Lecture 5: Controlling cells Flashcards
What components are needed to process signals?
signalling:
- signals
- membrane
- intracellular effector s
Gene expression:
- transcription factors
- Histones Chromatin remodelling factors
- leads to state change (one expression change)
cell signalling (communication) is critical for
normal development, and function
cells have evolved several signalling mechanisms to allow cells to
communicate with each other
-these mechanisms are highly conserved and used multiple times in a animals life
the general model of cellular signalling
1) Reception of signal
2) transduction of a signal
3) cellular response
signal transduction:
- receiving information into a cell
- acting on that information to make choices
signal transduction pathway:
Extracellular signals –> Signal transduction –> nucleus –> Protein expression –FEEDBACK TO NUCLEUS & SIGNAL TRANSDUCTION –> Response
Signalling cascades perform 5 crucial functions:
- TRANSUCE signal into molecular form that can stimulate response
- RELAY signal from point of reception to point of action in the cell
- AMPLIFY the received signal
- DISTRIBUTE the signal to influence several responses in parallel
- Each step is open to MODULATION by other signals
receptors relay signals via
…intracellular signalling pathways
- individual cells respond to a certain set of signals for which they have receptors (specificity)
- one cell may have 10 to 100,000 different receptors
- many signals acting together can elicit different cellular responses - a complex network
many signalling proteins act as
molecular “switches”
a signalling molecule may induce
different responses in different cell types
do extracellular signals act slowly or rapidly?
Either
signalling via chemical signals can be in two forms of communications
- direct (Gap junctions[animals], plasmodesmata [plants], interaction of cell-surface molecules
- local (local signalling =paracrine signaling, synaptic signalling, or hormonal signalling)
two classes of extracellular signalling molecules
1) small hydrophobic molecules
- small enough or hydrophobic and pass through the membrane
- Directly activate intracellular receptors in the cytoplasm
or nucleus of target cell
2) Hydrophilic molecules
-Molecules too large or too hydrophilic to cross the plasma membrane
- rely on membrane receptors
examples of small hydrophobic molecules in extracellular signalling
1) Steroid hormones
- steroids structurally similar to cholesterol
- hydrophobic
- signals through intercellular receptor
2) Nitric Oxide (NO)
- NO is a chemically unstable gas
- NO is a small,uncharged molecule
- signals through cytoplasmic receptor
Cell surface receptors convert…
chemical signals –> electrical signals
- Ion channel opening (i.e. K+ channels in heart muscle cells)
- Membrane-bound enzymes (e.g. adenyl cyclase, phospholipase)
- G protein linked receptors
Enzyme-linked receptors fall into 3 categories:
- Receptor tyrosine kinases
- Cytokine receptors
- TGF-beta- type receptors
receptor tyrosine kinases: ligands are
soluble or membrane-bound peptide or protein hormones (i.e. insulin, growth factors)
Some receptor tyrosine kinases have been identified in studies of
human cancers - mutant forms send proliferated signals to cells in absence of signal
receptor tyrosine kinases _____ themselves
autophoshorylate: phosphorylation of the kinase by itself.
activation of a receptor tyrosine kinase stimulates
assembly of a signalling complex
receptor tyrosine kinases activate
the G protein Ras
Ras activates
a cascade of kinases called MAP-kinases
receptor tyrosine kinases can activate the
PI-3-kinase-Akt pathway
Activated Akt serves as a
survival signal for the cell & stimulates growth
