Cell envelopes Flashcards
What is the envolope and cytoskeleton
- most species of bateria and achea have a cell wall (structural support) and a cell envelope containing at least one structural supporting layer
- The cell envelope = call wall + any associated layers
- few prokaryotes such as mycoplasmas (mollictures) have a cell membrane with no outer layers (no envelope either)
- cytoskeleton = complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including bacteria and archaea. It extends from the cell nucleus to the cell membrane
what is the gram stain based off of
- composition and structure of cell walls
- there are bacteria that do not stain with gram stain
- peptidoglycan is typically what peoplea re talking about when thtey say cell wall
Morphological diversity in bacterial cells: What are tenericutes / Mollicutes
- have DNA genome / nucleoid, ribosomes, cytoplasm and cytoplasmic membrane
- do NOT have: cell wall, exist as polymorphic blobs
* known as naked or soft skin bacteria
* the mollicute Cytoplasmic Membrane is strengthened by addition of unique lipoproteins, glycolipids and glycoproteins
ex: genus Mycoplasma, Mycoplasma pneumoniae, and M. genitalium
pros and cons of mollicute
Pros:
- Small, compact & can squeeze through small spaces
- Does not require a lot of energy to survive
- Opted for metabolic& structural simplicity
- Small size genomes
- Are among the smallest of bacteria
Cons:
- Difficult to maintain an independent lifestyle – are often parasites of eukaryote cells (nutrients, ‘protection’)
- nutreints and protections from other cells, too simple to sustain themselves
- Fastidious in culture –need very special media to sustain
- Amorphous in shape; Shape-less blobs!
Cell walls on bacteria
- composed of peptidoglycan/murein: Polymer of 2 sugars (N-acetyl glucosamine (G/NAG) and N-acetyl-muramic acid (M/NAM)) and amino acids (attached to NAM)
*memorize the sugar names
- forms a rigid porous sac (murein succulus) surrounding the cytoplasmic membrane
- protective, confers shape and helps to withstand turgor pressure (osmotic pressure arising from cytoplasm and against the CM)
what contains the peptido glycan layer
- gram positive and grma negative
- achaea do not have this type of peptidoglycan, they have a pseudopeptidoglycan layer
- the sugars that form it are different but in terms of function and structure it is the same
How is peptifoglycan unqiue to bacteria
- enzymes responsible for the biosynthesis of peptidoglycan are excellent targets for antibiotics
- ex: penicillin inhibits transpeptidase that crosslinks the peptides (link the glycan NAM-NAG chains)
- Vancomycin prevents cross rbidge formation by binding to terminal amino acids (D-ala-D-ala dipeptide)
- PG is a virulence factor - fragments of PG induce fever and inflamation during infection
- lysozime: enzyme in mucus secretion, tears and saliva that diests the bond between the sugars, breaks up the glycan chain. its part of out immune system
describe the basic gram positive cell
components: Nucleoid (DNA), ribosomes, cytoplasm, cytoplasmic/plasma membrane, thick! (multiple layers) 20-80nm cell wall of peptidoglycan
what is streptococcus aureus
- gram positive cell, cocci shape
pros and cons of gram-psotive cell wall
Pros: strong, thick murein succulus, lipoteichoic acids and teichoic acids thread through it adding strength, protect against osmotic lysis, impart shpae to cell
*lipoteichoic acids and teichoic acids: long polysccaride chains unique to gram positive, extend away from surface of cell
Cons: must be protected from Lysozyme (will digest bond between 2 sugars on glycan)
examples of cell shapes of gram positive bacteris
- Bacillus cereus: rad/bacillus shape
- Staphylococcus aurenus: round cells that form clusters
- Steptococcus pyogenes: round cells that form chains
*ake sure you know names to give examples of gram pos bacteria
what are mycobacteria
- taxonomically classified as gram positive but diff cell walls
- strain gram variable bc of structure of cell wall
- stain them suing ziehl-Nielsen acid fast stain
- Mycobacteria have very complex, thick and hydrophobic cell envelopes
- thich peptidoglycan, thick arabinogalactan layer, outer membrane contains unusual membrane lipids, mycolic acids, and thick capsule of lipids and glycolipids
- very thick cell wall
*bolded ones rae components unique to mycobacerial, memorize those
what components are unqiue to the mycobacterial cell wall
-Thick Arabinogalactan* layer and mycolic acids
what are mycobacteria resistant to?
- highly resistant to environmental stress
- dryness, osmitic stress, detergents, most antiseptics, most antibiotics (especially hydrophilic ones), phagocytosis by host efence cells, killing by host immune defenses
cons: must grow slowly, cell envelope is expensive to synthesize and maintian (takes a lot of nutrients and energy to make that intense cell wall)
ex: M. tuberculosis
desribe the basic gram negative cell
- contains: Nucleoid (DNA), ribosomes, cytoplasm, cytoplasmic/plasma membrane,
- THIN (1-3 sheets) of peptidoglycan, outer membrane (contains Lipopolysaccharides LPS), well defined periplasm
*periplasm = compartment between the CM and outer membrane, contains the thin PG
- periplasmic compartment contains lots of proteins
describe the gram-negative cell envelope-
- in addition to the thin peptidoglycan there is a periplasmic component and an outer membrane (bilayer, inside has phospholipids and outer is lipopolysaccharides)
- cell envelope is the outer membrane, its a lipid bilayer (unlike the sytoplasmic membrane)
- the outer leaflet has the G-bacteria unique Lipopolysaccharide
what is LPS
- lipopolysaccharide
- unique to gram negative
- all gram neg bacteria have an outer membrane and LPS which is a complex glycolipid with 3 distinct parts/regions
1. Lipid A endotoxoin, anchors LPS to the outer membrane - toxic when released from lysed cells into tissues/bloodstream (induces a cytokine storm)
2. Core polysachharide
3. O-antigen containing repreating units (2-5 sugars joined to eachother) - antibodies made against this unit, diff bacteria will have diff o-antigens so you can use to differentiate *used for serological typing of gram-neg bacteria
examples of gram negative bacteria
- escherichia coli: rod shpaed
- Neisseria gonorrhoeae: coccoid-shaped
- Helicobacter pylori and Treponema pallidum (syphilis): helical/spiral shaped
what are the different shape determining cytoskeleton patterns?
- FysZ: forms a Z-ring in spherical cells - function: maintains cell diameter
- MreB: forms a coil inside rod-shaped cells - function: MreB together with FtsZ are required for cell shape, growth and division
- CreS crescentin: forms a polymer along the inner side of crescent-shaped bacteria - cell shpae determining (only relevant for bac with crescent shape
what is the Surface layer
- an additive external-most protective layer - (someitmes called bacterial exoskeleton/chainmail) 5-25nm thick
- Crystalline layer of thick subunits, protein or glycoprotein
- highly ordered/crystalline - can flex and has pores to allow movement of molecules, protects against osmotic stress, predation
what are capsules
- added extra to cell
- sometiems called slime later: available for both G+ and G- models
- consist of a slippery coat of polysaccharides loosely bound to the cell envelope, protective layer
*bind water to form a hydration layer
- difficult to stain so appear as halos around cells
- may exist with S-layers: if so they are found external to the S-layer
functions: protection against immune system (resist phagocytosis, antibodies bound can easily be shed with the capsule), adherence, nutrient reserve and protects from dehydration
ex: Streptococcus and Rhizobium trifolii
what are nanotubes
- specialized structure
- hollow and extention of cytoplasmic membrane, share nutrients, excahnge genetic material between cells
- some bacteria and archaea can form membrane extensions that merge directly with the membranes of neighboring organisms
- these nanotubes allow bacteria to directly shpae proteins and mRNA useful under hostile conditions, such as when exposed to anti-biotics
what are storage granules
- during optimal conditions bacteria can store excess energy in form of storage granules
- are consumed later as needed when nutrient availability is low
- usually contain stored glycogen and polyhydroxybutyrate (PHB)
- some baccteria store sulfer granules in cytoplasm or outside as vesicles on membranes (found in some sulfer oxidizing bacteria, use sulfur as an electron source)
what are thylakoids and carboxysomes
- specialized strucutres
Thylakoids
- only found in gram NEG phototrophs
- specialist systems of extensively folded lamellae (sheets) of cytoplasmic membranes
- packed with photosynthetic pigments, proteins and electron carriers
- maximize photosyntheic capability of the cell (help to cov light to chem energy)
- infolding of cytoplasmic membrane, continuous with it
Carboxysomes: in ALL cyanobacteria and some gram negative AUTOTROPHS (bacteria that fix CO2)
- polyhedral shaped bodies packed with the enzyme Rubisco for CO2 fixation
what are pilli and fimbriae
- diff between the two mainly just how thick and long it is
- sex pilli are long structures that transfer DNA, during conjugation/mating from donor to recipient
- pilli can be targets for bacteriophage attachment and infection
- pathogens often use pili/fimbriae to attach/adhere to host cells and initiate disease, these appendages are a great therapeutic/vaccine strategy to prevent infection
*they are assocaited and attached to cell wall
what is rotary flagella
- prokaryotes that are motile gnerally swim by means of a rotary flagella (plural) vs flagellum
- present as singular, multiple or in bundles
- each flagellum is a RIGID spiral filament composed of protein monomers called Flagellin
(present in both G+ and G- bacteria)
- multiple flagella rotate together in a bundle like a propeller behind the swimming cell
how do flagellum enable motility
- filament is rotated by a motor driven by the proton motor force
- flagella work together with chemoreceptors in optimal directions using ‘runs’ and ‘tumbles’
- flagella only move in response to Chemotaxis: chemotactic motility, driven by sensing a chemical that the bacteria either uses or is toxic (moves towards or awar) *moving in response to a signal
- sensing is done my chemoreceptors
Where on the cell is a monotrichous, lophotrichous, amphitricous and peritricheous flagella
monotrichous: only one
lophotrichous: a bundle
amphitrichous: one ither side
Peritrichous: all over cell
describe chemotaxis
- movement of a bacterium in response to chemical gradients
- attractants cause CCW rotation: flagella bundle together and push cell fwds
- repellents (or absence of attractant) case CW rotation: flagellar bundle falls apart, tumble (bacterium briefly stops then changes direction)
* CW or CCW is relative to body of the cell
- OVERALL: appears as a ‘random walk’ alternating between the runs and tumbles
- receptors detects attractant conc gradient (sugars, amino acids), movement towards conc gradient means concentration around it is increasing to the run os prolonged (biased random walk)
*causes a net movement of bacteria towards attractants or away from repellents
what are Chemoreceptors
- bacteria dont have a brain they have a complex network of signal proteins within the cell
- chemoreceptors receive signals and transmit them to the flagellar motor which moves using the proton gradient
