Biology Chapter 11

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What is most likely to happen to an animal's target cells that lack receptors for local regulators?

They might not be able to multiply in response to growth factors from nearby cells.

Select the statement that correctly distinguishes between relay proteins and second messengers in signal transduction pathways.

Signal transduction pathways are multistep pathways that include relay proteins and small, nonprotein, water-soluble molecules or ions called second messengers.

Which statement correctly distinguishes the roles of protein kinases and protein phosphatases in signal transduction pathways?

Protein kinases activate enzymes by phosphorylating or adding phosphate groups to them. Protein phosphatases dephosphorylate or remove phosphate groups from enzymes, including protein kinases.

Cyclic GMP, or cGMP, acts as a signaling molecule whose effects include relaxation of smooth muscle cells in artery walls. In the penis, this signaling pathway and the resulting dilation of blood vessels leads to an erection. Select the correct statement about the effect of Viagra on this signaling pathway.

Viagra inhibits the hydrolysis of cGMP to GMP.

The cholera bacterium Vibrio cholerae produces an enzyme toxin that chemically modifies a G protein involved in regulating salt and water secretion in intestinal cells. Stuck in its active form, the modified G protein stimulates the production of a high concentration of cAMP, which causes the intestinal cells to secrete large amounts of salts into the intestines, with water following by osmosis. An infected person quickly develops profuse diarrhea and if left untreated can soon die from the loss of water and salts. What is the basic effect of the cholera toxin?

The basic effect of the cholera toxin is signal amplification.

What are the functions of signal transduction pathways?
Select all that apply.

Signal transduction pathways allow different types of cells to respond differently to the same signal molecule.
Signal transduction pathways convert a signal on a cell's surface to a specific cellular response.
Signal transduction pathways amplify the effect of a signal molecule.

Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because

they amplify the original signal manyfold.

What is most likely to happen to an animal's target cells that lack receptors for local regulators?

They might not be able to multiply in response to growth factors from nearby cells.

Which of the following is characterized by a cell releasing a signal molecule into the environment, followed by a number of cells in the immediate vicinity responding?

paracrine signaling

In the formation of biofilms, such as those forming on unbrushed teeth, cell signaling serves which function?

aggregation of bacteria that can cause cavities

In which of the following ways do plant hormones differ from hormones in animals?

Plant hormones may travel in air or through vascular systems.

When a neuron responds to a particular neurotransmitter by opening gated ion channels, the neurotransmitter is serving as which part of the signal pathway?

signal molecule

In yeast signal transduction, a yeast cell

secretes molecules that result in responses by other yeast cells.

Which of the following is true of transcription factors?

They control gene expression.

One of the major categories of receptors in the plasma membrane reacts by forming dimers, adding phosphate groups, and then activating relay proteins. Which type does this?

receptor tyrosine kinases

Use this description to answer the following question.

A major group of G protein-coupled receptors contains seven transmembrane α helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others.


Where would you expect to find the carboxyl end?

at the cytosol surface

Use this description to answer the following question.

A major group of G protein-coupled receptors contains seven transmembrane α helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others.


The coupled G protein most likely interacts with this receptor

...

Testosterone functions inside a cell by

binding with a receptor protein that enters the nucleus and activates specific genes.

In general, a signal transmitted via phosphorylation of a series of proteins

brings a conformational change to each protein.

Which of the following is the best explanation for the inability of a specific animal cell to reduce the Ca2+ concentration in its cytosol compared with the extracellular fluid?

insufficient ATP levels in the cytoplasm

Which of the following most likely would be an immediate result of growth factor binding to its receptor?

protein kinase activity

An inhibitor of phosphodiesterase activity would have which of the following effects?

prolong the effect of epinephrine by maintaining elevated cAMP levels in the cytoplasm

Adenylyl cyclase has the opposite effect of which of the following?

phosphodiesterase

Caffeine is an inhibitor of phosphodiesterase. Therefore, the cells of a person who has recently consumed coffee would have increased levels of

cAMP

If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound

to block G protein activity in liver cells.

If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound

...

An inhibitor of which of the following could be used to block the release of calcium from the endoplasmic reticulum?

phospholipase C

Which of the following statements is true of signal molecules?

Protein kinase A activation is one possible result of signal molecules binding to G protein-coupled receptors.

Which of the following is a correct association?

GTPase activity and hydrolysis of GTP to GDP

Which of the following amino acids are most frequently phosphorylated by protein kinases in the cytoplasm during signal transduction

...

The function of phosphatases in signal transduction is best described as to

inactivate protein kinases and turn off the signal transduction.

What explains the increased concentration of ca++ in the ER?

Calcium ions are actively imported from the cytoplasm into the ER.

In which of the following ways could signal transduction most probably be explored in research to treat cancer?

alteration of protein kinases in cell cycle regulation in order to slow cancer growth

The toxin of Vibrio cholerae causes profuse diarrhea because it

modifies a G protein involved in regulating salt and water secretion.

Which of the following would be inhibited by a drug that specifically blocks the addition of phosphate groups to proteins?

receptor tyrosine kinase activity

Viagra causes dilation of blood vessels and increased blood flow to the penis, facilitating erection. Viagra acts by inhibiting

the hydrolysis of cGMP to GMP.

A drug designed to inhibit the response of cells to testosterone would almost certainly result in which of the following?

a decrease in transcriptional activity of certain genes

At puberty, an adolescent female body changes in both structure and function of several organ systems, primarily under the influence of changing concentrations of estrogens and other steroid hormones. How can one hormone, such as estrogen, mediate so many effects?

Estrogen binds to specific receptors inside many kinds of cells, each of which have different responses to its binding.

What are scaffolding proteins?

large molecules to which several relay proteins attach to facilitate cascade effects

Why has C. elegans proven to be a useful model for understanding apoptosis?

The nematode undergoes a fixed and easy-to-visualize number of apoptotic events during its normal development.

Why is apoptosis potentially threatening to the healthy "neighbors" of a dying cell?

...

In C. elegans, ced-9 prevents apoptosis in a normal cell in which of the following ways?

...

In research on aging (both cellular aging and organismal aging), it has been found that aged cells do not progress through the cell cycle as they had previously. Which of the following would provide evidence that this is related to cell signaling?

Growth factor ligands do not bind as efficiently to receptors.

Which of the following describes the events of apoptosis?

The cell's DNA and organelles become fragmented, the cell shrinks and forms blebs, and the cell's parts are packaged in vesicles that are digested by specialized cells.

If an adult person has a faulty version of the human analog to ced-4 of the nematode, which of the following is most likely to result?

a form of cancer in which there is insufficient apoptosis

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