BIOL 151 Chapter 9 Practice Exam
receptor binding
After insulin binds to the cell-surface protein, cytoplasmic proteins are phosphorylated. What process occurs when those proteins are dephosphorylated?
In endocrine signaling the signal is produced by the signaling cell, is secreted, and then travelsthrough the circulatory system to reach responding cells that can be very far from the signalingcell. In contrast, paracrine signaling involves two cells (the signaling and responding cells) thatare close together, so the secreted signal is released outside of the signaling cell, and diffusesonly a short distance to reach the responding cell.
**Describe any differences between the process of endocrine signaling and the process ofparacrine signaling.
Each activated receptor (i.e. one bound to the signal) is able to activate several G-proteins. Eachtarget molecule activated by a G-protein is able to make large amounts of a second messenger(e.g., cAMP). Each kinase activated by cAMP is then able to phosphorylate/activate manyprotein targets.
**During cell signaling, the signal is typically amplified to ensure that even a small amount of thesignaling molecule leads to a large effect on the cell. Briefly describe how such signalamplification is achieved.
Ligands for cell surface receptors are generally polar, while intracellular receptors are generallysmall, nonpolar molecules.
**What are the principal molecular difference between ligands (signals, or signaling molecules)that are bound by cell surface receptors and ligands that are bound by intracellular receptors
binding to and activating the G protein-coupled receptor in these cells.
A bacterium releases a toxin that binds to and activates a G protein-coupled receptor in the mammalian gut. The result is high levels of cAMP in these cells. This toxin might work by:
a decrease in the transcription of certain genes
A drug designed to inhibit the response of cells to the steroid testosterone would almost certainly result in which of the answer choices
decrease
A mutation in a subunit of the G protein prevents it from binding to adenylyl cyclase but not the receptor. The amount of cAMP in cells will:
decrease
A mutation in a subunit of the G protein prevents the release of bound GDP. The amount of cAMP in cells will:
decrease
A mutation in the G protein-coupled receptor that prevents it from binding to the G protein. The amount of cAMP in cells will:
increase
A mutation of the G protein-coupled receptor allows it to bind a subunit of the G protein in the absence of ligand. The amount of cAMP in cells will:
decrease
A mutation of the G protein-coupled receptor removes the extracellular domain of the receptor. The amount of cAMP in cells will:
a receptor protein
A protein on a cell surface that binds to a signaling molecule is an example of which element of cellular communication
termination
After insulin binds to the cell-surface protein, cytoplasmic proteins are phosphorylated. What process occurs when those proteins are dephosphorylated
One molecule of adenylyl cyclase can activate many molecules of protein kinase A (PKA), One molecule of protein kinase A (PKA) can phosphorylate and activate many target proteins, One activated receptor can activate many G proteins
According to the figure shown, which of the answer choices is responsible for amplifying the signal in a cell responding to adrenaline? Select all that apply.
response
Activated proteins in the nucleus that cause transcription (and eventually translation in the cytosol) of proteins needed for cell division is an example of:
a Ras mutant that cannot hydrolyze GTP to GDP
An absence of the appropriate signaling molecule causes a change in the expression of genes. Which type of mutation is responsible for this malfunction in cellular response
endocrine
An increased heart rate caused by the release of adrenaline from the adrenal glands, which are located just above the kidney, is an example of _____ signaling.
paracrine signaling
Communication between neurons is an example of which type of cell signaling
ncreased cAMP and increased protein kinase A (PKA) activity.
Compared to cells with normal GTP, what would result if a G protein-coupled receptor was activated but treated with a nonhydrolyzable version of GTP (a form of GTP that cannot be converted to GDP) that was taken up by the cells? These treated cells would have:
inhibition of one signaling pathway by a component of another signaling pathway, an intersection of two signaling pathways that allow two signals to enhance the cellular response
Complexity in cell communication from molecular crosstalk can be due to:
bind intracellular receptors to form complexes that enter the nucleus
Despite their differences, steroid hormones:
the alpha subunit
GTP binding occurs on which subunit of a G protein?
a Ras mutant with high GDP affinity
Following ligand binding to receptor kinase, the MAP kinase pathway fails to activate. Which of the types of mutation listed is responsible for this malfunction in cellular response?
VEGF is a paracrine signaling molecule because it binds to receptors on nearby cells, at the site where new blood vessels are needed.
Given what you know about the different kinds of cell signaling and VEGF, which statement is true
Both types undergo a conformational change when they bind to their ligand, they receive signals from other cells and lead to a cellular response.
How are steroid hormone receptors and cell-surface receptors similar?
Phosphatases remove phosphate groups.
How do mitogen-activated protein (MAP) kinases get deactivated?
The signaling pathway would be activated even when no ligand was present.
How would signaling be affected if a mutation caused a G protein to replace GDP with GTP on its own without needing to be activated by the G protein-coupled receptor?
It must express receptor proteins.
In cell communication, which one of the answer choices is a requirement of the responding cell?
It prevents the receptor from becoming activated.
Many mutations in receptor kinases that lead to cancer allow the receptor to dimerize and become activated, even in the absence of signaling molecules. An example is a mutant form of the EGF receptor kinase called Her2/neu. An antibody that prevents dimerization of Her2/neu receptor kinases is being tested for its effectiveness in preventing cancer. At which stage does this drug work
signal termination
Nicotine from cigarette smoke acts as a ligand and associates with specific proteins on the surface of cells in the brain, causing feelings of pleasure and well-being. In the following four questions, select the appropriate event in the cellular response to nicotine. Rapid elimination of nicotine from the body is an example of:
receptor activation
Nicotine from cigarette smoke acts as a ligand and associates with specific proteins on the surface of cells in the brain, causing feelings of pleasure and well-being. In the following four questions, select the appropriate event in the cellular response to nicotine. The opening of an ion channel as a result of nicotine binding is an example of:
cell does not have the proper receptor
Of the answer choices, what is the most likely reason that paracrine signaling does not activate the cell that is producing the signaling molecule?
resoponse
One consequence of insulin binding its receptor is the uptake of glucose by the cell, which is an example of:
The response of the cell would last longer than it normally would.
Phosphatases are a family of enzymes that remove phosphate groups from specific proteins; these phosphate groups had been added to the proteins by protein kinases. Vanadate is an inhibitor of phosphatases in eukaryotic cells. What effect would vanadate have on the response of cells to signals received by receptor kinases?
receptor activation
Phosphorylation of transmembrane proteins caused by insulin binding to those proteins is an example of
paracrine signaling
Platelet-derived growth factor (PDGF) is a signaling molecule released by platelets at wound sites to cause nearby fibroblasts to divide and contribute to wound healing. Which of the answer choices best describes PDGF signaling
a Ras mutant that cannot hydrolyze GTP to GDP
The MAP kinase pathway is continually activated, even in the absence of a signaling molecule. Which type of mutation could be responsible for this malfunction in cellular response?
signaling molecule, responding cell, and a receptor
To have communication between cells, you must have a
A; B; D; C
Use the terms listed to fill in the blanks of each statement that follows. A. signaling cell B. ligand C. receptor D. responding cell In communication between cells, the _____ produces the signaling molecule, also known as the _____; the _____ produces the _____, to which the signaling molecule binds.
paracine signaling
Vascular endothelial growth factor (abbreviated VEGF and pronounced "Veg-F") is a peptide signaling molecule related to platelet-derived growth factor. VEGF is important in the formation of the circulatory system because its signaling pathway causes the formation of new blood vessels in developing embryos during normal development. Tumors also produce and secrete VEGF, causing the formation of new blood vessels that supply these tumors. Given what you know about the different kinds of cell signaling and about VEGF, which of the answer choices best describes VEGF signaling?
a change in gene expression
What is the cell's likely response to ligand binding to a steroid receptor located in the nucleus?
Signal transduction connects the activation of the receptor to the cellular response.
What is the role of signal transduction in cell signaling?
signal transduction and amplification
What occurs after the insulin receptors phosphorylate each other, making it possible for other proteins in the cytoplasm to bind to them?
The response to the signal would persist longer after activation
What would happen to a signaling pathway if phosphatases had reduced levels of function?
Blood serum is the liquid portion of blood that has been allowed to clot, and blood plasma is the liquid portion of blood that has not been allowed to clot.
What's the difference between blood serum and blood plasma?
autocrine signaling
When T cells in your immune system recognize a pathogen, they release Interleukin 6 (IL6), which binds back to receptors on the T cell surface. Which of the answer choices best describes this kind of IL6 signaling
Adenylyl cyclase activity increases.
When a ligand binds to a G protein-coupled receptor, which of the answer choices would you expect to happen before any of the others?
plasma
When blood is removed from the body, it clots. To prevent clotting, researchers can remove platelets (and cells) from the blood and treat it with anti-clotting agents. What is produced by this treatment?
adenylyl cyclase activity
Which answer choices are responsible for the amplification of an intracellular signal? Select all that apply.
The addition of a drug that prevents the final kinase from interacting with its target protein in the nucleus.
Which condition would be most likely to turn off this abnormally active signaling pathway
phosphatase activity, phosphodiesterase activity that breaks down cAMP, GTP activity to convert GTP to GDP
Which of the functions in termination of a cell-signaling event are initiated by a G protein-coupled receptor? Select all that apply.
a mutation that blocks the GTPase activity of Ras
Which of the scenarios would result in a persisting proliferation response to growth factor receptor activation after the ligand is no longer binding to its receptor kinase?
testosterone
Which signaling molecule would you expect to travel the longest distance in the human body?
protein kinase activity, adenylyl cyclase activity
Which steps in a signaling cascade initiated by a G protein-coupled receptor would be directly affected in cells cultured in the presence of a non-hydrolyzable ATP analog? (The analog could bind to other molecules but could not be converted to ADP and Pi.) Select all that apply
receptor kinase
Which type of receptor activates a signaling transduction pathway by transferring phosphate groups to a substrate?
G protein-coupled receptor, receptor kinase, ligand-gated ion channel
Which type of receptor is membrane-associated? Select all that apply.
receptor kinase, ligand-gated ion channel, intracellular receptor, G protein-coupled receptor
Which type of receptor undergoes a conformational change upon activation
The receptor monomers must move together and dimerize to be activated
Why do the functions of many receptor kinases depend on the fluid nature of the plasma membrane?
The concentration of a signaling molecule in the patient is higher than usual, The cells taken from the patient have more growth factor receptors than normal
You are a medical student working in a cancer research laboratory. Your boss has given you samples of cancer cells and blood from a patient. She has told you that the cells have no mutations in any of their signaling molecule proteins (that is, all the proteins are normal), but that the cells' signaling transduction properties are hyperactive, causing them to divide too rapidly. Which answer choices could account for the increased cell proliferation in the patient?
a mutation that inactivates the phosphatase that dephosphorylates the activated receptor, a mutation that prevents the GTPase activity of Ras.
You are studying a newly discovered growth factor. You find that this growth factor stimulates the proliferation of cells grown in the laboratory. You have also found that the receptor that binds the growth factor is a receptor kinase that activates Ras, which activates the MAP kinase pathway. Which mutations affecting this growth factor pathway would you expect to promote uncontrolled cell proliferation? Select all that apply.
he receptor for this signal is inside the cell, and the signaling molecule is nonpolar and can diffuse into the cell.
You strip off all proteins on the cell surface by using a protease (an enzyme that destroys proteins). Now, when you add a specific signaling molecule, the cell still responds. What is the most reasonable explanation of this?
a protein that forms a channel that allows ions to enter the cell when a ligand binds
a cell-surface receptor
protein kinase activity, adenylyl cyclase activity
are responsible for the amplification of an intracellular signal
Adenylyl cyclase catalyzes the formation of cAMP, which activates protein kinase A (PKA)
correct order of G protein-coupled signaling
steroid hormone receptor
could be found bound to the regulatory region of a gene
adenylyl cyclase (activates) and phosphodiesterase (terminates), protein kinase (activates) and phosphatase (terminates)
pair enzymes that activate and terminate the same step in a signaling even
providing binding sites to recruit and activate signal-transduction proteins.
phosphate groups play a key role in receptor kinase activation by:
Some G proteins are composed of three subunits, G proteins release GDP and bind GTP when associated with an activated receptor, G proteins become deactivated when bound GTP is hydrolyzed to GDP
true about G proteins
Delta is produced by embryonic stem cells as they differentiate into neurons in the brain. Delta directly signals to a Notch transmembrane protein in adjacent cells. Delta directs adjacent cells to differentiate into glial cells.
true about the Delta protein
contact-dependent signaling
type of cell signaling does not rely on the diffusion of a chemical signal molecule
a receptor that binds a nonpolar steroid hormone and activates transcription
would be found in the cytoplasm and not on the cell surface
autocrine signaling
you observe a cell that has a receptor protein that binds a signaling molecule that is produced by the same cell. What kind of signaling is occurring in this cell?
