Requirements of life

“ It takes a membrane to make sense out of disorder in biology….To stay alive, you have to be able to hold out against equilibrium, maintain imbalance, bank against entropy, and you can only transact this business with membranes in our kind of world.” Lewis Thomas, The Lives of a Cell

Maintenance of internal environment Cell wallMechanical stability Plasma membraneChemical stability

Metabolism Enzymes Multi-cellular organismsOrgans Eukaryotic cellsOrganelles Prokaryotic cellsPlasma membrane

Interactions with (sensing of) external environment Membrane and cytoplasmic proteins 2 component regulatory systems

Reproduction and inheritance of traits Chromosome (nucleoid)

Reproduction and inheritance of traits Chromosome (nucleoid)

Motility Flagella

Motility Flagella

Motility Flagella Some types of pili/fimbriae

Capsules and slime layers Both are commonly made of polysaccharides Some can be made of amino acids (B. anthracis) Always contain a great deal of water

Capsules Layer that is well organized and not easily washed off Protects cells from phagocytosis, desiccation and toxic substances

Slime layer More loosely attached to the cell surface than a capsule Contributes to the formation of biofilms

Biofilms Consist of layers of cells associated with each other through the external slime layer

Biofilms Can protect cell from environment Can allow for attachment and colonization of surfaces

Capsules and slime layers Production of components are tightly controlled by complex regulatory pathways

S-layers Crystalline-like structure external to the cell wall

S-layers Crystalline-like structure external to the cell wall Usually composed of protein subunits

S-layers Adhere to the outer membrane of gram negatives and peptidoglycan of gram positives

S-layers Serve to protect cells from the environment and maintain cell shape Very important in archaea lacking cell walls

S-layers

Cell walls Give cells shape

Cell walls Give cells shape

Cell walls Give cells shape

Cell walls Give cells shape Protect cells from osmotic lysis

Cell walls Give cells shape Protect cells from osmotic lysis May contain toxic compounds (e.g. LPS) May protect cells from toxic substances

Cell walls Most bacterial cell walls contain peptidoglycan Archaeal cell walls lack peptidoglycan Some Archaea contain pseudomurein Some Archaea substitute S-layers for peptidoglycan

Cell walls