Structure And Function In Bacteria Flashcards
What is meant by the term cell envelope?
Plasma membrane plus all surrounding external layers
Cell wall and glycocalyx for example
Name the parts of a prokaryotic cell
Glycocalyx Chromosome or nucleoid Plasmid Plus Ribosomes Actin cytoskeleton Flagellum Fimbriae Granule Cell wall Cell membrane Outer membrane Endospore Cytoplasm
What is the purposes of the cell wall?
Provides shape Rigidity Protects from osmotic forces Cell wall to cell wall attachment Eluding antimicrobials
What year was gram staining discovered?
1884
What colours do gram positive and gram negative bacteria stain?
Purple and pink respectively
What are cell walls composed of?
Composed of peptidoglycan (murein)
Peptidoglycan is a huge polymer consisting of interlocking chains of identical monomers
Backbone of peptidoglycan molecule is composed of 2 derivatives of glucos - N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) which are connected by interpeptide bridges
How do gram positive and negative cells differ in wall structure?
Gram positive walls are composed of 90% peptidoglycan and they may contain teichoic acid
Gram negative walls only have around 5-20% of walls made from peptidoglycan
Name three types of teichoic acid
GTA - glycerol TA
RTA - ribitol TA
LTA - Lipo TA
What roles does teichoic acid play?
Provides cell wall structure
Attachment to surfaces by increasing negative charges
Stimulates immunological response
Protects from harmful agents (antibiotics, host defences)
What is the best stain to use formycobacterium and norcardia and why?
Stain gram positive poorly and so acid fast stain is used as 60% of cell wall bulk made up of lipids (fatty acids)
What are mycoplasma?
Tiny bacteria that lack cell walls, some cause respiratory infections
What are glycocalyx?
Gelatinous sticky substance surrounding cell wall
Composed of - polysaccharides, proteins or both
Internally produced and extruded into cell surface, termed either capsule (rigid) or slime layer (loose)
What is the function of glycocalyx?
To attach to surfaces (teeth, biofilm)
Defence mechanism against ingestion by immune cells
Resistance to drying (contains large amounts of water)
Reservoir of nutrients
Reservoir of waste deposits
Prevents ingress of viruses
What is an endospore?
A dormant structure formed when bacterium face hostile environments, allows genetic material to be stored until environment becomes habitable
Resistance to - chemicals, high temperatures, radiation, disinfectants, desiccation (extreme dryness)
What are the four positions of spores within a cell?
Central, subterminal, terminal and terminal with swollen sporangium
What are the structural parts of an endospore?
Exosporium - thin delicate covering
Spore coat - one or more layers of protein
Cortex - peptidoglycan
Spore cell wall
Core - contains cytoplasm, ribosomes and nucleoid (inactive)
Why are spores resistant?
Calcium-dipicolinic acid complex in core possibly for the stabilisation of nucleic acids
DNA binding proteins (small acid soluble proteins SASP’s)
Dehydration of Protoplast - osmotic removal of water by cortex
Spore coat protects against enzymes and chemicals
DNA repair enzymes
Multiple mechanisms
Why and how does an endospore form?
Starts when growth halts (lack of nutrients)
Filament of nuclear material forms
Part of the cell membrane folds in to enclose part of the DNA - forms forespore septum
The forespore (immature spore) is engulfed in a second membrane
Layers of spore form
Lytic enzymes lyse the sporangium
How is a spore transformed into a cell again?
Activation - usually results from heating
Germination - spore swells, ruptures or absorbs the spore coat, loses resistance, spore components released and metabolism increases
Outgrowth - Protoplast makes new components and emerges from remains of spore, develops into vegetative bacterial cell
