intro to cells and procaryotic cell structure and function

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characteristics of cells and life procaryotics profiles: the bacteria and archaea bacterial external structures bacterial internal structures bacterial shapes, sizes, and arrangements

eucaryotic cells

animals, plants, fungi, and protists
-contain double-membrane bound nucleus with DNA chromosomes
-contain membrane-bound organelles that compartmentalize the cytoplasm and perform specific functions

procaryotic cells

bacteria and archaea
-no nucleus or other membrane-bound organelles

characteristics of life

-growth and development
-reproduction and heredity - genome composed of DNA packed in chromosomes, produce offspring sexually or asexualy
-metabolism - chemical and physical life process
-movement and/or irritability - respond to internal and external stimuli; self-propulsion of many organisms
-cell support, protection, and storage mechanisms (cell walls, vaccuoles, granules, and inclusions
-transport of nutrients and waste

procaryotic structures

external:
-appendages (flagells, pili, fimbriae)
-glycocalyx (capsule, slime layer)
cell envelope:
-cell wall
-cell membrane
internal:
-cytoplasmic matrix
-ribosomes
-inclusions
-nucleiod/chromosomes
-actin cytoskeleton
-endospore

appendages

cell extensions - two major groups of appendages:
-motility - flagella and axial filaments (periplasmic flagells)
-attachments or channels - fimbriae and pili

glycocalyx

surface coating

flagella

3 parts:
-filament: long, thin, helical struture composed of protein flagellin
-hook: curved sheath
-basal body: stack of rings firmly anchored in cell wall
rotates 360 degree
number and arrangement varies:
-monotrichous (single flagellum)
-lophotrichous (small bunches or tufts of flagells in the same site)
-amphitrichous (flagella at both poles of cell)
-peritrichous (flagella are dispersed randomly)

flagella function

guide bacteria in a direction in response to external stimulus:
chemotaxis : chemical stimuli, positive and negative (response to chemical signal)
phototaxis: light stimuli (response to light)
signal sets flagells into rotary motion clockwise or counterclockwise

axial filament

-periplasmic, internal flagella, enclosed between cell wall and cell membrane of spirochetes (corkscrew-shaped bacteria, e.g. borrelia burgdoferi)
-produce cellular motility by contracting and imparting twisting or flexing motion

pili

-rigid tubular structure made of pilin protein
-found only in gram negative cells
-function to join bacterial cells for partial DNA transfer called "conjugation"

fimbriae

fine, proteinaceous, hairlike bristles from the cell surface
-function in adhesion to other cells and surfaces

glycocalyx

coating of molecules external to the cell wall, made of sugars and/or protein
two types:
1) slime layer - loosely organized adn attached
2)capsule - highly organized, tightly attached (streptococcus, haemophilus)

function of glycocalyx

-protein cells from dehydration and nutrient loss
-inhibit killing by white blood cells by phagocytosis contributing to pathogenicity
-attachment - formation of bioflims

cell envelope

-external covering outside the cytoplasm
-composed of two basic layers (cell wall and cell membrane)
-maintains cell integrity
-two generally different groups of bacteria demonstrated by gram stain (positive/negative)

gram positive bacteria

thick cell wall composed primarily of peptidoglycan and cell membrane

gram negative bacteria

outer cell membrane, thin peptidoglycan layer, and cell membrane

structure of cell wall

determines cell shapes, pervent lysis (bursting) or collapsing due to change in osmotic pressure
peptidoglycan: a primary component
-unique macromolecule composed of a repeating framework of long glycan chains cross-linked by short peptide fragments

gram positive cell wall

thick homogenous sheath of peptidoglycan
-20-80nm thick
-includes teichoic acid and lipteichoic acid: function in cell wall maintenance and enlargement during cell division; move cations across the cell envelope, stimulate a specific immune responses
teichoic acid is a sort of virulence factor (relates pathogenecity)

gram negative cell wall

-composed of an outer membrane and a thin layer peptidoglycan layer
-outer membrane is similar to cell membrane bilayer structure
1) outermost layer contains lipopolysaccharides and lipoproteins (LPS) :endontoxins that may become toxic when released during infections - may function as receptors and blocking immune response - contains porin proteins in upper layer, regulates molecules entering and leaving the cell
2)bottom layer composed of phospholipids and lipoproteins
-single, thin sheet of peptidoglycan
-protective structure while providing some flexibility and sensitive to lysis
-periplasmic space surrounds peptidoglycan

gram stain

differential stain that distinguishes cells with a gram-positive cell wall from those with a gram-negative cell wall
-gram-positive: retain crystal violet and stain purple
gram-negative: lose crystal violet and stain red from safranin counterstain
important basis of bacterial classification and identification
practical aid in diagnosing infection and guiding drug treatment

nontypical cell walls

some bacterial groups lack typical cell wall structure (i.e. mycobacterium and nocardia)
-gram-positive cell wall structure with lipid mycolic acid (cord factor) - pathogenicity and high degree of resistance to certain chemicals and dyes - basis for acid-fast stain used for diagnosis of infections caused by these microorganisms
some have no cell wall i.e. mycoplasma (cell wall is stabilized by sterois), pleomorphic

cell membrane structure

phospholipid bilayer with embeded proteins - fluid mosaic model
functions in:
- providing sites for energy reactions, nutreint processing, and synthesis
-transport molecules into and out of the cell

bacterial internal structures

-cell cytoplasm
-chromosomes
-plasmids
-ribosomes
inclusions and granules
-endospores
-sporulation
-germination

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