BS 161 Homework #16 and #17-- Cell Signaling

which is true about G proteins?

-G proteins become deactivated when bound GTP is hydrolyzed to GDP. -G proteins release GDP and bind GTP when associated with an activated receptor. -Some G proteins are composed of three subunits

what is a growth factor?

-a soluble molecule that can alter gene expression in a cell -a signaling molecule involved in paracrine signaling -a small protein that influences cell growth and division.

Second messengers:

-are small intracellular molecules that participate in signal transduction. -amplify the effects of the signal. -play a role in activation of intracellular signal transduction. -are removed in order to terminate a cellular signaling response.

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

-gene expression patterns are changed -cell division is triggered -enzyme activities are changed -cell signals are released to communicate with other cells

the extent and duration of a cellular response to a signal depend on the:

-level of expression of the signal transduction proteins. -concentration of the signaling molecule in the vicinity of the receptor -level of expression of proteins that terminate the response -binding affinity of the receptor to the signaling molecule

defects in cell signaling can lead to a cancerous cell as a result of:

-overproduction of signals that trigger cell division. -overproduction of a receptor that triggers cell division. -a defective signal transduction protein that stays in the activated state and triggers cell division continuously. -a defective receptor that stays in the activated state and triggers cell division continuously.

termination is an important step in adrenaline signaling because it:

-prevents an excessive response to adrenaline -allows organisms to respond to new stresses -allows an appropriate level of response

to have communication between cells, you must have a:

-responding cell -signaling molecule -receptor

You are a medical student working in a cancer research laboratory. Your boss has given you samples of cancer cells and blood from a patient. She has told you that the cells have no mutations in any of their signaling molecule proteins (that is, all the proteins are normal), but that the cells' signaling transduction properties are not normal, causing them to be cancerous. Which of the following could account for the increased cell proliferation in the patient?

-the concentration of a signaling molecule in the patient is higher than usual -the cells taken from the patient have more growth factor receptors than normal

Choose from the following terms to fill in the blanks in the CORRECT order. A. ligand B. signaling cell C. receptor D. responding cell In communication between cells, the _____ produces the signaling molecule, also known as the _____; the _____ produces the _____, to which the signaling molecule binds,

B, A, D, C

How are steroid hormone receptors and cell-surface receptors similar?

Both types undergo a conformational change when they bind to their ligand.

Nicotine from cigarette smoke acts as a ligand and associates with specific cells in the nervous system. Nicotine eventually produces feelings of pleasure and well-being. Below are the events that happen in the cellular response to nicotine. 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

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.

what does a ligand-gated channel do?

It allows ions to move across the plasma membrane.

what would happen to the signaling cascade if phosphatases were nonfictional?

It would continue in the absence of ligand

During the signal transduction process, the signal often triggers a signal transduction cascade. For example, an activated receptor activates hundreds of protein A. Each activated protein A activates hundreds of protein B and so on until a cellular response occurs. What purpose does this cascade serve?

The cascade serves to amplify the signal, so one activated receptor can have a significant response

A number of mutations have been described in G proteins, such as Ras, that have profound effects on their activity. For example, some mutations greatly increase the affinity of the G protein for GDP, making it very difficult for GDP to be exchanged for GTP. Other mutations prevent the hydrolysis of GTP to GDP.

a Ras molecule that has not GTPase activity

what is the very FIRST effect of ligand binding to a G protein-coupled receptor?

a conformational change in the cytoplasmic domain of the receptor

You are studying a newly discovered growth factor. You find that this growth factor stimulates the proliferation of chicken cells grown in the laboratory. You have also found that the receptor that binds the growth factor is a receptor kinase. Which of the following mutations would you expect to promote uncontrolled cell proliferation?

a mutation that inactivates the phosphatase that dephosphorylates the activated receptor

A protein on a cell surface that binds to a signaling molecule is an example of which of the following elements of cellular communication?

a receptor protein

which of the following would NOT be considered a cell-surface receptor?

a receptor that binds a nonpolar steroid hormone and activities transcription

signal amplification relies on:

a sequential increase in the different components of the signal transduction pathway

A cell that responds to an environmental condition by the release of a chemical is an example of which of the following elements of cellular communication?

a signaling cell

in the context of cell signaling, to what does the term ligand refer?

a signaling molecule

which of the following CORRECTLY lists the types of cellular communication from shortest to longest distance traveled by the signaling molecule to reach its responding cell?

autocrine, paracrine, endocrine

where would you expect to find the receptor for a nonpolar ligand?

either in the nucleus or cytosol

in cell communication, which one of the following is a requirement of the responding cell?

it must have receptor proteins

Many mutations in receptor kinases that lead to cancer allow the receptor to dimerize and become activated, even in the absence of signaling molecules. An example is a mutant form of the EGF receptor kinase called Her2/neu. An antibody that prevents dimerization of Her2/neu receptor kinases is being tested for its effectiveness in preventing cancer. At which stage does this drug work?

it prevents the receptor from becoming activated

which type of receptor is involved in rapid responses of muscle cells and neurons?

ligand-gated ion channel

communication between neurons is an example of which type of cell signaling?

paracrine

phosphate groups play a key role in receptor kinase activation by:

providing binding sites to recruit and activate signal-transduction proteins.

Which type of cell-surface receptor undergoes changes in phosphorylation in response to binding of its ligand?

receptor kinase

Cyclic AMP (cAMP) is an example of:

second messenger

You examine a cell line in which Ras is always activated even in the absence of a signaling molecule. This causes constant activation of the kinases in the MAP kinase pathway. Which of the following conditions would be MOST likely to turn off this abnormally active signaling pathway?

the addition of a drug that prevents the final kinase from interacting with its target protein in the nucleus

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

what determines the specificity of a receptor protein?

the ligand-binding site

the first event that happens after a signaling molecule binds to a receptor is

the receptor is activated

Phosphatases are a family of enzymes that remove phosphate groups from specific proteins; these phosphate groups had been added to the proteins by protein kinases. Vanadate is an inhibitor of phosphatases in eukaryotic cells. What effect would vanadate have on the response of cells to signals received by receptor kinases?

the response of the cell would last longer than it normally would

How does an "activated" receptor transfer information into the cell?

through a conformational change of the receptor

how does an "activated" receptor transfer information into the cell?

through a conformational change of the receptor