Chapter 2 Microbial Cell Structure and Function Flashcards
Permeability barrier
prevents leakage and functions as a gateway for transport of nutrients into, and wastes out of the cell
Protein anchor
site of many proteins that participate in transport, bioenergies, and chemotaxis
Energy conservation
site of generation and dissipation of the proton motive force
Selective permeability
only small nonpolar and uncharged molecules can cross the membrane (H2O, O2, N2)
Ions
molecules or atoms with a charge (H+, K+, Na+, NO3-)
Glycerol-phosphate head group
made up of a glycerol backbone, a head group, and two fatty acid chains
Saturated fatty acid ______ membrane fluidity
decrease
Unsaturated fatty acid ______ membrane fluidity
increase
- double bond
cis bonds: greater fluidity
trans bonds: less fluidity
Bacterial membrane structure (5)
- Fatty acid is connected to head group with an ESTER bond (Bacteria and Eukarya)
- Composed of a phospholipid bilayer
- Phospholipid have a hydrophilic head group with a glycerol phosphate backbone
- Phospholipid properties vary for different side chains and fatty chains
Archaea membrane structure (4)
- Archaea have ETHER linked phospholipids
- Archaeal lipids are composed of isoprene units (methyl, double bond, dimethyl)
- Archaea have both glycerol diethers and tetra ethers
- Archea can have lipid monolayers, bilayers, or mixture
At high temperature, which lipid structure would provide the MOST stability to a cytoplasmic membrane?
A. diether phytanyl lipids
B. tetraether phytanyl lipids
C. Diester fatty acid lipids with lots of cis-bonds
C. Diester fatty acid lipids with lots of trans-bonds
E. Tetraether fatty acid lipids
B
Integral membrane proteins
embedded in membrane
Peripheral membrane proteins
one part anchored in the membrane
Passive transport
transport by diffusion across membrane or through integral membrane proteins
- can be with one solute or two solutes in opposite directions
Uniporters
- Intergral membrane proteins
- transport one type of molecule in one direction down its concentration gradient
Antiporters
- Intergral membrane proteins
- transport two types of molecules in opposite directions, one of them going down a concentration gradient
Symporters
- Intergral membrane proteins
- transport two types of molecules in same direction, one of them going down a concentration gradient
Active Transport
transport that uses energy (e.g ATP or PMF)
Simple transport
- driven by the energy in the proton motive force
- Ex: Lac permease of E.coli (lactose is transported into E.coli by a specialized symporter called lac permease; activity is driven by PMF)
Group translocation
Chemical modification of the transported substance driven by phosphoenolpyruvate
Phosphotransferase system
- type of group translocation
- the substance is chemically modified during transport
- used to transport glucose, fructose, and mannose
- energy derived from phosphate bond in phosphoenolpyruvate
ABC Transporter (ATP binding cassette)
- > 200 different systems
- High substrate specificity
- Three parts: periplamic binding protein, membrane spanning transporter, ATP hydrolyzing protein
Osmosis creates _______ pressure against the cytoplasmic membrane, filling the cell like a water balloon
turgor
The cell wall resists ______ pressure and prevents the cell from ____________
turgor
bursting
Peptidoglycan
A rigid layer, provides cell shape and strength, permeable. unique to BACTERIA, not found in Archaea or Eukarya
Polysaccharide backbone containing N-acetyglucosamine and N-acetylmuramic acid
Has peptide side chains
Has covalent crosslinks between DAP and D-ala or L-lys and D-ala
Transpeptidation (transpeptidase)
adds crosslinks
-peptide interbridge in gram positives
-direct crosslinks in gram negatives
Autolysins
Cut the beta1,4 bonds of polysaccharide backbone so that new polysaccharide can be added
Transpeptidase
adds new peptide crosslinks
Antimicrobials that target the cell wall (2)
Lysozyme
Beta-lactam antibiotics
Lysozyme
an enzyme that cleaves beta1,4 bonds of peptidoglycan backbone
Beta-lactam antibiotics
bind to and inhibits transpeptidase (e.g Penicillin)
Gram stain procedure
- Flood the heat fixed smear with crystal violet for 1 min; Result: All cells purple
- Add iodine solution for 1 min; Result: All cells remain purple
- Decolorize with alcohol briefly - about 20 sec; Result: Gram positive cells are purple; Gram negative cells are colorless
- Counterstain with safranin for 1-2 min; Result: Gram positive cells are purple; Gram negative cells are pink to red
Gram positive cell envelope
- up to 90% peptidoglycan
- often have teichoic acids and lipoteichoic acids (i.e teichoic acids covalently bound to lipids)
These molecules increase cell wall stability - peptidoglycan, cytoplasmic membrane
Which of the following conditions might allow bacteria to survive treatment with Penicillin?
They lack peptidoglycan in their cell walls
Where would you expect to find a porin?
the outer membrane
Gram negative cell envelope
- peptidoglycan, cytoplasmic membrane, outer membrane
- ~10% peptidoglycan
- outer membrane (aka LPS layer) makes up most of the Gram negative cell envelope
-periplasm
Periplasm
the space between cytoplasmic and outer membranes
- many proteins localized in periplasm
What explains the resistance of Gram negative bacteria to many beta-lactam antibiotics (eg penicillin)?
The antibiotic cannot diffuse across the outer membrane
Composition of the outer membrane (4)
- phospholipids
- contains lipopolysaccharides (LPS)
- contains porins
- contains proteins
Lipopolysaccharides (LPS)
a lipid on the outside of OM; Has three parts
- O-polysaccharide
- core polysaccharide
- Lipid A
Provokes a strong immune response in humans
Lipid A acts as an ‘endotoxin’ for some pathogens
Porins
channels for passive diffusion of hydrophilic low-molecular weight substances through outer membrane (e.g sugars, ions, amino acids)
different types porins have different selectivity
How might you modify the chemical structure of a beta-lactam antibiotic if you wanted to inhibit the growth the Gram negative bacteria?
Modify it so that it can pass through porins
S-layers
a tough paracrystalline structure, composed of protein or glycoprotein
- Extra layer found in some bacteria or archaea
- If present, it usually porous like peptidoglycan
- Presence is often conditional, depending on conditions
- The function of s-layers remains poorly defined
Archaeal Cell Envelopes
** Archaea do not have true peptidoglycan!!!
- Some archaea have pseudomurien instead
- Archaea typically lack an outer membrane
- Many archaea have an S-layer as cell wall
Pseudomurien
a polysaccraide similar to peptidoglycan BUT
- lacks D-amino acids
- has B1,3 bond between sugars instead of beta1,4 bond
- has N-acetyltalosaminuronic acid instead of N-acetylmuramic acid
Storage polymers
store energy and/or nutrients
Poly-beta-hydroxyalkanoate (PHA)
polyester, C and energy storage
Glycogen
glucose polymer, C and energy storage
Polyphosphates
phosphate and energy storage
Sulfur granules
energy storage for certain sulfur bacteria
Vacuoles
for gas or storing small molecules
Gas vacuoles
protein shell, filled with gas to provide buoyancy
Storage vacuoles
membrane bound storage compartment
Carbonate minerals
calcite inclusions
Magnetosomes
magnetic inclusions
Functional Structures
complex macromolecules and organelle-like structures
Ribosome
site of protein synthesis in all cells
Carboxysome
protein shell, contains enzymes for CO2 fixation in some bacteria
Anammoxosome
membrane bound compartment, contains enzymes for anaerobic ammonia oxidation in some bacteria
Survival Structures
Endospores
Endospores
Form when vegetative cell differentiates into a mother cell and an endospore
Dormant cells, ideal for survival and dispersal
-Highly resistant to heat, drying, harsh chemical and radiation
- Have dipicolinic acid, a unique molecule which promotes desiccation
- Germinate into a vegetative cell when conditions favor growth
- Found in the families Bacillales and clostrimiales of the phylum Furmicutes
Other survival structures - NOT endospores
- Myxospores of myxobacteria
- Arthrospores of streptomycetes
- Formed in a fruiting body
- NOT resistant to high heat, lack dipicolinic acid
Cysts
A survival structure formed when one cell changes physiologically to become dormant (does not require cell division)
- NOT resistant to high heat, not a spore
External Cell Structure
Glycocalyx
Fimbriae
Pili
Flagella
Glycocalyx
Capsules and slime layers
- external polysaccharide layers
- provide protection and attachment (Biofilms)
Capsules are ______ attached
Slime layer are _______ attached
tightly
loosely
Fimbriae
Short filamentous protein structures
- can attach to objects
Pili
Long straight filamentous protein structures, some can extend and contract
- can attach to object
- conjugate pili mediate “conjugation”
- Type IV pili mediate twitching motility
Flagella
Long helical protein structure that can rotate
- enables swimming motility
Petritichous, polar, lophotrichous
Flagella of Bacteria
Helical protein filament used for swimming motility
- Flagellin protein
- Uses proton motive force to rotate
- hollow and large (15-25nm)
-assembles at its tip
Flagella of Archaea
Helical protein filament used for swimming motility
- Archaelillin protein
- Uses ATP to rotate
- not hollow and smaller (10-13nm)
- assembles at its base
Eukaryal flagella
unrelated and dissimilar from flagella and archaella
- Eukaryal flagella are organelles NOT protein filaments
- These organelles are membrane bound and contain cytoskeleton
- very large and flexible, employ whiplike (NOT rotary) motion
- ATP hydrolysis powers contraction of the cytoskeleton
Swimming motility
Describes flagellar/dependent motility
-Flagella can be either reversible or unidirectional
- some cells can be very fast (60-120um fro e.coli)
Taxis
directed movement in response to chemical or physical gradients
Chemotaxis
response to chemicals
Phototaxis
response to light
Aerotaxis
response to oxygen
Osmotaxis
response to ionic strength
Hydrotaxis
response to water
Chemoreceptors
detect signals in concentration over time
Biased random walk
the operational principle for chemotaxis
- No attractant present: random movement
- Attractant present: biased movement
Twitching motility
- requires surface attachment by type IV pili
- ATP dependent pilus retraction
- very slow
Gliding motility
- requires surface attachment
- uses proton motive force for energy
- attachment protein is driven along a helical track found in the cell envelope
Spirochete motility
- Endoflagelellum (rigid, rotates, attached to one end of protoplasmic cylinder
- Outer sheath (flexible)
- Protoplasmic cylinder (ridgid, generally helical)
Magnetotaxis
- a specialized form of aerotaxis (sensing O2)
- magnetosomes are used to orient the cells to earth’s magnetic field lines thereby reducing a three dimensional biased random walk to a one dimensional biased random walk
- magnet does not pull cells!!! just turns them so they have their own compass to tell the which way to swim, up or down
