Chapter 4: Prokaryotes Flashcards
Prokaryotes
-no nucleus
-nucleoid contains DNA
-ribosomes present
-3 basic shapes
-most bacteria are monomorphic (one or single shape)
-few are pleomorphic
-1 circular chromosome, not in a membrane
-no histone proteins associated with w/ their DNA
-no sterols in plasma membrane
-reproduce by binary fission
-peptidoglycan in cell walls
Structures of external to prokaryotic cell wall?
-flagella
-pilus (plural: pili)
-glycocalyx
-capsule
-slime layer
-fimbriae
-axial filaments (only in spirochetes; function: motility)
Glycocalyx
-viscous
-gelatinous
-made of polysaccharide and/or protein
-a capsule (very tightly bound; organized; ex. Streptococcus pneumoniae)
-a slime layer (loosely bound; disorganized; ex. Streptococcus mutans- dental plaque)
-virulence factor
Functions of glycocalyx
-adherence to host and to surface
-antiphagototic
-contributes to biofilm (medical device)➡️ resistant to antibiotic, disinfectants, and host defenses
Flagella
-made of chains of flagellin
-anchored to the wall and membrane of basal body
-important in identification of bacteria
-motility
-H antigens- identification
-rotate, composed of flagellin
Flagella stain can show
1) # of flagella
2) arrangement of flagella
-peritrichous- around entire bacteria
-very motile
-ex. Proteus
Monotrichous and polar
Phototaxis
Move toward or away from light
Chemotaxis
WBC release chemical for bacteria to come toward WBC
Axial filaments
-“endofagella”
-wrap around cell between plasma membrane and cell wall
-In spirochetes
-anchored at one end of a cell
-corkscrew rotation causes cell to move
Fimbriae
-hair-like appendages
-functions:
1) adherence to surfaces and other cells
2) colonization of bacteria in a host
-E. coli: UTI
-N. gonorrhoeae
Pili (sex)
-shorts appendages made of pilin
-function of DNA transfer between bacteria (conjunction- bridge- transfer of DNA across appendage to another bacteria (plasmid))
Which structures of the prokaryotes are used for attachment to a host cell?
-fimbriae
-glycocalyx
-slime layer
-capsule
Cell wall functions
1) maintain cell structure
2) protection from changes in osmotic pressure
3) site of action of certain antibiotics (ex. Penicillin- acts on cell wall)
4) identification of bacteria
In bacteria, cell wall is made of
Peptidoglycan
Peptidoglycan
-Polymer of repeating disaccharide of N-acetylglucasmine (NAG) and N-acetelmuramic acid (NAM)
-linked by polypeptides
Gram-(+) cell wall
-Peptidoglycan (thick layer)
-teichoic acids (wall teichoic acids and lipoteichoic acids)
-regulate movement of ions and stabilize cell wall
-periplasmic space: absent
-out membrane: absent
-lipopolysaccarhide (LPS) content: absent
-lipid and lipoproteins acids content: absent
-toxin produced: exotoxins
-cell wall distribution by lysozyme: high
-susceptibility to penicillin: high (➖peptidoglycan synthesis)
Gram-(-) cell wall
-more intricate
-peptidoglycan (thin layer)
-outer membrane- where lipopolysaccharide (endotoxin) (“LPS”, “lipid A”) and o-polysaccharide, core polysaccharide are located- responsible for toxic properties
-porin proteins
-periplasmic space: present- rich in degradative enzymes
-stain pink
-teichoic acids: absent
-lipid and lipoprotein content: present
-toxin produced: endotoxin and exotoxin
-cell wall distribution by lysozyme: low
-suseptibility to penicillin: low (tetracycline sensitive- ➖ protein (ribosomes) synthesis)
Basic shapes of bacteria
Cocci (spherical)
-ex. Streptococci
-tetrads
-pairs
-chains
Bacilli (rod)
-random arrangement
Spiral
Bacterial arrangements
-pairs: Diplococci, Diplobacilli
-clusters: Staphylococci
-chains: Steptococci, Streptobacilli
Atypical cell walls
-archae lack peptidoglycan- walless; no gram stain
-Mycoplasma- lack cell wall
-sterols(help maintain the membrane fluidity and structural integrity)in plasma membrane
Endotoxin cause
fever and shock
Damage to cell wall
-lysozyme (enzyme in human secretions) digests peptidoglycan
-antibiotics (ex. Penicillin), interfere w/ cell wall synthesis
-penicillin ➖ peptide bridges in peptidoglycan
Cytoplasmic membrane/plasma membrane
Structure: phospholipid bilayer
Functions:
-selective permeability
-enzymes for ATP production
-photosynthetic pigments
Destruction of plasma membrane by alcohol, ammonium quartenary detergents (QUATS), and polymyxin antibiotic (causes leakage of cell contents (lyse))
Isotonic solutions
-0.85% NaCl solution
-effect on cell: no change