Lecture 8: Cell-Cell Communication Flashcards
Cells can respond to signals
inside and outside the body
why do cells need signals
• Need to respond to a changing environment
o Ex: increased availability of glucose, cells want to take it in. Need to increase their expression of glucose transporters
o Insulin signaling controls the response
• Cells need to communicate with each other for their own and the organism’s needs
o Cell-cell communication
o Muscle cell releases vasodilator when it needs more glucose/oxygen
other uses for signaling
• Communication btw organisms who cannot communicate verbally (yeast bacteria, insects)
o Find mates
o Communicate danger
o Ants
very local distance
: two cells are connected by gap junctions (animal; what happens in one cell happens to the other); surface proteins of two cells interact
local distance
secreted molecules and/or contact
long distance
secreted molecules that diffuse or are carried (by the bloodstream) throughout organism
autocrine signaling
a cell secretes a molecule that effects itself
paracrine siganling
a cell secretes a molecule that effects neighboring cells
endocrine signaling
a molecule is secreted into the bloodstream
targets
cells receiving the signal
is a receptor required
yes
ligand
secreted molecule for the receptor
gap junction
used for direct intercellular signaling
contact dependent signaling
target cell; membrane bound signaling molecule
stages of signaling
• Receptor activation: signal binds to receptor molecule on target cell surface
o Binding of a signaling molecule causes a conformational change in a receptor that activates its function
• Signal Transduction: the binding of the signaling molecule changes the receptor protein in some way; converting the signal to bring about a cellular response
o Amino acids are changed
o When proteins bind their ligand, they undergo shape changes
o Activated receptor stimulates a series of proteins that forms a signal transduction pathway
• Cellular Response: some cellular activity is triggered
o Signal transduction pathway affects the functions and/or amounts of cellular proteins, thereby producing a cellular response
reception
o Polar signaling molecules cannot enter the cell, so their receptors are found embedded in the membrane
3 major types of receptors
- enzyme-linked receptors
- G protein coupled receptors (GPCRs)
- Ligand gated ion channel receptors
- Make up 30% of the human body
enzyme linked receptors
o Found in all living species
o Extracellular domain binds signal
o Causes intracellular domain to become functional catalyst
o Most are protein kinases
protein kinases
an enzyme that catalyzes the transfer of phosphate group (from ATP onto a protein)
- Exist as monomers, ligand binding triggers dimerization and phosphorylation
- New conformation allows recognition by relay molecules
- Triggers downstream signaling events
what happens when you add a phosphate group
you change the shape of the protein which then changes the function
GPCR
o Ex: yeast mating signals, epinephrine, many hormones and neurotransmitters, embryonic development, sensory reception
o Many diseases wreak havoc by interfering with GPCR signaling (cholera, pertussis)
o 60% of all current prescription drugs work by influencing GPCR signaling
o receptor is associated with G protein
o G protein is inactive
o Ligand binds to receptor, receptor changes shape and binds G protein, activating it
o G protein, now activated, releases from receptor and diffuses along mb, activating nearby enzyme
ion channel receptors
o Ex: neurotransmitters and their receptors
o Ion channel is closed
o Ligand binds
o Channel opens
o Ions flow from one side of membrane to the other, changing the polarization
polar molecule receptors need to be on the ________ in order to diffuse across the membrane
outside
intracellular receptors
o Nonpolar signaling molecules can enter the cell, so their receptors are found in the cytoplasm or nucleus
• Steroid hormones, thyroid hormone, nitric oxide (bc of size not polarity)
o These signaling molecules enter ALL cells of the body, but only trigger reactions in those with receptors
o These signaling molecules often initiate gene transcription
transduction
o Often a chain of protein kinases phosphorylate each other until a downstream target is phosphorylated and activated
o Each of these kinases must be dephosphorylated by protein phosphatases and returned to the inactive state
Second messengers
o Not all components of signaling pathways are proteins
o Non-protein small molecuels can be activated by GPCRs or protein kinases and act as second messengers
• Ca^2+ ions
GPCR act
• Cyclic AMP
Why have so many levels of signaling
o Levels of control: being able to inhibit different levels of pathways allows for fine tuned control over responses
o Amplification: one molecule of ligand binds to the GPCR, but the activated enzyme can convert many molecules of ATP to cAMP
o Different responses by different cells
Apoptosis
o Programmed organized cell death
o A cell orchestrates its own destruction and cleans up after itself as it dies
o Necessary for
• Development
• Cancer prevention
• Neurological prioritizing
• Protection against viral and bacterial infection
• Cells stuff everything in their lysosomes before death
o Can be autonomous or regulated by other cells (immune)
Hormones
o Chemical messengers that travel in blood
o Have the potential to reach all cells of the body
o Only cells with receptors will bind and respond
o Widespread communication
o Different cells can have different receptors and produce different responses
