4 - Prokaryotic structure and function 2 Flashcards
What are the proteins contained in the periplasm involved in
- Nutrient acquisition
- Peptidoglycan biosynthesis
- Protein folding
4.Contact dependent stress response systems - Synthesis of pili and flagella
What two sugars make up cell walls (peptidoglycan)
Two alternating disaccharides:
- NAM (N-acetylmuramic acic)
- NAG (N-acetylglucosamine)
Stem peptide
Each glycan dimer is attached to a pentapepide (5 amino acids) this joins peptides
Glycan
Long strands of repeating sugar units
How is the NAG - NAM dimer connected
Beta - (1,4) - glycosidic bonds to form a long polymer
How are peptidoglycan strands linked
Crosslinked to each other by covalent bonds between the stem peptides. Can be direct (gram negative) or indirect (gram positive) using peptide inter bridge
Teichoic acid (+)
A polymer of glycerol or ribitol joined by phosphate groups. Unique to gram positive cell walls and negatively charged. Connected covalently to peptidoglycan and cytoplasmic membrane
Roles of teichoic acid
- Help maintain peptidoglycan structure,
- cell division
- protect against harmful substances (anti biotics)
- major inflammatory mediator
Bacteria outer membrane (-)
Unique to gram negative bacteria. Asymmetric bilayer. Contains Outer Membrane Proteins (OMPs)
Explain the asymmetric bilayer of the outer membrane
- Inner leaflet phospholipids and proteins (Braun’s lipoprotein)
- Outer leaflet 70% glycolipid (Lipopolysaccharides)
- Negatively charged
- Essential for life
- Endotoxin - simplitates immune cells (lipid A portion)
Function of the outer membrane and outer membrane channels
- Connect periplasm to environment
- Porins (form channels)
- Transport of nutrients
- Secretion of proteins
Mycobacterial cell wall
- Gram positive
- Thin layer of peptidoglycan surrounded by mycolic acid layers.
- Waxy, hydrophobic, high lipid content.
- Function: permeability and fluidity. Allows to thrive air water interfaces
How are Mycobacterium stained
Ziehl-Neelsen or Kinyoun’s stain
Archaea plasma membrane
- Composed of branched chain hydrocarbons attached to glycerol by ether links.
- Can be monolayer (C40 tetraether lipid) or bilayer (C20 diether lipid)
Special characteristic of archaea monolayer plasma membrane
More rigid and resist extreme heat
Archaea cell wall
Many different types (no peptidoglycan present). Can stain positive or negative
Gram negative Archaea cell wall stain
1 or 2 S-layers (20-40 nm) above cell membrane
Interlocking protein units
Gram positive Archaea cell wall stain
Made up of Pseudomurein, Not sensitive to penicillin or lysozyme
Bacteria external structures
- Capsules
- Slime Layers
- Sheaths and Prostheca
- Pili / Fimbriae, Flagella
Roles of bacterial ecternal structures
Protection from the environment, Adhesion, Motility
Capsule
Organised matrix firmly anchored to cell
Slime layer
Diffuse, disorganised matrix, easily removed
composition of capsules and slime layers
Polysaccharides (majority) and Poly amino acid
role of capsules and slime layers
- Resist phagocytosis, 2.Protection from desiccation,
- Adherence,
- Gliding motility (slime layer)
Sheaths
Stiff polysaccharide tube containing cells.
Function: Attach to solid surfaces
Protection from protozoan predators
Sieve for acquiring nutrients
Prosthecae
Extensions containing cell wall and plasma membrane.
Function: Attach to solid surfaces
Pili/Fimbriae
Short, fine, hair-like appendages, Hollow brittle tube
Consisting of multiple pilin subunits organised as a helix
how are types of pili defined
Types I-IV defined by Length, Diameter of the fibre and Location on the cell (Polar, Peritrichous, Single, multiple)
Function of pili/fimbriae
- Adherence
- Twitching motility
- Gliding motility
Sex pillus
Larger than other pili, transfer of DNA from host to recipient. Conferred by a conjugative plasmid (not encoded on host nucleoid)
Role of sex pillus
Exchange of genetic content, spread of antibiotic resistance on R plasmids
Flagella
Longer hair like appendage consisting of a hollow filament composed of flagellin protein, hook, basal body. Basal motor structure drives rotation of flagellum (act as propeller)
Role of flagella
Swimming in aqueous environments and seeking nutrients (chemotaxis)
What is chemotaxis (Tumbling)
The movement of cells or organisms in response to chemical gradients in their environment.
Positive chemotaxis
Movement towards a higher concentration (attractant)
Negative chemotaxis
Movement towards decreasing concentration (repellent)
Name two alternate cell structures
Endospores and Conidiospores
Endospores
Produced by a small number of bacteria (eg Bacillus), can be terminal (end), subterminal (just before end) or central (middle)
Characteristics of endospores
Dormant, resist extreme conditions which would kill the vegetative cell (eg. starvation, heat, salt) and core contains dipicolinic acid
Sporulation
Occurs in response to limited carbon, nitrogen, phosphorus. Endospore germination occurs in favourable conditions to become vegetative cell
What are the steps of sporulation
- Asymmetrical cell division
- Engulfment of forespore
- Cortex and coat synthesis
- Endospore maturation, 5. Sporangium lysis
Conidiospores
Produced by Streptomyces in response to nutrient starvation. Thin wall spores at the end of filaments. Resistant to desiccation but not heat.
Periplasm
Located: Gram -tve
Space between the Outer membrane and the Inner membrane
What are Sheaths made from
Ferric or Manganic Oxides
Attachment locations of Flagella
Polar- protruding from one end
Peritrichous - protruding from uniform points across the bacterial surface
Mono- or multiple
Axial filaments
- Specialised flagella that are trapped inside the periplasm of gram negative cell walls
- Arranged in a helical shape
Axial filaments Function
Function for locomotion
– Corkscrew through liquid
– Crawl on surfaces
Endospore Structure
Ribosomes
DNA
Core wall
Cortex
Spore coat
Exosporium
Compare the archaeal cell wall to Gram positive and Gram negative
bacterial call walls.
Describe the features of the cell wall of Mycobacteria and explain why this
organism is Gram positive.
Compare the structure and functions of pili and flagella.
What are capsules and slime layers and what functions do they perform?
Describe endospore formation. What are the characteristics of endospores?
Compare a Gram negative cell wall to Mycobacterial cell walls.
List four features of an endospore and describe the sporulation cycle of
endospores using a diagram.
