Microbiology

• The cytoplasmic membrane surrounds cytoplasm, separates it from the environment, is 8-10 nm wide, and is a phospholipid bilayer with hydrophobic fatty acids pointing inward and hydrophilic glycerol and phosphate pointing outward.
• Some species have layered structures surrounding cytoplasm called hopanoids, which are sterol-like.
• Embedded in the cytoplasmic membrane are proteins, which can be integral or peripheral membrane proteins.
• The cell wall outer membrane consists of two groups: Gram-negative (pink) with peptidoglycan and outer membrane, and Gram-positive (purple) with a thick peptidoglycan layer.
• The cell wall is a permeability barrier, protein anchor, and energy conservation barrier.
• The cell wall outer membrane is a barrier against harmful agents, with porins as transmembrane protein channels for entrance or exit of solutes.
• S-layers consist of a glycoprotein, have a paracrystalline structure, and are always the outermost layer, with functions of molecular sieve, attachment, protection, and in archaea for structural strength.
• Other cell surface structures include a few prokaryotes that lack cell walls, capsules and slime layers, and fimbriae and pili.
• Hamus are Archaeal grappling hooks, used for surface attachment and forming biofilms.
• Transporters are used to transport nutrients into the cell, with active transport accumulating solutes against a concentration gradient and transporters using energy.
• Endospores are survival structures to endure unfavorable growth conditions.
• Cell inclusions contain sulfur globules which are elemental sulfur found in the periplasm, oxidized to sulfate.
• Cell inclusions are enclosed by a thin membrane which reduces osmotic stress.
• Endospores are ideal for dispersal via wind, water or animal gut.
• Endospores only occur when growth ceases due to lack of essential nutrient.
• The core of endospores contains small acid-soluble spore proteins which bind and protect DNA and function as a carbon and energy source for outgrowth.
• Endospores convert a vegetative cell into a nongrowing, heat-resistant, light-reflective structure.
• Cell inclusions function as energy reserves, carbon reservoirs or have special functions.
• Endospores are a dormant stage of the bacterial life cycle.
• Endospores have many layers and are enriched in Ca2+ and dipicolinic acid which bind water and stabilize DNA.
• Endospores can remain dormant for years but convert rapidly back to being vegetative.
• Cell inclusions contain magnetostomes which allow the cell to undergo magnetotaxis and migrate along magnetic field lines.
• Cell inclusions contain polyphosphate granules which are inorganic phosphate and E-/P- storage.
• Cell inclusions contain carbonate minerals.
• Cell inclusions contain gas vesicles which provide buoyancy in planktonic cells, are conical-shaped, gas-filled structures made of protein, and are impermeable to water and solutes, functioning by decreasing cell density and benefiting phototrophic organisms by adjusting cells according to light intensity.
• Endospores are formed during sporulation and are highly differentiated cells resistant to heat, harsh chemicals, and radiation.
• Group translocation is a type of transport where the transported substance is chemically modified, an energy-rich organic compound drives transport, and examples include the phosphotransferase system in E. coli: glucose, fructose, and mannose, with five proteins required and energy derived from phosphoenolpyruvate.
• The ABC system consists of over 200 different systems, has high substrate affinity, uses ATP, and requires transmembrane and ATP-hydrolyzing proteins.
• Binary fission is a type of cell division following enlargement of a cell to twice original size, producing nearly identical cells.
• Micronutrients are nutrients required in minute amounts, such as trace metals and growth factors.
• Microscopic cell count involves observing and enumerating cells, dried on slides or on liquid samples.
• Limitations of microscopic cell count include inability to distinguish between live and dead cells, no precision, and overlooking.
• Batch culture is a closed system microbial culture of fixed volume, and the typical growth curve for a population of cells grown in a closed system is characterized by four phases: Lag phase, Log phase, Stationary phase, and Death phase.
• Turbidimetric measures involve measuring the opalescence of a cell suspension at a specified wavelength, and can be used to determine the number of living cells.
• Flagella and cilia are structures that provide mobility by swimming, with cilia being short flagella that whip instead of rotating or beating in synchrony, and a bundle of nine pairs of microtubules surrounding a central pair of microtubules.
• A septum is a parabon between dividing cells, pinching off between two daughter cells.
• General bacterial growth requirement is a bacterial cell requirement for doubling in number.
• Lysosomes are membrane-enclosed compartments containing digestive enzymes and recycling cell components.
• A viable count is a count of colonies on plates with 30-300 colonies, and is a measurement of living cells.
• All cells require certain elements such as carbon, nitrogen, oxygen, phosphorus, sulfur, potassium, magnesium, calcium, sodium, iron, trace elements, growth factors, and micronutrients.