Prokaryotes Flashcards
Prokaryotes versus Eukaryotes
Prokaryotes: -smaller
- lack internal membrane system around organelles -cell size is 0.5-4.0 um wide
- spherical prokaryotes (coccus) are very small
Eukaryotes: -have inner membranes around organelles -cell size 10-20 um wide
Coccus
spherical or oval shaped (little spheres)
diplococcus- 2 cocci linked together
streptococcus- chains of cocci linked together tetrad- 4 cocci group together
sarcinae- 8 cocci linked together
staphylococcus- many cocci bunched together in a bundle
Bacillus
cylindrical rod shaped
diplobacilli- 2 bacilli
streptobacilli- chain of bacilli
palisade- several parallel cells lined up next to eachother
vibrios- comma shaped rods
Spirillum
spiral shaped
spirilla- rigid helix
spirochetes- flexible helices
Mycelium
network of long, multinucleate filaments
prefix: (-myces)
Pleomorphic
organisms that are variable in shape
Surface area to volume ratio and Growth Rates
small cells have more surface area relative to their volume than larger cells (larger S/V ratio) which means there is greater nutrient exchange per unit cell volume
-more area for exchange relative to volume allows small prokaryotes to grow and replicate faster than larger cells
Functions of cell membrane (all domains)
- maintain cell’s integrity (separates cytoplasm from environment)
- regulates transport by being a highly selective permeable barrier
- energy metabolism in prokaryotes (not eukaryotes)
- proteins attachment (receptors/channels)
- receptors for detection and response to chemicals outside of cell
General Structure of Domain Bacteria membrane
phospholipid bilayer plus proteins
-no sterols but contain hopanoids
Membrane proteins (list)
Peripheral, Integral, Transmembrane
Peripheral proteins (fluid mosaic membrane)
loosely connected to membrane on cytoplasmic side -easily moved
Integral proteins (fluid mosaic membrane)
amphipathic (polar and nonpolar regions) -embedded within membrane and project outward or inward -carry out important functions
Transmembrane proteins (fluid mosaic membrane)
completely crosses membrane from one side to the other
Membrane strengthening lipids
sterols and hopanoids
-saturation levels of membrane lipids reflect environmental conditions such as temperature
Sterols
- rigid, planar lipids found in eukaryotic membranes
- strengthen and stabilize membranes
Hopanoids
- structurally similar to sterols
- present in membranes of many Bacteria
Membrane fluidity
cell membrane has properties of both liquid and solid
-membrane needs to be at right fluidity which is temperature dependent
too cold= solidification (gelling)
too hot= thermal lysis (cell death)
Adjusting to maintain correct membrane fluidity
- adjust fatty acid composition of phospholipids
1. cold- more unsaturated fatty acids (minimize van der waals forces)
2. hot- more saturated fatty acids (maximize van der waals forces *van der waals forces strength determines if fatty acid tails attract and stick to eachother or not - adjust ratio of sterols, hopanoids, or other lipids in the membrane to maximize or minimize van der waals forces
Transport in prokaryotes
active transport is always facilitated in prokaryotes
-no endocytosis/exocytosis in prokaryotes
Group translocation
simultaneous transport and chemical modification of transported substance
-energy (ATP) dependent transport that chemically modifies molecule as it is brought into the cell
Domain Bacteria Cell Walls
mostly structural polysaccharides and peptides/proteins -prevents osmotic lysis
-gram (+) and gram (-) cells
peptidoglycan- structural polysaccharide in cell walls of domain Bacteria
Osmotic lysis
pressure from water entering cell causing a rupture of the cell membrane and death of the cell
Breaking Bacterial cell walls
- Lysozyme- breaks the bond between N-acetyl glucosamine and N-acetylmuramic acid in cell wall
- Penicillin- inhibits peptidoglycan synthesis of cell wall
*breakdown of cell wall causes influx of water to rush into the cell from the hypotonic environment outside the cell, causing the cell to burst through lysis
Bacteria without cell wall
Mycoplasma: -does not produce a cell wall -plasma membrane stronger (has sterols) more resistant to osmotic pressure -hyper regulates internal solute concentration to stay slightly hypertonic (so cell doesn’t become dehydrated)
Gram positive and Gram negative bacteria (quick facts and staining)
gram (+): stain purple, thick layer of peptidoglycan
order- membrane, thick cell wall on outside
gram (-): stain pink, thin peptidoglycan wall
order- thin cell wall in between two membranes
Peptidoglycan Cell Wall Structure
mesh-like polymer wall of identical subunits forming long strands (structural polysaccharide with amino acids surrounding cell)
basic subunit- disaccharide of two alternating modified sugars (N-acetylglucosamine *NAG and N-aceylmuramic acid *NAM) joined by Beta glycosidic bonds
Peptidoglycan Cross-linked strands
- strands have a helical shape
- cross linked by covalent bonds between the tetrapeptides (4 amino acids) for strength
- In gram (-) bacteria crosslinks are directly between amino acids in the tetrapeptide
- In gram (+) bacteria, there are often interbridges of additional amino acids betwee the tetrapeptides
Gram Positive Cell Walls
composed primarily (90%) of peptodoglycan
-also contains large amounts of teichoic acids (negatively charged)
Teichoic acids function to: help maintain cell envelope, may bind to host cells, and may store phosphate (PO4) *may attract cations
- some gram (+) bacteria have layer of proteins on surface of peptidoglycan
- also have lipoteichoic acid which attaches to cell membrane
Picture: teichoic acid circled
Periplasmic Space
lies between plasma membrane and cell wall and is smaller than that of gram (-) bacteria
- has relatively few proteins
- enzymes secreted by gram (+) bacteria called exoenzymes (aid in degradation of large nutrients)
Gram Negative Cell Walls
consist of a thin layer of peptidoglycan surrounded by an outer and inner plasma membrane
-outer membrane composed of phospholipids, lipoproteins, and lipopolysaccharides
*Lipopolysaccharides- make up the outer part of outer membrane (no phospholipid heads)
*NO TEICHOIC ACIDS
-peptidoglycan is 5-10% of cell wall
Periplasmic space:
many enzymes present in periplasmic space (transport proteins)
-Braun’s lipoproteins connect outer membrane to peptidoglycan wall
Lipopolyssaccharides (LPS)
- contributes to negative charge on outer cell membrane surface
- helps stabilize outer membrane structure
- may contribute to attachment to surfaces and biofilm formation
- creates a permeability barrier
Gram-Negative Outer Membrane Permeability
-more permeable than plasma membrane due to presence of porin proteins and transporter proteins
*porin proteins form channels to let small molecules pass
Mechanism of Gram Stain Reaction
gram stain reaction due to nature of cell wall
- shrinkage of the pores of peptidoglycan layer of gram-positive cells (constriction prevents loss of crystal violet during decolorization step)
- thinner peptodoglycan layer and larger pores of gram (-) bacteria does not prevent loss of crystal violet
Structures Exterior to Cell Wall
glycocalyx, capsule, slime layer
Glycocalyx
polysaccharide rich (glucose or modified gluose subunits) material exterior to cell wall
*sometimes has protein component (2 types-capsule or slime layer)
Capsule
dense, tightly attached, regular arrangement of polysaccharides
*visible to light microscope
Slime layer
diffuse, loosely attached, irregular arrangement of polysaccharides
functions: attachement to solid surfaces, reserve source of energy, anti-phagocytic for some pathogens, prevents virus attachement *may aid in motility
