Lectures 15 and 16: Cell Communication Flashcards
3 types of cell communication
- Direct contact signaling
- Local signaling
- Long distance signaling
types of direct contact signaling
cell junctions and cell-cell contact
types of local signaling
autocrine, paracrine, synaptic
long distance signaling types
hormonal
In animal cells, direct contact communication of cell junctions occurs through
gap junctions
In cell junctions, direct contact in plant cells occurs via
plasmodesmata
what ensures that only the same types of cells mate with each other?
the unique matching between mating factor and receptor
what are the three major steps of a signal transduction pathway?
signal reception, signal transduction, and cellular response
how can cells communicate by direct contact?
- With cell junctions; also plasmodesmata (allow molecules to pass readily between adjacent cells without crossing plasma membranes)
- With cell surface molecules (cell-surface molecules on adjacent cells interact with each other, resulting in a signal passing between the cells)
paracrine signaling
A signaling cell acts on nearby target cells by secreting molecules of a local regulator (a growth factor, for example).—that signal affects itself
synaptic signaling
- an electrical signal along a nerve cell triggers the secretion of neurotransmitter molecules
- molecules act as chemical signals, diffusing across the synapse ( the narrow space between cells) triggering a response in the target cell
- in the nervous system
what do both animals and plants use for long-distance signaling
hormones
endocrine signaling
specialized cells (endocrine cells) release hormones, which travel through the circulatory sys-tem (via bloodstream) to other parts of the body, where they reach target cells that can recognize and respond to them
signal transduction
series of steps by which a cell converts a signal into a response
signal reception (step 1)
target cell’s detection of a signaling molecule coming from outside the cell (when molecule binds to receptor protein on target cell)
signal transduction (step 2)
- transduction stage (changes the receptor protein in some way) converts the signal to a form that can bring about a specific cellular response
- mostly occurs in a series of relay molecules
cellular response (step 3)
-The transduced signal finally triggers a specific cellular response
- cell signaling process helps ensure that crucial activities occur in the right cells, at the right time, and in proper coordination with the activities of other cells of the organism
ligand
- A molecule that binds specifically to another molecule, usually a larger one
- signaling molecule
types of ligands
growth factors, hormones, neurotransmitters
types of receptors
G protein linked receptors, tyrosine kinases, ion channel receptors, intracellular receptors
G protein-coupled receptor
a cell-surface transmembrane receptor that works with the help of a G protein
G protein
a protein that binds the energy-rich molecule GTP
pathway of GPCR (steps)
- protein is inactive when GDP is bound to it (on or off)
- when signaling molecule binds to receptor –> receptor then binds to inactive G protein –> switches to GTP (now activated)
- activated protein dissociates from receptor and binds to enzyme triggering next step leading to cellular response
- G protein returns to inactive state and can be reused
G-proteins function
like an on and off switch (on and off signaling)
GTP is mostly found in the
cytosol
pathway of tyrosine kinase receptors (RTKs)
- receptors exist as individual molecules with binding site on the extracellular side of membrane (alpha helix) tail inside contains multiple tyrosine
- binding of signaling molecule causes individual monomers to associate closely (form dimer)
- dimerization activates the kinase region of each monomer – phosphate groups are added
- activated receptor is recognized by specific relay proteins (specific molecules for specific tyrosine) –> triggers cellular response
what is a key difference between RTK’s and GPCR’s?
with a single ligand-binding, RTKs trigger many pathways
dimerization
bring together two receptor-hormone complexes
ligand-gated ion channel
- channel is closed when there is no signaling molecule
- channel opens when molecule binds to site –> ions can flow through
- when ligand dissociates channel closes
intracellular receptor pathway
- steroid hormone passes through the membrane
- hormone binds to receptor protein in cytoplasm
- hormon-receptor complex enters the nucleus and binds to specific genes
- bound protein acts as a transcription factor stimulating transcription of the gene into mRNA
- mRNA is translated into specific protein
Cyclical AMP (cAMP)
important second messenger in G-protein
second messengers
small molecules or ions that relay signals received by cell-surface receptors to effector proteins
why do cells with the same receptor proteins have different pathways?
because they contain different proteins therefore the proteins will react differently
