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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

Which of the following is a substance that acts at a long distance from the site at which it is secreted?


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.

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

aggregation of bacteria that can cause cavities

What is the function of tyrosine-kinase receptors?

enzymatic phophorylation of tyrosine in the receptor protein

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

Dioxin, produced as a by-product of various industrial chemical processes, is suspected of contributing to the development of cancer and birth defects in animals and humans. It apparently acts by entering cells by simple diffusion and binding to proteins in the cytoplasm, then altering the pattern of gene expression. Which of the following are likely to be the cytoplasmic proteins to which dioxin binds?

transcription factors

To what does the term "ligand" refer in cell biology?

any small molecule that can bind in aa specific manner to a larger one

Which of the following is true of transcription factors?

They control gene expression

Which of the following sequences is correct?

All of the above

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

brings a conformational change to each protein

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

serine theronine

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


Which of the following is a correct association?

GTPase activity and hydrolysis of GTP to GDP

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

inactivate protein kinases and turn off the signal transduction

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, causinf signal amplification as the cascade progresses

Why can a signaling molecule cause different responses in different cells?

The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor

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

a decrease in transcription activity of certain genes

What are scaffolding proteins?

large molecules to which several relay proteins attach to facillitate 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?

lysosomal enzymes exiting dying cell would damage surrounding cells

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

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