Overview of Bacterial cells Flashcards
3 types of surface appendages
- Capsule
- Flagella
- Pili
Extracellular components
Toxins, enzymes, acids etc.
Gram stain: Gram negative
Due to the thin cell wall and outer membrane, crystal violet/iodine complex is washed out during decolourization
Pink dyed stain due to counterstain with safranin
Gram stain: gram positive
Thick cell wall traps crystal violet/iodine complex during decolourization, resulting in a purple stain
Capsule: composition
Slime layer or glycocalyx
Made of carbohydrates
-except for the capsule of Bacillus anthracis which is a polypeptide
Not all bacteria will make them
Capsule: 6 functions
- Mediate adherence
- Constitute biofilm matrix
- Protect from phagocytosis
- Refractory to antibiotics
- Resist drying
- Nutrient reservoir
Flagella
Also called H antigen
Long threadlike proteinaceous structures
3 parts of the flagellum
Basal body, hook, filament
Monotrichous
Single flagellum at one end
Lophotrichous
Cluster of multiple flagella at one end
Amphitrichous
Single or multiple flagella at both ends
Peritichous
covered with flagella
Pili/Fimbriae
Fine hair like structures composed of proteins
Some can be receptors for bacteriophages
Somatic pili role
Mediate adherence and biofilm formation
Sex/F pili role
Mediate conjugation
Cell Wall: function
- Provide rigidity
2. Act as a physical barrier to hazardous agents
Gram pos. cell wall
single, uniform, and thick (15-80 nm) layer of peptidoglycan
-highly crosslinked polymer of NAG and NAM
Gram neg. cell wall
Thin peptidoglycan layer and an outer membrane
-periplasm is the space between the two
Mycobacteria cell wall
Contains a layer of mycolic acids and arabinogalactan in addition to peptidoglycan
*mycobacteria are technically G+
Makes mycobacteria resistant to most conventional antibiotics
Mycoplasma lack ___?
A cell wall
Peptidoglycan composition
Consists of repeating units
of a N-acetylglucosamine (NAG) & a N-acetylmuramic acid (NAM) forming the glycan chains
Chains are cross-linked by short peptides
Teichoic acids and lipoteichoic acids : composition
Unique to gram + bacteria
Linear polymers of glycerol or ribotol with phosphates
TA covalently linked to peptidoglycan
LTA contain FA chains, allowing molecules to anchor to cell membrane
TA and LTA: function
Provide negative charges and hydrophobic sites for adherence
Act as a bacterial surface antigenic determinants
-recognized by immune cells
Lipopolysaccharides (LPS): location
Unique to gram negative bacteria
-on outer leaflet of the outer membrane
also referred to as endotoxin
Lipopolysaccharides (LPS): Composition
has 3 parts
- lipid A
- core plysaccharide
- o-antigen (polysacchatide)
Lipopolysaccharides (LPS): function
Responsible for a broad spectrum of pathophysiological effect such as inflammation and shock
Porins
Located in the outer membrane of gram - bacteria and allow small hydrophilic molecules the enter the cell
-ie. AA and antibiotics
Cytoplasmic inner membrane: composition
Phospholipid bilayer with integral and peripheral proteins
Cytoplasmic inner membrane: functions
- Nutrient uptake
- Ultimate barrier to hostile agents
- Site of electron transport chain
Cytoplasmic contents
DNA, ribosomes, proteins, ions
Inclusion bodies
Endospores
Membrane invaginations (like photosynthetic structures)
Gas vacuoles
Inclusion bodies
Very useful to humans
-can be used in an industrial setting to decompose plastic bags (as an example)
Endospores
harmless until they germinate, endospores are involved in a number of diseases in humans, such as tetanus (lockjaw) and gas gangrene.
5 examples of extracellular products
Toxins, enzymes, acids, solvents, antibiotics
