Question 1

Type I diabetes is caused by ________.
A)degradation of insulin in the bloodstream
B)an inability to produce insulin
C)a decrease in the ability of target cells for insulin to respond to the presence of the hormone
D)insulin resistance
E)an overproduction of insulin

Accepted Answer

Type I diabetes is caused by an inability to produce insulin, which is usually due to destruction of insulin-producing cells in the pancreas by the body's immune system.

Question 2

How is Ras activity turned off?
A)It is turned off by phosphorylation.
B)It is turned off by hydrolysis of its bound GTP to GDP.
C)It is turned off by hydrolysis of its bound GDP to GTP.
D)It is turned off by an allosteric inhibitor.
E)It is turned off by hydrolysis of its bound GTP to GMP.

Accepted Answer

Ras activity is turned off by hydrolysis of its bound GTP to GDP, which is catalyzed by a GTPase-activating protein (GAP) in the presence of magnesium ions. This leads to a conformational change in Ras that disrupts its interaction with downstream effectors and allows it to dissociate from the plasma membrane.

Question 3

The enzyme below that has been identified as a negative regulator of glycogen synthase is ______.
A)glycogen phosphorylase
B)glycogen phosphorylase kinase
C)glycogen synthase kinase-3
D)insulin synthase kinase
E)protein kinase A

Accepted Answer

Glycogen synthase kinase-3 is identified as a negative regulator of glycogen synthase. This kinase phosphorylates and inhibits glycogen synthase, preventing glycogen synthesis.

Question 4

In cells exposed to stressful stimuli,like X-rays or damaging chemicals,what response does the MAP kinase cascade coordinate?
A)cell proliferation
B)withdrawal from the cell cycle
C)rapid differentiation
D)slowing of the Krebs cycle
E)a loss of sensory ability

Accepted Answer

The MAP kinase cascade is involved in coordinating the cellular response to stress stimuli. In particular, it is involved in promoting withdrawal from the cell cycle and halting progression through the cell cycle to allow the cell to repair any damage before continuing.

Question 5

Ora1 is a tetrameric _______ that has been identified as being involved in a particular type of inherited human immune deficiency that results from a lack of Ca2+ stores in ________. A)Ca^2+--ion channel,B lymphocytes B)Ca^2+--ion pump,B lymphocytes C)Ca^2+-ion channel,T lymphocytes D)Ca^2+--ion pump,T lymphocytes E)Ca^2+--ion channel,macrophages

Accepted Answer

Ora1 is a tetrameric ion channel that has been found in T lymphocytes and is involved in a type of inherited human immune deficiency called SCID, which is due to a lack of Ca2+ stores in T lymphocytes. Therefore, the best choice is C: Ca^2+--ion channel, T lymphocytes.

Question 6

What holds Ras at the inner surface of the plasma membrane?
A)weak interactions with the phospholipid head groups
B)weak interactions with integral membrane proteins
C)hydrophilic interactions of the Ras protein with the interior of the phospholipid bilayer
D)attachment to a lipid group that is embedded in the inner leaflet of the bilayer
E)attachment to a carbohydrate group that is embedded in the inner leaflet of the bilayer

Accepted Answer

Ras is attached to a lipid group, specifically a farnesyl or geranylgeranyl group, that is embedded in the inner leaflet of the plasma membrane. This anchor helps hold Ras in place at the inner surface of the membrane.

Question 7

Specificity in MAP kinase pathways is sometimes achieved by spatial localization of the pathway's component proteins.Spatial localization of these components is done by structural (i.e. ,nonenzymatic)proteins called _____________.
A)sequestration proteins
B)partitioning proteins
C)scaffolding proteins
D)framework proteins
E)spatial organization proteins

Accepted Answer

Spatial localization of MAP kinase pathway components is achieved by scaffolding proteins, which act as structural proteins to bind and localize key components of the pathway.

Question 8

What part of an insulin-receptor substrate binds to tyrosine phosphorylation sites on the activated insulin receptor?
A)an N-terminal PH domain
B)a PTB domain
C)a long tail containing tyrosine phosphorylation sites
D)a C-terminal PH domain
E)a PKB domain

Accepted Answer

The PTB domain of an insulin-receptor substrate binds to tyrosine phosphorylation sites on the activated insulin receptor.

Question 9

Two $\alpha$$\beta$ heterodimers of the insulin receptor are held together by ____ between the _______.
A)ionic bonds,$\alpha$ chains
B)ionic bonds,$\beta$ chains
C)disulfide bonds,$\alpha$ chains
D)disulfide bonds,$\beta$ chains
E)disulfide bonds,$\alpha$chain of one heterodimer and the  chain of the other

Accepted Answer

The insulin receptor is a dimer of heterodimers, and the two F1F1F1S1F1F1F10 chains are held together by disulfide bonds.

Question 10

What kind of enzyme is the RAS gene product,the Ras protein?
A)an ATPase
B)a kinase
C)a phosphodiesterase
D)a GTPase
E)a phosphatase

Accepted Answer

The RAS gene product, the Ras protein, is a GTPase enzyme. It plays a critical role in transmitting signals within cells and regulating cell growth and division. When active, Ras is bound to GTP, and when inactive, it is bound to GDP. The GTPase activity of Ras hydrolyzes GTP to GDP, leading to the cessation of downstream signaling pathways.

Question 11

Following a nerve impulse,what triggers the opening of plasma membrane voltage-gated Ca2+ channels? A)membrane hyperpolarization B)binding of an appropriate ligand C)membrane depolarization D)membrane hypopolarization E)binding of K⁺ ions

Accepted Answer

Voltage-gated Ca2+ channels open in response to membrane depolarization.

Question 12

What is activated by calcium ions entering an egg cell just after fertilization?
A)protein kinase A
B)insulin
C)cyclin-dependent kinases that drive the zygote toward its first mitotic division
D)cyclin-dependent kinases that drive the zygote toward its first meiotic division
E)glucagon-dependent kinases that drive the zygote toward its first mitotic division

Accepted Answer

Calcium ions entering an egg cell just after fertilization activate cyclin-dependent kinases that drive the zygote toward its first mitotic division.

Question 13

Among the agents that can cause ryanodine receptors to open are _______ ions,in a phenomenon called _______.
A)calcium,calcium-integrated calcium release
B)calcium,calcium-induced calcium release
C)potassium,potassium-induced calcium release
D)chlorine,chlorine-induced calcium release
E)copper,copper-induced calcium release

Accepted Answer

Ryanodine receptors are calcium release channels located in the sarcoplasmic reticulum of muscle cells. They are activated by the binding of calcium ions, which causes a conformational change and leads to the release of more calcium ions from the sarcoplasmic reticulum. This process is called calcium-induced calcium release (CICR). Therefore, choice B is the correct answer as it accurately describes the mechanism of ryanodine receptor activation.

Question 14

In which organism below has calmodulin not been found?
A)plants
B)animals
C)bacteria
D)yeasts
E)humans

Accepted Answer

Calmodulin has not been found in bacteria, while it is present in plants, animals, yeasts, and humans.

Question 15

The concentration of calcium ions in the ER lumen,the plant cell vacuole and the extracellular space are on average more than _______ times higher than in the cytosol.
A)10
B)100
C)1,000
D)10.000
E)1,000,000

Accepted Answer

The concentration of calcium ions in the ER lumen, the plant cell vacuole, and the extracellular space is on average more than 10,000 times higher than in the cytosol. This is due to the important roles of calcium ions in signal transduction and regulation of cellular processes, making it necessary to maintain such high concentrations in specific compartments.

Question 16

What is responsible for deactivating glycogen synthase kinase-3?
A)its phosphorylation by PKB
B)its dephosphorylation by protein phosphatase 1
C)its dephosphorylation by PKB
D)its phosphorylation by protein phosphatase 1
E)its degradation by PKB

Accepted Answer

Glycogen synthase kinase-3 (GSK3) is deactivated by its phosphorylation by protein kinase B (PKB), also known as Akt. This phosphorylation causes a conformational change that inhibits the kinase activity of GSK3. Dephosphorylation by protein phosphatase 1 (PP1) would reactivate GSK3, not deactivate it. Degradation by PKB is not a known mechanism for deactivating GSK3.

Question 17

What is the name of a calcium-binding protein that acts in conjunction with calcium to bring about the responses associated with cytoplasmic rises in calcium ion concentration?
A)calpectin
B)calmodulin
C)calcariain
D)callistin
E)modulocalcin

Accepted Answer

Calmodulin is a widely distributed calcium-binding protein that mediates the actions of calcium in many cellular processes, including muscle contraction, neurotransmitter release, and gene expression. It acts in conjunction with calcium to bring about the responses associated with cytoplasmic rises in calcium ion concentration.

Question 18

What generally triggers the release of calcium ions by ryanodine receptors? A)potassium efflux B)sodium influx C)an action potential D)IP₃ release E)IP₃ uptake

Accepted Answer

The release of calcium ions by ryanodine receptors is triggered by an action potential.

Question 19

What is the reason for the withdrawal of cells from the cell cycle after exposure to stressful stimuli,like X-rays and damaging chemicals?
A)It gives the cell time to repair damage resulting from such adverse conditions.
B)It allows the cell to initiate programmed cell death.
C)It allows cells to initiate sodium transport.
D)It allows the cell to secrete defensive chemicals.
E)It gives the cell time to switch its developmental pathways.

Accepted Answer

When cells are exposed to stressful stimuli, such as X-rays and damaging chemicals, they may experience DNA damage. In order to prevent mutations and other harmful effects, cells can withdraw from the cell cycle to allow time for repair mechanisms to fix any damage. This can prevent the propagation of damaged cells, and allow for the maintenance of genetic stability.

Question 20

How is the distribution of free calcium ions in the living cell detected?
A)fluorescent probes that emit light in the presence of calcium ions
B)antibodies bound to ferritin
C)an electron microscope
D)autoradiography and the distribution of radioisotope
E)NMR imaging

Accepted Answer

Fluorescent probes can bind to calcium ions and emit light in the presence of the ions, allowing for detection of their distribution within the cell.

Quiz 15: Cell Signaling and Signal Transduction: Communication Between Cells

Type I diabetes is caused by ________.

How is Ras activity turned off?

The enzyme below that has been identified as a negative regulator of glycogen synthase is ______.

In cells exposed to stressful stimuli,like X-rays or damaging chemicals,what response does the MAP kinase cascade coordinate?

Ora1 is a tetrameric _ that has been identified as being involved in a particular type of inherited human immune deficiency that results from a lack of Ca2+ stores in __.

What holds Ras at the inner surface of the plasma membrane?

Specificity in MAP kinase pathways is sometimes achieved by spatial localization of the pathway's component proteins.Spatial localization of these components is done by structural (i.e. ,nonenzymatic) proteins called _____________.

What part of an insulin-receptor substrate binds to tyrosine phosphorylation sites on the activated insulin receptor?

Two $\alpha$ $\beta$ heterodimers of the insulin receptor are held together by between the ___.

What kind of enzyme is the RAS gene product,the Ras protein?

Following a nerve impulse,what triggers the opening of plasma membrane voltage-gated Ca2+ channels?

What is activated by calcium ions entering an egg cell just after fertilization?

Among the agents that can cause ryanodine receptors to open are _ ions,in a phenomenon called _.

In which organism below has calmodulin not been found?

The concentration of calcium ions in the ER lumen,the plant cell vacuole and the extracellular space are on average more than _______ times higher than in the cytosol.

What is responsible for deactivating glycogen synthase kinase-3?

What is the name of a calcium-binding protein that acts in conjunction with calcium to bring about the responses associated with cytoplasmic rises in calcium ion concentration?

What generally triggers the release of calcium ions by ryanodine receptors?

What is the reason for the withdrawal of cells from the cell cycle after exposure to stressful stimuli,like X-rays and damaging chemicals?

How is the distribution of free calcium ions in the living cell detected?