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BIOLOGY 151 Lecture Notes - Paracrine Signalling, Chemical Synapse, Electrochemical Potential

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School
UMASS-Amherst
Department
Biology
Course
BIOLOGY 151
Professor
Caleb Rounds

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SIGNALING MOLECULES AND CELLULAR
RECEPTORS
● Intercellular signaling: communication between cells
● Intracellular signaling: communication within a cell
● Signaling cells: releases chemical signals in the form of small, usually volatile or soluble
molecules called ligands
● Ligand: a molecule that binds another specific molecule-delivering a signal in the process
● Target cells: where ligands interact with proteins; cells that are affected by chemical
signals; also called RECEPTORS
FORMS OF SIGNALING
● Paracrine signaling, endocrine, autocrine, and direct
PARACRINE
● Signals that act locally between cells that are close together
● They move by diffusion through the extracellular matrix
● Ex. is the transfer of signals across synapses between nerve cells
○ Nerve cell consists of a cell body, dendrites, and axon
● Synaptic signal: chemical signal that travels between nerve cells
● Neurotransmitters: chemical ligands that release signal by the presynaptic cell
● When the neurotransmitter binds the receptor on the surface of the postsynaptic cell, the
electrochemical potential of the target cell changes and the next electrical impulse is
launches
● The neurotransmitters that are released into the chemical synapse get reabsorbed by the
presynaptic cell so the recipient nerve cell can recover quickly and be able to respond
quickly to the next synaptic signal
ENDOCRINE
● Signals from distant cells which originate from endocrine cells
● This signaling usually produce a slower response but have a longer-lasting effect
● The ligands released are hormones
○ They travel the large distances between endocrine cells and their target cells
through the bloodstream
○ They get diluted and are present in low concentrations when they act on their
target cell
AUTOCRINE
● Produced by signaling cells that can also bind to the ligand that’s released
● Regulate pain sensation and inflammatory responses
● If a cell’s infected with a virus, the cell can signal itself to undergo programmed cell
death which kills the virus
DIRECT SIGNALING ACROSS GAP JUNCTIONS
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Related Questions

From the following list, select all options that are correctwith respect to the synapse.

Question 5 options:

A)

the synapse is the site where the plasma membrane that coversthe axon terminal of one neuron makes direct contact with and fusesto the plasma membrane on the cell body or dendrite of anotherneuron
B)

the action potential travels through extracellular fluid in thesynapse to get from one neuron to the next
C)

presynaptic nerve terminals release chemical messengers into thesynapse in response to arrival of an action potential
D)

signaling molecules in the synapse can be broken down by enzymesthat are present on the post synaptic cell membrane
E)

signaling molecules in the synapse can bind to 're-uptake'receptors and be taken back into the presynaptic neuron forbreakdown or for repackaging/reuse
F)

signaling molecules can be taken into and degraded within thepostsynaptic cell
G)

signaling molecules in the synapse function as chemicalmessengers that regulate the opening of ligand-gated channels inthe plasma membranes of post synaptic cells

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

The junction specialized for the transmission between a neuron and another cell is called a (1) _____ ______. Usually, the signal being sent to the receiving cell is carried by chemical messengers called (2) _____. (3) _____ is an example of this type of chemical messenger, which diffuses across the synaptic cleft, combines with protein receptor molecules on the muscle cell membrane, and soon thereafter is rapidly broken down by enzymes. At an (4) ____ synapse, the membrane potential is driven toward the threshold value and increases the likelihood that depolarization and an action potential will occur. At an (5) ____ synapse, the membrane potential is driven away form the threshold value, and the receiving neuron becomes hyperpolarized and is less likely to achieve an action potential. A specific transmitter substance can have either excitatory or inhibitory effects depending on which type of protein channel it opens up in the (6) ____ membrane. (7) ____ are neuromodulators that inhibit perceptions of pain and may have roles in memory and learning, emotional states, temperature regulation, and sexual behavior. (8) ____ ________ at the cellular level is the moment-by-moment tallying of all excitatory and inhibitory signals acting on a neuron. Incoming information is (9) ____ by the cell bodies, and the charge differences across the membranes are either enhanced or inhibited. Some narrow-diameter neurons are wrapped in lipid-rich (10) _______ produced by specialized neuroglial called Schwann cells; each of these is separated from the next by a(n) (11) ________ ________ - a small gap where the axon is exposed to extracellular fluid. A (12) ____ is an involuntary sequence of events elicited by a stimulus. During a (13) _______ ________, a muscle contracts involuntary whenever conditions cause a stretch in length; many of these help you maintain an upright posture despite small shifts in balance. Imbalances can occur at chemical synapses; a neurotoxin produced by Clostridium tetani blocks the release of GABA and glycine, thus freeing the motor neurons from (14) _____ control, which may cause tetanus – a prolonged, spastic paralysis that can lead to death. A. Excitatory H. Stretch reflex B. Inhibitory I. Summed C. Myelin J. Neurotransmitters D. Chemical synapse K. Postsynaptic E. Synaptic integration L. Endorphins F. Exposed node M. Acetylcholine (ACh)