Chapter 11: Cell Communication Flashcards
Describe the process of cell communication between mating yeast cells
- Exchange of mating factors: each mating cell secretes a mating factor that binds to receptors on the other mating type
- Mating: binding of the factors to receptors induces changes in the cells that lead to their fusion
- New A/a cell: nucleus of the fused cells includes all the genes from both cells
What is the purpose of a unique match between mating factors and receptors?
Ensures mating between cells only of the same species
The three major steps of the signal transduction pathway are
- signal reception
- signal transduction
- cellular response
How do cell junctions allow for communication between cells?
Allow molecules, including signaling molecules, to pass between adjacent cells WITHOUT passing through plasma membranes by connecting the cytoplasms
Paracrine signaling can best be defined as____
a form of local signaling in which the signaling molecules only travel short distances
Growth factors are a type of ____ signaling. They stimulate target cells to..
Local signaling
grow and divide
Synaptic signaling is a type of ____ signaling in the ___system.
Local signaling in the nervous system
Describe the process of synaptic signaling
Electrical signal along a nerve cell triggers the release of NTs
The NTs diffuse across the synapse and trigger a response
Hormones are typically used in ____ signaling and travel through the body’s ___ system
long distance
circulatory
TorF: plant hormones can only travel through vessels within the organism
false, can diffuse through cells if they’re small enough
Define signal reception and how it fits into the stages of cell signaling
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
Define signal transduction and how it fits into the stages of cell signaling
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
Define cellular response and how it fits into the stages of cell signaling
final stage
Any imaginable activity
Explain how signaling is involved in ensuring that yeast cells
fuse only with cells of the opposite mating type.
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.
In liver cells, glycogen phosphorylase acts in which of the
three stages of the signaling pathway associated with an
epinephrine-initiated signal?
Glycogen phosphorylase acts in the third stage, the cellular response to epinephrine signaling.
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?
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
Describe the process of cell signaling in GPCRs
- A GPCR is only activated when attached to a G protein
- When the signaling molecule binds to the GCPR, a GTP displaces the GDP on the G protein and it can attach to the receptor.
- The active G protein dissociates from the receptor and binds to an enzyme, triggering the next response
- The G protein acts as a GTPase to become inactive, causing its GTP to become GDP
Describe the process of cell signaling in RTKs
- The binding of a ligand causes to two receptor monomers to form a dimer
- 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
- Now that the receptor is activated, it is recognized by relay proteins
Describe the process of cell signaling in Ion channel receptors
- When a ligan binds to the receptor and the channel opens, ions from through and change the ion concentration inside the cell
- When the ligand detaches, the channel closes and ions no longer enter
Intracellular receptors are typically found in the ___ or ____ of target cells
cytoplasm or nucleus
To reach intracellular receptors, signaling molecules typically…. They are capable of this because…
Pass through the cell;s plasma membrane
They are hydrophobic, small, or both
Describe the behavior of the steroid aldesterone’s cells ignaling
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
How does the activated hormone-receptor complex turn on genes? Use aldesterone as an example
Aldesterone acts as a transcription factor and is able to be both the receptor and transducer
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
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.
What would the effect be if a cell made defective receptor tyrosine kinase proteins that were unable to dimerize?
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
A protein kinase can best be defined as..
an enzyme that transfers phosphate groups from ATP to a protein
How do RTKs differ from most cytoplasmic kinases?
Most kinases act of proteins different than themselves
Most phosphorylate serine or threonine rather than tyrosine
The shape changes during each step of a phosphorylation cascade are the result of
interaction of newly added phosphate groups with charged/polar amino acids on the protein
Protein phosphatases are enzymes responsible for
rapidly removing phosphate groups from proteins in a process known as dephosphorylation
TorF: second messengers are typically small and water soluble to spread easily through regions of the cell by diffusion
true
How does cyclic AMP act as a second messenger
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
______ converts ATP to cyclic AMP in response to a signal from ___
adenylyl cyclase
epinephrine
The immediate effect of an elevation in cAMP molecules is usually the activation of a
protein kinase
Why can Ca 2+act as a second messenger?
The concentration of calcium in the cytosol is normally lower than the concentration outside the cell
Calcium ions are ____ transported out of the cell and imported into the ER
actively
Why is the calcium concnetration in the ER usually higher than the cytosol?
Various proteins actively import calcium from the cytosol into the ER
In response to a signal relayed bya signal transduction pathway, the cytosolic calcium level may
rise
The pathways leading to calcium release form the ER involve the second messengers ____ and ___. They are produced by ….
IP3 and DAG
produced by cleavage of a specific phospholipid in the plasma membrane
What is a protein kinase, and what is its role in a signal
transduction pathway?
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
When a signal transduction pathway involves a phosphory-
lation cascade, how does the cell’s response get turned off?
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.
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
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.
Describe how amplification might work in the epinephrine triggered pathway involving cAMP and adenylyl cyclase
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.
Explain why different kinds of cells have different collections of proteins?
Because differentiated cells turn on different sets of genes
Scaffolding proteins can best be defined as
large relay proteins that are simultaneously attached to other relay proteins in order to increase signal transduction efficiency.
How do scaffolding proteins enhance the speed and accuracy of signal transfer?
The rate of protein-protein interaction is not limited by diffusion
TorF: In order for a cellular response to be initiated, the concentration of ligands bound to receptors must be above a certain threshold
True
How can a target cell’s response to a single hormone molecule
result in a response that affects a million other molecules?
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
If two cells have different scaffolding proteins,
explain how they might behave differently in response to
the same signaling molecule
. 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.
TorF: two types of cell signals that can lead to apoptosis originate from inside the cell
True
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?
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.
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
ligand-gated ion channel
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
dimerization and phosphorylation.
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.
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.
(A) cAMP
(B) G protein
(C) GTP
(D) adenylyl cyclase
cAMP
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
fragmentation of the DNA
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.
activation of protein kinase molecules.
