Archaeal cell walls Can be gram-positive or gram-negative Gram-positives often have a thick surface layer Gram-negatives often have a thin layer of protein or glycoprotein (S-layer)

Pseudomurein Often found in gram- positive archaea Similar to peptidoglycan N-acetylalosaminuronic acid replaces NAM Cross-bridges do not contain D-amino acids

Plasma membrane Composed of lipids and proteins

Membrane lipids Amphipathic molecules Hydrophilic heads and hydrophobic tails

Membrane lipids Amphipathic molecules Hydrophilic heads and hydrophobic tails Allows lipids to interact with water on one end and each other on the other end Formation of lipid bilayers

Archaeal lipids Contain branched chain hydrocarbons attached to glycerol via ether links Other cells have fatty acids attached to glycerol via ester links (bacteria and eukaryotes)

Archaeal lipids Two glycerol groups can be linked to form a tetraether Tetraether chains are usually 40 carbons long Diether chains are usually 20 carbons long Length of tetraethers can be adjusted by cyclizing the chain to form pentacyclic rings

Archaeal lipids Various combinations of lipids can result in differences in rigidity and thickness of membrane

Sterols and hopanoids Eukaryotic cell membranes often contain sterols Also found in the membrane of some bacteria that lack a cell wall Stabilize the membrane and add rigidity

Sterols and hopanoids Hopanoids are sterol-like molecules that are found in bacterial membranes Play similar role as sterols

Plasma membrane Composed of two layers of lipids with hydrophobic ends in the interior of the membrane Proteins can be peripheral or integral

Fluid mosaic model Most widely accepted model for membrane structure Lipid composition varies with temperature to maintain fluidity

Internal membrane systems Mesosomes Invaginations of membrane Often in the form of vesicles, tubules or lamellae Some believe they are artifacts generated during chemical fixation

Internal membrane systems Photosynthetic prokaryotes Often have extensive infoldings of the plasma membrane In the form of flattened or spherical vesicles or tubules May serve to provide larger surface area for metabolic processes

Cytoplasmic matrix

Area between the plasma membrane and the nucleoid Composed largely of water Specific proteins positioned at particular sites (e.g. poles or septum)

Inclusion bodies Organic inclusion bodies usually contain glycogen or poly-  -hydroxybutyrate Inorganic inclusion bodies can store phosphate or sulfur

Inclusion bodies Magnetosomes Iron containing inclusion bodies used to orient cell in the Earth’s magnetic field

Inclusion bodies Gas vacuoles Used by bacteria to regulate buoyancy Composed of a collection of collapsible gas vesicles

Ribosomes Can be free in the cytoplasmic matrix or loosely attached to the plasma membrane Membrane-associated ribosomes synthesize proteins that are transported to the outside

Ribosomes Are 70S vs. 80S Are composed of a 50S and a 30S subunit

The nucleoid The region of the cell where the chromosome is located Irregularly-shaped Often appears to be attached to plasma membrane Can rarely be bound by a membrane

The nucleoid Most prokaryotes have a single circular chromosome Some bacteria have linear chromosomes Some bacteria have two chromosomes DNA-binding proteins associated with chromosome

Endospores Dormant structures that are resistant to environmental stresses Can remain viable for 100,000 years Can survive boiling (must be autoclaved)

Endospores True endospores are only found in gram positive bacteria

Endospores Location of endospore in cell can aid in identification Mother cell is called the sporangium

Endospores Are complex structures Covered by exosporium Next layer is the spore coat (responsible for resistance to chemicals)

Endospores Cortex is beneath the spore coat and contains peptidoglycan Spore cell wall surrounds the core

Resistance of endospores Large amounts of dipicolinic acid is complexed with calcium ions in the core May aid in resistance DNA-binding proteins, dehydration of core and DNA repair systems all contribute to resistance Dipicolinic acid

Sporogenesis/sporulation

Transformation into vegetative cells Occurs in three stages 1. Activation 2. Germination 3. Outgrowth