Cell Communication Flashcards
Significance of Communication
Allows for multicellular organisms to coordinate activities for their trillions of cells Responsible for: – Recognition of pathogens – Creating responses to the environment – Growth & division – Movement – Metabolic activities
Local & Long Distance Signaling
• Cells use chemical signals for means of communication
– Chemical messengers may travel a very short distance or throughout an entire organism to reach their target cell
Local Regulators
For communication with cells that are touching (juxtacrine) or within a very short distance (paracrine)
• These messages can reach several local cells quickly to elicit a response
– The chemical messenger will be short lived & degraded easily
• Examples:
– Growth factors released to induce cell growth & division
– Neurotransmitters crossing the synapse
Long Distance Signaling
Hormones are used to send messages throughout animals to target specific cells (endocrine signaling)
– These travel great distances & create responses in multiple cells simultaneously
– Moved by the circulatory system
– Do not degrade quickly
Three Stages of Cell Signaling
Cells will have three stages of response to a signal
– Reception
– Transduction
– Response
Reception
The target cell detects a signaling molecule from outside the cell
• The molecule will bind with receptors embedded in the plasma membrane or receptors located within the cell
Transduction
Conversion of the signal into a form that creates a cellular response
• Typically, this is a multistep process that involves numerous relay molecules
– AKA: the signal transduction pathway
– Different pathways exist for different cells, even with the same signaling molecule
Response
The last transduced molecule will trigger a specific cellular response
– This can be almost any cell activity: activation of an enzyme, rearrangement of the cytoskeleton, activation or deactivation of a gene
• This process ensures that only the correct cells are completing the proper activities at a specific time
Intracellular Responses
• Receptor proteins are located within the cytoplasm or nucleus of a cell
• Chemical messengers must pass through the plasma membrane to stimulate the target cell
– Signal molecule must be hydrophobic
• Example: testosterone
– Secreted from the testes this hormone crosses the plasma membrane & attaches to its receptor, where together they travel to the nucleus & turn on genes that control male sex characteristics
Receptors on the Plasma Membrane
• Most molecules bind to specific proteins that span the cell membrane
– The binding of the ligand will cause a change to the shape of receptor protein starting thetransduction pathway within the cytoplasm of the cell
• Key examples:
– G-protein-linked receptors (aka: G protein-coupled receptors)
– Receptor tyrosine kinases
– Ion channel receptors (ligand-gated ion channels)
G-Protein-Linked Receptors
A receptor protein that works with the help of a G protein
– G proteins bind the energy-rich molecule GTP
• A signaling molecule bonds to the extracellular side of the receptor which will become activated & change shape
• The cytoplasmic side of the receptor binds & activates a G protein which carries GTP
• The activated G protein leaves the receptor & diffuses along the membrane until it binds to an enzyme
• The activated enzyme can then trigger the next step in the transduction pathway
• All these processes are reversible & all molecules will inactivate for reuse
Receptor Tyrosine Kinases
Receptors that can trigger more than one signal transduction pathway at once by phosphorylating multiple relay molecules
– 10 or more pathways can be activated simultaneously
• A ligand will bond to the active site on both individual proteins which causes them to form a dimer (work together)
• The dimerization activates the tyrosine-kinase region adding a phosphate from ATP to each tyrosine
• The fully activated protein is recognized by relay proteins
which bind to the
phosphorylated tyrosine becoming active & triggering a transduction pathway
Ion Channel Receptors
A membrane receptor that has a gate that blocks the passage of ions until a ligand bonds to the receptor to open/close the gate
– The gate will return to its original position once the ligand dissociates
– Crucial in the nervous system
Signal Transduction Pathway
Multistep pathway that turns the signal into a cellular response
• Typical pathway include the activation of one protein by the addition/removal of a phosphate groups or the release of small molecules or ions that act as second messengers
• Benefits:
– Ability to amplify the signal
– Opportunity for more coordination & regulation
Phosphorylation Cascades
Phosphorylation (add a phosphate group) & dephosphorylation are mechanisms for regulating protein activity
– Protein kinase is an enzyme that transfers phosphate groups from ATP to proteins
– When multiple protein kinases act upon each other a phosphorylation cascade can be created
