Microbiology

Microbiology Study Guide

o o Cell wall: The semi-rigid cell wall maintains the characteristic shape of the prokaryotic cell and prevents the cell from bursting when fluids flow into the cell. Its single most important component is peptidoglycan.  Other components include the outer membrane and the periplasmic space. Certain properties of cell walls result in different staining reactions. On the basis of these reactions, you can distinguish between gram-positive, gram-negative, and acid-fast bacteria. Gram-positive bacteria have a thick peptidoglycan layer and teichoic acid polymers. Gram-negative bacteria have a thin peptidoglycan layer and an outer bilayer membrane with endotoxins. The cell membrane, otherwise known as the plasma membrane, is a living membrane that forms the boundary between a cell and its environment. It is selectively permeable and is made up of seven lipid proteins. The internal structure found in bacterial cells includes: • Ribosomes: Serve as sites for protein synthesis • Nuclear region or nucleoid: Consists mainly of DNA (usually contains a single, long, continuous, and frequently circularly arranged thread of double stranded DNA called the bacterial chromosome); has some RNA and protein associated with it (plasmids- extrachromosomal genetic elements that are not connected to the main bacterial chromosome and replicate independently of chromosomal DNA) • Internal membrane systems: Sometimes known as chromatophores or mesosomes • Inclusions: Small bodies in the cytoplasm • Endospores: Help the organism survive The external structure includes: • Flagella: Help bacteria to move in processes like chemotaxis or phototaxis • Axial filaments: Cause rigid spirochetes to rotate like a corkscrew • Pili: Used to attach bacteria to surfaces • Glycocalyx substances: Include capsules and slime layers The bacterial endospore is a special, resistant, dormant structure formed by some bacteria, which enables them to resist harsh environmental conditions. Endospore formation (sporulation) normally commences when growth ceases because of lack of nutrients; it is a complex, multistage process. Transformation of dormant endospores into active vegetative cells is also a complex, multistage process that includes activation (preparation) of the endospore, germination (breaking of the endospore’s dormant state), and outgrowth (emergence of the new vegetative cell). Cyanobacteria Cyanobacteria are the aquatic, gram-negative oxygenic phototrophic bacteria in which the Variety of external structures

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