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Cell Structure and Function

Cell Structure and Function - Cell Structure and Function...

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Cell Structure and Function Processes of life Growth (size and number) Reproduction Responsiveness (positive or negative response to stimuli) Metabolism (Catabolism=break down and Anabolism=build up) Prokaryotes Do not have membrane surrounding their DNA; no nucleus Lack various internal structures bound with phospholipid membranes Small; ~1.0 µm in diameter Simple structure Comprised of bacteria and archaea Eukaryotes Have membrane surrounding DNA; have nucleus Have internal membrane-bound organelles ( Compartmentalization ) Are larger; 10-100 µm in diameter Have more complex structure Comprised of algae, protozoa, fungi, animals, and plants Prokaryotes vs Eukaryotes
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External structures of prokaryotes Glycocalyces (Mostly external) Flagella Fimbriae and pili Glycocalyces Gelatinous, sticky substance surrounding the outside of the cell Composed of polysaccharides, polypeptides, or both Two types o Capsule o Slime layer Capsule Composed of organized repeating units of organic chemicals Firmly attached to cell surface Protects cells from drying out May prevent bacteria from being recognized and destroyed by host
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Example of capsule Slime layer Loosely attached to cell surface Water soluble Protects cells from drying out Sticky layer that allows prokaryotes to attach to surfaces Example of slime layer Flagella Are responsible for movement
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Have long structures that extend beyond cell surface Not all prokaryotes have flagella Bacteria flagella Composed of filament, hook, and basal body Flagellin protein (filament) is deposited in a helix at the lengthening tip Base of filament inserts into hook Basal body anchors filament and hook to cell wall by a rod and a series of either two or four rings of integral proteins Filament capable of rotating 360º Bacterial flagella (Anti clockwise rotation - Gram Positive) Bacterial flagella (Gram Negative - Presence of two different membranes)
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Arrangements Function of bacteria flagella Rotation propels bacterium through environment Rotation can be clockwise or counterclockwise; reversible Bacteria move in response to stimuli (taxis) o Runs – movements of cell in single direction for some time due to counterclockwise flagellar rotation; increase with favorable stimuli (positive chemotaxis, positive phototaxis) o Tumbles – abrupt, random, changes in direction due to clockwise flagellar rotation; increase with unfavorable stimuli (negative chemotaxis, negative phototaxis Fimbriae and pili Nonmotile extensions Fimbriae
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o Sticky, proteinaceous, bristlelike projections o Used by bacteria to adhere to one another, to hosts, and to substances in environment o May be hundreds per cell and are shorter than flagella o Serve an important function in biofilms Fimbriae vs flagella Pili Long hollow tubules composed of pilin Longer than fimbriae but shorter than flagella Bacteria typically only have one or two per cell Join two bacterial cells and mediate the transfer of DNA from one cell to another (conjugation) Also known as conjugation pili or sex pili Pili vs fimbriae
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