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24 Cards in this Set

  • Front
  • Back
Prokaryote Cell Structure
no membrane-bound organelles;

single cytoplasmic compartment
Eukaryote Cell Structure
internal, membrane-bound organelles;
example: endosomes, lysosomes
Common Features of Cell Structure
* cytoplsmic membrane bounds the outer surface of the cell

* can also be surrouded by the cell wall (plants and fungi)
Prokaryote Genome Organization
* single circular chromosome organized into a nucleoid

* not surrounded by a membrane

* can have extrachromosomal DNA (plasmids)

* smallest: 500,000 bp;
typically: 1 x 10^6 to 10 x 10^6
Eukaryote Genome Organization
multiple linear chromosomes;

1 x 10^7 to 3 x 10^9 bp
Prokaryote Cell Size
radius: 1 micron;

higher surface to volume ratio than eukaryotes:
* high exchange of molecules
* higher growth rate
* higher growth density
* able to live inside eukaryotes
Eukaryote Cell Size
radius: 5 to 25 microns;

lower surface area to volume ratio
* lower exchange of molecules
* slower growth rate
* low density growth
Classify Bacteria by Cell Shape
* coccus: spherical shape (ex. Streptococcus)
* rod: bacillus anthracis
* spirochetes: include spiral-shaped bacteria
* formation of spores: an infection of herbivores -
the animal is killed and the bacteria run out of nutrients;
they undergo sporulation and go into the soil;
they are inhaled by other animals
Classification by Gram Staining
* fix the bacteria
* react the bacteria with crystal violet
* add iodine, which will precipitate the dye in the bacteria
* treat with organic solvent like ethanol to remove the stain
* counterstain - gram positive are purple and gram negative are pink
Phylogenetic classification
takes advantage of genome sequencing technology

can reflect differences in evolutionary histories of organisms
Bacterial Cell Structure - Cytoplasmic Membrane
* composed of phospholipids, like eukaryotes
* unlike eukaryotes, has no sterols (e.g. cholesterol)
* hapanoids modulate the fluidity of the membrane
* acts as a permeability barrier - hydrophilic molecules enter/leave through transport proteins
Bacterial Cell Structure - Cell Wall
* composed of peptidoglycan (PGN)
* PGN makes the surface rigid to prevent lysis of bacteria thru osmosis
* orientation of the cell wall in relation to the cytoplasm determines if gram negative or positive
Gram Positive Bacteria
PGN is outermost layer
Gram Negative Bacteria
PGN is not outermost layer

* additional membrane outside of PGN layer (outer membrane)
* outer membrane interacts with host components
Glycan Tetrapeptide
* glycan = sugar portion connected by B 1-4 linkages
- N acetylglucosamine
- N acetylmuramic acid
* peptide portion made of several amino acids; not every species has the same tetrapeptides
- normal peptides: L alanine
- unusual forms: D-glutamic acid, D-lysine
Transpeptidation Reaction - Crosslinking of Glycan Strands
* cross-links glycan tetrapeptide to produce PGN
* two chains of the glycan on the outside are cross-linked in the center by peptide interbridges
natural peptide in the body that specifically degrades PGN by cleaving β 1-4 linkages
* break down bacterial molecules, reversing the reactions carried out by transpeptidases and transglycosidases

* transpeptidases: make the bond between the two peptide groups

* transglycosidases: catalyze the reaction that produces the B 1-4 linkage
antibiotic that targets the PGN

binds to penicillin binding proteins, which carry out functions important in synthesizing peptidoglycan
Gram Positive Cell Surface
* much thicker layer of PGN on surfaces (~ 25 layers)

* since PGN is on the surface, it is more readily targeted by antibiotics and display molecules that interact with host cells

* teichoic acid (TA)
* lipoteichoic acid (LTA): recognized by the innate immune system and causes inflammation
Gran Negative Cell Surface
PGN is not the outermost layer, and has fewer layers

* periplasm: space between outer membrane and inner membrane

* since there are two layers, bacteria must have special way of getting different molecules in and out of cells

* Type III secretions help deliver proteins to host cells
Structure of LPS
* lipid A: fatty acids and sugars
- both lipid A and LPS are endotoxins
- endotoxins are associatedly intimately with bacteria
- exotoxins are released by bacteria

* core polysaccharides: unusual sugars

* o-antigen: recognized by Abs and complement components
- heterogenous structure: host can recognize it and make Abs against it
Outer Membrane (OM)
* permeability barrier: move molecules across the outer membrane via porins

* impt for interactions with host and environment (resistance to stress)

* resistance to antimicrobial molecules, esp outer leaflet of OM (LPS)
The Capsule
* outer layer of carbohydrates or protein

* coats the surface of the bacterium

1) adheres to host cells

2) inhibits intrxns between bacteria and host cells
ex. phagocytosis

3) confers resistance to antimicrobial molecules

4) provides an interface for Abs to interact with surface of bacteria