Cell signalling Flashcards
How do cells detect and respond to chemical signals?
- Only cells with the right receptor can detect a signal
- Signaling molecules (ligands) bind to specific receptors
- Receptor binding triggers shape/activity changes
- Signal relayed through intracellular chemical messengers
- Results in cellular changes (e.g., gene activity, cell division)
- Intercellular signal converted to intracellular response
What is paracrine signaling and what are its key features?
Cell signaling where cells release chemical messengers affecting nearby cells
Short-distance communication (local action)
Quick, short-term responses
Signaling molecules quickly degraded or removed
Important in development, tissue repair, blood clotting, and vasodilation
Specialized form: synaptic signaling (neurotransmitters in nerve cells)
Allows local coordination of cellular activities
What is autocrine signaling and its significance?
Cell signals to itself by releasing ligands that bind to its own receptors
Important in development for cell identity reinforcement
Crucial in cancer progression and metastasis
Can have both autocrine and paracrine effects
Maintains cellular homeostasis
Involved in virus-infected cells
Potential target for cancer therapies (e.g., STI571 drug)
What is endocrine signaling and how does it function?
Long-distance cell communication using circulatory system
Specialized cells produce hormones released into bloodstream
Hormones travel to distant target cells
Key endocrine glands: thyroid, hypothalamus, pituitary, gonads, pancreas
Hormones regulate development and physiology
Hormones often affect multiple cell types throughout the body
How do cells communicate through direct contact?
Gap junctions (animals) and plasmodesmata (plants):
Tiny channels connecting neighboring cells
Allow small molecules and ions to diffuse between cells
Create cell networks for coordinated responses
Direct protein binding:
Complementary surface proteins bind
Binding changes protein shape, transmitting signal
Important in immune system (e.g., recognizing “self” cells)
Key features:
Allows rapid, localized communication
Coordinates group cellular responses
Essential for immune function and plant physiolog
What is quorum sensing in bacteria?
Cell-cell communication process
Bacteria monitor population density using chemical signals (autoinducers)
When signal reaches threshold, bacteria change behavior/gene expression simultaneously
First discovered in Aliivibrio fischeri (symbiont of Hawaiian bobtail squid)
Regulates processes like bioluminescence, virulence, biofilm formation
How does the quorum sensing mechanism work?
Bacteria produce and detect autoinducers (e.g., AHL)
Low density: autoinducers diffuse away
High density: autoinducers accumulate, bind to receptors
Receptors act as transcription factors, altering gene expression
Often creates positive feedback loop
What are the roles of quorum sensing in bacterial behavior?
Coordinates group behaviors in bacterial populations
Regulates symbiotic relationships (e.g., A. fischeri and bobtail squid)
Controls biofilm formation and maintenance
Manages virulence factor production in pathogens
Enables interspecies communication in some cases
How do yeasts use signaling for mating?
Yeasts secrete mating factors to find compatible mates
Mating factors bind to G protein-coupled receptors
Triggers MAP kinase signaling pathway
Causes “shmooing” (outgrowth formation) for cell fusion
Similar signaling components found in human cells
What are the steps in a signal transduction pathway?
- ligand binds to a receptor
- Transmembrane receptor: change in shape ➡️ phosphorylation events and second messenger (Second messengers amplify signals by binding to and activating multiple target proteins, often leading to a cascade effect.)
- Intracellular receptor: ligand-receptor complex that activates
What are internal receptors?
- found in cell cytoplasm
- respond to hydrophobic ligands
- mostly bind to proteins that regulate mRNA synthesis and mediate gene expression
Describe cell-surface receptors
- spans plasma membrane, performs signal transduction where extracellular signals become intracellular
- ligands do not have to enter the cell
- specific to individual cells
Describe ion channel-linked receptors
- bind a ligand and open a channel for specific ions
- when ligand binds, there is a conformational change that allows ions to pass
Describe G-protein-linked receptors
Ligand binds GPCR, activating G-protein (GDP to GTP). Activated G-protein subunits interact with effectors. GTP hydrolyzes to GDP, G-protein reassembles, cycle restarts.
Describe enzyme-linked receptors
Ligand binds, receptor activates enzyme domain. Enzyme triggers signaling cascade, leading to cellular response.
Small hydrophobic ligands vs water-soluble ligands
Hydrophobic ligands: Membrane-permeable, bind internal receptors. Examples: steroids, thyroid hormones. Need carriers in blood.
Water-soluble ligands: Membrane-impermeable, bind cell-surface receptors (ion-channel, G-protein, enzyme-linked). Examples: peptides, proteins.
Key difference: Receptor location (internal vs. external) and blood transport method.
What cellular responses can occur as a result of signal transduction?
- regulation of gene expression
- change in metabolic activity
- cell death
