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Exam 9: Cell Communication

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Question 21

Multiple Choice

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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:

A) NO activates guanylyl cyclase,which catalyzes the synthesis of cGMP,which acts as an intracellular messenger in a pathway leading to smooth muscle relaxation.
B) NO activates a protein kinase which catalyzes the synthesis of cGMP,which acts as an intracellular messenger in a pathway leading to smooth muscle relaxation.
C) NO inhibits guanylyl cyclase,which allows the build up of cGMP,which acts as an intracellular messenger in a pathway leading to smooth muscle relaxation.
D) NO activates cGMP,which catalyzes the synthesis of guanylyl cyclase,which acts as an intracellular messenger in a pathway leading to smooth muscle relaxation.

E) None of the above
F) B) and C)

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Question 22

Multiple Choice

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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 cofactors to allow for optimal protein kinase activity.If you add molecule X to the reaction,what do you predict will be the outcome?

A) The substrate will be phosphorylated normally in the presence of molecule X.
B) Less phosphorylation of the substrate will be seen in the presence of molecule X.
C) More phosphorylation of the substrate will be seen in the presence of molecule X.

D) B) and C)
E) A) and B)

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Question 23

Multiple Choice

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The function of adenylyl cyclase is to:

In synaptic signaling,neurotransmitters are released into a space that is referred to as a:

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?

What enzyme phosphorylates MAP kinase kinase?

The protein Sonic Hedgehog (SHH) plays a role in specifying the identity of digits (such as fingers and toes) in mammals.Several digits arise directly from cells that both express and respond to secreted SHH.What type of signaling would this be considered?

You have identified a novel cytoplasmic protein.Through sequence analysis you are able to identify the presence of a number of serine/threonine phosphorylation motifs.Based on these data,you hypothesize that this protein may be a substrate for what kind of enzyme?

One cell sends second messengers to another cell through gap junctions.What type of signaling would this be considered?

A small number of cell surface receptors can ultimately generate a large intracellular response due to activation of kinase cascades.This is referred to as:

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

When bound to ligand,this type of receptor changes conformation to allow ions to move down their concentration gradient across the membrane:

Growth of new blood vessels is stimulated by vascular endothelial growth factor (VEGF) .This ligand binds to the VEGF receptor,which leads to the dimerization and autophosphorylation of this receptor on cytoplasmic tyrosines.What type of receptor is the VEGF receptor?

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?

What second messenger is directly involved in activating protein kinase C (PKC) ?

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?

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:

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

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

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?