BIOB11H3 Lecture Notes - Lecture 23: Signal Transduction, Guard Cell, Sea Urchin

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19 Feb 2017

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Lec 23- Signal Transduction III

Lecture Notes

• Calcium Signaling

• Ca2+ stored in ER, IP3 activates ion channel, triggering Ca2+ release which is a…

• Second messengers: a substance formed inside a cell in response to the binding of a first

messenger (e.g. hormone)

• Like cAMP, Ca2+ acts a s potent second messenger but effect may be variable depending

on cell type & presence of components affected by changes in Ca2+ levels

• Following are 3 examples of calcium induced calcium release →

• Fig 15-28: Example #1 –Cardiac muscle

• 1. Depolarization in membrane voltage causes the opening of the voltage-gated calcium

channels in the plasma membrane, allowing entry of small amount of Ca2+ into cytosol

• 2. Calcium ions bind to receptors in SER membrane

• 3. Release of stored Ca2+ into the cytosol which triggers cells contraction

• 4. Calcium ions removed from cytosol by Ca2+ pumps located in SER membrane

• 5. Na+/Ca2+ secondary transport system in plasma membrane also helps transport

• Fig 15-29: Example #2- Sea urchin eggs

• Calcium wave initiated by fertilization drives cell division

• Unfertilized egg was injected w/ calcium-sensitive fluorescence dye, fertilized &

photographed to see rise in Ca2+ as internal calcium released from SER

• Now Ca2+ activates cell division through CDK activation; rapid embryogenesis occurs

• Fig 15-32: Example #3- Guard cells & stomata

• Stomate: pore

• Guard cells: specialized pair that controls stomatal aperature

• Guard cell shape changes to control pore opening

• Stomata are kept open as turgor pressure is kept high within the guard cells, causing them

to bulge outward

• ABA: hormone controlling stomatal pore size as calcium responds to it

o High temp, low humidity causes ABA to be produced

o H2O loss regulated by changes in solute (K+) concentration

• 1. When ABA levels rise, calcium ion channels in the plasma membrane are opened

allowing the influx of Ca2+

• 2. Triggers the release of Ca2+ from internal stores

• 3. Subsequent elevation of intracellular [Ca2+] closes K+ influx channels & opens K+

efflux channels

• 4. These ion movements lead to a drop in internal solute concentration & the osmotic loss

of water

• Receptor Tyrosine Kinases (RTK)

• Two general intracellular STPs; one is G-protein mediated & other uses RTKs

• Fig 15-17: Steps in the activation of an RTK

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Document Summary

Depolarization in membrane voltage causes the opening of the voltage-gated calcium channels in the plasma membrane, allowing entry of small amount of ca2+ into cytosol: 2. Calcium ions bind to receptors in ser membrane: 3. Release of stored ca2+ into the cytosol which triggers cells contraction: 4. Calcium ions removed from cytosol by ca2+ pumps located in ser membrane: 5. When aba levels rise, calcium ion channels in the plasma membrane are opened allowing the influx of ca2: 2. Triggers the release of ca2+ from internal stores: 3. Subsequent elevation of intracellular [ca2+] closes k+ influx channels & opens k+ efflux channels: 4. Once bound tyrosine residues on the docking protein are phosphorylated by the receptor. Insulin receptor exists as a tetramer w. 2 extracellular subunits & 2 transmembrane subunits: 1. Conformational change in , kinase activation: 3. Insulin receptor substrate (irs) molecules also phosphorylated (when they bind to receptor. Activation of pi3k enzyme leads to pip3 lipid formation: 2.

Related Questions

Biochemistry Help!!

1. Which statement is True regarding the Na+ voltage-gated channel in neurons?

a) aspartate residues are parrt of the Voltage-sensing helices

b)similiar to the potassium ion channel, it exisits as a tetramer in the membrane

c) Positivie membrane potentials on the extracellular side will close the channel.

2. Which membrane lipid serves as a reservoir of messenger molecules for signal transduction?

a)Shingomyelin (SM)

b) tarucholic acid (TA)

c) thromboxane A2 (TXA2)

d) Phosphatidylserine (PS)

e) Phosphatidylinositol 4,5-bisphosphate (PIP2)

3) G protein-coupled activation of phospholipase C directly generates which second messenger?

a) inositol-1,4,5-trisphosphate

b)calcium

c) diacylglycerol

d) both diacylglyerol and inositol-1,4,5-trisphosphate

e) both inositol-1,4,5-trisphosphate and calcium

4) Protein Kinase C is allosterically regulated by which second messangers?

a)diacylglyerol (DAG)

b) Calcium (Ca+2)

c) inositol trisphosphate (IP3)

d) both diacylglyerol (DAG) and Calcium (Ca+2)

e) both inositol trisphosphate (IP3) and diacylglyerol (DAG)

5) Phospholipase C hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) to form which signaling molecule that triggers Ca+2 release from the endoplasmic reticulum?

a) diacylglycerolphosphate (DAGP)

b) inositol 1,4,5-triphosphate (IP3)

c) diacylglycerol (DAG)

d) inositol 4,5- bisphosphate (IP2)

e) insoitol 5-monophosphate (IP1)

QUESTION 1

Which of the following is an example of an extracellular signal molecule?

	a.	IP₃
	b.	cAMP
	c.	Insulin
	d.	Diacylglycerol

2 points

QUESTION 2

Nuclear hormone receptors _____

	a.	Bind to water soluble ligands
	b.	Activate second messengers
	c.	Regulate transcription in response to ligand binding
	d.	Are normally located on the plasma membrane

2 points

QUESTION 3

Which of the following does not occur when a receptor tyrosine kinase is bound by ligand?

	a.	Phosphorylation of the RTK
	b.	Cytoplasmic proteins bind the phosphorylated RTK
	c.	Dimerization of the RTK
	d.	The RTK binds to DNA to regulate transcription

2 points

QUESTION 4

Which of these is a logical signal-transduction pathway?

	a.	An intracellular receptor activates phospholipase C, which cleaves a membrane protein to form IP₃, which then activates the opening of an ER channel protein, which releases cyclic AMP into the cytoplasm, where it binds to an intracellular enzyme that carries out a response.
	b.	A G-protein-linked receptor activates G protein, which activates phospholipase C, which cleaves a membrane lipid to form IP₃, which binds to a calcium channel on the ER, which opens to release calcium ions into the cytoplasm, which bind to an intracellular enzyme that carries out a response.
	c.	An ion-channel receptor opens, allowing a steroid hormone to enter the cell; the steroid hormone then activates protein kinases that convert GTP to GDP, which binds to an intracellular enzyme that carries out a response.
	d.	A tyrosine-kinase receptor activates adenylyl cyclase, which activates phospholipase C, which converts ATP into cyclic AMP, which binds to an intracellular enzyme that carries out a response.

2 points

QUESTION 5

Which of the following is an example of signal amplification?

	a.	activation of an enzyme molecule
	b.	activation of a specific gene by a growth factor
	c.	Breakdown of many cAMP molecules
	d.	activation of 100 molecules by a single signal binding event

2 points

QUESTION 6

Consider a signal transduction pathway that utilizes cAMP as a second messenger to activate PKA (Protein Kinase A). Which of the following situations will result in the cellular response?

		The G protein releases GDP and binds to GTP
		The target protein (adenylyl cyclase) is inactive
		The regulatory subunits of PKA (Protein Kinase A) are bound to the catalytic subunits
		The appropriate G protein is bound to GDP

2 points

QUESTION 7

Which of the following is found in only some signal transduction pathways? [In other words, which is not found in all signal transduction pathways?]

		Receptor protein
		Extracellular signal molecule
		Intracellular signaling molecule
		Cellular response
		Effector protein

2 points

QUESTION 8

The enzyme that specifically catalyzes the conversion of ATP to cAMP is:

		Adenylyl phosphatase
		Adenylyl kinase
		Adenylyl dehydrogenase
		Adenylyl cyclase

2 points

QUESTION 9

If an animal cell suddenly lost the ability to produce GTP, what might happen to its signaling system?

		It would use ATP instead of GTP to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane.
		It would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane.
		It would employ a transduction pathway directly from an external messenger.
		It would be able to carry out reception and transduction but would not be able to respond to a signal.

2 points

QUESTION 10

A hormone signal is sent from the brain to other parts of the body via the bloodstream. Why do only certain cells respond to this signal?

		Hormones do not last long enough in the bloodstream to stimulate a cellular response
		Only cells that have a specific transcription factor gene will be able to respond to the signal
		Only cells in the immediate vicinity of the cell sending the signal will respond
		Only cells that have a receptor for the specific signal will be able to respond to it

cerisehedgehog846

The insulin receptor is a
a. phosphatase.
b. kinase.
c. phosphodiesterase.
d. cAMP molecule.
e. G protein.

What do the following receptors all have in common: G protein-linked receptors, protein kinases, and ion channels?
Select one:
a. Conformational change once the ligand is bound
b. Ligand binding
c. Amplification of the signal
d. All of the above

Diacylglycerol
Select one:
a. activates G proteins.
b. hydrolyzes phosphatidyl inositol-bisphosphate.
c. is released from the cell as a paracrine-signaling molecule.
d. opens Ca2+ channels.
e. activates protein kinase C

Gap junctions
Select one:
a. permit metabolic cooperation among linked cells.
b. are present on few copies per cell.
c. contain membrane lined bridges.
d. are channels about 1. 5 mm in diameter.
e. allow large molecules and ions to pass rapidly between cells.

Smooth muscle cells in the airways relax while those in the blood vessels contract in response to the hormone epinephrine. What would you expect to be different in these two types of cells exposed to epinephrine?
Select one:
a. Presence of epinephrine receptors.
b. Exposure to epinephrine released by neighboring cells.
c. Activation of protein kinases.
d. Rate of metabolism.
e. Types of proteins expressed.

The second messenger IP3
Select one:
a. is released from the cell as a paracrine-signaling molecule.
b. hydrolyzes phosphatidyl inositol-bisphosphate.
c. activates protein kinase C.
d. opens Ca2+ channels.
e. activates G proteins.

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BIOB11H3 Lecture Notes - Lecture 23: Signal Transduction, Guard Cell, Sea Urchin

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