Signal Transduction Practice

Which of the following correctly displays the order of cell signaling?

• response, transduction, reception

• transduction, reception, response

• response, reception, transduction

• reception, transduction, response

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

• they are species specific

• they always lead to the same cellular response

• they amplify the original signal manyfold.

• they counter the harmful effects of phosphatases.

• the number of molecules used is small and fixed.

Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane?

• a receptor tyrosine kinase

• G protein-coupled receptor

• phosphorylated receptor tyrosine kinase dimer

• ligand-gated ion channel

• intracellular receptor

The activation of receptor tyrosine kinase is characterized by

• dimerization and phosphorylation

• dimerization and IP3 binding

• a phosphorylation cascade

• GTP hydrolysis

• channel protein shape change.

Lipid-soluble signaling molecules, such as testosterone, cross the membranes of all cells but affect only target cells because

• only target cells retain the appropriate DNA segments

• intracellular receptors are present only in target cells

• most cells lack to Y chromosome required.

• only target cells possess the cytosolic enzymes that transduce the testosterone.

• only in target cells is testosterone able to initiate the phosphorylation cascade leading to activated transcription factor.

Consider this pathway: epinephrine--> G protein-coupled receptor --> G protein --> adenylyl cyclase --> cAMP. Identify the second messenger.

• cAMP

• G protein

• GTP

• adenylyl cyclase

• G protein-coupled receptor

Apoptosis involves all but which of the following?

• fragmentation of the DNA

• cell signaling pathways

• activation of cellular enzymes

• lysis of the cell

• digestion of cellular contents by scavenger cells

The bacterium Vibrio cholerae causes cholera, an infectious disease that often leads to severe dehydration as a result of ongoing diarrhea. During an infection, Vibrio cholerae releases a protein complex called cholera toxin.

After its release, cholera toxin enters intestinal epithelial cells and binds to a G protein. This causes the G protein to be permanently activated. The downstream effects of this G protein activation are shown in the signal transduction pathway above.

Based on the information above, which of the following correctly describes cholera toxin and its effect on intestinal epithelial cells?

Choose 1 answer:

• Cholera toxin is an intracellular signal that increases extracellular chloride ion concentration.

• Cholera toxin is an extracellular signal that increases the dephosphorylation of protein kinase A.

• Cholera toxin is an extracellular signal that decreases adenylyl cyclase activity.

• Cholera toxin is an intracellular signal that decreases intracellular cAMP concentration.

Mutations within genes coding for G protein-coupled receptors (GPCRs) can lead to one of two major outcomes—a loss-of-function or a gain-of-function. Loss-of-function mutations prevent signaling in GPCR pathways, even in the presence of signaling molecules. Gain-of-function mutations activate signaling in GPCR pathways, even in the absence of signaling molecules.

Which of the following will most likely be found in an individual with a gain-of-function GPCR mutation?

Choose 1 answer:

• Signal transduction pathways that are activated even if ligand-to-receptor binding does not occur

• Signal transduction pathways that are activated only if ligand-to-receptor binding occurs

• Signal transduction pathways that are inactive if ligand-to-receptor binding does not occur

• Signal transduction pathways that are inactive even if ligand-to-receptor binding occurs

The information in the image shows and describes the initial steps of the MAPK/ERK signaling cascade.

When epidermal growth factor (EGF) ligands bind to their receptors, the receptors pair up and act as kinases, attaching phosphate groups to one another’s intracellular tails. The activated receptors then trigger a series of events that activate the kinase Raf.

Which of the following toxins will most likely inhibit the activation of MEK?

Choose 1 answer:

• A toxin that prevents the transfer of a phosphate group to Raf

• A toxin that prevents the kinase activity of Raf

• A toxin that prevents MEK from phosphorylating Raf

• A toxin that prevents the dephosphorylation activity of Raf