Chapter 11: Cell Communication

Question 1

Describe the process of cell communication between mating yeast cells

Answer 1

1. Exchange of mating factors: each mating cell secretes a mating factor that binds to receptors on the other mating type
2. Mating: binding of the factors to receptors induces changes in the cells that lead to their fusion
3. New A/a cell: nucleus of the fused cells includes all the genes from both cells

Question 2

What is the purpose of a unique match between mating factors and receptors?

Answer 2

Ensures mating between cells only of the same species

Question 3

The three major steps of the signal transduction pathway are

Answer 3

1. signal reception
2. signal transduction
3. cellular response

Question 4

How do cell junctions allow for communication between cells?

Answer 4

Allow molecules, including signaling molecules, to pass between adjacent cells WITHOUT passing through plasma membranes by connecting the cytoplasms

Question 5

Paracrine signaling can best be defined as____

Answer 5

a form of local signaling in which the signaling molecules only travel short distances

Question 6

Growth factors are a type of ____ signaling. They stimulate target cells to..

Answer 6

Local signaling
grow and divide

Question 7

Synaptic signaling is a type of ____ signaling in the ___system.

Answer 7

Local signaling in the nervous system

Question 8

Describe the process of synaptic signaling

Answer 8

Electrical signal along a nerve cell triggers the release of NTs
The NTs diffuse across the synapse and trigger a response

Question 9

Hormones are typically used in ____ signaling and travel through the body’s ___ system

Answer 9

long distance
circulatory

Question 10

TorF: plant hormones can only travel through vessels within the organism

Answer 10

false, can diffuse through cells if they’re small enough

Question 11

Define signal reception and how it fits into the stages of cell signaling

Answer 11

first step in cell signaling
reception is the target cell’s detection of a signaling molecule from outside the cell when the molecule has bound to a receptor

Question 12

Define signal transduction and how it fits into the stages of cell signaling

Answer 12

Second stage of cell signaling
The binding of the signal receptor changes its shape in some way.
Converts the signal to a form that can bring about a cellular response.
The molecules involved in the signal transduction pathway are often called relay molecules

Question 13

Define cellular response and how it fits into the stages of cell signaling

Answer 13

final stage
Any imaginable activity

Question 14

Explain how signaling is involved in ensuring that yeast cells
fuse only with cells of the opposite mating type.

Answer 14

The two cells of opposite mating type (A and a) each secrete a unique signaling molecule, which can only be bound by receptors carried on cells of the
opposite mating type. Thus, the A mating factor cannot bind to another a cell and cause it to grow toward the first a cell. Only an a cell can “receive” the signaling molecule and respond by directed growth.

Question 15

In liver cells, glycogen phosphorylase acts in which of the
three stages of the signaling pathway associated with an
epinephrine-initiated signal?

Answer 15

Glycogen phosphorylase acts in the third stage, the cellular response to epinephrine signaling.

Question 16

If epinephrine were mixed with glycogen phos-
phorylase and glycogen in a cell-free mixture in a test tube,
would glucose 1-phosphate be generated? Why or why not?

Answer 16

Glucose 1-phosphate would not be generated because the activation of the enzyme requires an intact cell, with an intact receptor in the membrane and an
intact signal transduction pathway. The enzyme cannot be activated directly by
interaction with the signaling molecule in the cell-free mixture

Question 17

Describe the process of cell signaling in GPCRs

Answer 17

1. A GPCR is only activated when attached to a G protein
2. When the signaling molecule binds to the GCPR, a GTP displaces the GDP on the G protein and it can attach to the receptor.
3. The active G protein dissociates from the receptor and binds to an enzyme, triggering the next response
4. The G protein acts as a GTPase to become inactive, causing its GTP to become GDP

Question 18

Describe the process of cell signaling in RTKs

Answer 18

1. The binding of a ligand causes to two receptor monomers to form a dimer
2. Dimerization activates the tyrosine kinase region of each minomer, each tyrosine kinase adds a phospahte from an ATP molecule to a tyrosine that is part of the tail of another monomer
3. Now that the receptor is activated, it is recognized by relay proteins

Question 19

Describe the process of cell signaling in Ion channel receptors

Answer 19

1. When a ligan binds to the receptor and the channel opens, ions from through and change the ion concentration inside the cell
2. When the ligand detaches, the channel closes and ions no longer enter

Question 20

Intracellular receptors are typically found in the ___ or ____ of target cells

Answer 20

cytoplasm or nucleus

Question 21

To reach intracellular receptors, signaling molecules typically…. They are capable of this because…

Answer 21

Pass through the cell;s plasma membrane
They are hydrophobic, small, or both

Question 22

Describe the behavior of the steroid aldesterone’s cells ignaling

Answer 22

uses intracellular receptors because its hydrophobic
Secreted by adrenal gland, travels throughout the body via circulatory system
A response only occurs in kidnays because of receptor specificity
When aldesterone attaches, the active receptor protein enters nucleus and turns on genes that control water and sodium flow into kidney cells

Question 23

How does the activated hormone-receptor complex turn on genes? Use aldesterone as an example

Answer 23

Aldesterone acts as a transcription factor and is able to be both the receptor and transducer

Question 24

Nerve growth factor (NGF) is a water-soluble signaling mol-
ecule. Would you expect the receptor for NGF to be intracel-
lular or in the plasma membrane? Explain

Answer 24

NGF is water-soluble (hydrophilic), so it cannot pass through the lipid membrane to reach intracellular receptors, as steroid hormones can. Therefore, you’d
expect the NGF receptor to be in the plasma membrane—which is, in fact, the
case.

Question 25

What would the effect be if a cell made defective receptor tyrosine kinase proteins that were unable to dimerize?

Answer 25

The cell with the faulty receptor would not be able to respond appropriately to the signaling molecule when it was present. This would most likely
have dire consequences for the cell since regulation of the cell’s activities by
this receptor would not occur appropriately

Question 26

A protein kinase can best be defined as..

Answer 26

an enzyme that transfers phosphate groups from ATP to a protein

Question 27

How do RTKs differ from most cytoplasmic kinases?

Answer 27

Most kinases act of proteins different than themselves
Most phosphorylate serine or threonine rather than tyrosine

Question 28

The shape changes during each step of a phosphorylation cascade are the result of

Answer 28

interaction of newly added phosphate groups with charged/polar amino acids on the protein

Question 29

Protein phosphatases are enzymes responsible for

Answer 29

rapidly removing phosphate groups from proteins in a process known as dephosphorylation

Question 30

TorF: second messengers are typically small and water soluble to spread easily through regions of the cell by diffusion

Answer 30

true

Question 31

How does cyclic AMP act as a second messenger

Answer 31

it carries the signal initiated by epinephrine from the plasma membrane of a liver or muscle cell into the cell’s interior, where the signal eventually brings about glycogenic breakdown

Question 32

______ converts ATP to cyclic AMP in response to a signal from ___

Answer 32

adenylyl cyclase
epinephrine

Question 33

The immediate effect of an elevation in cAMP molecules is usually the activation of a

Answer 33

protein kinase

Question 34

Why can Ca 2+act as a second messenger?

Answer 34

The concentration of calcium in the cytosol is normally lower than the concentration outside the cell

Question 35

Calcium ions are ____ transported out of the cell and imported into the ER

Answer 35

actively

Question 36

Why is the calcium concnetration in the ER usually higher than the cytosol?

Answer 36

Various proteins actively import calcium from the cytosol into the ER

Question 37

In response to a signal relayed bya signal transduction pathway, the cytosolic calcium level may

Answer 37

rise

Question 38

The pathways leading to calcium release form the ER involve the second messengers ____ and ___. They are produced by ….

Answer 38

IP3 and DAG
produced by cleavage of a specific phospholipid in the plasma membrane

Question 39

What is a protein kinase, and what is its role in a signal
transduction pathway?

Answer 39

A protein kinase is an enzyme that transfers a phosphate group from ATP to a
protein, usually activating that protein (often a second type of protein kinase).
Many signal transduction pathways include a series of such interactions, in which
each phosphorylated protein kinase in turn phosphorylates the next protein
kinase in the series. Such phosphorylation cascades carry a signal from outside the
cell to the cellular protein(s) that will carry out the respons

Question 40

When a signal transduction pathway involves a phosphory-
lation cascade, how does the cell’s response get turned off?

Answer 40

Protein phospha-
tases reverse the effects of the kinases by dephosphorylation, and unless the signal-
ing molecule is at a high enough concentration that it is continuously rebinding
the receptor, the kinase molecules will all be returned to their inactive states by
phosphatases.

Question 41

If you exposed a cell to a ligand that binds to a
receptor and activates phospholipase C, predict the effect the
IP3-gated calcium channel would have on Ca2 + concentration
in the cytoso

Answer 41

The IP3-gated channel would open, allowing calcium ions to flow out of the ER
and into the cytoplasm, which would raise the cytosolic Ca2 + concentration.

Question 42

Describe how amplification might work in the epinephrine triggered pathway involving cAMP and adenylyl cyclase

Answer 42

Each adenylyl cyclase catalyzes the formation of 100 cAMP molecules. The amplification comes from the fact that the proteins are in their active form for enough time to process multiple substrate molecules.

Question 43

Explain why different kinds of cells have different collections of proteins?

Answer 43

Because differentiated cells turn on different sets of genes

Question 44

Scaffolding proteins can best be defined as

Answer 44

large relay proteins that are simultaneously attached to other relay proteins in order to increase signal transduction efficiency.

Question 45

How do scaffolding proteins enhance the speed and accuracy of signal transfer?

Answer 45

The rate of protein-protein interaction is not limited by diffusion

Question 46

TorF: In order for a cellular response to be initiated, the concentration of ligands bound to receptors must be above a certain threshold

Answer 46

True

Question 47

How can a target cell’s response to a single hormone molecule
result in a response that affects a million other molecules?

Answer 47

At each step in a cascade of sequential activations, one molecule or ion may
activate numerous molecules functioning in the next step. This causes the
response to be amplified at each such step and overall results in a large amplifica-
tion of the original signal

Question 48

If two cells have different scaffolding proteins,
explain how they might behave differently in response to
the same signaling molecule

Answer 48

. Scaffolding proteins hold molecular components
of signaling pathways in a complex with each other. Different scaffolding proteins
would assemble different collections of proteins, facilitating different molecular
interactions and leading to different cellular responses in the two cells.

Question 49

TorF: two types of cell signals that can lead to apoptosis originate from inside the cell

Answer 49

True

Question 50

If apoptosis occurred when it should not, what
types of protein defects might be the cause? What types
could result in apoptosis not occurring when it should?

Answer 50

If a receptor protein for a death-signaling
molecule were defective such that it was activated even in the absence of the
death signal, this would lead to apoptosis when it wouldn’t normally occur. Simi-
lar defects in any of the proteins in the signaling pathway would have the same
effect if the defective proteins activated relay or response proteins in the absence
of interaction with the previous protein or second messenger in the pathway.
Conversely, if any protein in the pathway were defective in its ability to respond
to an interaction with an early protein or other molecule or ion, apoptosis would
not occur when it normally should. For example, a receptor protein for a death-
signaling ligand might not be able to be activated, even when ligand was bound.
This would stop the signal from being transduced into the cell.

Question 51

Binding of a signaling molecule to which type of receptor
leads directly to a change in the distribution of substances on
opposite sides of the membrane?
(A) intracellular receptor
(B) G protein-coupled receptor
(C) phosphorylated receptor tyrosine kinase dimer
(D) ligand-gated ion channel

Answer 51

ligand-gated ion channel

Question 52

The activation of receptor tyrosine kinases is characterized by
(A) dimerization and phosphorylation.
(B) dimerization and IP3 binding.
(C) a phosphorylation cascade.
(D) GTP hydrolysis

Answer 52

dimerization and phosphorylation.

Question 53

Lipid-soluble signaling molecules, such as aldosterone, cross
the membranes of all cells but affect only target cells because
(A) only target cells retain the appropriate DNA segments.
(B) intracellular receptors are present only in target cells.
(C) only target cells have enzymes that break down aldosterone.
(D) only in target cells is aldosterone able to initiate the phosphorylation cascade that turns genes on.

Answer 53

intracellular receptors are present only in target cells.

Question 54

Consider this pathway: epinephrine –> G protein-coupled
receptor –> G protein –> adenylyl cyclase —> cAMP. Identify the
second messenger.
(A) cAMP
(B) G protein
(C) GTP
(D) adenylyl cyclase

Answer 54

cAMP

Question 55

Which of the following occurs during apoptosis?
(A) lysis of the cell
(B) direct contact between signaling cells
(C) fragmentation of the DNA
(D) release of proteases outside the cell

Answer 55

fragmentation of the DNA

Question 56

Protein phosphorylation is commonly involved with which of
the following?
(A) ligand binding by receptor tyrosine kinases.
(B) activation of G protein-coupled receptors.
(C) activation of protein kinase molecules.
(D) release of Ca2+ from the ER lumen.

Answer 56

activation of protein kinase molecules.