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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.

What is true of the mating signal transduction pathway in yeast?

Mating type a secretes a signal called a factor.

What could happen to the target cells in an animal that lack receptors for local regulators?

They would not be able to multiply in response to growth factors from nearby cells.

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.

When a cell releases a signal molecule into the environment and a number of cells in the immediate vicinity respond, this type of signaling is

paracrine signaling.

Synaptic signaling between adjacent neurons is like hormone signaling in what way?

It requires binding of a signaling molecule to a receptor.

A small molecule that specifically binds to another molecule, usually a larger one

is called a ligand.

Which of the following is (are) true of ligand-gated ion channels?
A) They are important in the nervous system.
B) They lead to changes in sodium and calcium concentrations in cells.
C) They open or close in response to a chemical signal.
D) Only A and B are true.
E) A, B, and C are true.

A, B, and C are true.

A receptor protein in a membrane that recognizes a chemical signal is most similar to

the active site of an allosteric enzyme in the cytoplasm that binds to a specific substrate.

What would be true for the signaling system in an animal cell that lacks the ability to produce GTP?

It would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane.

G proteins and G-protein-linked receptors

are thought to have evolved very early, because of their similar structure and function in a wide variety of modern organisms.

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

called receptor tyrosine-kinases.

Up to 60% of all medicines used today exert their effects by influencing what structures in the cell membrane?

G proteins

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


Testosterone functions inside a cell by

binding with a receptor protein that enters the nucleus and activates specific genes.

Which is true of transcription factors?

They control which genes are expressed.

Chemical signal pathways

often involve the binding of signal molecules to a protein on the surface of a target cell.

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

The receptors for a group of signaling molecules known as growth factors are often

receptor tyrosine kinases.

In general, a signal transmitted via phosphorylation of a series of proteins

brings a conformational change to each protein.

Sutherland discovered that epinephrine

elevates the cytosolic concentration of cyclic AMP.

What explains the inability of an animal cell to reduce the Ca2+ concentration in its cytosol compared with the extracellular fluid?

insufficient ATP levels in the cytoplasm

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

protein kinase.

What describes cell communication systems?

In response to a signal, the cell may alter activities by changes in cytosol activity or in transcription of RNA.

The toxin of Vibrio cholerae causes profuse diarrhea because it

modifies a G protein involved in regulating salt and water secretion.

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

receptor tyrosine kinase activity

What most likely would be an immediate result of growth factor binding to its receptor?

protein kinase activity

An inhibitor of phosphodiesterase activity would have which of the following effects?

prolong the effect of epinephrine by maintaining elevated cAMP levels in the cytoplasm

Adenylyl cyclase has the opposite effect of which of the following?


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


If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to:
A) design a compound that blocks epinephrine receptor activation.
B) design a compound that inhibits cAMP production in liver cells.
C) design a compound to block G-protein activity in liver cells.
D) design a compound that inhibits phosphorylase activity.
E) All of the above are possible approaches.

All of the above are possible approaches.

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

phospholipase C

Which of the following statements is true?
A) When signal molecules first bind to receptor tyrosine kinases, the receptors phosphorylate a number of nearby molecules.
B) In response to some G-protein-mediated signals, a special type of lipid molecule associated with the plasma membrane is cleaved to form IP3 and calcium.
C) In most cases, signal molecules interact with the cell at the plasma membrane and then enter the cell and eventually the nucleus.
D) Toxins such as those that cause botulism and cholera interfere with the ability of activated G proteins to hydrolyze GTP to GDP, resulting in phosphodiesterase activity in the absence of an appropriate signal molecule.
E) Protein kinase A activation is one possible result of signal molecules binding to G protein- linked receptors.

Protein kinase A activation is one possible result of signal molecules binding to G protein- linked receptors.

Which of the following is a correct association?
A) kinase activity and the addition of a tyrosine
B) phosphodiesterase activity and the removal of phosphate groups
C) GTPase activity and hydrolysis of GTP to GDP
D) phosphorylase activity and the catabolism of glucose
E) adenylyl cyclase activity and the conversion of cAMP to AMP

GTPase activity and hydrolysis of GTP to GDP

One inhibitor of cGMP is Viagra. It provides a signal that leads to dilation of blood vessels and increase of blood in the penis, facilitating erection. cGMP is inhibited, therefore the signal is prolonged. The original signal that is now inhibited would have

hydrolyzed cGMP to GMP.

A drug designed to inhibit the response of cells to testosterone would almost certainly result in what?

a decrease in transcriptional activity of certain genes

What substance is a protein that can hold several other relay proteins as it binds to an activated membrane receptor?

scaffolding protein

As humans, we have receptors for two kinds of beta adrenergic compounds such as catecholamines. Cardiac muscle cells have beta 1 receptors that promoteincreased heart rate. Some drugs that slow heart rate are called beta blockers. Smooth muscle cells, however, have beta 2 receptors which mediate muscle relaxation. Blockers of these effects are sometimes used to treat asthma.
The description above illustrates what?

Just because a drug acts on one type of receptor does not mean that it will act on another type.

The use of beta 2 antagonist drugs may be useful in asthma because

they may dilate the bronchioles by relaxing their smooth muscle.

What are scaffolding proteins?

large molecules to which several relay proteins attach to facilitate cascade effects

The termination phase of cell signaling requires what?

reversing the binding of signal molecule to the receptor

Why has C. elegans proven to be a useful model for understanding apoptosis?

The nematode undergoes a fixed and easy-to-visualize number of apoptotic events during its normal development.

What describes the events of apoptosis?

Its DNA and organelles are fragmented, the cell shrinks and formsblebs, and the cell self- digests.

The main proteases involved in apoptosis are


Human caspases can be activated by

irreparable DNA damage or protein misfolding.

If an adult person has a faulty version of the human-analog to ced-4 ofthe nematode, what might likely result?

a form of cancer in which there is insufficient apoptosis

Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because

they amplify the original signal manyfold.

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.

Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells?

Glycogen breakdown was observed only when epinephrine was administered to intact cells.

Protein phosphorylation is commonly involved with all of the following except:
A) regulation of transcription by extracellular signal molecules.
B) enzyme activation.
C) activation of G protein-coupled receptors.
D) activation of receptor tyrosine kinases.
E) activation of protein kinase molecules.

activation of G protein-coupled receptors.

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.

Apoptosis involves all of the following except:
A) fragmentation of the DNA
B) cell-signaling pathways
C) activation of cellular enzymes
D) lysis of the cell
E) digestion of cellular contents by scavenger cells

lysis of the cell

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