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33 Cards in this Set
- Front
- Back
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Prokaryotic Cytoplasmic membranes are similar to eukaryotic membranes but do not contain _______
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steroids (e.g., cholesterol).
* Mycoplasmas are the exception |
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Functions of the Prokaryotic cytoplasmic membrane include:
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Osmotic or permeability barrier
Energy generating functions eg. respiratory and photosynthetic electron transport systems Location of transport systems for specific solutes (nutrients and ions) Anchoring point for flagella and chemotaxis sensors Location of enzymes needed for synthesis of cell wall peptidoglycan Location of enzymes needed for assembly and secretion of extracytoplasmic proteins Location of enzymes needed for synthesis of membrane lipids (including lipopolysaccharide in Gram-negative cells) Location of specialized enzyme systems Coordination of DNA replication and segregation with septum formation and cell division |
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Which have a thicker cell wall, gram + or gram - ?
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Gram +
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What are the basic steps of the Gram Stain?
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1. Crystal violet
2. Gram's iodine 3. Decolorizer (alcohol or acetone) 4. Safranin Red |
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True/False?
Both Gram-positive and Gram-negative bacteria take up crystal violet (CV) and iodine (I). |
True
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Why do Gram-positive bacteria remain purple after the decolorizing step?
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The crystal violet and iodine complex is trapped inside the thick cell wall of Gram-positive cells
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Why do Gram negative cells appear colorless after the decolorizing step?
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the thin peptidoglycan layer in Gram-negative bacteria does not impede solvent extraction of the Crystal Violet-Iodine complex. The outer membrane is permeabilized by the solvent treatment
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What gives gram-negative bacteria their pink color?
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Safranin counterstain
the purple color of the Gram positive bacteria is not affected. |
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Why is the Gram stain not dependable for old, starved culture or bacteria treated with antibiotics?
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Autolytic wall-degrading enzymes that cause cell wall breakage may account for Gram-negative or variable reactions in cultures of Gram-positive organisms.
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How might a gram positive organism give a gram negative reaction?
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Mechanical disruption of the cell wall of Gram-positive organisms or its enzymatic removal with lysozyme results in complete extraction of the CV-I complex and conversion to a Gram-negative reaction.
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What are some organisms that are an exception to Gram's stain?
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Mycoplasma and Ureoplasma do not have cell wall and therefore cannot be differentiated by Gram stain.
Mycobacteria cannot be classified by Gram stain due to the waxy outer shell preventing the entry of the stain. An acid fast stain is used to identify Mycobacteria. |
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What are the important Unique features in Gram-negative cell wall?
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Peptidoglycan layer in Gram-negative bacteria is thin
Outer membrane (about 7.5 to 10 nm thick) of Gram-negative bacteria is outside the peptidoglycan layer. Lipopolysaccharides (LPS) of the Gram-negative cell envelope form part of the outer leaflet of the outer membrane structure. Periplasmic space is the space between the inner and outer membranes. Gram negative bacteria store degradative enzymes in the periplasmic space |
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What are the important Unique features in Gram-positive cell wall?
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Teichoic acids: Teichoic acids are polyol phosphate polymers (see next slide) bearing a strong negative charge. They are covalently linked to the peptidoglycan in some Gram-positive bacteria. They are strongly antigenic, but are generally absent in Gram-negative bacteria.These highly negatively charged polymers of the bacterial wall are believed to be involved in concentrating metal ions from the surroundings.
Lipoteichoic acids: Teichoic acids attached to fatty acids and anchored in the cytoplasmic membrane. They are antigenic, cytotoxic and can be involved in adherence (e.g., Streptococcus pyogenes). |
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What is the basic structure of Peptidoglycan?
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rigid mesh made up of linear polysaccharide chains cross-linked by peptides
(The polysaccharide is made up of repeating disaccharides of N-acetylglucosamine (NAG) and N-acetylmuramic acid. A tetrapeptide is attached to the muramic acid. This peptide contains both D and L amino acids) |
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Components of the bacterial cell wall are synthesized ______ the cell, then they are transported ______ the cell to be linked together
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inside; outside
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What are the three regions of LPS molecules?
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Lipid A, a structure required for insertion in the outer leaflet of the outer membrane bilayer; consists of a phosphorylated glucosamine disaccharide backbone with fatty acids that anchors the structure in the outer membrane
It is essential for viability of almost all gram negatives* Core a covalently attached complex polysaccharide composed of 2-keto-3deoxyoctanoic acid (KDO), heptose, ethanolamine, N-acetylglucosamine, glucose, and galactose. contains an unusual sugar: ketodeoxyoctanoic acid (KDO), and is phosphorylated Most of the core region is essential for LPS structure and bacterial viability. Nature & arrangement of sugars and amino sugars in the core can vary between different types of bacteria O-antigen polysaccharide chains linked to the core, contains species-specific antigens. O-antigen allows distinguishing of serotypes (strains) of a bacterial species |
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LPS is also called _______
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endotoxin
The name refers to its cell-bound property in contrast to exotoxins which are secreted to the medium or surrounding environment |
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The endotoxic properties of LPS reside largely in what component?
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lipid A component
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LPS transit through inner membrane (IM) involves a _______ mechanism
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“flipping”
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What are bacterial capsules?
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Capsules are structures surrounding the outside of the cell envelope.
(When more defined, they are referred to as a capsule; when less defined as a slime layer or glycocalyx). They usually consist of polysaccharide They are not essential to cell viability |
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Some bacteria with capsules form _______ colonies; without capsules _______ colonies
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smooth; rough
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What are the functions of Capsules of pathogenic bacteria?
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inhibiting ingestion and killing by phagocytes,
protecting bacteria from detergent and complement mediated lysis. Escape from killing by lysosomal enzymes Toxicity to the host Adhesion to host cells Protection of anaerobes from oxygen toxicity |
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Flagella located at both ends are called?
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amphitrichous
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Flagella located all over the outer surface are called?
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peritrichous
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Many Flagella located at one end are called?
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lophotrichous
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A single flagellum located at one end is called?
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monotrichous
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A flagellum consists of three parts:
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long filament: external to the cell surface
- hook structure: at the end of the filament - basal body: to which the hook is anchored & which imparts motion to the flagellum. The basal body traverses the outer wall and membrane structures. It consists of a rod and one or two pairs of discs. |
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bacterial sexual conjugation involves what external structures?
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sex pili
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True/False?
Sporulation does not occur in Gram-negative bacteria |
True
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What are L-Forms?
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stable spheroplasts, grow indefinitely w/o wall, but derived from parents with normal walls.
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What is a spheroplast?
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cell from a gram-positive parent that lacks rigid shape (may be due to lysozyme or penicillin). Still able to survive if isotonic, but will lyse if in hypotonic environment.
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What is a protoplast?
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cell from a gram-negative parent that lacks rigid shape (may be due to lysozyme or penicillin). Still able to survive if isotonic, but will lyse if in hypotonic environment.
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The size of bacteria ranges from?
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0.2 microns to 5 microns
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