Microbial Cell Structure Flashcards
Define cell envelope
Plasma membrane and all layers external to it
Define protoplast
The whole cell excluding the cell wall
What is the PM mainly composed of
Bilayer of amphipathic phospholipids
Give 3 roles of membrane proteins
- Structural support
- Secretion of communication signals
- Transportation of ions
What are the two types of membrane proteins and which is more abundant
Integral - 70% - 80%
Peripheral - 20% - 30%
What is the bacterial version of cholesterol
Hopanoids
What is the main difference between archaeal and bacterial PM
Archaea lack fatty acids and instead have isoprene which forms an ether bond with glycerol rather than an ester bond
What is the bacterial cell wall also known as
Sacculus
What is the cell wall made of - 2 names
Peptidoglycan or Murein
Give 3 functions of the cell wall
- Structure and support
- Protection from toxic substances
- Withstand osmotic pressures
What is PDG replaced by in archaea
Pseudomurein
Which two sugars make up PDG, what bond do they form and what shape does it make
NAM and NAG - beta
1-4 glycosidic bond
Helical
What can destroy PDG
Lysosomes
The cell wall in gram +ve bacteria is primarily made of PDG - what colour do they stain - monoderm or diderm
Purple
Monoderm
What does the cell wall of gram +ve bacteria also contain - what are their function (1)
Teichoic acid
Protection from environmental substances
What does the cell wall of gram -ve bacteria consist of
PDG and an outer membrane made of LPS
What colour do gram -ve cells stain - monoderm or diderm
Pink/red
Diderm
Give one function of the LPS in the OM
Stabilises OM structure
How is the OM and PDG linked in gram -ve bacteria
Braun’s lipoproteins
Is the periplasmic space bigger in gram -ve or gram +ve bacteria
gram -ve bacteria
What are the 2 barriers that a solute must cross in gram -ve bacteria and what are the channels called
Outer membrane into the periplasm
Plasma membrane
Porins
Why do the pores in the cell wall of gram +ve bacteria close during staining whereas the cell wall of gram -ve bacteria doesn’t
The PDG is much thicker in gram +ve bacteria
How do extra-cellular vesicles develop - what do they transfer between cells
Membrane buds out, pinches off and is released from the cell
Genetic information
What makes up a gram -ve EV
OM surrounding periplasm
What makes up a gram +ve EV
PM surrounding periplasm
What are the 4 structures outside the cell wall and what are their functions - G(CS)S
Glycocalyx - aid in attachment to solid surfaces
Capsules - Protective advantages
Slime layers - Similar to capsules but easily removed
S-layers - maintain shape and rigidity
What are the three structures that form the cytoskeleton - give 2 bacterial examples
Actin filaments
Microtubules
Intermediate filaments
FtsZ and MreB
What are inclusions aggregated of - what is their function (2)
Organic and inorganic substances
- Segregate cellular components
- Storage of glycogen or carbon
What are microcompartments encapsulated by
selectively permeable protein shell
What are endospores and how are they advantageous (2)
Dormant bacterial cells
Survive heat damage and dessication
What are the 3 processes involved in an endospore becoming a vegetative cell
Activation
Germination
Outgrowth
What are fimbriae and what is their function
Short, thin hair-like projections
Surface attachment and motility
What are pili and what is their function
Long, thick projections
Surface attachment and gene transfer mechanisms (conjugation)
What are the 3 constituents of the flagella - in order
basal body - hook - filament
What are 2 functions of flagella
Attachment and motility
Define chemotaxis
Movement to or from chemical attractants or chemical repellents
What does CW and CCW rotation cause
CW - Tumble
CCW - Forward run
In the presence of an attractant what is the frequency of tumbles and runs
tumbling frequency is reduced and runs in a direction are longer
How is gliding an anomaly - what is it aided by
Requires no appendages - aided by slime secretion
