* 11 Flashcards
Saccharomyces cerevisiae mating
- identify mates by chem signaling
- 2 mating types: a and alpha
- ‘a’ cells secrete a signaling molecule called ‘a factor’, which can bind to specific receptor proteins on nearby ‘alpha’ cells
- binding of the factors induces changes in the cells that lead to their fusion
signal transduction pathway
- A series of steps linking a mechanical, chemical, or electrical stimulus to a specific cellular response.
- strikingly similar in yeast and mammals, bacteria and plants
quorum sensing
- bacterial cells secrete small molecules that can be detected by other bacterial cells
- the concentration of such signaling molecules, sensed by the bacteria, allows them to monitor the local density of cells, a phenomenon called QUORUM SENSING
- allows bacterial populations to coordinate their behaviors so they can carry out activities that are only productive when performed by a given number of cells in synchrony – ex: biofilm
cell-cell recognition
two cells in an animal may communicate by interaction btwn molecules protruding from their surfaces
local regulators
- messenger molecules secreted by the signaling cell that travel only short distances
- influence cells in the vicinity
- ex: growth factors – compounds that stimulate nearby target cells to grow and divide
- numerous cells can simultaneously receive and respond to the molecules of growth factor produced by a single cell in their vicinity
glycogen breakdown
- Sutherland studied how epinephrine, aka adrenaline, stimulates glycogen breakdown
- releases glucose 1-phosphate, which the cell (liver/muscle) converts to glucose 6-phosphate
- the cell can use this compound, an early intermediate in glycolysis, for energy production OR
- the compound can be stripped of phosphate and released from the cell into the blood as glucose, which can fuel cells throughout the body
- thus, 1 effect of epinephrine is the mobilization of fuel reserves
Sutherland’s observations
- epinephrine stimulates glycogen breakdown W/O PASSING THRU PLASMA MEMBRANE by somehow activating a cytosolic enzyme, GLYCOGEN PHOSPHORYLASE
- but no breakdown occurred when epinephrine was added to a test-tube mixture of glycogen phosphorylase + glycogen – epinephrine could activate glycogen phosphorylase only when the hormone was added to a sol’n containing intact cells
- the binding of epinephrine to a receptor protein in a liver cell’s plasma membrane leads to activation of glycogen phosphorylase
Sutherland’s 2 conclusions
- epinephrine doesn’t interact directly w/ the enzyme responsible for glycogen breakdown; an intermediate step(s) must be occurring inside the cell
- plasma membrane is somehow involved in transmitting the signal
reception
- target cell’s detection of a signaling molecule coming from outside the cell
- a chem signal is ‘detected’ when the signaling molecule binds to a receptor protein
transduction
- initiated when the binding of the signaling molecule changes the receptor protein in some way
- the transduction stage converts the signal to a form that can bring about a specific cellular response
ligand binding
- generally causes a receptor protein to undergo a change in shape
- -> (most) shape change directly activates the receptor, enabling it to interact w/ other cellular molecules OR
- -> for others, the immediate effect is to cause the aggregation of 2 or more receptor molecules, which leads to further molecular events inside the cell
GPCR
- G protein coupled receptor
- A signal receptor protein in the plasma membrane that responds to the binding of a signaling molecule by activating a G protein.
G protein
A GTP-binding protein that relays signals from a plasma membrane signal receptor, known as a G protein-coupled receptor, to other signal transduction proteins inside the cell.
GPCR structure
- they make up a large family of eukaryotic receptor proteins w/ a secondary structure in which the single polypeptide has SEVEN transmembrane ALPHA helices
- specific loops btwn the helices form binding sites for signaling and G protein molecules
kinase
enzyme that catalyzes the transfer of phosphate groups
RTKs vs GPCRs
for RTKs, a single ligand-binding event is able to trigger MANY pathways
RTK structure
- before signaling molecule binds, the receptors exist as individual units (monomers)
- each monomer has an extracellular ligand-binding site, an ALPHA helix spanning the membrane, and an intracellular tail containing multiple tyrosines
RTK
- receptor tyrosine kinases
- belong to a major class of plasma membrane receptors characterized by having enzymatic activity
cancer
abnormal RTKs that function even in the absence of signaling molecules are associated w/ many types of cancer
intracellular receptors
- found in cytoplasm/nucleus of target cells
- these chem messengers are able to pass thru the target cell’s plasma membrane b/c they’re either hydrophobic enough or small enough; ex: steroid hormones, thyroid hormones, nitric oxide
protein kinase
An enzyme that transfers phosphate groups from ATP to a protein, thus phosphorylating the protein.
RTK vs most protein kinases
- most cytoplasmic protein kinases act on proteins diff from themselves
- most phosphorylate either 2 of other amino acids, serine or threonine, rather than tyrosine
phosphorylation
- each brings a shape change
- each shape change results from the interaction of the newly added phosphate groups w/ charged or polar amino acids
- often changes a protein from inactive –> active, but can decrease the protein’s activity
PP
- protein phosphatases
- enzymes that catalyze the removal of the phosphate groups from the proteins (dephosphorylation), making them inactive and available for reuse
- provide the mechanism for turning off the signal transduction pathway when the initial signal is no longer present