* 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
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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
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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
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4
Q

cell-cell recognition

A

two cells in an animal may communicate by interaction btwn molecules protruding from their surfaces

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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
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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
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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
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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
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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
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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
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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
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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.
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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.

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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
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15
Q

kinase

A

enzyme that catalyzes the transfer of phosphate groups

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16
Q

RTKs vs GPCRs

A

for RTKs, a single ligand-binding event is able to trigger MANY pathways

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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