Cell Communication, Feedback, and Homeostasis Quiz

review notes, FRQ, lab, webquest

how do cells communicate?

they send out ligands, which binds to and activates a receptor, inducing a response

ligand

signaling molecule

receptor

place where the ligand bonds; its activation causes a response in the cell

types of communication

juxtacrine signaling, autocrine signaling, paracrine signaling, endocrine signaling

juxtacrine signaling

involves direct contact between adjacent cells

example of juxtacrine signaling in animal cells?

gap junctions

example of juxtacrine signaling in plant cells?

plasmodesmata

autocrine signaling

cell sends signal to itself

examples of autocrine signaling

cancer cells (self growth), apoptosis in a cell infected by virus

paracrine signaling

cell secretes chemical messenger that induces changes to nearby cells

examples of paracrine signaling

growth factors, synaptic signaling

endocrine signaling

cells release chemical messenger to cells far away

examples of endocrine signaling

steroids like insulin or adrenaline travel through the bloodstream to target cells

signal transduction

process of receiving and inducing response in the cell

steps of signal transduction

reception, transduction, response

reception

ligand bonds to the receptor, causes conformational changes to cause a cascade of events in the cell

types of receptors

plasma membrane receptors, intracellular receptors

plasma membrane receptors

if the ligand is hydrophilic, bind to receptors on the surface of the cell

intracellular receptor

binds to small, hydrophobic ligands in the cytoplasm of the cell; can directly influence gene expression

G protein coupled receptor

ligand binds to plasma membrane receptor —> activates the G protein —> activates adenyl cyclase —> cAMP production —> activates kinases —> phosphorylation cascade —> activates response

receptor tyrosine kinases

ligand binds to plasma membrane receptor —> P from ATP binds to tyrosines on the receptor —> tyrosines phosphorylate proteins —> activated proteins initiate response

ligand gated ion channel receptors

act as a gate that opens and closes when the plasma membrane receptor changes shape

transduction

process by which signal is transferred and amplified into a form that can cause cellular response

kinase enzymes

enzymes that add a phosphate group from ATP to another molecule to activate it

phosphorylation cascade

when kinases activate each other through phosphorylation

phosphatase enzymes

enzymes that remove a phosphate group to deactivate a molecule, returning it to its inactive form

second messengers

small non-protein molecules that relay and amplify signals received by receptors to proteins

examples of second messengers

cyclic AMP (cAMP), Ca²⁺

response

the “end result”, can affect gene expression (turning it on/off), enzyme activity, cell behavior

possible reasons for response

cell division, alter phenotypes, secrete other hormones/signaling molecules, initiate apoptosis

homeostasis

ability to maintain stable internal environment despite changes in external conditions (balance)

parts/steps of homeostasis

set points, stimulus, receptor/sensor, effector, response

set points

ideal values/ranges for environment (temperature, pH, glucose levels, etc.)

stimulus

any change that triggers a response

receptor/sensor

detects stimuli

effector

organ/cell that responds to stimulus

response

action taken by effector to restore homeostasis

feedback loops

mechanisms that help maintain homeostasis

negative feedback loop

work to reduce/inhibit original stimulus to bring conditions back to set point

exmaple of negative feedback loop

thermoregulation in humans

positive feedback loop

moves further away from homeostasis to amplify a response, then conditions return to the set point

example of positive feedback loops

childbirth

what does an arrow represent?

activates/increases

what does a blunt arrow represent?

inhibits/decreases

what do two “inhibits” (2 blunt arrows) equal?

an activation

what factors can change a response?

blocked receptor, mutations in any molecules involved in the pathway, chemicals that can activate/inhibit the process, adding more receptors to receive more signals