Cell-Cell Interactions Flashcards
How are adjacent cells held together?
- tight junctions
- desmosomes
- gap junctions
- plasmodesmata (plants only)
Tight junctions are ___________ formed between adjacent cells
water-tight seals
Tight junctions prevent what?
passage of molecules between cells
Tight junctions are found between _________ cells
epithelial (intestines, lungs, etc)
Desmosomes are __________ that anchor the _________
strong adhesions; cytoskeleton
Desmosomes provide __________________ between cells
continuous structural support
Where are desmosomes found?
tissues that experience intense mechanical support (cardiac muscle, bladder, epithelia)
Gap junctions are _________ between adjacent cells
protein channels
Gap junctions allow __________ between cells
direct communication (animal and plant)
What are plasmodesmatas?
gaps in cell walls
Describe plasmodesmata?
no proteins involved and continuous plasma membrane and cytoplasm
What is involved in cell-cell signaling and distant communication?
hormones
What are hormones?
small molecules secreted to act on distant target cells
What are some examples of hormones?
steroids, peptides, gas, amino acid derivatives
What are the steps of cell-cell signaling?
- signal reception
- signal processing (transduction)
- signal response
- signal deactivation
What is signal reception?
different for lipid-soluble (hydrophylic) and lipid insoluble (hydrophobic) hormones
What is signal processing?
second messengers or phosphorylation cascade
What is a signal receptor?
protein that changes shape and activity after binding to a signal molecule
receptors are _______ and the number of receptors can ________ over time
dynamic; change
What does the dynamic characteristic of receptors cause?
increased/decreased sensitivity
How can receptors be blocked?
drugs (beta blockers- block adrenaline binding to lower blood pressure)
Describe signal reception with lipid soluble molecules
- diffuse across cell membranes
- bind to receptors in cytosol
- can skip signal processing
- typically transported to nucleus to affect transcription of DNA
For signal reception w/ insoluble molecules, receptors are ___________
transmembrane proteins (signal binding initiates signaling pathway)
Instead of direct response, lipid insoluble receptors trigger ________.
signal transduction
What is signal transduction?
conversion of an extracellular signal to an intracellular signal
What are examples of signal transduction?
second messengers and phosphorylation cascade
What are the steps for signal reception with a lipid-insoluble molecules?
- signal molecule binds
- receptor undergoes conformational change
- receptor activates signal transduction inside the cell
Receptor examples for lipid-insoluble
gated ion channels; GPCRs and RTKs
What are second messengers in signal transduction?
small molecules that relay intracellular signals (ex cAMP derivative of ATP - activates kinases; and ions)
What are phosphorylation cascades?
each kinase phosphorylates a different kinase until a response is triggered
What are the typical responses of signal response?
- change in gene expression
- change in the activity of proteins
Describe the characteristics of signal deactivation.
- responses and deactivation can occur very rapidly
- deactivation is different for different signal types
When are G proteins deactivated?
- after GTP hydrolysis
Describe the deactivation of phosphorylation cascades.
Phosphatases remove phosphate groups from components
Describe deactivation with second messengers.
- Ca2+ - membrane pumps to return storage
- cAMP, etc - enzymes break down
What are the steps of cell signaling for lipid-soluble molecules?
lipid soluble –> directly to signal response –> signal deactivation
What are the steps of cell signaling for lipid-INsoluble molecules?
lipid insoluble (GPCRs or RTKs) –> signal transduction (phosphorylation cascade OR second messengers) –> signal response –> signal deactivation
What do unicellular organisms use for signaling?
quorum sensing
What is quorum sensing?
organisms secrete signaling molecules into the surrounding environment, sensed by others of the same type
