Ch 11 DSM

Which of the following statements best describes the process of hormonal signaling?

Specialized cells release hormone molecules, which travel via the circulatory system to other parts of the body, where they reach target cells that can recognize and respond to the hormones.

Certain yeast cells secrete a molecule called the -factor. The purpose of this molecule is to __________.

stimulate an a yeast cell to grow toward the cell

Ras, a small G protein located at the plasma membrane, is often mutated in different types of cancer. Ras normally signals to a cell that it should divide. Cancer cells divide uncontrollably. Which of the following changes to Ras would you expect to see in a cancer cell that has mutated Ras present?

A mutation that means Ras cannot hydrolyze GTP to GDP Loosely attached to the cytoplasmic side of the membrane, the G protein functions as a molecular switch that is either on or off, depending on which of two guanine nucleotides is attached, GDP or GTP—hence the term G protein. (GTP, or guanosine triphosphate, is similar to ATP.) When GDP is bound to the G protein, the G protein is inactive. The receptor and G protein work together with another protein, usually an enzyme. Normally, when a signal reaches an inactive G protein, it causes a GTP to displace the GDP. This activates the G protein. After passing on the signal, the G protein hydrolyzes its GTP to GDP. A mutation preventing Ras from hydrolyzing GTP to GDP would mean that Ras would always be turned on, and would thus signal to the cell to divide continuously. Such division could lead to cancer. If Ras could not bind GTP, then no signal would be sent to the cell to start dividing. If GDP were constantly bound, Ras would be turned off all the time.

Which of the following statements describes what happens to cells undergoing apoptosis?

Cells shrink and form lobes, which are eventually shed as membrane fragments.

In which part of cell are calcium ions usually found?

Endoplasmic reticulum

After a signaling molecule binds to a G protein-coupled receptor, what activates the associated G protein?

GTP displaces GDP on the G protein. GTP displaces GDP on the G protein. Ligand binding activates receptor tyrosine kinases, not G proteins. Receptor tyrosine kinases do not form dimers in response to G protein activation. Ion-gated channels do not involve G protein activation. Hormone binding does not activate G proteins. The receptor and G protein work together with another protein, usually an enzyme. When the appropriate signaling molecule binds to the extracellular side of the receptor, the receptor is activated and changes shape. Its cytoplasmic side then binds an inactive G protein, causing a GTP to displace the GDP. This activates the G protein.

A G protein is active when __________.

GTP is bound to it

Which of the following statements describes the function of inositol trisphosphate (IP3) as a second messenger?

Inositol trisphosphate binds to an IP3-gated calcium channel, causing the release of calcium ions from the endoplasmic reticulum. IP3 causes the release of calcium ions from the endoplasmic reticulum. IP3 does not catalyze the conversion of ATP to cAMP. IP3 does not catalyze the conversion of cAMP to AMP. IP3 does not activate G proteins. IP3 has a significant effect on cellular calcium ion concentrations.

How does adenylyl cyclase help transmit signals within a cel

It converts ATP to cAMP, which then broadcasts the signal to the rest of the cell.

How is nitric oxide different from other signal molecules?

It is a gas. Nitric oxide binds to an intracellular receptor. Nitric oxide does not phosphorylate cAMP. Nitric oxide passes through the phospholipid bilayer, not a ligand-gated ion channel. Nitric oxide does not activate a G protein.

What effect does ligand binding have on receptor tyrosine kinase proteins?

Ligand binding causes them to phosphorylate and form dimers. Ligand binding causes RTKs to phosphorylate, not dephosphorylate. Receptor tyrosine kinases do not activate G proteins. Receptor tyrosine kinases do not affect ligand-gated ion channels. Ligand binding has a significant effect on receptor tyrosine kinases. Receptor tyrosine kinases do not convert ATP to cAMP.

Testosterone and estrogen are lipid-soluble signal molecules that cross the plasma membrane by simple diffusion. If these molecules can enter all cells, why do only specific cells respond to their presence?

Nontarget cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cell's nucleus. A number of important signaling molecules can enter cells through the plasma membrane because they are either hydrophobic enough or small enough to cross the hydrophobic interior of the membrane. Such hydrophobic chemical messengers include the steroid hormones, such as testosterone and estrogen. Testosterone and estrogen are nonpolar signal molecules that easily enter cells, but only those cells with functional intracellular receptors respond. Testosterone and estrogen bind to these receptors, causing a response in the target cell. Nontarget cells that lack the intracellular receptors exhibit no response to these hormones. Nontarget cells do not produce enzymes that attack hormones or cause signal activation. Concentration gradients do not affect the ability of a hormone to enter a cell. Hormone receptors are not typically found in the endoplasmic reticulum of cells.

What happens during the process of paracrine signaling?

Numerous cells simultaneously receive and respond to the molecules of growth factor produced by a single cell in their vicinity. Cell-to-cell recognition is the process in which communication between adjacent cells occurs between membrane-bound cell-surface molecules. Synaptic signaling is the process in which molecules diffuse across the synapse between adjacent nerve cells. Hormonal signaling is the process in which specialized cells release hormone molecules, which travel via the circulatory system to other parts of the body, where they reach target cells that can recognize and respond to the hormones

Why does testosterone not affect all cells in the body?

Only certain cells have cytoplasmic receptors for testosterone. Testosterone does not bind to membrane receptors. Testosterone is not a local regulator. Testosterone does not bind to G protein-receptor proteins. Testosterone does not bind to receptor tyrosine kinases. Testosterone does not bind to ligand-gated ion channels.

What is the general name for an enzyme that transfers phosphate groups from ATP to other molecules?

Protein kinase Ligand-gated ion channels are not enzymes. They regulate the passage of ions through the plasma membrane. G proteins respond to G protein-coupled receptors by coupling with GTP. They do not transfer phosphate groups from ATP to other molecules. Hormones are signal molecules that can easily pass through the plasma membrane. They do not transfer phosphate groups from ATP to other molecules. A ligand is a molecule that specifically binds to another, often larger molecule. It does not transfer phosphate groups from ATP to other molecules.

What did Sutherland discover about glycogen metabolism in liver cells?

The hormone epinephrine binds to a specific receptor on the plasma membrane of the liver cell. Glycogen breakdown releases the sugar glucose 1-phosphate, which the cell converts to glucose 6-phosphate. The cell can then use this compound, an early intermediate in glycolysis, for energy production. Alternatively, the compound can be stripped of phosphate and released from the liver cell into the blood as glucose, which can fuel cells throughout the body. Sutherland's research team discovered that epinephrine stimulates glycogen breakdown by somehow activating a cytosolic enzyme, glycogen phosphorylase. Epinephrine could activate glycogen phosphorylase only when the hormone was added to a solution containing intact cells. epinephrine does not interact directly with the enzyme responsible for glycogen breakdown; an intermediate step or series of steps must be occurring inside the cell. Second, the plasma membrane is somehow involved in transmitting the signal. Glucagon does not trigger glycogen breakdown. Sutherland found that the hormone epinephrine never enters the cell where glycogen is metabolized to glucose.

The process of phosphorylation is very important as a cellular mechanism for regulating protein activity. Phosphorylation does this by ___________.

activating or inactivating proteins

G-protein-linked receptors __________, whereas receptor tyrosine kinases __________.

are not enzymes; have enzymatic function A kinase is an enzyme that catalyzes the transfer of phosphate groups. The part of the receptor protein extending into the cytoplasm functions as a tyrosine kinase, an enzyme that catalyzes the transfer of a phosphate group from ATP to the amino acid tyrosine on a substrate protein. Thus, receptor tyrosine kinases are membrane receptors that attach phosphates only to tyrosines and not other amino acids. Ligand-gated ion channels are the only type of receptor that allows ions to cross a membrane directly in response to a signal.

A difference between the mechanisms of cAMP and Ca2+ in signal transduction is that cAMP __________ and Ca2+ __________.

is synthesized by an enzyme in response to a signal; is released from intracellular stores Many signaling pathways involve small, nonprotein, water-soluble molecules or ions called second messengers. Cyclic AMP (cAMP) is one of the most widely used second messengers and is involved in some G protein signaling pathways. An enzyme embedded in the cell membrane, adenylyl cyclase, converts ATP to cAMP in the cytoplasm in response to an extracellular signal. cAMP then activates protein kinase A. cAMP does not enter the cell via a transmembrane protein channel. Calcium enters the cell through specific channels and is stored in the endoplasmic reticulum.

A small molecule that specifically binds to a larger molecule is called a(n) __________.

ligand

When a platelet contacts a damaged blood vessel, it is stimulated to release thromboxane A2. Thromboxane A2 in turn stimulates vascular spasm and attracts additional platelets to the injured site. In this example thromboxane A2 is acting as a

local regulator Thromboxane is a local regulator and is not a neurotransmitter, transcription factor, or G protein. Protein kinases are enzymes that catalyze the transfer of phosphate groups between molecules.

cAMP usually directly activates __________.

protein kinase A

In a phosphorylation cascade, __________ phosphorylate proteins, and __________ dephosphorylate them.

protein kinases; protein phosphatases

Second messengers tend to be water-soluble and small. This accounts for their ability to __________.

rapidly move throughout the cell by diffusion Not all components of signal transduction pathways are proteins. Many signaling pathways also involve small, nonprotein, water-soluble molecules or ions called second messengers. Diffusion permits a wide dispersal of the molecules or ions from the site of their entry or production at a membrane. Because second messengers are small and water-soluble, they can readily spread throughout the cell by diffusion. Second messengers cannot penetrate the hydrophobic core of the plasma membrane and therefore do not typically pass from cell to cell. During a phosphorylation cascade, each substrate becomes the activator for the next substrate. Second messengers can start the process of a phosphorylation cascade but do not participate further. These molecules do not interact with DNA.

The stage of cell signaling in which a chemical signal is "detected" when the signaling molecule binds to a receptor protein located at the cell's surface is called __________.

reception

IP3 (inositol trisphosphate) is produced from __________.

the cleavage of a certain kind of phospholipid in the plasma membrane In response to a signal relayed by a signal transduction pathway, the cytosolic calcium level may rise, usually by a mechanism that releases Ca2+ from the cell's ER. The pathways leading to calcium release involve other second messengers, inositol trisphosphate (IP3) and diacylglycerol (DAG). These two second messengers are produced by cleavage of a certain kind of phospholipid, PIP2, in the plasma membrane. The enzyme that catalyzes the cleavage is phospholipase C.

In liver cells, epinephrine stimulates the breakdown of glycogen. As the signal-transduction pathway progresses, __________.

the signal is amplified

Evidence that cell signaling evolved early in the history of life comes from __________.

the similarity of the mechanisms in organisms that have a very distant common ancestor The molecular details of signal transduction in yeast and mammals are strikingly similar, suggesting that early versions of the cell-signaling mechanisms used today evolved well before the first multicellular creatures appeared on Earth. Due to these similarities, studies of the mechanisms are more likely to provide evidence that these mechanisms evolved early in the history of life. Mitochondrial DNA and ribosomal RNA comparisons would provide genetic evidence of evolutionary relationships between organisms but would not indicate when signal transduction mechanisms first evolved. Because receptors for signaling molecules are located in the plasma membrane or in the cytoplasm or nucleus, studying receptors on the nuclear envelope would not provide any information concerning the evolution of signaling mechanisms. Lastly, cell membranes and their associated proteins do not fossilize, so the fossil record would not provide any evidence of signal transduction evolution.

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

they amplify the original signal manyfold

The stage of cell signaling in which the signal is converted to a form that can bring about a response in the cell is called __________.

transduction