MCB Chapter 9- cell communication

Cellular communication consists of four essential components

a signaling cell, a signaling molecule, a receptor protein, and a responding cell

signal trasnduction

The process in which an extracellular molecule acts as a signal to activate a receptor, which transmits information through the cytoplasm. - during this once molecule activates the next molecule, and so on - an important aspect is that the signal is often amplified at each step in the pathway, as a result a low signal concentration can have a large effect on the responding cell

Phosphatases remove the phosphate groups added by PKA, inactivating PKA's target proteins

The signal to increase heart rate carried by adrenaline can be reversed in at least four ways: (1) by decreasing the amounts of the signaling molecule available to bind and activate the G protein-coupled receptor; (2) by inactivating the G protein; (3) by decreasing the amount of the second messenger cAMP; and (4) by dephosphorylating the target proteins that cause the increased rate of contraction of the muscle cells.

Recall from the text the example of cell communication in Streptococcus pneumoniae: the rate of DNA uptake by pneumococcal cells increases sharply when they are at high density due to changes in gene expression brought about by signaling between cells. If the pneumococcal cells did not express receptor protein, how would the rate of DNA uptake be affected when the cells reach high density? There would be a larger than normal increase in the rate of DNA uptake. There would be a smaller than normal increase in the rate of DNA uptake. There would be no change in the rate of DNA uptake. There would be a decrease in the rate of DNA uptake.

There would be no change in the rate of DNA uptake.

Step in cell signanling Example: Adrenaline

- AD binds to a g protein coupled receptor - when bound onto a g protein coupled receptor on cardiac muscle cells, GDP in the G protein is replaced by GTP and the G protein is activated. - The GTP bound alpha subunit then binds to and activates an enzyme in the cell membrane called adenyly cyclase. -Adenylyl cyclase converts the nucleotide ATP into cyclic AMP (cAMP). Cyclic AMP is known as a second messenger. - cAMP then binds to and activates another molecule, a kinase called protein kinase A (PKA).

Kit (a well studied receptor kinase)

- In vertebrates, signaling through the Kit receptor kinase is important for the production of pigment in skin, feathers, scales, and hair. The conserved function of this receptor can be seen in individuals with mutations in the kit gene, think of the snake that had diff. colors

how does cell signaling lead to cancer

- Many cancers arise when something goes wrong with the way a cell responds to a signal that leads to cell division or, in some cases, when a cell behaves as if it has received a signal for cell division when in fact it hasn't. Defects in cell signaling that lead to cancer can take place at just about every step in the cell signaling process. - In some cases, a tumor may form as the result of the overproduction of a signaling molecule or the production of an altered form of a signaling molecule. - In other cases, the source of the problem is the receptor. For example, individuals with some forms of cancer have from 10 to 100 times the normal number of receptors for a signaling molecule called epidermal growth factor (EGF). As a result, the cell is more responsive to the normally low levels of EGF in the body. The EGF receptor is a receptor kinase, like the PDGF receptor. Under normal conditions, binding of EGF to its receptor leads to the controlled division of cells. However, in cancer, the presence of excess receptors heightens the response of the signaling pathway, leading to abnormally high gene expression and excess cell division. This is the case, for example, in certain breast cancers, in which an EGF receptor called HER2/neu is overexpressed. - Farther down the pathway, mutant forms of the Ras protein are often present in cancers. One especially harmful mutation prevents Ras from converting its bound GTP to GDP. The protein remains locked in the active GTP-bound state, causing the sustained activation of the MAP kinase pathway. More than 30% of all human cancers involve abnormal Ras activity as a result of one or more mutations in the ras gene.

The four basic steps in cell communication

- The signal binds to a receptor which is them activates - the signal is transmitted to the interior of the cell by a signal transduction pathway - the cell responds for example by activating an enxyme or turning on transcription of a gene - the response is terminated so that new signals can be received

example of receptor kinases When you get cut

- The signaling molecule platelet-derived growth factor (PDGF) helps the healing process get started. When platelets in the blood encounter damaged tissue, they release a number of proteins, including PDGF. PDGF is the signaling molecule that binds to PDGF-specific receptor kinases on the surface of cells at the site of a wound. - (Receptor kinases have an extracellular portion that binds the signaling molecule and an intracellular portion that is a kinase, an enzyme that transfers a phosphate group from ATP to another molecule.) - A single molecule of PDGF binds to the extracellular portion of two receptors, causing the receptors to partner with each other. This partnering of two similar or identical molecules is called dimerization. Dimerization activates the cytoplasmic kinase domains of the paired receptors, causing them to phosphorylate each other at multiple sites on their cytoplasmic tails - The addition of these phosphate groups provides places on the receptor where other proteins bind and become active - One of the downstream targets of an activated receptor kinase is Ras. Ras is a G protein, but in contrast to the three-subunit G proteins discussed earlier, Ras consists of a single subunit, similar to the α subunit of the three-subunit G proteins. In the absence of a signal, Ras is bound to GDP and is inactive. However, when Ras is activated by a receptor kinase, it exchanges GDP for GTP. Activated GTP-bound Ras triggers the activation of a protein kinase that is the first in a series of kinases that are activated in turn, as each kinase phosphorylates the next in the series. - The final activated kinase in the series enters the nucleus, where it phosphorylates target proteins. Some of these proteins include transcription factors that turn on genes needed for cell division so that your cut can heal. - he signals received by receptor kinases are amplified as the signal is passed from kinase to kinase. Each phosphorylated kinase in the series activates multiple molecules of the downstream kinase, and the downstream kinase in turn activates many molecules of another kinase still farther downstream. In this way, a very small amount of signaling molecule (PDGF in our example) can cause a large-scale response in the cell. - Receptor kinase signaling is terminated by the same basic mechanisms that are at work in G protein-coupled receptor pathways. For example, protein phosphatases inactivate receptor kinases and other enzymes of the MAP kinase pathway. Furthermore, Ras hydrolyzes GTP to GDP, just like the G protein α subunit. Shortly after Ras binds to GTP and becomes active, Ras converts GTP to GDP and becomes inactive. Without an active receptor kinase to generate more active Ras, activation of the MAP kinase pathway stops.

ligand binding site

- a specific part of the receptor protein in which a singnaling molecule binds to. This binding causes a conformational change which activates the receptor, because it is through this change that the receptor passes the message from the signaling molecule to the interior of the cell. (this is similiar to when the substrate binds to the active site of an enzyme) - the bond is noncolvalent and highly specific: The signaling molecule binds only to a receptor with a ligand-binding site that recognizes the molecule

how is the signaling pathway for adrenaline terminated

- first: most ligands, including adrenaline, do not bind to their receptors permanently. The length of time a signaling molecule remains bound to its receptor depends on how tightly the receptor holds on to it, a property called binding affinity. - Once adrenaline leaves the receptor, the receptor reverts to its inactive conformation and no longer activates G protein - Even when a receptor is turned off, a signal will continue to be transmitted unless the other components of the signaling pathway are also inactivated. A second place where the signal is terminated is at the G protein itself.G proteins can catalyze the hydrolysis of GTP to GDP and inorganic phosphate. This means that an active, GTP-bound α subunit in the "on" position automatically turns itself "off" by converting GTP to GDP. In fact, the α subunit converts GTP to GDP almost as soon as a molecule of GTP binds to it. -Farther down the pathway, an enzyme converts the second messenger cAMP to AMP, which no longer activates protein kinase A - Phosphatases remove the phosphate groups added by PKA, inactivating PKA's target proteins

contrast betw g protein coupled receptors and kinase activation

- g typically leads to shorter term changes like activating enzymes or opening ion channels while kinase is a used for longer term processes like development

paracrine signaling

- happens when cells are close to each other and don't require the circulatory system to deliver the signaling molecule - instead the SM can move by diffusion - the signal is usually small, h2o soluble molecule such as a growth factor.

autocrine signaling

- happens when signaling molecules are released by a cell and then bind to receptors on the very same cell - esspecially important to mutlicellular organisms during the development of the embryo - can be used by cancer cells to promote cell division -

how does communication between cells occur in complex mutlicellular eukaryotes

- it involves communication between cells within the same organism - the distance between communicating cells varies considerably - when the cells are far apart, the signaling molecule is transported by the circulatory system - when they are close, the signaling molecule simply moves by diffusion - some cells are attached to one another, in this case the signaling molecule is not released from the signaling cell at all.

how does communication between cells occur in prokaryotes and unicellular eukaryotes

- it occurs between individual organisms

what is required when a cell communicates with another cell through direct contact

- requires that the two communicating cells be in physical contact with each other - without diffusion - A transmembrane protein on the surface of one cell acts as the signaling molecule, and a transmembrane protein on the surface of an adjacent cell acts as the receptor. In this case, the signaling molecule is not released from the cell, but instead remains associated with the plasma membrane of the signaling cell. - they connect - this form of signaling is important during embryonic development

what is the first step in signal transduction

- the process in which a signal present on the outside of the cell leads to a change on the inside of the cell

Two common characteristics of G protein coupled receptors

- they have a similiar structure, consisteing of a single polypeptide chain that has seven transmembrane spanning regions with the ligand binding site on the outside of the cell and the portion that binds to the G protein on the inside of the cell - when activated, they associate with a G protein. In this way, they are able to transmit the signal from the outside to the inside of the cell.

why do bacteria take up foreign DNA

- to defend themselves against antibiotics - at low cell density the bacteria are making a singlaling molecules

g protein coupled receptor

A receptor that couples to G proteins, which bind to the guanine nucleotides GTP and GDP. - they are transmembrane proteins that bind signaling molecules

receptor kinase

A receptor that is an enzyme that adds a phosphate group to another molecule. - a kinase is an enzyme that catakyzes the transfer of a phosphate group from ATP to a substrate. to catalyze this reaction, it binds both ATP and the substrate in a process call phosphorylation. Phosphorylation is important because it affects the activity of the substrate: When a protein is phosphorylated by a kinase, it typically becomes active and is switched on. The addition of a phosphate group to a protein can activate it by altering its shape or providing a new site for other proteins to bind.

Which of the following statements best summarizes the function of G protein-coupled receptors? Question 3 choices Choice A., A G protein present on the outside of the cell leads to a change on the inside of the cell. Choice B., A signal present on the outside of the cell leads to a change on the inside of the cell. Choice C., A signal molecule on the outside of the cell is transported to the inside of the cell. Choice D., A GTP molecule is bound to the receptor, which causes a conformational change inside the cell.

A signal present on the outside of the cell leads to a change on the inside of the cell.

Many diseases are the result of a problem with cell signaling. Which of the following diseases best exemplifies this fact? Familial hypercholesterolemia (high cholesterol in the blood), caused by a decrease in the number of receptors for cholesterol. Congestive heart failure, caused by chronic high blood pressure due to excessive sodium intake. Cystic fibrosis, caused by a mutation in a channel protein, resulting in a buildup of mucus. A specific type of cancer, caused by a truncated receptor that becomes stuck in the activated form.

A specific type of cancer, caused by a truncated receptor that becomes stuck in the activated form.

When a G protein-coupled receptor binds a signal molecule, it activates a G protein. The active G protein is bound to a molecule of ______, and in its active state can _________ Question 4 choices Choice A., GDP; inactivate another target protein Choice B., GTP; inactivate another target protein Choice C., GDP; activate another target protein Choice D., GTP; activate another target protein

GTP; activate another target protein

Question 5 of 5 If a mutation caused the G protein to become permanently bound to GTP, what result can be predicted? Question 5 choices Choice A., It constantly signals its pathway to be "on." Choice B., It constantly signals its pathway to be "off." Choice C., It is unable to signal subsequent steps in the pathway. Choice D., It is unable to separate from the beta and gamma subunits. Submit

It constantly signals its pathway to be "on."

How is a G protein classified? It is an integral membrane protein. It is a transmembrane protein. It is a peripheral membrane protein. It is a second messenger.

It is a peripheral membrane protein.

In cell communication, which one of the following is a requirement of the responding cell? It must have receptor proteins. It must produce signaling molecules. It must be a eukaryotic cell. It must be a prokaryotic cell.

It must have receptor proteins.

Which of the following statements is not true regarding a neurotransmitter? Neurotransmitters can be growth factors. Like Delta or Notch, neurotransmitters are usually attached to the cell surface. Neurotransmitters are typically dispersed over small distances. Neurotransmitters play a role in muscle contraction. Neurotransmitters are produced by neurons.

Like Delta or Notch, neurotransmitters are usually attached to the cell surface.

Why are some mutations of Ras associated with cancer? Ras is a type of second messenger. Ras activates the MAP kinase signal transduction pathway. Ras binds to growth factor receptors. Ras alters ion flow across the cell membrane.

Ras activates the MAP kinase signal transduction pathway.

Cellular response

can take different forms depending on the nature of the signal and the type of responding cell.

Is the term "G protein" just a shorter name for a G protein-coupled receptor?

No. A G protein-coupled receptor is a transmembrane receptor that interacts with a G protein located inside the cell on the cytoplasmic side of the plasma membrane.

Notch and Delta are both transmembrane proteins involved in cell communication in the developing nervous system of vertebrate animals. What makes Notch different from Delta? Notch is a receptor and Delta is a signaling molecule. Notch is a signaling molecule and Delta is a receptor. Notch is required at higher density than Delta to alter cell fate. All of these choices are correct.

Notch is a receptor and Delta is a signaling molecule.

If a hormone is released into the bloodstream and therefore comes into contact with many cells, what determines which cells in the body respond to the hormone?

Only cells that have receptors for the hormone respond to the signal. Therefore, signaling can be specific for particular cells.

enzymes in the MAP kinase pathway can be inhibited by active

Recall that PKA is activated by elevated cAMP levels associated with the G protein-coupled receptor pathway. The regulation of the MAP kinase pathway by PKA illustrates how one signaling pathway can inhibit another.

How do mitogen-activated protein (MAP) kinases become inactive? Receptor kinases move apart in the membrane. Ras hydrolyzes GTP to GDP. Ligand diffuses away from the ligand-binding site. Phosphatases remove phosphate groups.

Phosphatases remove phosphate groups.

what type of receptors on are the surface of the cell and which are in the intracellular

SURFACE: - receptors for polar SM. since PSM can't cross the plasms membrane and must rely on cell surface receptors. The receptor proteins are transmembrane proteins with an extracellular domain and a transmembrane domaine, and a cytoplasmic domain. The entire receptor undergoes a conformational change. In this way, the receptor acts as a bridge between the inside and outside of the responding cell that carries the message of the hydrophilic signal across the hydrophobic core of the plasma membrane INTRACELLULAR: - receptors for small non polar SM. small NPSM can freely pass through the plasma membrane and activate cytoplasmic receptors. example:Since steroids are hydrophobic, they pass easily through the hydrophobic core of the phospholipid bilayer and into the target cell. Once inside, steroid hormones bind to receptor proteins located in the cytosol or in the nucleus to form receptor-steroid complexes

When an appropriate signal binds to a G protein-coupled receptor, what is the best description of how the information is passed across the plasma membrane? Question 2 choices Choice A., Binding of the signal molecule triggers the cell to produce G protein. Choice B., The signal molecule is transported across the plasma membrane by the receptor protein. Choice C., Signal binding causes a conformational change in the cytoplasmic portion of receptor protein.

Signal binding causes a conformational change in the cytoplasmic portion of receptor protein.

Why don't steroid hormones bind to transmembrane cell-surface receptors? Steroid hormones are nonpolar and therefore are able to cross the cell's plasma membrane, binding to receptors inside the cell. Steroid hormones are not signaling molecules. Steroid hormones are nonpolar and therefore cannot bind to receptors. Steroid hormones don't require receptors because they bind directly to DNA.

Steroid hormones are nonpolar and therefore are able to cross the cell's plasma membrane, binding to receptors inside the cell.

What causes the inactivation of a G protein? A phosphatase removes the inorganic phosphate group from GTP. The alpha subunit catalyzes the hydrolysis of GTP to GDP and inorganic phosphate. The beta and gamma subunits trigger the hydrolysis of GTP to GDP. The inactive receptor catalyzes the replacement of GTP by GDP.

The alpha subunit catalyzes the hydrolysis of GTP to GDP and inorganic phosphate.

signaling molecule

The carrier of information transmitted when the signaling molecule binds to a receptor; also referred to as a ligand.

responding cell

The cell that receives information from the signaling molecule.

Imagine that a researcher is studying the embryonic development of mice that do not express the signal molecule Delta. What will likely be true of these mice? These mice will have fewer neurons compared to their normal counterparts. These mice will have more glia compared to their normal counterparts. The mice will have fewer glia compared to their normal counterparts. These mice will have more neurons compared to their normal counterparts. The mice will have fewer neurons and more glia compared to their normal counterparts.

The mice will have fewer glia compared to their normal counterparts

receptor protein

The molecule on the responding cell that binds to the signaling molecule.

Which of the following is not a true statement about receptors that are localized to the nucleus? They carry a nuclear-localization signal. They bind polar ligands. They move through a nuclear pore. They are synthesized in the cytosol.

They bind polar ligands.

In the case of the heart, activated PKA leads to the opening of calcium channels that are present in heart muscle cells. The resulting influx of calcium ions results in shorter intervals between muscle contractions and thus a faster heart rate. As long as adrenaline is bound to its receptor, the heart rate remains rapid. This increase in the heart rate in turn results in increased blood flow to the brain and skeletal muscles to deal with the stress that set off the signal in the first place.

This example is typical of signaling through G protein-coupled receptors. These receptors tend to activate downstream enzymes or, in some cases, open ion channels. Because they often modify proteins that are already synthesized in the cell, their effects tend to be rapid, short-lived, and easily reversible.

Many patients with breast cancer have elevated MAP kinase activity in their tumor cells.

When human breast cancer cells are genetically modified to express an activated G protein α subunit, their growth after transplantation into mice is significantly inhibited. In addition, in cell culture, elevated cAMP levels block cells from responding to growth factors that signal through Ras to the MAP kinase pathway. As we better understand how different signaling pathways integrate in specific cell types, we have a chance to alter the activity of particular pathways and ultimately the response of the cell.

What is the cell's likely response to ligand binding to a steroid receptor located in the nucleus? initiation of a signal transduction pathway a change in gene expression activation of a kinase change in ion transport

a change in gene expression

What is the end-result of activating the MAP kinase pathway? synthesis of second messenger molecules phosphorylation of multiple cytosolic proteins a change in gene expression ion flow

a change in gene expression

What is one of the possible cellular responses following activation of the MAP kinase pathway? the formation of second messengers in the cytosol the activation of adenylyl cyclase a change in gene expression resulting in cell division both the activation of adenylyl cyclase and the formation of second messengers

a change in gene expression resulting in cell division

The activation of protein kinase A by cyclic AMP binding likely occurs because of: the phosphorylation of protein kinase A. the activity of a phosphatase. the binding of GTP to protein kinase A. a conformational change to protein kinase A.

a conformational change to protein kinase A.

In the example of adrenaline signaling, which steps represent an amplification of the signal? activated receptor activates G proteins, G protein binding by GTP, cyclic AMP activation of protein kinase A , activated receptor activates G proteins, activated adenylyl cyclase produces cAMP, active protein kinase A phosphorylates target proteins ., receptor signal binding, activated receptor activates G proteins, activated adenylyl cyclase producing cAMP , receptor signal binding, activated adenylyl cyclase producing cAMP, active protein kinase A phosphorylating target proteins

activated receptor activates G proteins, activated adenylyl cyclase produces cAMP, active protein kinase A phosphorylates target proteins

A researcher is evaluating the role of a growth factor during embryonic development. She notices that this factor functions in both neural development and limb development. How is that possible? The effects of the growth factor may be concentration-dependent. The effects of the growth factor may be dependent on location. The growth factor may result in the transcription of different genes depending on cell type. The growth factor may be signaling through different transduction pathways. All of these choices are possible explanations for the observations.

all

A researcher is studying a G protein-coupled receptor in eukaryotic cells. In one group of cells, he notices that even though a ligand can bind to its G protein-coupled receptor, nothing happens. Why could this happen? The G protein-coupled receptor might carry a mutation so that it fails to undergo a conformational change upon the binding of its ligand. The G protein-coupled receptor might carry a mutation that affects the receptor's transmembrane portion. These cells might carry mutations in the downstream signaling pathway associated with this G protein-coupled receptor. All of these choices are correct.

all

If two signaling pathways are activated simultaneously: they may inhibit each other. they may strengthen each other. one may inhibit the other. All of these choices are correct.

all

Termination is an important step in adrenaline signaling because: it prevents an excessive response to adrenaline. it allows organisms to respond to new stresses. it allows an appropriate level of response. All of these choices are correct.

all

Which of the following is a cellular response to signal transduction? a change in the proteins found in the cytosol the release of more signal molecules a change in the activity of an enzyme All of these choices are correct.

all

some g proteins are composed of three subunits....

alpha, beta, and gamma (Y) -alpha: is the part of the g protein that binds to either GDP or GTP. When GDP bound to the α subunit is replaced by GTP, the α subunit separates from the β and γ subunits.

ligand

an alternative term for a signaling molecule that binds with a receptor, usually a protein.

phosphatse

an enzyme that removes a phosphate group from another molecule (dephosphoru=ylation) this causes the protein to become inactive or switched off

second messenger

are signaling molecules found inside cells that relay information to the next target in the signal transduction pathway

ion channels

cell surface receptors that open and close, therby altering the flow of ions across the plasma membrane. - some open in response to changes in voltage across the membrenae (voltage gated ion channels), others open when bound by their ligand (lignang gated ion channels) - channel proteins help ions and other molecules diffuse into and out of the cell by providing a hydrophilic pathway through the hydrophobic core of the plasma membrane. Most of the time, the channels are closed. -However, when a signaling molecule binds to the extracellular portion of a ligand-gated ion channel, the channel undergoes a conformational change that opens it and allows ions to flow in and out. This type of signaling is especially important for nerve and muscle cells since their functions depend on a rapid change in ion flow across the plasma membrane.

Which of the following steps does not result in an amplification of the signal information? Question 2 choices Choice A., activation of G protein by activated receptor Choice B., production of cyclic AMP by adenylyl cyclase Choice C., activation of adenylyl cyclase by active G protein Choice D., phosphorylation of target proteins by protein kinase A

ctivation of adenylyl cyclase by active G protein

Which signaling system involves the longest time interval between release of a signaling molecule and activation of a receptor? autocrine contact-dependent paracrine endocrine

endocrine

Given that most ligands form covalent bonds with their associated receptors, these complexes are more or less permanent and can only be broken through the hydrolysis of ATP. true false

false

The cellular responses that result from receptor kinase activation tend to involve changes in

gene expression, which in turn allows cells to grown, divide , differentiate, or change shape.

The series of kinases collectively are called the...

mitogenactivated protein kinase pathway

When a ligand binds to a G protein-coupled receptor, it is ...

on or active. - When a ligand binds to a G protein-coupled receptor, the receptor in turn binds to and activates a G protein by causing it to release GDP and bind GTP. As long as the G protein is bound to GTP, it is in the on position. The activated G protein goes on to activate additional proteins in the signaling pathway.

G protein-coupled receptors are found: Question 1 choices Choice A., in the cytoplasm. Choice B., on the nuclear membrane. Choice C., on the cell surface. , Choice D., inside the nucleus.

on the cell surface

The location of a particular receptor in a cell depends....

on whether the signaling molecule is polar or nonpolar.

when a g protein is bound to GTP it is... and when its bound to GDP it is...

on/ active off/inactive

what happens when we cut a finger

platelet-derived growth factor (PDGF) is released from platelets in the blood and binds to its receptor kinase on the surface of cells at the site of the wound, where it triggers cell division necessary to repair the wound.

Signaling through receptor kinases follows the same basic sequence of events that we saw in signaling though G protein-coupled receptors, including

receptor activation, signal transduction, cellular response, and termination

what is the receptor kinase signaling responsible for during embryonic development

responsible for the formation and elongation of limb buds that eventually become our arms and legs.

it is thought that G protein-coupled receptors used for cell communication in multicellular organisms evolved from

sensory receptors in unicellular eukaryotes

endocrine signaling

signaling by molecules that travel through the bloostream. - this relates to cells that are really far apart and have to use the circulatory system -Adrenaline provides a good example of endocrine signaling. Adrenaline, which is produced in the adrenal glands, is carried by the bloodstream to target cells that are far from the signaling cells.

growth factor

small, h2o soluble molecule. (polar) - it is a type of SM that causes the responding cells to grow, divide, or differentiate

Signaling through receptor kinases: is limited to just a few cell types. only occurs in humans. takes place in most eukaryotic organisms. takes place only in prokaryotes.

takes place in most eukaryotic organisms.

receptor activation

the "turning on" of a receptor which often occurs when a signaling molecule binds to a recpetor on a responding cell. This is the first step when a signanling molecule binds to a receptor on a responding cell. - this signal acitvates the receptor by causing a conformational change in the receptor, As a result, some receptors bind to and activate other proteins located inside the cell. Other receptors are themselves enzymes, and binding of the signal changes the shape and activity of the enzyme. Still other receptors are channels that open or close in response to binding a signaling molecule.

GTP binding occurs on which subunit of a G protein? the alpha subunit the gamma subunit the beta subunit GTP binds both beta and gamma subunits.

the alpha subunit

In order for a G protein to be active: the alpha subunit must bind GTP and the beta and gamma subunits must separate from the alpha subunit. the alpha subunit must bind GTP. the beta and gamma subunits must separate from the alpha subunit. both the beta and gamma subunits must bind GTP.

the alpha subunit must bind GTP and the beta and gamma subunits must separate from the alpha subunit.

Ras is most similar to: the gamma subunit of three-subunit G proteins. the beta subunit of three-subunit G proteins. the alpha subunit of three-subunit G proteins. ion channels. receptor kinases.

the alpha subunit of three-subunit G proteins.

Cell signaling between two nerve cells can be thought of as an example of paracrine signaling because: the responding cell releases more signaling molecule (neurotransmitter). a signaling molecule (neurotransmitter) is released. a receptor is activated. the cells are in close proximity.

the cells are in close proximity.

termination

the last step in which the cellular response is stopped. - the response can be terminated at any point along the signanling pathway. - termination protects the cell from overreacting to existing signals and therfore helps the cell to have an appropriate level of response. it also allows for new signals to be formed

when a ligand is in an active state what does it do with the g protein-coupled receptor

the ligand couples (binds) to a g protein coupled receptor. the g protein is located on the cytoplasmic side of the plasma membrane

What determines the specificity of a receptor protein? the extracellular domain the cytoplasmic domain the ligand-binding site the transmembrane domain

the ligand-binding site

In the G protein-coupled signal transduction pathway, phosphatases are responsible for the inactivation of: the alpha subunit of a G protein. protein kinase A. adenylyl cyclase. the protein target activated by protein kinase A. All of these choices are correct.

the protein target activated by protein kinase A.

once the receptor is activated.....

the receptor often triggers a series of downstream events in a process called signal transduction.

signaling cell

the source of a signaling molecule

what determines the response of the cell to a specific signaling molecule

the type of receptors present on the sruface of the cell becuase they determin which signals the cell is able to respond to. - also depends on the set of protein that is found in it, as different cell types have different sets of intracellular proteins and signanling pathways. -As a result, the same signaling molecule can have different effects in different types of cells.

How does an "activated" receptor transfer information into the cell? by decreased phosphorylation of the receptor through a conformational change of the receptor by altering the ligand-binding site of the receptor by increased translation of the receptor

through a conformational change of the receptor

Signaling molecules involved in paracrine and autocrine signaling: remain attached to the plasma membrane. travel by diffusion. travel in the circulatory system.

travel by diffusion

When bound to their signaling molecule, the molecular switch is..... When the signaling molecule is no longer bound, the switch is...

turned on and turned off