Exam 9: Cell Communication

These molecules can directly convert extracellular signals into intracellular signals.

A mutation that affects Ca⁺⁺ binding to calmodulin is most likely to interfere with what aspect of a signal transduction pathway?

Many receptor tyrosine kinase (RTK) pathways lead to the activation of Ras.To activate Ras, it is necessary to recruit a guanine nucleotide exchange factor to the plasma membrane, because Ras is a membrane associated protein.Guanine nucleotide exchange factors, such as SOS, stimulate the exchange of GDP for GTP.However, SOS cannot bind directly to most RTKs.The protein Grb2 has a domain that can bind to phosphorylated tyrosines, and another domain that can bind to SOS.Therefore, Grb2 can bind to active RTKs and recruit SOS to the plasma membrane.Grb2 is an example of what kind of signaling molecule?

Many receptor tyrosine kinase pathways have MAPK as a downstream signaling component.MAPK can phosphorylate target proteins.What type of signaling molecule is MAPK?

Why are phosphorylation and dephosphorylation reactions commonly used to regulate signal transduction pathways?

The protein SOS is a guanine nucleotide exchange factor for Ras.SOS helps facilitate the exchange of GDP for GTP.What would be the effect of a mutation that inhibits the interaction between SOS and Ras?

You have identified a molecule, molecule X, that can bind to the ATP binding site of a specific protein kinase, and prevent ATP binding.You are conducting a kinase assay using this protein kinase and a known substrate of this kinase, and have set up the reaction using the proper conditions and co-factors to allow for optimal protein kinase activity.If you add molecule X to the reaction, what do you predict will be the outcome?

Tamoxifen is a drug that is used to treat breast cancer.It inhibits the activities of the estrogen receptor in breast epithelial cells, which are the cells that are relevant to breast cancer.One of the concerns that scientists had during the development of Tamoxifen as a therapy for breast cancer was that other cell types require estrogen signaling for their function.For example, it is known that cells in bone tissue require estrogen signaling.As a result, there was a concern that use of Tamoxifen would lead to bone loss in patients.In reality, however, researchers were surprised to find that Tamoxifen actually led to an increase in bone density in breast cancer patients.At the same time, Tamoxifen did inhibit the activity of the estrogen receptor in breast epithelial cells in these patients.What is the best explanation for this finding?

You are having lunch with an elderly friend when suddenly he begins to experience chest pain and tightness.He reaches into his pocket, gets out one of his nitroglycerin tablets and quickly takes it.After the episode passes, your friend asks you how the nitroglycerin helps his angina.You explain that nitroglycerin gets converted by cells to nitric oxide (NO) causing the smooth muscle cells of the blood vessel to relax and increase blood flow to the heart.He pushes you for a more detailed explanation, so you explain further that:

You are planning to perform some protein-protein interaction studies to identify a receptor for a steroid hormone you have been working on.You start by fractionating the cell.What cell fraction would you want to work with to identify the steroid hormone receptor of interest?

G protein-coupled receptors are the largest family of cell surface receptors.Each receptor passes through the plasma membrane how many times?

Some enzymatic receptors and most G protein-coupled receptors transmit the signal into the cytoplasm by utilizing other substances within the cytoplasm that are referred to as:

You are performing an experiment to assay phosphorylation of a substrate by a protein kinase.Based on the data in the table below, what do these experimental results suggest?

Addison's disease is a disorder that results from a reduction in production of glucocorticoids and mineralocorticoids.Individuals with Addison's disease suffer from a variety of systemic symptoms including: muscle weakness, fever, issues with the gastrointestinal tract, and increased tanning.Considering this information, what type of signaling do you think that glucocorticoids and mineralocorticoids stimulate?

How are receptor tyrosine kinases and steroid hormone receptors similar?

Some cancers are caused by the overexpression of receptor tyrosine kinases (RTKs).It is known that RTK signaling pathways commonly stimulate cell division.Why would the overexpression of receptor tyrosine kinases lead to cancer development?

What is the difference between Ras and the G proteins bound to G protein coupled receptors (GPCRs)?

Ste5 binds to MAPKKK, MAPKK, and MAPK to organize the kinase cascade.What type of signaling molecule is Ste5?

A mutation in the DNA-binding domain of a steroid hormone receptor is most likely to affect what aspect of receptor function?

In response to injury, cell fragments called platelets get activated to induce clotting.Activated platelets release factors that can in turn bind to specific membrane receptors on nearby cells.What type of signaling would this be considered?