Component Of A Bacteria Flashcards
What are the components of a bacteria?
Cell wall
Plasma membrane
Cytoplasm
Components external to the cell
One of the most important structures
Layer that is usually fairly rigid that lies outside the plasma
membrane
- Confers shape
- Protects the cell from osmotic lysis
- Anchors the flagellum
- Adds to the pathogenicity of the cell
- Protects the cell from toxic substances and pathogen
- Used in identification
Cell wall
Why is gram positive violet/blue stain while gram negative is red stain?
The peptidoglycan layer enables the differentiation with the gram staining action. In gram positive, the peptidoglycan layer only absorbs the crystal violet stain –giving the violet/bluish color. In gram negative, when the colorizer is applied, because of the very thin peptidoglycan layer, the crystal violet is being washed off. And then, when the counterstain, safranin, which is red in color is applied, it gives off a red stain.
CHARACTERISTICS OF A GRAM POSITIVE (+) CELL WALL
- Thick layer of peptidoglycan
- Presence of Teichoic acid
- Other substances found in cell wall
what are the other substances found in cell wall?
Teichuronic acid
Neutral polysaccharides
Other glycolipids
Mycolic acids
Refers to the major composition of the cell wall.
Peptidoglycan
Peptidoglycan subunit
Peptidoglycan subunit:
1. N-acetylglucoseamine (G)
2. N-acetylmuramic acid (M)
3. L-alanine
4. D-glutamic acid
5. D-alanine
6. Meso-diaminopimelic-acid
the one responsible for the gram positivity of microorganism. Because of its presence in the peptidoglycan layer, it retains the crystal violet stain.
Teichoic acid
Linear polymers of 16-40 phosphodiester-linked
glycerophosphate residues covalently linked to the cell membrane
Lipoteichoic acid (LTA)
These are the
viruses that infects bacteria.
Bacteriophages
Periplasmic space in gram (+) and (-)
(+) plasma membrane and cell wall
(-) plasma membrane and outer membrane
Characteristics of a gram negative (-) cell wall includes thin layer of peptidoglycan and what outer membranes
Lipopolysaccharides (LPS)
Lipoproteins
Porins
Lipopolysaccharides (LPS) contains High toxin.
NOTE: The difference between gram positive and gram negative is:
Gram negative: the LPS would be released after the microorganism is already ______
Gram positive: the LPS is released continuously while the microorganism is_______
(+) alive
(-) already dead
3 parts of LPS
- Lipid A
- Core polysaccharide region
- O-antigen
In E. coli and Salmonella typhimurium: fatty acids are
β-hydroxymyristic acid (3-hydroxytetradecanoic acid)
Composed of 2 glucosamine residues linked β-1,6 (backbone) with four identical fatty acids
Lipid A
Inner core of the polysaccharide region consists of
- 2-keto-3-deoxyoctonate (KDO) 2. Heptose
- Ethanolamine
- Phosphate
− Short polysaccharide extending outward from the core
− Consists of peculiar sugars which varies between bacterial strains
− NOT essential for viability
O-antigen
Importance of Lipopolysaccharides (LPS)
Avoidance of host defenses (O-antigen)
Contributes to the negative charge on the cell’s
surface.
Stabilizes membrane structure
Act as endotoxin
Mediate interconnection between OM and
murein
Synthesized within the cell and contains a
leader sequence of 20 amino acids at its amino
terminal end
After transport through the CM, the leader
sequence is removed and the terminal residue
is modified to make it hydrophobic
Facilitates integration to the OM
Lipoproteins
Small holes in the cell wall
Porins
Importance of outer membrane
Proteins in OM are used as attachment sites
by bacteriophages
Permeability barrier to heavy metals, lipid-
disrupting agents and larger molecules
There are heavy metals that are toxic to the bacteria.
Outer surface with strong negative charge is important in evading phagocytosis
Space between the cell wall and the peptidoglycan layer (aqueous compartment)
Periplasm
Space between the cell wall and the peptidoglycan layer (aqueous compartment)
Periplasm
Activities of periplasm
Redox reactions
For transport of materials
Osmotic regulations
So that limited materials would enter. Otherwise, it would lead to shrinkage or the cell would burst.
Solute transport Protein secretion Hydrolysis
Composition of plasma membrane
- Phospholipid
- Proteins
- Hopanoids
In phospholipid, most membrane associated lipids are
Structurally asymmetric
Parts of phospholipid
Phosphatidylethanolamine
Phosphatidylglycerol
Fatty acids
Major phospholipid in the cytoplasmic membrane
Phosphatidylethanolamine
Phosphatidylethanolamine is formed from
Glycerol-3-P
Serine
Fatty acids
1:1:2
Phosphatidylglycerol, next most prevalent is formed from
Glycerol-3-P
Serine
Ratio is equimolar
Part of phospholipid that varies depending on the species and environmental conditions
Fatty acids
2 types of proteins
A. Integral proteins
B. Peripheral proteins
− embedded in the CM
− Amphipathic
− bound to the fatty acids of the phospholipids via hydrophobic bonding
Integral proteins
− attached to membrane surfaces by ionic
interactions
Peripheral proteins
− Rigid, planar molecules found associated with
bacterial CM
− Molecules similar to sterol
Hopanoids
− Most widely accepted model of the CM
− Shows that the CM is a lipid bilayer with which proteins
and lipids “float” freely
Fluid Mosaic Model
The fatty acid responsible for the fluidity of the cytoplasmic membrane is the
unsaturated acids.
What is the component of the lipid bilayer?
Phosphatidylcholine and phosphatidylethanolamine
Prokaryotic cytoskeleton
Cresentin
FtsZ
MreB
− Invaginations of the plasma membrane in the shape
of vesicles, tubules, or lamellae
− Believed to be involved in:
cell septum formation electron transport
photosynthesis
cell wall formation
DNA replication
Segregation and sporulation
Mesosomes
− Complex structures made of both protein and
ribonucleic acid
− Present in the cytoplasmic matrix or loosely attached
to the plasma membrane
− Site of protein synthesis
Ribosomes
Characteristics of a bacterial chromosomes
- Circular
- Very tightly-coiled
- Histones are absent
Granules and Globules
- Glycogen
- Poly- β - hydroxyalkanoates
- Cyanophycin granules
- Carboxysomes
- Chlorosomes
- Polyphosphate granules
- Sulfur granules
- Gas vesicles
- Magnetosomes
Aids in orienting bacteria in the earth’s magnetic field
Magnetosomes
− Small, hollow, cylindrical structures composed entirely of a single small protein
− Impermeable to water but freely permeable to gases
Gas vesicles
− Used to store sulfur temporarily
− Accumulate in the periplasmic space of in special cytoplasmic globules
− Can be found in sulfur bacteria
Sulfur granules
− Linear polymer of orthophosphates joined by ester bonds
− Functions as storage reservoir for phosphates or as energy reserve
− Can be found in Mycobacterium tuberculosis
or Corynebacterium diphtheriae
Polyphosphate granules
− Ellipsoidal vesicles where photosynthetic pigments are located
− Attached to the plasma
membrane but not continuous with it
− Can be seen in photosynthetic bacterias.
Chlorosomes
− Polyhedral bodies about 100 nm in diameter
− Containing the enzyme ribulose-1-5-
bisphosphate
carboxylase
− May serve as site for CO2
fixation
Carboxysomes
− Composed of large polypeptides containing approximately equal amount equal amount of amino acids arginine and aspartic acid
Cyanophycin granules
− Also: PHB
− Contains β –hydroxybutyrate molecules joined by ester bonds
Poly- β - hydroxyalkanoates
− A polymer of glucose units composed of long chains formed by α(1-4)
− Reservoir of food of bacteria
Glycogen
If it is a photosynthetic bacteria it has
Carboxysomes
Components of the cell wall
Glycocalyx
Pili/Fimbrae
Glycocalyx layers
- Capsule
- Slime layer
Well-organized glycocalyx
Attached firmly to the cell wall Compact
Excludes particles like India Ink
Capsule
Zone of diffused, unorganized material
Loose association
Does not exclude particles
Slime layer
Importance of glycocalyx
Exclude viruses and most hydrophobic toxic substances
Protection from physical injury
Aid attachment to surfaces
Provide resistance to phagocytes
Reservoir of stored food
Prevent desiccation
Confers pathogenicity
“Cellular garbage dump”
Antigenicity
− Hair-like structures on the surfaces of prokaryotic cells
− Composed of protein subunits called “pilins”
Pili/Fimbrae
Types of pili
Adhesion pili
Conjugation pili
Involved in attachment of cells to surfaces
Composed of a single protein
Major determinant of bacterial virulence up to
1000 per cell
IF THE BACTERIA HAS THIS, THE RATE OF INFECTION IS FAST
Adhesion pili
Vehicles for transfer of genetic information
between bacteria
Composed of phosphoglycoprotein
About 1 to 10 per cell
Conjugation pili
− Thread-like locomotor appendages extending outward from the plasma membrane and cell wall
− Slender, rigid structures about 20 nm across and 15-20 μm long
− Rotary structure driven from a motor at the base, with the filament acting as the propeller
Bacterial flagella
The attachment of flagella is deep in the
Plasma membrane
The movement of the flagellated microorganisms are so called the
“tumbling movement”
Filament
A hollow rigid cylinder constructed if a single protein called
Flagellin
Types of flagella
- Monotrichous
- Amphitrichous
- Lophotrichous
- Petrichous
- Atrichous
found inside the cytoplasm [bailey & scott’s 15th ed]
− A type of dormant cell formed by some groups of bacteria − A cryptobiotic
− Highly resistant to environmental stresses
If they encounter a very harsh environment, they would transform themselves into spores. But not all can be turned to spores. It depends on the species and their genes.
− Formed by vegetative cells in response to environmental signals that indicate a limiting factor for vegetative growth
− A mechanism of survival
Bacterial endospore
Location of spores
Terminal spores
Central spores
Subterminal spores
