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Oct 30, 2023

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KEY TERMS ● Capsule : a distinct, thick gelatinous material that surrounds some microorganisms; helps protect the cell or allows it to attach to certain surfaces ○ Bacterial cells often have capsule; archaeal cells rarely do ● Cell Envelope: surface layers of a prokaryotic cell; cytoplasmic membrane, the cell wall, capsule (outer membrane) ● Chemotaxis : movement of a cell toward or away from a certain chemical in the environment ● Cytoplasm : thick substance filled with nutrients, ribosomes, & enzymes; encloses the cell envelope; fluid portion of the cytoplasm is cytosol ○ Nucleoid is the gel-like region in cytoplasm where cell’s chromosome is found ● Cytoplasmic membrane : a thin, delicate phospholipid bilayer embedded with proteins that surrounds the cytoplasm & defines the boundary of the cell ○ Serves as the crucial permeability barrier b/w the cell & its external environment ● Endospore : an extraordinarily resistant dormant cell produced by some types of bacteria ○ Dormant cell that is resistant to heat, desiccation, ultraviolet light, toxic chemicals ● Flagellum : a type of structure used for cell movement ● Gram-Negative Bacteria : cell wall characterized by a thin layer of peptidoglycan surrounded by an outer membrane; stained pink ● Gram-Positive Bacteria : cell wall characterized by a thick layer of peptidoglycan; these cells are stained purple ● Lipopolysaccharide (LPS) : molecule that makes up the outer layer of the outer membrane of Gram-negative bacteria ● Peptidoglycan : a macromolecule that provides strength to the cell wall; it is found only in bacteria ● Periplasm : the gel-like material that fills the region between the cytoplasmic membrane and the outer membrane of Gram-negative bacteria and the cytoplasmic membrane and peptidoglycan layer ot at least some Gram-positive bacteria ● Pili : cell surface structures that allow cells to adhere to certain material; some types are involved in a mechanism of DNA transfer ● Plasmid : extrachromosomal DNA molecule that replicates independently of the chromosome ● Ribosome : structure involved in protein synthesis ● Transport systems : mechanisms cells use to transport nutrients and other small molecules across the cytoplasmic membrane *IMPORTANT * ★ Eukaryotic cells are much more complex than prokaryotic cells. Not only are they larger, but many of their cellular processes take place within membrane-bound compartments. Eukaryotic cells are defined by the presence of the NUCLEUS . ★ Archaeal cytoplasmic membranes have the same general structure as bacterial membranes, but are CHEMICALLY distinct. (ie: hydrophobic tails of archaeal membrane phospholipids are not fatty acids, they are connected to glycerol component of hydrophilic head by different type of chemical linkage) 3.0 Prokaryotic Cell Structures & their Functions I. Prokaryotic Cell: surface layers is the cell envelope → cytoplasmic membrane, cell

wall, & capsule 3.1 The Cytoplasmic Membrane of Prokaryotic Cells I. Cytoplasmic membrane : thin delicate structure that surround cytoplasm & defines boundary of cell A. Role : serves as a permeability barrier b/w cell & external environment 1. Selectively permeable: can cross freely → O 2 , CO 2 , N 2 ; small hydrophobic compounds; water 2. Aquaporins: channels that increase/decrease in osmotic shock 3. Converting the energy of food or sunlight into ATP 4. Electron transport chain (ETC); series of protein complexes within the membrane, that generates an electrochemical gradient & moves protons OUT of the cell; a form of energy called proton motive force B. Structure : Phospholipid bilayer embedded with a variety of different proteins 1. Hydrophobic tails face in , toward the other layer; hydrophilic heads face outward , interacting freely w/aqueous solutions 2. Fluid Mosaic model: dynamic nature C. Functions : 1. Transport/Secretion of small molecules across cytoplasmic membrane: a) Facilitated diffusion moves compounds by exploiting a concentration gradient (1) Passive; energy is NOT required (floating downstream in a river) (2) Not commonly used by prokaryotes; can eliminate a gradient, not create one b) Active transport : energy in the form of a proton motive force or ATP is used to move molecules against a concentration gradient (1) Used by prokaryotes c) Group translocation chemically modifies a molecule during its transport (1) A phosphate group is added to a sugar 2. Energy transformations = ETC of photosynthesis & cellular respiration 3. Receptors for signal transduction 4. Cell division D. Permeability : few compounds pass through phospholipid bilayer by simple diffusion ; molecules move from a region of high concentration to one of low until equilibrium is reached 1. Osmosis : diffusion of water across a selectively permeable membrane; occurs when concentrations of solute (dissolved substances) on two sides of a membrane

are unequal a) Hypotonic (less solute) → water flows from hypotonic solution to hypertonic b) Hypertonic (more solute) c) Isotonic (same) Summary: The cytoplasmic membrane is a phospholipid bilayer embedded with proteins. Molecules that pass through the bilayer move in and out by simple diffusion; osmosis is the diffusion of water across the membrane. The electron transport chain generates a proton motive Force, which is used to drive several cellular processes, including ATP synthesis, certain Transport Systems, and some types of motility. Transport Systems move molecules across the membrane using facilitated diffusion, active transport, or group translocation. Proteins destined for secretion have a characteristic signal sequence. 3.2 The Cell Wall of Prokaryotic Cells I. Gram-Positive Cell Wall A. Contains thick layer of peptidoglycan (provides rigidity; composed of glycan strands connected via tetrapeptide chains) B. Teichoic acids project out of the peptidoglycan C. P eriplasm is b/w the cytoplasmic membrane and the peptidoglycan layer II. Gram-Negative Cell Wall A. THIN layer of peptidoglycan B. Outer membrane contains lipopolysaccharides 1. LPS = endotoxin C. Porins permit small molecules to pass through the outer membrane; found in OM D. Periplasm fills the space b/w the inner and outer membranes III. Antibacterial substances that target peptidoglycan A. Penicillin (antibiotic) interferes with peptidoglycan synthesis 1. Inhibits enzymes that normally catalyze the cross-linking of the peptidoglycan sub- units 2. More effective against Gram (+) 3. Not effective against nongrowing cells B. Lysozyme destroys the structural integrity of peptidoglycan; 1. Breaks covalent bond b/w NAMs & NAGs 2. Most effective against Gram (+); can’t cross OM IV. Bacteria that lack a cell wall A. Mycoplasma species are variable in shape and not affected by lysozyme or penicillin V. Cell walls of Archaea A. Archaea have a greater variety of cell wall types than do bacteria, & they all lack peptidoglycan Summary : Peptidoglycan is a molecule unique to bacteria that provides strength to the cell wall. The gram-positive cell wall is composed of a relatively thick layer of peptidoglycan as well as teichoic acids. Gram-negative cell walls have a thin layer of peptidoglycan and a lipopolysaccharide-containing outer membrane. Penicillin and lysozyme interfere with the structural Integrity of peptidoglycan. Mycoplasma species lack a cell wall. Archaea have a variety of cell wall types.

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