* 11 Flashcards
1
Q
Saccharomyces cerevisiae mating
A
- 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
2
Q
signal transduction pathway
A
- 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
3
Q
quorum sensing
A
- 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
4
Q
cell-cell recognition
A
two cells in an animal may communicate by interaction btwn molecules protruding from their surfaces
5
Q
local regulators
A
- 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
6
Q
glycogen breakdown
A
- 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
7
Q
Sutherland’s observations
A
- 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
8
Q
Sutherland’s 2 conclusions
A
- 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
9
Q
reception
A
- 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
10
Q
transduction
A
- 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
11
Q
ligand binding
A
- 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
12
Q
GPCR
A
- 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.
13
Q
G protein
A
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.
14
Q
GPCR structure
A
- 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
15
Q
kinase
A
enzyme that catalyzes the transfer of phosphate groups
16
Q
RTKs vs GPCRs
A
for RTKs, a single ligand-binding event is able to trigger MANY pathways
17
Q
RTK structure
A
- 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
18
Q
RTK
A
- receptor tyrosine kinases
- belong to a major class of plasma membrane receptors characterized by having enzymatic activity
19
Q
cancer
A
abnormal RTKs that function even in the absence of signaling molecules are associated w/ many types of cancer
20
Q
intracellular receptors
A
- 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
21
Q
protein kinase
A
An enzyme that transfers phosphate groups from ATP to a protein, thus phosphorylating the protein.
22
Q
RTK vs most protein kinases
A
- most cytoplasmic protein kinases act on proteins diff from themselves
- most phosphorylate either 2 of other amino acids, serine or threonine, rather than tyrosine
23
Q
phosphorylation
A
- 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
24
Q
PP
A
- 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
25
Q
second messengers
A
- small non-protein water-soluble molecules/ions involved in signaling pathways
- b/c they’re small and water-soluble, they can readily spread throughout the cell by diffusion
- ex: cyclic AMP, Ca ions (Ca2+ more popular)
26
Q
cAMP pathways
A
- cyclic adenosine monophosphate
- G proteins, GPCRs, protein kinases
- the immediate effect of cAMP is usually the activation of a serine/threonine kinase called PROTEIN KINASE A
- the activated protein kinase A then phosphorylates various other proteins
27
Q
cAMP and epinephrine
A
- when epinephrine outside the liver cell binds to a specific receptor protein, the protein activates the enzyme ADENYLYL CYCLASE (embedded in plasma membrane), which in turn can catalyze the synthesis of many molecules of cAMP
- cAMP broadcasts the signal to the cytoplasm; doesn’t last long b/c another enzyme, PHOSPHODIESTERASE, converts cAMP to AMP (another surge of epinephrine is needed to boost cAMP’s cytosolic concentration again)
28
Q
cholera
A
- Vibrio cholerae bacteria form a biofilm on the lining of the small intestine and produce a toxin
- this toxin is an enzyme that chemically modifies a G protein involved in regulating salt and water secretion
- the modified G protein is unable to hydrolyze GTP to GDP; it remains stuck in its ACTIVE form, continuously stimulating adenylyl cyclase to make cAMP
- the resulting high concentration of cAMP causes the intestinal cells to secrete large amounts of salts into the intestines, w/ water following by osmosis
29
Q
cGMP
A
acts as a signaling molecule whose effects include relaxation of smooth muscle cells in artery walls
30
Q
Viagra
A
- compound that inhibits the hydrolysis of cGMP to GMP, thus prolonging the signal
- originally prescribed for chest pains b/c it increased blood flow to the heart muscle
- leads to blood vessel dilation
31
Q
other second messengers involved in Ca2+ release
A
inositol triphosphate (IP3) and diacylglycerol (DAG), produced by cleavage of the phospholipid PIP2 by phospholipase C
32
Q
fine tuning: signal amplification
A
the amplication effect stems from the fact that these proteins persist in the active form long enough to process numerous molecules of substrate before they become inactive again
33
Q
diverging pathway (produces 2 responses)
A
often involve RTKs (which can activate multiple relay proteins) or 2nd messengers (which can regulate numerous protiens)
34
Q
scaffolding protein
A
A type of large relay protein to which several other relay proteins are simultaneously attached, increasing the efficiency of signal transduction.
35
Q
WAS
A
- Wiskott-Aldrich syndrome; inherited disorder
- absence of a single relay protein; normally, it’s located just beneath the cell surface; it interacts w/ microfilaments of cytoskeleton and w/ several diff components of signaling pathways that relay information from the cell surface
- effects: abnormal bleeding, eczema, predisposition to infections and leukemia
36
Q
signal termination
A
- as the external concentration of signaling molecules falls, fewer receptors are bound at any given moment, and the unbound receptors revert to their inactive form
- cellular response occurs only when the concentration of receptors w/ bound signaling molecules is above a certain threshold
37
Q
apoptosis
A
- cellular agents chop up the DNA and fragment the organelles
- cell shrinks and becomes lobed (“blebbing”)
- the cell’s parts are packaged up in vesicles that are engulfed and digested by specialized scavenger cells
- neighboring cells are protected from damage that they would otherwise suffer if a dying cell leaked out its concentrs, including its digestive enzymes
38
Q
mitochondrial apoptotic pathway: intracellular signals
A
- from nucleus: generated from DNA has suffered irreparable damage
- from ER: when excessive protein misfolding occurs
39
Q
apoptotic pathways in mammals
A
- certain mitochondrial proteins are triggered to form molecular pores in the mitochondrial outer membrane, causing it to leak and release other proteins that promote apoptosis
- these other proteins include cytochrome c, which functions in mitochondrial e- transport in healthy cells but acts as a cell death factor when released from mitochondria
40
Q
C. elegans apoptotic genes
A
- ced-3 and ced-4: encode proteins essential for apoptosis; these and most other proteins involved in apoptosis are continually present in cells, but in in active form
- protein Ced-3 is the chief caspase in C. elegans.caspases are the main proteases of apoptosis.
- Ced-9 protein: in outer mitochondrial membrane; as long as it’s active (inhibiting Ced-3 and Ced-4 activity), apoptosis is inhibited
