Cell Signalling 1 (19)

Question 1

what type of organisms are entirely reliable on signals from their envr?

Answer 1

single celled organisms

Question 2

multi cell organisms receive signals form other cells that signal for what?

Answer 2

cell division

differentiation

death

Question 3

Autocrine signaling

Answer 3

bind to receptors on cells that secrete them

Question 4

what type of signaling do T-cell lymphocytes practice? & what molecule is excreted?

Answer 4

autocrine signaling

interleukin-2, cytokine

Question 5

paracrine signaling

Answer 5

bind receptors & stimulate nearby cells

Question 6

endocrine signaling

Answer 6

occurs when cells secrete signaling molecules into the blood
long distance, goes throughout the body

Question 7

what type of signaling molecules are hormones?

Answer 7

endocrine signaling

Question 8

synaptic signaling

Answer 8

similar to paracrine signaling but the signal is passed through a synapse (space) b/w the transmitting cell & the receiving cell; occurs b/w a neuron & another cell (usually another neuron or muscle cell)

specialized paracrine signaling

Question 9

signaling by cell contact

Answer 9

must have cells with adjacent PMs (direct conduction from one cell to another without passing through the ECF)

Question 10

gap junctions are what kind of signaling?

Answer 10

signaling by cell contact

Question 11

whats the difference b/w lipophilic & lipophobic signals?

Answer 11

Lipophilic –> cross the PM, receptors are intracellular
Steroid hormones

Lipophobic –> don’t cross PM, receptors are extracellular
Any PRO based signal
Signals are transduced & amplified

Question 12

transduction

Answer 12

process by which a signal crosses the membrane or is transferred to other molecules

Question 13

amplification

Answer 13

process by which the effect of a signal is multiplied/increased

Question 14

what are 2 ways transduction occurs?

Answer 14

phosphorylation

GPROs

Question 15

phosphorylation transduction & ex

Answer 15

ligand binds to receptor, PRO gets phosphorylated & receptor may be mediating it & triggering events inside the cell

RTK receptors

Question 16

G PRO transduction

Answer 16

extracellular receptor binds ligand, once bound will trigger a G PRO & that will amplify a signal causing cell to respond accordingly

Question 17

summary of transduction & amplification

Answer 17

receptor binds signaling molecule

receptor changes shape

Shape change enables the receptor to interact with intracellular PROs

2nd messenger molecules are produced to amplify the signal

various effects can occur from 1 ligand

Question 18

what are 2nd messengers responsible for?

Answer 18

transduction

Question 19

what are 3 reasons why amplification is important?

Answer 19

Initial signaling molecule (hormone) to be in limited concentrations & still be effective

One hormone to activate numerous enzymes (one kinase molecule can activate many other kinase molecules)
(so it has a large enough effect to cause an event)

Coordination of several pathways simultaneously as all are induced by a single signal

Question 20

summary of steroid hormones producing an endocrine signal

Answer 20

steroids are made from cholesterol (small & fat soluble)

travel through blood via carrier PROs

enter cells via diffusion

steroid has a high affinity for receptors in the cytoplasm or nucleus

hormone receptor complex binds to DNA at the promoter region, upstream of genes

transcriptional enhancement occurs

(slow, long-term response)

Question 21

what are some types of steroid hormones?

Answer 21

glucocorticoids (including cortisol)

estradiol

testosterone

progesterone

Question 22

what are the steps in activating glucogenesis?

Answer 22

1. Diffuses into cell
2. Binds specific receptor (PRO)
3. Receptor dimerizes
4. Dimer enter nucleus
5. Dimer binds to GRE response element (DNA) on the PEPCK promoter (& other genes)
6. Increases transcription rate, enzyme amount & enzyme activity gluconeogenesis

Question 23

what are the kinds of lipophobic hormones?

Answer 23

water soluble hormones

PROs

neurotransmitters

cell-cell contacts

Question 24

when is signal transduction used?

Answer 24

lipophobic signaling molecules

Question 25

what are the steps in the signaling pathway for lipophobic signals?

Answer 25

1. Recognition of stimulus by cell-surface receptor (specific, sensitive) 2. “Transfer” across the membrane doesn’t ship ligand, receptor changes shape b/c of ligand & can now interact with an effector 3. Effector (ex: adenylyl cyclase) molecules or a series of molecules on the interior of the membrane or cytosol create the next message (cAMP or calcium ions); usually a series of intervening steps before ultimate response (activations/inactivations) Can produce 2nd messengers 4. Cessation of the response when signal disappears (ex: cAMP phosphodiesterase)

Question 26

what are the diff kinds of movements in the nematode?

Answer 26

normal = sinusoldial mutant G PRO - hyperactivity, sidewinding & twisting mutant G PRO - lethargy, slow & limited tracks

Question 27

what is the structure of a G PRO coupled receptor?

Answer 27

7 transmembrane domains alpha helices

Question 28

how do G PRO coupled receptors work?

Answer 28

through heterotrimeric G PROs Alpha, beta & gamma subunits Alpha & gamma both are embedded in the membrane Beta subunit is free to move elsewhere Turn on effector molecule which makes the 2nd messenger Ex: epinephrine & glucagon turn on adenylyl cyclase to make cAMP (2nd messenger) Others (ex: acetylcholine) use phosphoinositol, DAG 2nd messengers Others (ex: photoreceptors) use cyclic GMP

Question 29

how are GPCRs involved in making 2nd messengers?

Answer 29

binding the ligand causing a conformational change allowing the G-PRO to interact with the effector that produces the 2nd messenger signal

Question 30

GPCR steps

Answer 30

1. Ligand binds to receptor, shape changes & alpha subunits binds to receptor PRO 2. Activation of the G PRO: exchanges GDP for GTP (no hydrolysis) 3. RELAY: alpha dissociates from beta & gamma & binds to effector 4. Activated effector produces 2nd messenger 5. Alpha subunit hydrolyzes GTP --> GDP & deactivates itself 6. Alpha subunit with GDP binds with beta & gamma subunits (trimeric PRO) 7. G PRO coupled receptor kinase (GRK/GPCRK) phosphorylates the receptor 8. Arrestin binds to phosphorylated receptor preventing it from binding with G PROs

Question 31

how do G PROs differ from one another?

Answer 31

alpha subunits

Question 32

what subunit besides the alpha subunit can activate effectors?

Answer 32

beta-gamma complex

Question 33

steps of the cholera toxin causing water loss

Answer 33

Toxin binds to the receptor Toxin brought into the cell via endocytosis Cholera toxin binds to the alpha subunit alpha subunit binds to adenyl cyclase with the toxin & is active adenyl cyclase produces cAMP cAMP activates the chloride channel Na+ & water follow chloride ions out of the cell

Question 34

Steps in stopping the GPCR signal

Answer 34

G RPO hydrolyzes GTP, inactivating itself Receptor is phosphorylated Phosphorylated receptor binds arrestin Arrestin binds to clathrin Endocytosis of receptors occurs