Unit 4- Ch. 9

In the example of adrenaline signaling used in the animation, the signal is amplified in the activation of G protein, the production of cAMP and the phosphorylation of target proteins. Suppose each amplification step (3 steps) produces one hundred active molecules. How many total modified protein target molecules result from a single activated signal receptor?

(100)^3= 1,000,000

How are receptors that bind polar and nonpolar signaling molecules similar?

******

What is one way endocrine, paracrine, autocrine, and contact-dependent signaling are different from one another?

- distance between the signaling and responding cell - whether the signaling molecule is released by the signaling cell or is a transmembrane protein

How are receptors that bind polar and nonpolar signaling molecules different?

- polar signaling molecules cannot diffuse across the membrane, bind on surface - nonpolar can easily diffuse, bind to receptors in cytoplasm or nucleus

What are the 4 essential elements of cell signaling?

1- signaling cell 2- signaling molecule 3- receptor protein 4- responding cell

In this example, the signal is amplified in the responding cell through a phosphorylation cascade in which molecules are activated through the addition of phosphates. Where do all of those phosphates come from?

ATP

Nicotine acts as a ligand and associates with acetylcholine receptor on specific cells in the nervous system. Nicotine eventually produces feelings of pleasure. Place the events in the correct order to describe the steps in the signaling pathway. A) The acetylcholine receptor is an ion channel, and when a ligand binds, the ion channel opens. B) An influx of ions carries the signal to the reward areas of the brain. C) Nicotine binds to the transmembrane protein that normally binds the neurotransmitter acetylcholine. D) The signal causes release of dopamine in the brain, which causes good feelings. E) Nicotine is quickly eliminated from the body (causing cravings for more cigarettes to produce good feelings).

C; A; B; D; E C) Nicotine binds to the transmembrane protein that normally binds the neurotransmitter acetylcholine. A) The acetylcholine receptor is an ion channel, and when a ligand binds, the ion channel opens. B) An influx of ions carries the signal to the reward areas of the brain. D) The signal causes release of dopamine in the brain, which causes good feelings. E) Nicotine is quickly eliminated from the body (causing cravings for more cigarettes to produce good feelings).

What is a key difference between cell signaling by a cell-surface receptor and cell signaling by an intracellular receptor?

Cell-surface receptors bind polar signaling molecules; intracellular receptors bind nonpolar signaling molecules.

How can cells respond to external signaling molecules, even when those signaling molecules cannot enter the cell?

Cells respond by way of receptors that bind to the signal (ligand) at specific site. Binding of the ligand to its receptor causes conformational change in the receptor, activating it. Activated receptor transmits signal inside the cell, generating a response. The type of ligand and receptor determine how the cell responds to the signal.

In the developing nervous system, delta cells display on their surface the protein Delta, which interacts with and activates the Notch protein present on neighboring Notch cells. What is the developmental fate of these two cell types?

Delta cells become neurons, and the activation of Notch causes neighboring cells to become glial cells.

How is the information contained in a signaling molecule received by a cell?

Depending on the nature of the signaling molecule, it may either bind to and activate a receptor protein embedded in the plasma membrane, or it may move across the plasma membrane and bind to a receptor protein in the cytoplasm.

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. [T/F]

False

Which types of cellular activities can be a response to cell signaling?

Gene expression patterns are changed. Cell division is triggered. Cell signals are released to communicate with other cells. Enzyme activities are changed.

In cell communication, what is one requirement of the responding cell?

It must express receptor proteins. For cells to respond to a signal, there must be some kind of receptor that binds to the signal to activate a response.

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.

If a protein is activated by the addition of a phosphate, it will most likely be inactivated by the action of:

Protein phosphatase

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?

Receptors for the growth factor must be present in both neurons and cells in the developing limb.

What is the role of signal transduction in cell signaling?

Signal transduction connects the activation of the receptor to the cellular response. Signal transduction involves the activation of cytoplasmic molecules and/or proteins to transmit the changes in the receptor from signal binding to the ultimate cellular response

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.

One example of a cellular response to a signal is the triggering of cell division. If a mutation occurred in the gene for the signal receptor in this pathway that caused the receptor to reject binding of the signal, what response can be predicted?

The cell does not divide.

What is the most likely reason that paracrine signaling does not activate the cell that is producing the signaling molecule?

The cell does not have the proper receptor.

When the ligand binds to the membrane receptor, the receptor transmits the signal to the tranduction pathway. How does it do this?

The receptor changes shape

You strip off all proteins on the cell surface by using a protease (an enzyme that destroys proteins). Now, when you add a specific signaling molecule, the cell still responds. What is the most reasonable explanation of this?

The receptor for this signal is inside the cell, and the signaling molecule is nonpolar and can diffuse into the cell. Because cell signaling requires the activation of some kind of receptor, and any receptor on the plasma membrane would have been destroyed, the receptor must be protected inside the cell. The only signals that can activate such receptors are nonpolar molecules, such as steroid hormones, that can pass through the plasma membrane.

Recall from the text in the example of cell communication in Streptococcus pneumoniae that 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 no increase in the rate of DNA uptake.

Many scientists use chemical inhibitors to interfere with normal signaling pathways within eukaryotic cells. If such inhibitors are large, nonpolar molecules, what is the likely method of action of these chemical inhibitors?

These chemical inhibitors likely bind to receptors on the cell surface and interfere with receptor activation or signal-receptor binding.

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 glial cells compared to their normal counterparts.

Which is a true statement about receptors that are localized to the nucleus?

They move through a nuclear pore. They carry a nuclear-localization signal. They bind nonpolar ligands. They are synthesized in the cytosol.

A researcher has discovered a new ligand that can pass through the cell membrane and bind to a receptor in the nucleus. Which statement is likely true of this ligand?

This ligand is likely nonpolar. This ligand likely has a similar structure to cholesterol. This binding of this ligand to its receptor likely plays a role in transcription. This ligand is likely a steroid.

A researcher introduces a large polar signaling molecule produced by bacteria to eukaryotic cells that she is culturing in the laboratory. Remarkably, she notices that the signaling of the bacteria results in an increase in eukaryotic gene expression. How is this possible?

This signal is likely similar in structure to ligands utilized by eukaryotic cells.

Vascular endothelial growth factor is a peptide signaling molecule related to platelet-derived growth factor. VEGF is important in the formation of the circulatory system because its signaling pathway causes the formation of blood vessels in developing embryos during normal development. Tumors also produce and secrete VEGF, causing nearby blood vessels to branch and grow to form new blood vessels that supply these tumors.

VEGF is a paracrine signaling molecule because it binds to receptors on nearby cells, at the site where new blood vessels are needed.

What are 3 possible initial steps following the binding of a signaling molecule to a receptor?

When a signaling molecule binds and changes shape of receptor: G protein-coupled receptors bind and activate G proteins, receptor kinases are activated and phosphorylate other proteins, and ion channels open or close

What is the cell's likely response to ligand binding to a steroid receptor located in the nucleus?

a change in gene expression Steroid hormone receptors in the nucleus bind to DNA upon activation and regulate transcription.

G protein definition

a proetin that binds to the guanine nucleotidees GTP and GDP

G protein-coupled receptors definition

a receptor that binds to G proteins, which bind to guanine nucleotides GTP and GDP

receptor kinases definition

a receptor that is an enzyme that adds a phosphate group to another molecule

Which one of the answer choices would be found inside the cell and not on the cell surface?

a steroid receptor

Steroid (choloesterol based) hormones....

affect gene expression.

The primary advantage of a signaling cascade is that it:

allows a large intracellular response from a small number of extracellular signal molecules.

ligand definition

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

phosphatases definition

an enzyme that removes a phosphate group from another molecule

growth factor definition

any one of a group of small soluble molecules, usually the signal in paracrine signaling, that affect cell growth, cell division, and changes in gene expression

signaling molecule definition

carrier of information transmitted when the signaling molecule binds to a receptor; also called ligand

ion channel definition

cell surface receptors that open and close, thereby altering the flow of ions across the plasma membrane

responding cell definition

cell that recieves information from the signaling molecule

reponse definition

change in cellular behavior, such as activation of enzymes or genes, following a signal

The signaling molecule is a transmembrane protein in ____________ signaling.

contact-dependent signaling

Mammalian steroid hormones are signaling molecules that function in which type of cell signaling?

endocrine

Cell signaling over a long distance is known as:

endocrine signaling.

receptor protein definition

molecule on the responding cell that binds to the signaling molecule

A receptor that is inside the cell would require a __________ signal molecule that can ____________________ the plasma membrane.

nonpolar; pass through

If a hormone is released into the bloodstream so that it 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, so signaling can be specific for particular cells. - different cell types express a different assortment of receptor types on their surface

Growth factors such as platelet-derived growth factor (PDGF) function in:

paracrine signaling.

Signal molecules that are _______ usually have their corresponding receptor ______________ of the cell.

polar; on the surface

What are the steps that occur when a signaling molecule binds to a receptor on a responding cell?

receptor activation > signal transduction > response > termination

Which components of cell signaling is involved in only some types of cell communication?

signal transduction molecules

autocrine signaling definition

signaling between different parts of one cell; signaling cell is also responding cell

paracrine signaling definition

signaling by a molecule that travels a short distance to the nearest neighboring cell to bind to its receptor and deliver message

endocrine signaling definition

signaling by molecules that travel throught the bloodstream

A _________ expresses a gene or genes that direct production of the signaling molecule, and the _______________ expresses a gene or genes that direct production of the _________________.

signaling cell; responding cell; receptor protein

When cells communicate by the signaling process, one cell produces a _________________ that must be received by the ___________ on or in the responding cell.

signaling molecule; signal receptor

signaling cell definition

source of a signaling molecule

ligand-binding site definition

specific location on the receptor protein where a signaling molecules binds

What is one way in which endocrine, paracrine, autocrine, and contact-dependent signaling are similar to one another?

steps involved are all the same: receptor activation > signal transduction > response > termination

termination definition

stopping of a signal

signal transduction definition

the process in which an extracellular molecules acts as a signal to activate a receptor, which transmits information through the cytoplasm

receptor activation definition

the turning on of a receptor, often occurs when a signaling molecule binds to a receptor on a responding cell

Signaling molecules involved in paracrine and autocrine signaling:

travel by diffusion.