Ch. 9- Cell Communication

The system of communication between cells through signaling pathways is called homeostasis.

false

In the liver, the enzyme glycogen phosphorylase catalyzes the breakdown of glucose.

false

Steroid hormones, such as testosterone and estrogen, are polar signaling molecules.

false

After the binding of a signaling molecule to a surface receptor, the signaling molecule does not enter the cell.

true

After signal transduction has run its course, receptor molecules are removed from the surface by endocytosis; one possible fate of the receptor is to be separated from its signaling molecule and returned to the cell surface.

true

G-protein-coupled receptors are found in both prokaryotes and eukaryotes.

false

In plants, the IP3/DAG pathways control the organism's responses to water loss and changes in light intensity.

true

Steroid hormones are nonpolar molecules derived from cholesterol.

true

In breast cancer, ERα is often lost, which increases cell proliferation.

false

Cross-talk between second messenger pathways is probably involved in particular types of olfactory signal transduction in many animals.

true

In order for a target cell to receive a signal, it must possess a ____ specific to the signaling molecule.

receptor

Adjacent animal cells utilize ____ to rapidly communicate with each other.

gap junctions

Adjacent plant cells utilize ____ to rapidly communicate with each other.

plasmodesmata

How do cells in the body of a multicellular organism communicate with each other?

by way of signaling molecules that interact with specific receptors

Substance B is synthesized in neurons, travels through gap junctions, and triggers the transduction of an electrochemical signal. This is an example of ____.

communication by direct contact

Substance A is synthesized in the liver, travels through the circulatory system bound to a carrier protein, and causes a change in gene expression in a target cell. This is an example of ____.

long-distance signaling

In order for a cell to respond to the signaling molecule epinephrine, it must have ____.

receptors with an epinephrine binding site on the plasma membrane surface

Receptors for polar molecules are found ____, while receptors for nonpolar molecules are located ____.

on the cell surface; within the cell

Nonpolar signaling molecules enter the cell by ____.

simple diffusion

An example of a nonpolar signaling molecule is ____.

testosterone

How does a cell surface receptor respond to the binding of a signaling molecule?

the signal is transduced through the plasma membrane and into the cell

The overall process by which information carried by a signaling molecule is translated into changes that occur inside the cell is called signal ____.

transduction

You have recently identified a molecule you believe to be a signaling molecule associated with signal transduction. All you know about this molecule is that it is hydrophilic; therefore, you expect it to interact with a receptor ____.

on the cell surface

In the 1950s, Earl Sutherland and colleagues discovered that epinephrine ____.

triggers the release of a second messenger which leads to the hydrolysis of glycogen to glucose

In general, a cell receiving a message undergoes three stages of cell signaling. What are these stages?

signal reception, signal transduction, and cellular response

A pathway for cell growth control is conserved between Drosophila and humans, indicating that the pathway is ____.

at least 800 million years old

In the process of quorum sensing, bacteria release signaling molecules in ____ concentrations as cell density ____.

increasing; increases

Quorum sensing ____.

is a type of communication between unicellular organisms

The evolution of which class of molecules played an important role in the development of multicellular organisms?

protein kinases

The two major categories of extracellular signaling molecules that bind to cell surface receptors are ____.

peptide hormones and neurotransmitters

Neurotransmitters are molecules released by ____.

neurons

The surface receptors that recognize and bind signaling molecules are ____.

glycoproteins

The recognition of a chemical signal by a receptor protein in the membrane is most similar to ____.

binding of a specific substrate to the active site of an enzyme

The last protein in a signaling pathway is called the ____.

target protein

Amplification of a signal increases as the ____.

number of enzyme-catalyzed steps increases

In the first step of signal transduction, what is the trigger for the cellular response?

ligand

What is the second step of signal transduction?

transduction

Protein kinases ____.

add phosphate groups to proteins

The effects of protein kinases are reversed by another group of enzymes called ____.

phosphatases

Once transduction of a signal is complete, the receptor and its bound signaling molecule are removed from the cell surface by ____.

endocytosis

The protein kinase activity of the receptor tyrosine kinase (RTK) is located ____ region of the protein.

on the cytoplasmic region

During autophosphorylation, RTKs add phosphate groups to which amino acids?

tyrosine

What happens immediately after a signaling molecule binds to an RTK?

receptor dimerization

Structurally similar RTKs have been found in all multicellular animals, suggesting that ____.

RTKs evolved relatively early in the history of animals

The insulin receptor is an example of a(n) ____.

receptor tyrosine kinase

Substance E is made in the pancreas, travels through the blood, and binds to a surface receptor on a target cell. After dimerization and autophosphorylation, the receptor activates a signaling protein. Substance E is therefore the ligand for ____.

a receptor tyrosine kinase

Arrange the events in the pathway activated by G-protein-coupled receptors (GPCRs) in the correct order.

3→5→1→4→2

Inactive G proteins are ____.

bound to GDP

Activated G proteins ____.

separate into two parts

How many transmembrane domains are present in a G-protein-coupled receptor?

seven

Many of the different types of GPCRs in humans function to ____.

distinguish different volatile molecules for odor recognition

More than 60% of all prescribed drugs target ____, due to their wide physiological impact.

G-protein-coupled receptors

G proteins are inactivated when ____.

GTP is converted to GDP

Many signal transduction pathways utilize second messengers to ____.

relay the message from the inner surface of the plasma membrane throughout the cytoplasm

The amino acid targets of protein kinases in all GPCR pathways are ____.

serine and threonine

Which molecule is a common second messenger?

diacylglycerol

In the cAMP pathway, the G protein activates ____.

adenylyl cyclase

Once activated, cAMP is quickly degraded to AMP by ____, switching off the signal pathway.

phosphodiesterase

In the IP3/DAG pathway, what is the effector molecule?

phospholipase C

Substance C is secreted from a neuron, and binds to its receptor on a nearby cell, triggering an increase in intracellular cAMP. Substance C is therefore a ligand for a ____.

a G-protein-coupled receptor

Ras proteins are of interest to researchers because of their role in ____.

the development of many types of cancer

Inactive Ras is bound to receptor tyrosine kinases by ____.

adapter proteins

Activated Ras ____.

activates MAP kinase (MAP K)

Acetylcholine, a neurotransmitter, binds to ____.

ligand-gated ion channels

Which cellular response follows activation of a ligand-gated ion channel?

generation of an electrical signal

A neuron synthesizes and secretes substance D, which binds to a receptor on the neuron cell membrane, triggering an influx of calcium. Substance D therefore is a ligand for a ____.

a ligand-gated ion channel

Steroid and thyroid hormones do not bind to membrane surface receptors because they ____.

are soluble in the lipid bilayer

Steroid hormones ____.

include testosterone, estrogens, and cortisol

Why are steroid hormones bound to carrier proteins in the blood?

to mask hydrophobic groups on the steroids to allow for circulation in the blood

How do cells distinguish between estrogen and testosterone?

estrogen and testosterone have the same basic structures, but different side chains that are easily distinguished by their individual receptors

Estrogen receptor (ER) α typically ____, while ERβ typically ____.

stimulates cell proliferation; inhibits cell proliferation

Researchers have determined that the growth of hormone-responsive breast cancer cells depends upon ____.

the relative concentrations of ERα and ERβ in the tumor cells

Hormone receptors are comprised of two domains, the hormone binding domain and the ____, which triggers the cellular response.

DNA-binding domain

Substance A is secreted by the liver, travels through the circulatory system bound to a carrier protein and causes a change in gene expression in its target cell. Substance A is therefore a ligand for .

a steroid hormone receptor

Nitric oxide (NO) binds to an .

internal receptor and activates a second messenger cascade

NO can only function as a paracrine regulator because.

it is rapidly converted into nitrates and nitrites

How is the NO pathway manipulated by Viagra to treat erectile dysfunction?

the breakdown of cGMP is inhibited

NO binds to and activates to trigger its cellular response.

guanylyl cyclase

Communication and integration of responses between simultaneously occurring cell signaling pathways is called ____.

cross-talk

Hormone-independent steroid hormone receptor activation is an example of ____.

cross-talk

Cell communication by direct contact

direct contact

Paracrine regulation

paracrine regulation

Autocrine regulation

autocrine regulation

Long-distance signaling

long-distance signaling

Communication used by neurotransmitters acting on neuron across a synapse

paracrine regulation

Communication used by cardiac muscle cells to synchronize heart contractions

direct contact

Mediation of the fight-or-flight response by epinephrine

long-distance signaling

Binds to and activates the enzyme guanylyl cyclase

nitric oxide

Directly bind to DNA to affect transcription

hormone receptors

Lithium reduces the activity of this pathway

IP3/DAG

G protein activated by a receptor tyrosine kinase

Ras

Binds to acetylcholine

ligand-gated ion channel

Pathway triggered by glucagon to stimulate glycogen breakdown

cAMP

Defects in this receptor type can lead to diabetes and dwarfism

receptor tyrosine kinase

Converts an extracellular signal into an intracellular response

signal transduction

Why is it necessary for cells to communicate with each other in a regulated way?

regulated communication controls growth and development and coordinates the functions of tissues and organs

Why is cell communication considered evolutionarily ancient?

key protein components and even entire pathways are shared by prokaryotes and eukaryotes and conserved across distant organisms (e.g., Drosophila and humans)

What is the function of signal transduction?

conversion of an external chemical signal into intracellular biochemical reactions that produce a specific cellular response

Amplification is an important characteristic of signal transduction pathways involving surface receptors. What is amplification and how is it accomplished in the cell?

amplification increases signal magnitude because activated enzymes in the cascade can activate hundreds or thousands of downstream molecules

How does cAMP regulate glucose levels in mammals?

when blood glucose falls, glucagon triggers a cAMP pathway leading to glycogen breakdown to glucose