Biology Chapter 11: Cell Communication
What two types of yeast cells are involved in reproduction ?
"A" and alpha
What initiates the process of Transduction (Stage 2) of cell signaling?
The binding of the signaling molecule changes the receptor protein in some way, initiating the process od transduction.
Why is the cell-signaling process crucial to activities, such as the ones that occur in stage 3 (response)?
The cell-signaling process helps ensure that crucial activities, such as the ones that occur in stage 3 (response), occur in the right cells, at the right time, and in proper coordination with the activities of other cells of the organism.
A difference between the mechanisms of cAMP and Ca2+ in signal transduction is that cAMP __________ and Ca2+ __________.
is synthesized by an enzyme in response to a signal ... is released from intracellular stores
A signal molecule is also known as a(n) _____.
ligand
A small molecule that specifically binds to a larger molecule is called a(n) __________.
ligand
What generally causes a receptor protein to undergo a change in shape?
ligand binding
Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane?
ligand-gated ion channel
When a platelet contacts a damaged blood vessel, it is stimulated to release thromboxane A2. Thromboxane A2 in turn stimulates vascular spasm and attracts additional platelets to the injured site. In this example thromboxane A2 is acting as a __________.
local regulator
A mutation in the active site of adenylyl cyclase that inactivates it would most likely lead to __________.
lower activity of protein kinase A
Nitric oxide is unusual among animal signal molecules in that it __________.
is a gas
What are the three major types of cell-surface transmembrane receptors?
-G protein-coupled receptors (GPCRs) -Receptor tyrosine kinases -ion channel receptors
Apoptosis involves:
-digestion of cellular contents by scavenger cells -activation of cellular enzymes -cell-signaling pathways -fragmentation of the DNA
What two facts were stated by the result of Sutherland's experiment and the fact that glycogen phosphorylase could only be activated by epinephrine when the hormone is added to intact cells in a solution?
1. Epinephrine doesn't interact directly with the enzyme responsible for glycogen breakdown; an intermediate step or series of steps must be occurring inside the cell. 2. The plasma membrane itself is necessary for transmission of the signal to take place.
The process by which a signal is converted to a specific cellular response involves three stages, what are they?
1.reception of a signaling molecule 2.transduction of the signal 3.response to the signal
What are growth factors?
A class of local regulators in animals; compounds that stimulate nearby target cells to grow and divide
Once received by the cell surface receptor, what happens to the mating signal in a yeast cell?
A mating signal is changed, or transduced, into a form that brings about a cellular response of mating. This occurs in a series of steps called a signal transduction pathway.
What triggers the fight-or-flight response in an animal?
A signaling molecule called epinephrine (adrenaline).
What does phosphodiesterase convert cAMP into in the absence of a hormone (signaling molecule)?
AMP
The source of phosphate for a phosphorylation cascade is __________.
ATP
What triggers transcription?
Activated transcription factors trigger transcription.
Which of the following statements about apoptosis is true?
Apoptosis is essential for normal development of the nervous system. Apoptosis typically involves multiple signaling pathways. Some apoptotic signals originate from outside a cell. Some apoptotic signals come from the nucleus, when DNA has suffered irreparable damage. Some apoptotic signals come from the endoplasmic reticulum when excessive protein misfolding occurs. Some apoptotic signals come from mitochondria.
Beyond communication through plasmodesmata, why is local signaling in plants not as well understood?
Because they have cell walls, they use different mechanisms.
How do cells of the yeast Saccharomyces Cerevisae identify their mates?
By Chemical Signaling
What role does a transcription factor play in a signal transduction pathway?
By binding to DNA it triggers the transcription of a specific gene. This is the function of a transcription factor.
How does epinephrine stimulate glycogen breakdown?
By somehow activating a cytosolic enzyme, glycogen phosphorylase, that could only be activated by epinephrine when the hormone is added to intact cells.
What process may animals cells use to communicate via direct contact between membrane-bound cell-surface mole
Cell-cell recognition. This sort of local signaling is especially important in embryonic development and the immune response.
What systems of cell-to-cell communication allow the trillions of cells in an impala (animal) to "talk" to each other, coordinating their activities?
Cells can signal to each other and interpret the signals they receive from other cells and the environment. The signals may include light and touch, but are most often chemicals.
Different types of cells can respond differently to the same signaling molecule. Which of the following explains this apparent paradox?
Different types of cells possess different proteins.
How do two yeast cells bind together (mate)?
Each type secretes a specific factor that binds to receptors only on the other type of cell. When exposed to each other's mating factors, a pair of cells of opposite type change shape, grow toward each other, and fuse (mate).
How does the change in shape of a receptor affect it?
For many receptors, this change in shape directly activates the receptor, enabling it to interact with other cellular molecules. For other kinds of receptors, the immediate effect of ligand binding is to cause the aggregation of two or more receptor molecules, which leads to further molecular events inside the cell.
What is an example of quorum sensing?
Formation of biofilm (an aggregation of bacterial cells adhered to a surface). The cells in the biofilm generally derive nutrition from the surface they are on.
A toxin that inhibits the production of GTP would interfere with the function of a signal transduction pathway that is initiated by the binding of a signal molecule to _____ receptors.
G-protein-linked GTP activates G proteins.
Epinephrine acts as a signal molecule that attaches to _____ proteins.
G-protein-linked receptor
What are the three major types of transmembrane recepetors?
GPCR's Ion channel receptors G protein coupled receptors
A G protein is active when __________.
GTP is bound to it
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.
What is endocrine signaling?
Hormonal signaling in animals. Specialized cells release hormone molecules, which travel via the circulatory system to other parts of the body, where they reach target cells that can recognize and respond to the hormones.
What chemicals do both plants and animals use for long-distance signaling?
Hormones
What did Earl W. Sutherland investigate?
How the animal hormone epinephrine (adrenaline) stimulates the breakdown of the storage polysaccharide glycogen within liver cells and skeletal muscle cells.
Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect only target cells because
intracellular receptors are present only in target cells.
Which of the following statements about calcium ions in a typical cell is true?
In a typical cell, calcium ions are often concentrated within the endoplasmic reticulum.
When do scientists think that signaling mechanisms first evolved?
In ancient prokaryotes and single-celled eukaryotes and then were adopted for new uses by their multicellular descendants.
How are some messenger molecules secreted?
In many cases of local signaling, messenger molecules are secreted by the signaling cell. Some of these only travel short distances, such local regulators influence cells in the vicinity.
How do the liver or muscle cell use the compound glucose 6-phosphate (an early intermediate in glycolysis) after its produced?
It can use it for energy production. Alternatively, the compound can be stripped of phosphate and released from the cell into the blood as glucose, which can fuel cells throughout the body.
What distinguishes between relay proteins and second messengers in signal transduction pathways?
Signal transduction pathways are multistep pathways that include relay proteins and small, nonprotein, water-soluble molecules or ions called second messengers.
Which of these are correct?
Kinases are enzymes that phosphorylate other molecules. Ion channels are found on both the plasma membrane and the endoplasmic reticulum. Tyrosine-kinase receptors consist of two polypeptides that join when activated by a signal molecule. Phospholipase C catalyzes the formation of IP3.
What is paracrine signaling?
Local signaling that uses growth factors. Numerous cells can receive and respond to the molecules of a growth factor produced by a single cell in their vicinity.
Where are most signal receptors located?
Most are plasma membrane proteins, but others are located inside the cell.
Testosterone and estrogen are lipid-soluble signal molecules that cross the plasma membrane by simple diffusion. If these molecules can enter all cells, why do only specific cells respond to their presence?
Nontarget cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cell's nucleus.
Which statements are true about the binding of histamine to the histamine H1 receptor?
Once the G protein is active, it binds to the enzyme phospholipase C, activating it. Histamine is likely hydrophilic. Histamine binds extracellularly to the H1 receptor. When histamine binds to the H1 receptor, the receptor undergoes a conformation change and binds the inactive G protein. Histamine is a chemical substance released in inflammatory and allergic responses. The histamine H1 receptor on target cells is a G protein-coupled receptor that activates phospholipase C in response to the binding of histamine.
What are the functions of signal transduction pathways?
Signal transduction pathways allow different types of cells to respond differently to the same signal molecule. Signal transduction pathways convert a signal on a cell's surface to a specific cellular response. Signal transduction pathways amplify the effect of a signal molecule.
_____ catalyzes the production of _____, which then opens an ion channel that releases _____ into the cell's cytoplasm.
Phospholipase C ... IP3 .... Ca2+ Phospholipase C cleaves IP3 from a membrane protein, and IP3 then binds to a calcium channel on the ER.
What distinguishes the roles of protein kinases and protein phosphatases in signal transduction pathways?
Protein kinases activate enzymes by phosphorylating or adding phosphate groups to them. Protein phosphatases dephosphorylate or remove phosphate groups from enzymes, including protein kinases.
What is Reception (Stage 1) of cell signaling?
Reception is the target cell's detection of a signaling molecule coming from outside the cell.
What is the term for a large relay protein that several other relay proteins are attached to?
Scaffolding protein
What are the three stages for cell signaling?
Stage 1: Reception Stage 2: Transduction Stage 3: Response
What happens when a cell encounters a secreted signaling molecule?
The ability of a cell to respond is determined by whether it has a specific receptor molecule that can bind to the signaling molecule . The information conveyed by this binding (the signal) must then be changed into another form (transduced) inside the cell before a cell can respond.
What is responsible for initiating a signal transduction pathway?
The attachment of a signal molecule to a plasma membrane receptor initiates a signal transduction pathway.
The cholera bacterium Vibrio cholerae produces an enzyme toxin that chemically modifies a G protein involved in regulating salt and water secretion in intestinal cells. Stuck in its active form, the modified G protein stimulates the production of a high concentration of cAMP, which causes the intestinal cells to secrete large amounts of salts into the intestines, with water following by osmosis. An infected person quickly develops profuse diarrhea and if left untreated can soon die from the loss of water and salts. What is the basic effect of the cholera toxin?
The basic effect of the cholera toxin is signal amplification. The effect of the toxin is to prevent the inactivation of the G protein. Because the modified G protein is unable to hydrolyze GTP to GDP, it remains stuck in its active form, continuously stimulating adenylyl cyclase to make cAMP. This amplifies the effect of the signal.
What is a histamine H1 receptor?
The histamine H1 receptor is one of several existing histamine G protein-coupled receptors. Depending on many factors, including the type of receptor, histamine can trigger a variety of responses, including vasodilation, smooth muscle contraction, stimulation of gastric secretion, cardiac stimulation, and increased vascular permeability (causing runny nose and watery eyes).
What did Sutherland discover about glycogen metabolism in liver cells?
The hormone epinephrine binds to a specific receptor on the plasma membrane of the liver cell.
Domoic acid is a neurotoxin produced by some species of alga. Domoic acid binds to the kainate receptor on neurons in parts of the brain. The kainate receptor facilitates the movement of calcium into the cell. Excess domoic acid-induced stimulation of the neural kainate receptors causes neural damage and short-term memory loss. Based on this, which of the following is likely true?
The kainate receptor is a ligand-gated ion channel and domoic acid is a ligand.
How do the molecules of synaptic signaling trigger a response in the target cell?
The molecules act as chemical signals, diffusing across the synapse (narrow space between the nerve cell and its target cell) triggering a response in the target cell.
What genes does the yeast cell formed from two mating cells contain?
The new a/alpha cell contains all the genes of both original cells, a combination of genetic resources that provides advantages to the cell's descendants, which arise by subsequent cell divisions.
What is Response (Stage 3) of cell signaling?
The response may be almost any imaginable cellular activity- such as catalysis for an enzyme (Ex: glycogen phosphorylase), rearrangement of the cytoskeleton, or activation of specific genes in the nucleus.
How does the signaling molecule attach to the receptor?
The signaling molecule is complementary in shape to a specific site on the receptor and attaches there. The signaling molecule acts as a ligand (the term for a molecule that specifically binds to another molecule, often a larger one).
What triggers the third stage (response) of cell signaling?
The transduced signal finally triggers a specific cellular response
What is Transduction (Stage 2) of cell signaling?
The transduction stage converts the signal to a form that can bring about a specific cellular response.
What do the cell junctions in both plants and animals do?
They directly connect the cytoplasms of adjacent cells. Signaling substances dissolved in the cytosol can pass freely between adjacent cells.
How do plant hormones (often called plant growth regulators) travel?
They sometimes travel in vessels but more often reach their targets by moving through cells or by diffusing through the air as gas.
What is quorum sensing?
This is a phenomenon where bacteria cells secrete molecules that can be detected by other bacterial cells, and sensing the concentration of such signaling molecules allows bacteria to monitor the local density of cells. Quorum sensing allows bacterial populations to coordinate their behaviors in activities that require a given number of cells acting synchronously.
What is suggested by the fact that the molecule details of signal transduction in yeasts and mammals are similar?
This is suggesting that early versions of cell-signaling mechanisms evolved well before the first multicellular creatures appeared on Earth.
Where does synaptic signaling occur and what is it?
This type of local signaling occurs in the nervous system. This is when an electrical signal along a nerve cell triggers the secretion of neurotransmitter molecules.
How can the mobilization of fuel reserves (an effect of epinephrine) be used by an animal?
To either defend itself (fight) or escape whatever elicited a scare (flight)
Where do most water-soluble signaling molecules bind?
To specific sites on transmembrane proteins that transmit information from the extracellular environment to the inside of the cell.
True or false, one signaling molcule (eg. a hormone) can trigger cell signaling pathways in more than one cell type in the body
True
In Reception, how/when is a chemical signal "detected"?
When the signaling molecule binds to a receptor protein located at the cell's surface (or inside the cell).
Can the size or amount of a hormone vary?
Yes, EX: plant hormone ethylene, is a hydrocarbon of only 6 atoms (C2H4), small enough to pass through cell walls. Mammal hormone insulin, (regulates blood sugar levels) is a protein with thousands of atoms.
What are the two sexes/mating types of a yeast cell?
a and alpha
ATPgammaS is a form of ATP that CANNOT be hydrolyzed by enzymes. If this compound were introduced to cells so that it replaced the normal ATP present in the cell, which of the following would you predict?
a decrease in phosphorylated proteins in the cell
In the inherited disorder Wiskott-Aldrich syndrome, __________.
a multifunctional relay protein involved with the proliferation of immune cells is defective
Ras, a small G protein located at the plasma membrane, is often mutated in different types of cancer. Ras normally signals to a cell that it should divide. Cancer cells divide uncontrollably. Which of the following changes to Ras could explain uncontrolled division in a cancer cell that has mutated Ras present?
a mutation that means Ras cannot hydrolyze GTP to GDP
What allows the cell to hear/respond to its signal?
a receptor protein on or in the target cell
What is a signal transduction pathway?
a sequence of changes in a series of different molecules required for transduction most times it occurs
What is direct cell contact?
a type of local signaling that eukaryotic cells may use to communicate
Protein phosphorylation is commonly involved with all of the following except
activation of G protein-coupled receptors
The binding of a signal molecule to a ligand-gated ion channel __________.
affects the membrane potential
A protein kinase activating many other protein kinases is an example of _____.
amplification By activating many other molecules the initial signal is amplified.
G-protein-coupled receptors __________, whereas receptor tyrosine kinases __________.
are not enzymes ... have enzymatic function
Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP. Identify the second messenger.
cAMP
What is the most widely used second messenger?
calcium
During the transduction of a signal, one molecule or ion may be closely associated with the activity of another. Which of the following pairs correctly combines two associated molecules?
calcium, IP3 cAMP, adenylyl cyclase cAMP, protein kinase A DAG, IP3
What is activated by calcium ions?
calmodulin Calmodulin is a calcium-binding protein.
Phosphorylation __________.
can either activate or inactivate a protein
What are some diseases associated with cell-surface receptor malfunctions and how can they be treated?
cancer, heart disease, and asthma They can be treated by analyzing the structures of these receptors.
In eukaryotic cells, which of the following is a second messenger that is produced as a response to an external signal such as a hormone?
cyclic AMP
What acts as a second messenger?
cyclic AMP
The activation of receptor tyrosine kinases is characterized by
dimerization and phosphorylation.
Steroid hormones can enter a cell by simple diffusion. Therefore steroids __________.
do not initiate cell signaling by interacting with a receptor in the plasma membrane
Calcium ions that act as second messengers are stored in _____.
endoplasmic reticula
Which of the following is a response from a cell signaling pathway?
gene is turned on gene is turned off enzyme is activated cell division
The cleavage of glycogen by glycogen phosphorylase releases _____.
glucose-1-phosphate Glycogen is a polysaccharide composed of glucose monomers.
Apoptosis involves all but which of the following?
lysis of the cell
Receptors for signal molecules __________.
may be found embedded in the plasma membrane, or found within the cytoplasm or nucleus
Testosterone does NOT affect all cells of the body because __________.
not all cells have cytoplasmic receptors for testosterone
What cells "hear" the signals emitted by an a yeast cell?
only its prospective mates (alpha cells)
IP3 (inositol trisphosphate) acts by __________.
opening Ca2+ channels
Cholera develops when the bacterial toxin __________.
prevents G-protein inactivation, which leads to the continuous production of cAMP
The general name for an enzyme that transfers phosphate groups from ATP to a protein is __________.
protein kinase
The molecule cAMP usually directly activates __________.
protein kinase A
Second messengers tend to be water-soluble and small. This accounts for their ability to __________.
rapidly move throughout the cell by diffusion
Which of the following is activated when the binding of single molecules causes it to form a dimer?
receptor tyrosine kinases
What are the molecules in the signal transduction pathway often called?
relay molecules
What event would activate a G protein?
replacement of GDP with GTP
What is the third stage of cell signaling?
response
Ligand binding generally causes a receptor protein to undergo a change in
shape
A signal transduction pathway is initiated when a _____ binds to a receptor.
signal molecule
A signal transduction pathway is initiated when a _____ binds to a receptor.
signal molecule The binding of a signal molecule to a receptor initiates a signal transduction pathway.
Cells use different signaling strategies to achieve different goals. In hormonal signaling __________.
specialized cells release hormone molecules into the circulatory system, permitting distant cells to be affected
Certain yeast cells secrete a molecule called the α factor. The purpose of this molecule is to __________.
stimulate cells of the opposite mating type, a yeast cells, to grow toward the α cell
Which specialized type of signaling occurs in the nervous system?
synaptic
If a modified form of GTP that CANNOT be enzymatically converted to GDP were added to a culture of cells, the likely result would be __________.
that the activated G proteins would remain locked in the "on" position, transmitting signal even in the absence of a signaling molecule
What could account for the different cellular responses to histamine?
the cell type in which the histamine receptor is located, the types of relay molecules within the cell, the enzyme that is activated by the G protein associated with the receptor, the type of second messengers involved in the signal transduction pathway
IP3 (inositol trisphosphate) is produced as a result of __________.
the cleavage of a specific phospholipid in the plasma membrane
What is the largest family of human cell surface receptors?
the nearly 1,000 G protein-coupled receptors (GPCRs)
In liver cells, epinephrine stimulates the breakdown of glycogen. As the signal-transduction pathway progresses, __________.
the signal is amplified
Early work on signal transduction and glycogen metabolism by Sutherland indicated that __________.
the signal molecule did not interact directly with the cytosolic enzyme, but required an intact plasma membrane before the enzyme could be activated
Evidence that cell signaling evolved early in the history of life comes from __________.
the similarity of cell-signaling mechanisms in organisms that have a very distant common ancestor
What does glycogen breakdown release?
the sugar glucose 1-phosphate, which the cell converts to glucose 6-phosphate
The cellular response of a signal pathway that terminates at a transcription factor would be __________.
the synthesis of mRNA
Cells of the gastrointestinal (GI) tract and cells of the heart respond differently to epinephrine because __________.
there are differences in the proteins found in the two types of cells
Which is the second of the three stages of cell signaling?
transduction
When histamine binds to a histamine receptor, the specific cellular response that results is determined by the following factors:
•the type of histamine receptor •the type of cell in which the receptor is located •the enzyme that is activated by the G protein associated with the receptor •the types of second messengers involved in the signal transduction pathway •the proteins activated by the second messengers
