Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because __________.
they are species specific
the number of molecules used is small and fixed
they counter the harmful effects of phosphatases
they
they amplify the original signal manyfold
Which of the following statements describes the function of inositol trisphosphate (IP3) as a second messenger?
- Inositol trisphosphate binds to an IP3-gated calcium channel, causing the uptake of calcium ions from the endoplasmic reticulum.
- IP3 cataly
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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.
- The hormone that breaks down glycogen into glucose enters the liver cell.
- Glucose i
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Certain yeast cells secrete a molecule called the -factor. The purpose of this molecule is to __________.
- kill other yeast cells nearby, which may be competing for access to food
- attract other yeast cells of the same mating type to assemble
- kill bac
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In a phosphorylation cascade, __________ phosphorylate proteins, and __________ dephosphorylate them.
protein phosphatases; protein kinases
protein kinases; protein phosphatases
cAMPs; adenylyl cyclases
growth factors; hormones
ligands; ligand-gated ion c
protein kinases; protein phosphatases
cAMP usually directly activates __________.
phosphodiesterase
receptor tyrosine kinases
protein kinase A
adenylyl cyclase
G proteins
protein kinase A
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
The process of phosphorylation is very important as a cellular mechanism for regulating protein activity. Phosphorylation does this by ___________.
synaptic signaling
inactivating proteins
opening ligand-gated ion channels
cell-to-cell recognition
activat
activating or inactivating proteins
What effect does ligand binding have on receptor tyrosine kinase proteins?
- Ligand binding causes them to open ligand-gated ion channels.
- Ligand binding causes them to dephosphorylate and form dimers.
- Ligand binding causes them to activate a G protei
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Which of the following statements describes what happens to cells undergoing apoptosis?
- An external signal triggers a phosphorylation cascade.
- Cells enter the cell cycle and undergo mitosis.
- Cells undergo lysis.
- The protein ced-9 remains active.
-
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G-protein-linked receptors __________, whereas receptor tyrosine kinases __________.
- form a dimer when activated; catalyze the transfer of a phosphate group from ATP to an amino acid
- phosphorylate the amino acid guanine; phosphorylate the amino acid t
- are not enzymes; have enzymatic function
In liver cells, epinephrine stimulates the breakdown of glycogen. As the signal-transduction pathway progresses, __________.
glycogenesis is stimulated
the number of molecules involved remains constant
the signal is reduced
the signal is amplified
the num
the signal is amplified
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 would you expect to see i
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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 recepto
- Nontarget cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cell's nucleus.
What happens during the process of paracrine signaling?
- Communication between adjacent cells occurs between membrane-bound cell-surface molecules.
- None of the listed responses is correct.
- Molecules diffuse across the synapse between adjacent nerve c
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A difference between the mechanisms of cAMP and Ca2+ in signal transduction is that cAMP __________ and Ca2+ __________.
- enters the cell via a transmembrane protein channel; enters the cell by diffusing across the plasma membrane
- is stored in the endo
- is synthesized by an enzyme in response to a signal; is released from intracellular stores
How is nitric oxide different from other signal molecules?
It can phosphorylate cAMP.
It activates a G protein.
It enters the cell through a ligand-gate ion channel.
It is a gas.
None of the listed responses is correct.
It binds to a membrane receptor.
It is a gas.
After a signaling molecule binds to a G protein-coupled receptor, what activates the associated G protein?
Receptor tyrosine kinase proteins form a dimer.
GTP displaces GDP on the G protein.
GDP displaces GTP on the G protein.
An ion-gated channel opens.
GTP displaces GDP on the G protein.
What is the general name for an enzyme that transfers phosphate groups from ATP to other molecules?
Ligand
G protein-coupled receptor
Protein kinase
Hormone
G protein
Ligand-gated ion channel
Protein kinase
Why does testosterone not affect all cells in the body?
- Testosterone binds only to G protein-receptor proteins.
- Testosterone binds only to receptor tyrosine kinases.
- Only certain cells have cytoplasmic receptors for testosterone.
- Testosterone is a
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The stage of cell signaling in which a chemical signal is "detected" when the signaling molecule binds to a receptor protein located at the cell's surface is called __________.
reception
secretion
response
cell-to-cell recognition
transduction
exchange of
reception
IP3 (inositol trisphosphate) is produced as a result of __________.
- the cleavage of a certain kind of phospholipid in the plasma membrane
- phospholipase C
- protein kinase A activation
- Ca2+
- DAG
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Evidence that cell signaling evolved early in the history of life comes from __________.
- the similarity of the mechanisms in organisms that have a very distant common ancestor
- comparative studies of ribosomal RNA
- comparative studies of mitochondrial
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A small molecule that specifically binds to a larger molecule is called a(n) __________.
competitive inhibitor
ligand
protein kinase
DAG
A protein
ligand
How does adenylyl cyclase help transmit signals within a cell?
- It activates a G protein.
- It deactivates a G protein.
- It binds to a G protein-coupled receptor.
- It converts cAMP to ATP, which then broadcasts the signal to the rest of the cell.
- It
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The stage of cell signaling in which the signal is converted to a form that can bring about a response in the cell is called __________.
cell-to-cell recognition
ligand binding
response
paracrine signaling
reception
transduction
transduction
In which part of cell are calcium ions usually found?
Golgi apparatus
Cytosol
Endoplasmic reticulum
Mitochondrion
Nucleus
Chloroplast
ER
A G protein is active when __________.
it is bound by its ligand and transported to the nucleus
it is phosphorylated by protein kinase
GTP is bound to it
Ca2+ binds to a G-protein-linked receptor
GDP replaces GTP
GTP is bound to it
Which of the following statements best describes the process of hormonal signaling?
- Molecules diffuse across the synapse between adjacent nerve cells.
- Growth factors stimulate nearby cells to grow and divide.
- Communication between adjacent cells occ
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Second messengers tend to be water-soluble and small. This accounts for their ability to __________.
- move from substrate to substrate during a phosphorylation cascade
- pass quickly from cell to cell
- rapidly move throughout the cell by diffusion
- cro
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