Exercises: Cell Communication and Signal Transduction Pathways
Define the terms ligand* and receptor*. Then describe in one or two sentences what usually happens to a receptor protein when the correct ligand binds to it.
Define the terms ligand and receptor. Then describe in one or two sentences what usually happens to a receptor protein when the correct ligand binds to it.
Classify each example as autocrine, paracrine, endocrine, or direct (juxtacrine) signaling: (a) insulin released by the pancreas travels in the blood to liver cells; (b)…
Classify each example as autocrine, paracrine, endocrine, or direct (juxtacrine) signaling:
(a) insulin released by the pancreas travels in the blood to liver cells;
(b) a cell secretes a growth factor that binds to receptors on that same cell;
(c) a neuron releases a neurotransmitter that diffuses across a synapse to the neighboring cell;
(d) a signal molecule on the surface of one cell binds a receptor on a touching cell.
The three stages of cell signaling are reception, transduction, and response. For each event below, name the stage it belongs to: (a) epinephrine binds to a G…
The three stages of cell signaling are reception, transduction, and response. For each event below, name the stage it belongs to:
(a) epinephrine binds to a G protein-coupled receptor on a liver cell;
(b) a series of protein kinases phosphorylate one another in turn;
(c) glycogen is broken down into glucose.
In a heart muscle cell, epinephrine binds a G protein-coupled receptor, which activates a G protein, then adenylyl cyclase, which makes the second messenger cAMP. cAMP…
In a heart muscle cell, epinephrine binds a G protein-coupled receptor, which activates a G protein, then adenylyl cyclase, which makes the second messenger cAMP. cAMP activates protein kinase A, and the heart beats faster. The enzyme phosphodiesterase breaks down cAMP into AMP. A drug blocks phosphodiesterase. Predict how the drug changes the cell's response to a given amount of epinephrine, and explain your reasoning.
A growth factor normally binds a receptor tyrosine kinase, which starts a phosphorylation cascade that tells the cell to divide. A mutation in the receptor gene makes…
A growth factor normally binds a receptor tyrosine kinase, which starts a phosphorylation cascade that tells the cell to divide. A mutation in the receptor gene makes the receptor active even when no growth factor is present. Predict what happens to the rate of cell division in cells with this mutation, and explain why this kind of mutation is linked to cancer.
Three types of cultured cells are exposed to hormone X, and researchers measure whether the cells make protein Y. | Cell type | Has receptor for hormone X? | Downstream…
Three types of cultured cells are exposed to hormone X, and researchers measure whether the cells make protein Y.
| Cell type | Has receptor for hormone X? | Downstream kinase | Protein Y made? |
|---|---|---|---|
| A | Yes | Functional | Yes |
| B | No | Functional | No |
| C | Yes | Nonfunctional | No |
Explain why cells B and C both fail to respond, even though they fail for different reasons. Then propose one experiment that would show whether the defect in cell C is upstream or downstream of the kinase.
Researchers add a ligand to normal cells and to mutant cells that lack a phosphatase enzyme. They then measure the amount of phosphorylated signaling protein (arbitrary…
Researchers add a ligand to normal cells and to mutant cells that lack a phosphatase enzyme. They then measure the amount of phosphorylated signaling protein (arbitrary units) over time.
| Time (min) | Normal cells | Mutant cells |
|---|---|---|
| 0 | 1 | 1 |
| 5 | 9 | 9 |
| 15 | 6 | 9 |
| 30 | 2 | 9 |
(a) Describe the pattern in each cell type. (b) Explain what role the phosphatase plays in the pathway. (c) Predict how the cellular response of the mutant cells differs from that of normal cells over 30 minutes, and justify your prediction. (d) Describe one control you would include in this experiment.
Cholera toxin, produced by Vibrio cholerae*, chemically modifies the G protein in intestinal cells so that it cannot turn itself off and stays active. This keeps…
Cholera toxin, produced by Vibrio cholerae, chemically modifies the G protein in intestinal cells so that it cannot turn itself off and stays active. This keeps adenylyl cyclase active and raises cAMP, which causes the cells to secrete large amounts of chloride ions and water into the intestine, producing severe diarrhea. (a) Trace the pathway from the G protein to the symptom. (b) Explain why the toxin has a much larger effect than a single signal molecule binding a receptor once. (c) A researcher proposes a drug that blocks the cell-surface receptor. Evaluate whether it would reverse the toxin's effect, and justify your answer.