozyme insensitive bond (B1,3; as opposed to B1,4)
- N-Acetyltalosaminuronic acid element
- retains its N-acetylglucosamine component and peptide crosslinkers
- most commonly arranged in S-layer
Describe the polysaccharide capsule
- outside the murein cell wall
- extensive and strongly attached slime layer
- can be perceived under staining with India ink
List the motile elements of bacteria outside of the cell wall
- flagella
- fimbriae
- pilli
What are fimbriae?
very short protein filaments
What is the archaeal equivalent of a pillus?
- the Hami
- microscopic grappling hook, intended for the functional of cell attachment into a biofilm
- for nutrient acquisition in benthic arenas
Describe the bacterial cell membrane
- 6-8nm in diameter
- phospholipid bilayer
- both integral and peripheral membrane proteins that complete a variety of functions
- strengthened by hopanoid, not sterol compounds
Describe the archaeal cell membrane
- can be unilayered as well as bilyarered
- ether, rather than ester bonds, joining the glycerophopshate groups to their fatty acid chains
- contain proteinous elements
Describe the fatty acid chains of archaeal cell membranes
composed of isopropene-derived compounds
Describe the isopropene-derived compounds that make up the fatty acid chains of archaeal cell membranes
- phytanyl
- biphytanyl
- sometimes crenarchaeol, in unilayered membranes
Describe the functions of the pills
- HGT
- transfer attenuated viruses from bacteria to bacteria to aid immunity
Describe storage polymers in bacterial cells
- polyhydroxybutyrate
- polyphosphate
- elemental sulfure storage granules
Describe polyhydroxybutyrate in bacterial cells
- acetyl-coA derived storage polymer
- carbon storage
Describe polyphosphate in bacterial cells
- ATP-derived storage polymer
- phosphorus and energy storage
- can produce ATP on hydrolysis
Describe elemental sulfur storage granules in bacterial cells
found in purple photosynthetic S bacteria
Describe B & C magnetosomes
- cell membrane structure
- found in magnetotactic bacteria
- detect the magnetic pole of the Earth, allowing vertical bacteria migration down to lower oxygen concentrations
How can magnetosomes detect the magnetic pole of the Earth?
Because the contain iron magnetite
Describe gas vacuoles in bacterial cells
- allow bacteria to undergo density adjustments
- allowing vertical migration through water columns
Describe the flagellum
- 4 ring structure, hook and helical fiament
- L ring; P ring; MS ring and the C ring
- can take many structures
Describe the flagella L ring
found within the LPS segment of the cell wall
Describe the flagella P ring
found in the peptidoglycan
Describe the flagella MS ring
in the membrane
Describe the flagella C ring
in the cytoplasm
Describe the flagella structure found in Salmonella and Escherichia coli bacteria
the radial peritrichous
Describe potential flagella forms
- radial peritrichous
- lateral polar
- singular tuft-like lophotrichous
- double tuft-like amphitricous
Describe the primary function of flagella
motility – rotation of the flagellum can result in both bidirectional (reversing) and unidirection (cessation) movement
How is flagella rotation achieved?
Mot proteins receives energy from chemiosmotic proton flow, allowing rotation of the entire basal body
What are the motor proteins referred to as
- Mot
- a stator
Describe flagellum assembly
- must grow outwards from the bacterial cytoplasmic base
- from the MS and C rings, to the Mot proteins, to the P ring, L ring, early hook, Capped late hook, the hook-filament junction and finally the filament itself
- during assembly flagellin can migrate through the core of the flagellum, allowing assembly of the tip and the filament
Describe flagellin
proteinous monomer
Describe the core of the flagellum
hollow
Describe the archaeal flagellum equivalent
- archaellum
- half the width of a bacterial flagellum
- uses ATP to rotate
Describe archaellum assembly
FlI and FlaX external and FlaJ rotary motor proteins, which roatte the filament
Describe the archaellum filament
protrudes from the S-layer membrane
Describe the secondary function of flagella and archaella
- faciliation of chemotaxis
- walking is biased by chemical gradients over time
Describe the method of walking in flagella and archaella
- random in three dimensions
- both running and tumbling
Describe the flagella of Spirochaetes Treponema pallidum and Borrellia burgdorferi
rigid endoflagella inside the flexible outer sheath, in the periplasm space
Describe the structure of endoflagella
attached to one end of the protoplasmic cylinder
Describe the protoplasmic cylinder
generally helical
Describe endoflagella rotation
- directly results in sheath rotation
- corkscrew action
- allows for crossing of bodily mucus membranes
What is the contrivance of endoflagella
crossing of bodily mucus membranes of supreme importance to pathogenic, parasitic bacteria
Describe gliding motility in bacteria and archaea
slime, or pilli-mediated pulling forces
Describe gliding motility in Flavobacterium johnsoniae
- gliding proteins released from the cell surface
- pulling force in antithesis to the cell motion
- requires a proton motive force
Describe swarming behaviours in bacteria
- mediated via the pilli
- when bacteria exist on surfaces
Describe retractile spores in bacteria
- thermo-, osmo- and chemical resilience
- death will only occur at typically 121 degrees Celsius
Describe the structure of bacterial retractile spores
- exosporium outside the spore coat, itself outside of the core wall
- inside of this is the cortex and finally the DNA
Describe the physiology of bacterial retractile spores
- very little water
- internal pH is one unit lower than that of its parent vegetative cell
Why do bacterial retractile spores exhibit slightly acidic pH
- high volume of constituent dipicolonic acid
- small acid soluble spore proteins
Describe the formation of bacterial retractile spores
- during germination of a vegetative cell
- assymetric cell division of vegetative cells post-growth is the commitment to sporulation Stage I
Describe Stage II of bacterial retractile sporulation
- pre-endospore forms within the vegetative mother cell
- cell becomes septated
Describe Stage III of bacterial retractile sporulation
- endospore becomes engulfed
- cell is now sporulating cell
Describe Stage IV of bacterial retractile sporulation
- formation and differentiation of the cortex, cell wall and cytoplasmic membrane
Describe Stage V of bacterial retractile sporulation
- formation of the spore coat
- uptake of calcium ions, SASps and the dipicolinic acid
- gives the spore its lower pH
Describe Stage VI of bacterial retractile sporulation
results in maturation
Describe Stage VII of bacterial retractile sporulation
results in cell lysis, and mature endospore release
