Cell Communication

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Author:
irenakk
ID:
978
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Cell Communication
Updated:
2009-11-16 17:04:31
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Bio
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Description:
Chapter 11
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  1. Botulism toxin acts by interfering with ____ function
    A) Ion-channel
    B) G-protein
    C) Tyrosine-kinase
    D) Adenylyl cyclase
    E) Calmodulin
    B) G-protein.

    The bacteria that cause botulism make their victims ill by producing toxins that interfere with G-protein function.
  2. Which of the following is not a potential source of Ca2+ for the cytosol?
    A) blood
    B) extracellular fluid
    C) mitochondria
    D) endoplasmic reticulum
    E) lysosomes
    E) Lysosomes
  3. The cellular response of a signal pathway that terminates at a transcription factor would be ____
    A) the synthesis of mRNA
    B) activation of an inactive enzyme
    C) alteration of the cytoskeleton
    D) change in the chemical composition of the cytosolic environment
    E) the activation of a metabolic pathway
    A) the synthesis of mRNA

    Transcription factors are proteins that regulate the transcription of DNA into mRNA
  4. Nitric oxide is unusual among animal signal molecules in that it ____.
    A) enters the cell via a protein channel
    B) acts by directly binding to DNA
    C) binds to both membrane receptors and cytoplasm receptors
    D) is a gas
    E) activates proteins by removing a phosphate
    D) is a gas

    Chemical messengers with intracellular receptors include the steroid hormones and even the small gaseous molecule nitric oxide.
  5.  What event would activate a G protein?
    A) hydrolysis of GTP to GDP
    B) hydrolysis of GDP to GTP
    C) phosphorylation of GDP to GTP
    D) replacement of GDP with GTP
    E) phosphorylation of GTP to GDP
    D) replacement of GDP with GTP

    Inactive G proteins are bound to GDP. The activated receptor replaces the GDP with GTP, thereby activating the G protein.
  6. In a typical cell, calcium ions are ___
    A) are far more abundant in the cytoplasm compared to blood and other extracellular fluid
    B) are rapidly transported into the endoplasmic reticulum in response to G-protein-mediated signals
    C) are often concentrated within the endoplasmic reticulum
    D) are not very widely used as second messengers
    E) all of the above
    C) are often concentrated within the ER

    Low intracellular concentrations are achieved by transporting calcium across the plasma membrane or into storage sites within the ER.
  7. Testosterone does not affect all cells of the body because ____
    A) testosterone cannot cross the plasma membrane
    B) not all cells in the body have membrane receptors for testosterone
    C) it is a local regulator
    D) it affects only cells that have ion-channel receptors
    E) not all cells have cytoplasmic receptors for testosterone
    E) not all cells have cytoplasmic receptors for testosterone

    Steroid hormones readily enter cells all over the body, but they stimulate a response only in target cells--those with receptor molecules in the cytoplasm.
  8. A substance that acts at a long distance from the site at which it is secreted is a____
    A) neurotransmitter
    B) paracrine signal
    C) local regulator
    D) hormone
    E) synaptic signal
    D) hormone

    Both plants and animals use hormones for signaling at greater distances.
  9. Which of the following is activated when the binding of single molecules causes it to form a dimer?
    A) ion-channel receptors
    B) protein phosphatase receptors
    C) G-protein linked receptors
    D) adenylyl cyclase receptors
    E) tyrosine-kinase receptors
    B) tyrosine-kinase receptors

    Ligand binding causes two tyrosine-kinase receptor polypeptides to aggregate, forming a dimer.
  10. In the inherited disorder Wiskott-Aldrich syndrome ____
    A) muscle cells lack the appropriate membrane receptor
    B) a multifunctional relay protein involved with the proliferation of immune cells is defective
    C) nerve cells lack the ability to produce cAMP
    D) G proteins are unable to phosphorylate GDP
    E) the ER is unable to store calcium
    B) a multifunctional relay protein involved with the proliferation of immune cells is defective

    the defective protein is thought to represent an important intersection point for a complex transduction network.
  11. Why are there often so many steps between the original signal event and the cell's response?
    Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses.

    This amplificatino permits the signal molecule to have a widespread effect throughout the cell.
  12. Cholera develops when the bacterial toxin ____
    A) inhibits the enzyme that normally breaks down cAMP
    B) prevents G-protein inactivation, which leads to the continuous production of cAMP
    C) inhibits adenylyl cyclase, preventing cell from producing cAMP
    D) blocks the receptor site for cAMP
    E) phosphorylates the cAMP, producing ADP
    B) prevents G-protein inactivation, which leads to the continuous production of cAMP

    The activated G protein continuously stimulates adenylyl cyclase to make cAMP, which causes the intestinal cells to secrete large amounts of water and salts into the intestines
  13. IP3 (inositol trisphosphate) is produced as a result of ___
    A) Protein kinase A activation
    B) Ca2+
    C) the cleavage of PIP2
    D) DAG
    E) phospholipase C
    C) the cleavage of PIP2

    Phospholipase C cleaves a special membrane phospholipid, PIP2, producing diacylglycerol and inositol triphosphate.
  14. Receptors for signal molecules ____
    A) all work via protein kinases
    B) are never found in the nucleus of a cell
    C) can be found as part of the plasma membrane or found within the cytoplasm
    D) all work by opening ion channels
    E) are only found associated with the plasma membrane
    C) can be found as part of the plasma membrane or found within the cytoplasm.

    Not all signal receptors are membrane proteins. Some are located in the cytoplasm of target cells.

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