Ch 10 - Cell Communication/Signaling

ligands

chemical signals that are shared within and between cells for the survival of a living organism

hydrophilic ligands

can’t cross the phospholipid bilayer of the cell membrane and enter the cell

hydrophobic ligands

slide between the phospholipids of the cell membrane to enter the cell and bind to intracellular receptors —> bind to DNA

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); ex) cancer cell

juxtacrine signaling

signaling molecules are passed directly between adjacent cells via a surface receptor; ex) plasmodenta in plants

paracrine signaling

cell secretes a ligand (local regulators) that travels a short distance, eliciting an effect on cells in the nearby area; ex) neurotransmitters

endocrine signaling

ligands (hormones) travel a long distance between sending and receiving cells; ex) insulin

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

step 1 - signal amplification

signaling cascades (a series of chemical in which one molecule activates multiple molecules) —> amplifies cell’s response

step 2 - kinases

transfer phosphate groups to other molecules (activates these molecules)

step 3 - phosphates

remove phosphate groups from other molecules (which inactivates those molecules)

step 4 - enzymes

produce secondary messengers; ex) adenylyl cyclase — produces AMP from ATP

response

ultimate response generated by the ligand; ex) activation of genes by steroid hormones

signal transduction pathways

series of chemical reactions that mediate the sensing/processing of stimuli

step 1 - mutation in gene coding for receptor protein

change in shape may prevent binding to specific ligand (ex. AIS)

signal transduction pathways step 2

molecules in the environment interfere with ligand’s ability to bind to receptor (ex. cholera toxin)

signal transduction pathways step 3

disruption to any step affects the subsequent steps dependent on the products of previous steps

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

ex) sweat and cooling of body temperature

positive feedback

magnifies cell processes

ex) hormone oxytocin stimulates contractions during childbirth