Chapter 9

Apoptosis

programmed cell death

Biofilm

a matrix of proteins and sugars that protects colonies of pathogenic bacteria from the host immune system

Ligand

a molecule produced by a signaling cell that binds with a specific receptor, delivering a signal in the process

Second messenger

a small, non protein molecule that propagates a signal within the cell after activation of a receptor causes its release

Signaling mechanisms

autocrine

direct signaling

paracrine

endocrine

Receptors

Intracellular

Cell surface

Autocrine

ligand binds to receptors on the signaling cell

Paracrine

ligad binds to receptors on nearby cell

rapid degraded ligand ensures signal is local

Endocrine

ligand binds to receptors on distant cells

stable ligand ensures it can travel across body

Direct Signaling

ligand travels from cytoplasm to from signaling cells to target cells

Intracellular

receptor protein in cytoplasm of cell

ligands for this must be small and hydrophopic to diffuse across membrane

steroid hormones

Cell surface

receptor protein on surface of cell

anchored in plasma membrane

must posses 3 domains (transmembrance, extracellular, cytoplasmic domain)

ligands must be hydrophilic

small molecules or proteins

Transmembrance

domain that spans membrane

Extracellular

domain thats exposed to the outside of the cell and binds ligand

Cytoplasmic

domain thats exposed to cytoplasm

Signal Transduction

binding of ligand leads to change in shape of receptor

Ex an intracellular receptor may enter nucleus, cause genes to be turned on/off 

Ex may lead to release/creation of second messenger

Ex a cell surface receptor may phosphorylate proteins 

Result in, Altered cell behavior, Cell growth/divison, Apoptosis 

Phosphorylation

modification of proteins by the addition of a phosphate groups from ATP 

Catalyzed by a class of enzymes called kinases

function of a protein can be turned on and off

Dephosphorylation

removal of a phosphate groups from a protein 

Catalyzed by a class of enzymes called phosphatases 

Mating factor

ligand that single celled yeats secrete to find other yeasr cells to mate with

Quorum sensing

Released ligands (called autoinducers) communicate cell density to other bacteria 

Some bacteria can form biofilms but this requires high cell density to form 

Would waste energy to try to form with few bacteria

low ligand density

high ligand density

Low ligand density

ligand diffuses

no response

High Ligand density

signaling pathway activated

formation of biofilm