Chapter 11: Cell Communication

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A signal transduction pathway is initiated when a _____ binds to a receptor.

signal molecule

A signal molecule is also known as a(n) _____.


Which of these is the second of the three stages of cell signaling?


In the yeast signal transduction pathway, after both types of mating cells have released the mating factors and the factors have bound to specific receptors on the correct cells,

binding induces changes in the cells that lead to cell fusion.

Paracrine signaling

involves secreting cells acting on nearby target cells by discharging a local regulator into the extracellular fluid.

From the perspective of the cell receiving the message, the three stages of cell signaling are

signal reception, signal transduction, and cellular response.

The process of transduction usually begins

when the signal molecule changes the receptor protein in some way.

Which of these extracellular signal molecules could diffuse through a plasma membrane and bind to an intracellular receptor?


A(n) _____ is an example of a signal molecule that can bind to an intracellular receptor and thereby cause a gene to be turned on or off.


Thyroid hormones bind to _____ receptors.


Membrane receptors that attach phosphates to specific animo acids in proteins are

called receptor tyrosine-kinases.

Which of the following are chemical messengers that pass through the plasma membrane of cells and have receptor molecules in the cytoplasm?


A major group of G protein-linked receptors contain seven transmembrane alpha helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others.

The coupled G protein most likely interacts with this receptor

at the loop between H5 and H6

One of the major categories of receptors in the plasma membrane reacts by forming dimers, adding phosphate groups, then activating relay proteins. Which type does this?

receptor tyrosine kinases

What role does a transcription factor play in a signal transduction pathway?

By binding to DNA it triggers the transcription of a specific gene.

A signal transduction pathway is initiated when a _____ binds to a receptor.

signal molecule

Which of these acts as a second messenger?

cAMP (cyclic AMP)

Calcium ions that act as second messengers are stored in _____.

endoplasmic reticula

_____ catalyzes the production of _____, which then opens an ion channel that releases _____ into the cell's cytoplasm.

Phospholipase C ... IP3 .... Ca2+

A protein kinase activating many other protein kinases is an example of _____.


Sutherland discovered that epinephrine

elevates the cytosolic concentration of cyclic AMP.

The general name for an enzyme that transfers phosphate groups from ATP to a protein is

protein kinase

Which of the following would be inhibited by a drug that specifically blocks the addition of phosphate groups to proteins?

receptor tyrosine kinase activity

Caffeine is an inhibitor of phosphodiesterase. Therefore, the cells of a person who has recently consumed coffee would have increased levels of


An inhibitor of which of the following could be used to block the release of calcium from the endoplasmic reticulum?

phospholipase C

Which of the substances below is a protein that can hold several other relay proteins as it binds to an activated membrane receptor?

scaffolding protein

The main proteases involved in apoptosis are


Human caspases can be activated by

irreparable DNA damage or protein misfolding

Binding of a signaling molecule to which type of receptor leads directly to a change in distribution of ions on opposite sides of the membrane?

ligand-gated ion channel

The activation of receptor tyrosine kinases is characterized by

dimerization and phosphorylation

Lipid-soluble signal molecules, such as testosterone, cross the membranes of all cells but affect only target cells because

intracellular receptors are present only in target cells

Consider this pathway: epinephrine --> G protein-coupled receptor --> G protein adenylyl cyclase --> cAMP.
Identify the second messenger.


Apoptosis involves all but the following:

lysis of the cell

Molecular biologists think that signal transduction pathways evolved early in the history of life because ____. (Concept 11.1)

the molecular details of cell signaling are quite similar in organisms whose last common ancestor was a billion years ago

A substance that acts at a long distance from the site at which it is secreted is a ____. (Concept 11.1)


Cell biologists use the term "ligand" to refer to _____. (Concept 11.2)

any small molecule that can bind in a specific manner to a larger one

Dioxin, produced as a by-product of various industrial chemical processes, is suspected of contributing to the development of cancer and birth defects in animals and humans. It apparently acts by entering cells by simple diffusion and binding to proteins in the cytoplasm, altering the pattern of gene expression. Among the cytoplasmic proteins to which dioxin binds are likely to be _____. (Concept 11.2)

transcription factors

Tyrosine-kinase receptors are characterized by their _____. (Concept 11.2)

enzymatic phosphorylation of tyrosine in the receptor protein

Two of the most common second messengers are _____. (Concept 11.3)

calcium ion and cAMP

Which of the following sequences is correct? (Concept 11.3)

binding of a signaling molecule to its receptor ® G-protein activation ® phospholipase C activation ® IP3 production ® increase in cytoplasmic calcium concentration
binding of a growth factor to its receptor ® phosphorylation cascade ® activation of transcription factor ® transcription
diffusion of a signaling molecule across the plasma membrane ® binding of the signaling molecule to its receptor ® movement of the signal molecule-receptor complex into the nucleus ® transcription
binding of a signaling molecule to its receptor ® G-protein activation ® adenylyl cyclase activation ® cAMP production ® protein phosphorylation
~ All of the choices are correct. ~

Why are there often so many steps between the original signal event and the cell's response? (Concept 11.4)

Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses.

A signal molecule can cause different responses in different cells because _____. (Concept 11.4)

the transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor

Apoptosis is _____. (Concept 11.5)

controlled cell suicide

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