Cell Signaling

what are ligands

signaling molecules that bind to other molecules to create a complex that transmits signals

ligand’s shape must be ___ to the receptor

complementary

what is autocrine signaling

secreted molecules trigger a response in the cells that secrete them

example of autocrine signaling

some cancer cells release their own growth factors, allowing tumors to grow more rapidly

what is juxtacrine signaling

cells communicate via direct contact

example of juxtacrine signaling

muscle cells of the heart are linked by gap junctions- this allows all the cells of the heart to contract at the same time. or, some immune cells interact through direct contact

what are gap junctions

cytoplasmic channels between animal cells

what is plasmodesmata

cytoplasmic channels between plant cells

what is paracrine signaling

secreted molecules trigger a response in nearby cells

example of paracrine signaling

quorum sensing in bacteria, induction during development

what is quorum sensing

signal molecules are produced by individuals; if enough bacteria are present, lots of signal molecules are produced, resulting in a response that would only be beneficial if large numbers of bacteria are present

example of quorum sensing

dental plaque

what is induction

signals from neighboring cells cause changes in gene expression, causing cells to differentiate

what is endocrine signaling

molecules (hormones) secreted into the bloodstream, affects cells anywhere only if they have the appropriate receptors

steroid hormones function

affect DNA expression to initiate long-term changes to the target cell, bind to intracellular receptors

examples of steroids

testosterone and estrogens

steroid hormones are ____ soluble

lipid soluble

first step of steroid action

hormone diffuses across cell membrane of all cells

second step of steroid action

hormone binds to receptor

third step of steroid action

hormone-receptor complex diffuses into the nucleus, binds to DNA, and act as a transcription factor

fourth step of steroid action

transcription factor causes specific genes to make new proteins

steroid hormones alter…

gene expression

water soluble hormones function

affect enzyme activity to initiate short-term changes in a cell

examples of water-soluble hormones

epinephrine, melatonin, insulin

mechanism of water-soluble hormone action

signal-transduction pathway

what is a signal-transduction pathway

a series of steps where signaling molecule binding results in a cellular response

what are G-proteins

a protein activated when bound to GTP, inactivated when bound to GDP

what are G protein coupled receptors

binds and activates G protein when activated by ligand

what is protein kinase

enzyme that transfers phosphate group from ATP to a protein, activating the enzyme via phosphorylation

what are second messengers

small molecules/ions that act as intermediaries between activated receptor and activation of other proteins

first step of signal-transduction pathways

epinephrine binds to G protein coupled receptor

second step of signal-transduction pathways

receptor activates G protein by allowing it to bind to GTP

third step of signal-transduction pathways

activated G protein activates an enzyme, converting ATP to cAMP, a second messenger

result of signal-transduction pathways

a signal cascade: cAMP activates kinase, which activates another, and another, until the target enzyme is reached. then, glycogen is broken down into glucose by the target enzyme

signal-transduction pathways always have…

reception, transduction, and response

description of reception

signal molecule binds to a receptor

description of transduction

bound receptor stimulates another molecule, then another, this result is known as amplification

description of response

cell change

define amplification

enzyme activates many other enzymes in the next step

function of tyrosine kinase receptors

binding of ligand makes two receptors join together, causing phosphorylation and initiating a transduction pathway

function of ion channel receptors

ligand binding causes these channels to open, thus allowing ions to enter and exit the cell

examples of second messengers

inositol triphosphate and ca²⁺