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ligands
chemical signals that are shared within and between cells for the survival of a living organism
hydrophilic
can't cross the phospholipid bilayer of the cell membrane and enter the cell
hydrophobic
slide between the phospholipids of the cell membrane to enter the cell
bind to intracellular receptors
located in the cytosol of the cell —> cross the nuclear membrane and bind to DNA in nucleus
target cells
respond to the presence of the ligand
autocrine signaling
cell signals itself to generate a response by releasing a ligand that binds to the receptors on its own surface (ligand goes from inside the cell to connect to the receptor)
juxtacrine signaling
signaling molecules are passed directly between adjacent cells via a surface receptor
paracrine signaling
cell secretes a ligand (local regulators) that travels a short distance, eliciting an effect on cells in the nearby area
endocrine signaling
ligands (hormones) travel a long distance between sending and receiving cells
signal transduction
how a cell responds internally to a signal in its environment; important for gene expression, cell growth and division
reception
ligand binds to a specific receptor (specific binding domains) on or in the target cell —> receptor undergoes shape change
transduction
series of chemical reactions that helps the cell choose the appropriate response
signal amplification
signaling cascades (a series of chemical in which one molecule activates multiple molecules) —> amplifies cell's response
kinases
transfer phosphate groups to other molecules (activates these molecules)
phosphates
remove phosphate groups from other molecules (which inactivates those molecules)
enzymes
(produce secondary messengers); ex) adenylyl cyclase — produces AMP from ATP
response
ultimate response generated by the ligand
signal transduction pathways
series of chemical reactions that mediate the sensing/processing of stimuli
feedback mechanisms
help living organisms respond to changes in environment, while maintaining cell's internal environment
negative feedback
returns system to its original condition and helps maintain homeostasis
positive feedback
magnifies cell processes
