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Which of the following provides molecular evidence that signal transduction pathways evolved early in the history of life?

The molecular details of cell signaling are quite similar in organisms whose last common ancestor was a billion years ago.

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


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

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

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

What is the function of tyrosine-kinase receptors?

enzymatic phosphorylation of tyrosine in the receptor protein

Which of the following are among the most common second messengers?

calcium ion and cAMP

Which of the following sequences is correct?

binding of a signaling molecule to its receptor → G protein activation → phospholipase C activation → IP3 production → increase in cytoplasmic calcium concentration; binding of a growth factor to its receptor → phosphorylation cascade → activation of transcription factor → transcription; diffusion of a signaling molecule across the plasma membrane → binding of the signaling molecule to its receptor → movement of the signaling molecule-receptor complex into the nucleus → transcription; binding of a signaling molecule to its receptor → G protein activation → adenylyl cyclase activation → cAMP production → protein phosphorylation

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.

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.

What is apoptosis?

controlled cell suicide

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 true of transcription factors?

They control gene expression.

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.

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