Seminar 12: Cell sensing & responding to the environment Flashcards
(39 cards)
what are the steps of cell to cell communication?
- Signal perception
a. Comes from outside cell, usually a chemical signal - Intracellular signal transduction
a. Binding of signalling molecule to receptor protein (on surface OR inside cell)
b. Changes tertiary structure of protein, initiates transduction
c. Transduction stage : converts signal from molecule TO FORM that can BRING ABOUT specific cellular responses
i. Can occur in 1 STEP, but usually occurs in SEQ OF CHANGES in DIFF molecules (Signal transduction pathway) - Cellular response
a. Final stage
b. When transduced signal finally triggers a cellular specific response
i. E.x catalysis by enzyme, rearrangement of cytoskeleton, activation of gene etc
function of cell signalling process?
ensure that crucial activities occur in the RIGHT cells @ the RIGHT TIME & in PROPER COORDINATION w/ other activities happening w/in the cell
what is signal transduction
1 type of signal converted to another
- Target cell converts EXTRACELLULAR SIGNAL MOLECULE into INTRACELLULAR SIGNALLING MOLECULE
Explain why each hormone specifically affects one cell type and not others.
Each cell has receptors for the hormones needed to signal changes in that cell and lacks receptors for hormones not needed for signalling changes. Each receptor has a specific shape and molecular makeup that recognizes and binds to one specific hormone. This enables cells to respond only to hormones that are of importance to those cells’ functions
define autocrine signalling
- cell > cell comm
- signals affect the cells that made them
- bind only to receptors on the same cell that made it (causes change in cell activity)
define Juxtacrine signalling
- cell > cell comm
- signals affect only adj cells
- ligand on 1 cell interact w/ receptor on adj (direct contact)
define paracrine signalling
- cell > cell comm
- signals affect nearby cells of gland secreting it
define hormones signalling
travel to distant cells, usually via the circular system (bloodstream)
desc how intracellular receptors work
- NP &/or SMALL signal (can diffuse through bilayer)
- binds to receptor in cytosol causing CHANGE in SHAPE (allows signal to be give)
- causes cellular response to occur
desc how membrane receptors work
- LARGW &/or POLAR (can’t diffuse thru bilayer)
- receptor binding site on the top surface to allow for binding (connected to inside & outside of cell)
- ligand fits into receptor, causes CHANGW in protein conformation (leads to CHANGE INSIDE cell)
desc the way an enzyme-linked receptor creates a cellular response & GIVE EX
- receptor is extracellular but embedded in bilayer (connected to in&outside of cell)
- intracellular side is the “active enzyme” domain
- when ligand binds to it, causes conformational change to the receptor, ACTIVATING ENZYME
- activated enzyme trigger cascade of intracellular events (e.x insulin response substrate)
e.x: insulin receptor
desc the way a GPCR receptor works & ex
- embedded in plasma membrane (contact w/in&outside cell)
- works via an intermediary (G protein)
- ligand (hormone) binds to the receptor, to ACTIVATE the G protein (GDP connected is phosphorylated to GTP, now ACTIVE)
- Activated G protein SUBUNIT ACTIVATES EFFECTOR protein
- GTP hydrolysed back to GDP to activate
- ACTIVATED effector protein can now cause cellular responses
e.x: epinephrine receptor
desc the way ligand-gated ion channel receptors work & give e.x
- embedded in bilayer
- when activated (ligand binds), ion channel changes shape (opens, ions can pass)
- channel is lined with charged A.A that allow the specific ions to flow into cell
e.x: Acetylcholine receptor
desc an intracellular receptor & give e.x
- INSIDE cell (cytosol, nucleus)
- turn ON transcription of specific genes
- can only interact w/ NP&/or small ligands (diffused thru bilayer on its own)
- ligand binds to receptor & chaperone protein complex
- causes receptor to CHANGE shape, releases chaperone
- receptor & ligand complex enter nucleus (because CORRECT shape)
- initiate cellular response (transcription of particular gene)
e.x: estrogen receptor
what are the 4 diff ways cells initiate cellular responses? (Diff signalling pathways)
- relay signal onward & help it to spread through a cell
- AMPLIFY the signal received (stronger) so that a FEW extracellular ligands are ENOUGH to evoke a LARGE INTRACELLULAR response
- DETECT signals from 1+ intracellular signalling pathway & INTEGRATE them before RELAYING a signal onward
- DISTRIBUTE the signal to 1+ effector protein, creating braches in flow diagram to evoke a COMPLEX response
How is it a benefit to the cell to have so many protein kinase molecules participating in the signal transduction pathway shown?
The protein kinase cascade provides a means for amplifying the signal so that a single signal molecule can cause many thousands of molecules to be activated at the end of the pathway as part of the cellular response.
what is crosstalk
interactions b/w diff signal transduction pathways
what can crosstalk result in
- activation of 1 pathway / inhibition of another
under what CONDITIONS would autocrine signalling be most adv for a cell?
- imp for cell to maintain a specialised role
- e.x: cell might receive signal to specialise & form a tissue of many cells
- 1st cell would SELF-STIMULATE to GROW & DIVIDE to form tissue in response to SELF-SIGNALING
is binding of ligand > receptor covalent or non covalent & WHY
non covalent
- because only IM forces form between the site of the receptor & the ligand
- H bond, VDW, LDF, DF
what is the dissociation constant (KD)
- measure of the affinity of the receptor for its ligand
- lower KD = HIGHER AFFINITY of ligand > receptor
- low KD values allow receptors to bind to their ligands even at very low [ ligand ]
why is it important that binding of receptor & ligand is REVERSIBLE
- if ligand was never released, receptor would CONSTANTLY be stimulated, cell WON’T STOP RESPONDING
desc Agonists
- resemble the ligand & bind to the receptor
- set a receptor into signal transduction mode like the ligand does
desc Antagonists
- inhibitors
- bind > receptor & freeze it in place
- prevents real ligand from binding
- doesn’t set off signal transfuction
