AP BIO CHAPTER 5

There is a U-tube in which solutions in two arms A and B are separated by a membrane. Arm A contains glucose with concentration of 0.4 mol per liter and sodium chloride with concentration of 0.5 mol per liter. Arm B contains glucose with concentration of 0.8 mol per liter and sodium chloride with concentration of 0.4 mol per liter. The solutions in the arms of a U-tube (the figure) are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same. Refer to the figure to answer the following questions. If you examine side A in the figure after three days, the concentrations of glucose and NaCl should be

0.4 M glucose, 0.45 M NaCl.

Histamine is a chemical substance released in inflammatory and allergic responses. The histamine H1 receptor is a G protein-coupled receptor that activates phospholipase C in response to the binding of histamine. Complete the flowchart showing the process of histamine signal transduction from the H1 receptor.

After the reception of the histamine signaling molecule, the active G protein activates the enzyme phospholipase C. Phospholipase C cleaves PIP2 into DAG and IP3. IP3 diffuses through the cytosol and binds to an IP3-gated calcium channel in the ER membrane, causing it to open. As a result, Ca2+ ions flow out of the ER and into the cytosol. The increase in the calcium ion concentration in the cytosol helps activate the cellular response. Signal transduction pathways that involve phosphorylation cascades or multiple second messengers, such as histamine's signal transduction pathway, enable a signal to be amplified and regulated at different points. Similarly, multistep pathways can facilitate the coordination of cellular responses to multiple signals.

Unlike steroid hormones, signaling molecules that are large and/or hydrophilic cannot pass through the cell's plasma membrane and therefore must bind extracellularly to receptor molecules in the plasma membrane. Two types of signal receptors embedded in the cell's plasma membrane are G protein-coupled receptors and receptor tyrosine kinases. Classify each phrase by whether it applies to G protein-coupled receptors only, receptor tyrosine kinases only, both receptors, or neither receptor.

Both G protein-coupled receptors and receptor tyrosine kinases are transmembrane receptors that have a binding domain located on the extracellular side of the plasma membrane. The binding of a signaling molecule to these receptors is the first step in a signaling pathway. However, what happens after a signaling molecule binds is different for each receptor. An activated G protein-coupled receptor activates a G protein inside the cell, which involves the release of GDP and the binding of GTP. The activated G protein then activates an associated enzyme, leading to a cellular response. Receptor tyrosine kinases form dimers after binding signaling molecules. The tyrosines are then phosphorylated, fully activating the receptor. Each phosphorylated tyrosine can bind a relay protein, each of which can trigger a transduction pathway. In this way, a single signaling-molecule binding event can trigger multiple signal transduction pathways and thus multiple cellular responses.

Cortisol is a steroid hormone that can pass through the plasma membrane. Complete the flowchart describing the interaction of cortisol with intracellular receptors.

Cortisol is a small, hydrophobic steroid hormone that can pass through the plasma membrane of cells. In target cells, cortisol binds to the intracellular receptor protein in the cytoplasm, forming a hormone-receptor complex. The hormone-receptor complex then moves into the nucleus and acts as a transcription factor, binding to specific genes and activating their transcription into mRNA. The mRNA that is produced is eventually translated into specific proteins. Proteins produced in response to the cortisol signal function in the stress response. For example, some of these proteins aid in elevating glucose levels in the blood, helping an animal to meet the demands of starvation or intense physical activity.

Cell signaling involves converting extracellular signals to specific responses inside the target cell. Different molecules are involved at each stage of the process. In this activity, you will sort items based on which stage they are involved in: reception, transduction, or response.

Receptor proteins (located in the plasma membrane or inside the cell) bind signaling molecules. The reception of the signal causes a shape change in the receptor molecule, to which other molecules inside the cell respond. The message is then relayed through signal transduction, which may involve a phosphorylation cascade or second messengers such as cAMP, Ca2+, or IP3. Possible responses to the signal may include synthesis of a particular protein or regulation of a particular enzyme.

The solutions in the two arms of this U-tube (the figure) are separated by a membrane that is permeable to water and glucose but not to sucrose. Side A is half-filled with a solution of 2 M sucrose and 1 M glucose. Side B is half-filled with 1 M sucrose and 2 M glucose. Initially, the liquid levels are equal. Refer to the figure to answer the following question. After the system depicted in the figure reaches equilibrium, what changes are observed with respect to the concentrations of sugars?

The concentrations of glucose and sucrose are equal in sides A and B.

A patient has had a serious accident and lost a lot of blood. In an attempt to replenish body fluids, distilled water equal to the volume of blood lost − is transferred directly into one of his veins. What will be the most probable result of this transfusion?

The patient's red blood cells will swell because the blood fluid has become hypotonic compared to the cells.

Which of the following statements about osmosis is correct?

The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis.

Which of the following is most likely true of a protein that cotransports glucose and sodium ions into the intestinal cells of an animal?

Transport of sodium ions down their electrochemical gradient facilitates the transport of glucose against its concentration gradient.

Part C - Cellular response to the histamine signalPart complete The histamine H1 receptor is one of several existing histamine G protein-coupled receptors. Depending on many factors, including the type of receptor, histamine can trigger a variety of responses, including vasodilation, smooth muscle contraction, stimulation of gastric secretion, cardiac stimulation, and increased vascular permeability (causing runny nose and watery eyes).

When histamine binds to a histamine receptor, the specific cellular response that results is determined by the following factors: the type of histamine receptor the type of cell in which the receptor is located the enzyme that is activated by the G protein associated with the receptor the types of second messengers involved in the signal transduction pathway the proteins activated by the second messengers Signaling molecules can trigger a multitude of cellular responses, which may ultimately affect the transcription of genes, the activity of proteins, or cell growth and division.

The solutions in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same. Refer to the figure to answer the following question. If you examine side A after three days, you should find

a decrease in the concentration of NaCl and a decrease in the water level.

To what does the term "ligand" refer in cell biology?

any small molecule that can bind in a specific manner to a larger one; Ligands are the small signaling molecules that bind specifically to corresponding receptor protein molecules on the target cells.

The sodium-potassium pump is called an electrogenic pump because it

contributes to the membrane potential.

Sutherland discovered that the signaling molecule epinephrine

increases concentrations of cyclic AMP in the cytoplasm.

The solutions in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same. Refer to the figure to answer the following question. At the beginning of the experiment, side A

is hypotonic to side B.

The solutions in the two arms of this U-tube (the figure) are separated by a membrane that is permeable to water and glucose but not to sucrose. Side A is half-filled with a solution of 2 M sucrose and 1 M glucose. Side B is half-filled with 1 M sucrose and 2 M glucose. Initially, the liquid levels are equal. Refer to the figure to answer the following question. Initially, in terms of tonicity in the figure, the solution in side A with respect to that in side B is

isotonic.

In receptor-mediated endocytosis, receptor molecules are initially localized on the outer surface of the plasma membrane. Where do the receptors end up following endocytosis?

on the inside surface of a vesicle

Which of the following is the first event that occurs following the binding of a ligand by a membrane receptor protein?

The membrane receptor protein undergoes a conformational change.

Which of the following is the most likely fate of animal cells that lack receptors for local paracrine signal molecules?

They would be unable to grow and divide in response to growth factors from nearby cells.

In which of the following ways could signal transduction most probably be explored in research to treat cancer?

alteration of protein kinases in cell cycle regulation in order to slow cancer growth

Which of the following are among the most common second messengers?

calcium ion and cAMP; These are the most commonly observed second messengers.

Proteins that allow the diffusion of ions across membranes in the direction of their concentration gradients are most likely

channel proteins.

Which of the following is a substance that acts at a long distance from the site at which it is secreted?

hormone; Both animals and plants use hormones for signaling at greater distances.

The primary function of phosphatases in signal transduction is to

inactivate protein kinases to turn off signal transduction.

Water passes quickly through cell membranes because

it moves through aquaporin channel proteins.

Which of the following statements is TRUE with regard to this animation?

Both sodium and potassium ions are transported against their concentration gradients.

Why are there often so many steps between the original signal event and the cell's response?

Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses; This amplification permits the signaling molecule to have a widespread effect throughout the cell.

Which of the following is the greatest advantage of having multiple steps in a transduction pathway?

Having multiple steps provides for greater possible amplification of a signal.

Celery stalks that are immersed in fresh water for several hours become turgid (stiff). Celery stalks left in a 0.15 M salt solution become flaccid (limp). From this we can deduce that

the fresh water is hypotonic and the salt solution is hypertonic to the cells of the celery stalks.

The primary function of G proteins in signal transduction is

transducing the signal from an activated receptor to the next protein in the pathway.

Which of the following is true of steroid receptors?

The receptor molecules may be soluble proteins in the cytoplasm.

A major group of G protein-coupled receptors contains seven transmembrane α helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others. The coupled G protein most likely interacts with this receptor

at the loop between helices 5 and 6.

Which of the following types of signaling is represented between the nerve cells in the figure?

synaptic

Submerging a red blood cell in distilled water will result in

lysis of the cell.

A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in

lysosomes.

Dioxin, produced as a by-product of various industrial chemical processes, is suspected of contributing to the development of cancer and birth defects in animals and humans. It apparently acts by entering cells by simple diffusion and binding to proteins in the cytoplasm, then altering the pattern of gene expression. Which of the following are likely to be the cytoplasmic proteins to which dioxin binds?

transcription factors; Steroid hormone receptors located in the cytoplasm could be bound by dioxin, just as they are bound by the steroids that diffuse into the cell. Once bound by the dioxins, the cytoplasmic receptor/dioxin complexes could move into the nucleus, where they may act as transcription factors, instigating the synthesis of mRNA.

Which of the following provides molecular evidence that signal transduction pathways evolved early in the history of life?

The molecular details of cell signaling are quite similar in organisms whose last common ancestor was a billion years ago; Yeast and mammal cells, for example, are very distantly related yet share many similarities in cell signaling.

Why can a signaling molecule cause different responses in different cells?

The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor; The signal simply initiates a process by binding to and activating a membrane receptor. How transduction proceeds may be quite different for different cells.

The solutions in the two arms of this U-tube (the figure) are separated by a membrane that is permeable to water and glucose but not to sucrose. Side A is half-filled with a solution of 2 M sucrose and 1 M glucose. Side B is half-filled with 1 M sucrose and 2 M glucose. Initially, the liquid levels are equal. Refer to the figure to answer the following question. After the system depicted in the figure reaches equilibrium, what changes are observed?

The water level is higher in side A than in side B.

Mammalian blood contains the equivalent of 0.15 M NaCl. Seawater contains the equivalent of 0.45 M NaCl. What will happen if red blood cells are transferred to seawater?

Water will leave the cells, causing them to shrivel and collapse.

In research on aging (both cellular aging and organismal aging), it has been found that aged cells do not progress through the cell cycle as they had previously. Which of the following would provide evidence that this is related to cell signaling?

decreased affinity of growth factor receptors for their respective ligands

Active and passive transport of solutes across a membrane typically differ in which of the following ways?

Active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy; Active and passive transport can be distinguished by whether or not they use cellular energy.

Which of the following characteristics is unique to plant hormones?

Plant hormones may be delivered to target cells through the air.

Proton pumps are used in various ways by members of every domain of organisms: Bacteria, Archaea, and Eukarya. What does this most probably mean?

Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life.

A drug designed to inhibit the response of cells to testosterone would almost certainly result in which of the following?

a decrease in transcriptional activity of certain genes

The primary function of kinases in signal transduction is to

activate protein kinases or other relay molecules in a series.

Immediately following binding of a growth factor, an activated receptor would most likely stimulate

activation of a protein kinase.

Which of the following membrane activities requires energy from ATP hydrolysis?

movement of sodium ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid

Approximately what proportion of human genes are thought to encode protein kinases?

2%

Which of the following statements correctly describes the normal tonicity relationships between typical plant and animal cells and their respective environments?

Animal cells are generally in an isotonic solution, and plant cells are generally in a hypotonic solution.

At puberty, an adolescent female body changes in both structure and function of several organ systems, primarily under the influence of changing concentrations of estrogens and other steroid hormones. How can one hormone, such as estrogen, mediate so many effects?

Estrogen binds to specific receptors inside many kinds of cells, each of which has different responses to its binding.

Which of the following correctly describes some aspect of exocytosis or endocytosis?

Exocytosis and endocytosis change the surface area of the plasma membrane; The fusion or budding of transport vesicles at the plasma membrane either adds or removes proteins and phospholipids, thus changing the surface area.

Following activation of a receptor, which sequence below represents the correct order in which components will be involved in a signaling pathway that utilizes the second messenger cAMP?

G protein → adenyl cyclase → cAMP → protein kinase

If an animal cell suddenly lost the ability to produce GTP, what might happen to its signaling system?

It would not be able to activate G proteins on the cytoplasmic side of the plasma membrane.

Histamine is a chemical substance released in inflammatory and allergic responses. The histamine H1 receptor on target cells is a G protein-coupled receptor that activates phospholipase C in response to the binding of histamine.

When histamine encounters a target cell, it binds extracellularly to the H1 receptor, causing a change in the shape of the receptor. This change in shape allows the G protein to bind to the H1 receptor, causing a GTP molecule to displace a GDP molecule and activating the G protein. The active G protein dissociates from the H1 receptor and binds to the enzyme phospholipase C, activating it. The active phospholipase C triggers a cellular response. The G protein then functions as a GTPase and hydrolyzes the GTP to GDP. The G protein dissociates from the enzyme and is inactive again and ready for reuse.

Which of the following would increase the electrochemical gradient across a membrane?

a proton pump

If the concentration of phosphate in the cytosol is 2.0 mM and the concentration of phosphate in the surrounding fluid is 0.1 mM, how could the cell increase the concentration of phosphate in the cytosol?

active transport; For the cell to accumulate phosphate, it must move phosphate against the concentration gradient. This process requires energy.

Which of the following sequences is/are correct?

binding of a growth factor to its receptor → phosphorylation cascade → activation of transcription factor → transcription; diffusion of a signaling molecule across the plasma membrane → binding of the signaling molecule to its receptor → movement of the signaling molecule-receptor complex into the nucleus → transcription; binding of a signaling molecule to its receptor → G protein activation → adenylyl cyclase activation → cAMP production → protein phosphorylation

The mechanism by which testosterone alters cell function is by

binding to a receptor protein that enters the nucleus and activates specific genes.

The movement of glucose into a cell against a concentration gradient is most likely to be accomplished by which of the following?

cotransport of the glucose with a proton or sodium ion that was pumped across the membrane using the energy of ATP hydrolysis; Movement of most solutes against their concentration gradient couples the movement of one solute down its concentration gradient to the movement of another (glucose in this case) against its concentration gradient.

The phosphate transport system in bacteria imports phosphate into the cell even when the concentration of phosphate outside the cell is much lower than the cytoplasmic phosphate concentration. Phosphate import depends on a pH gradient across the membranemore acidic outside the cell than inside the cell. Phosphate transport is an example of

cotransport.

Which of the following is least likely to be important in holding the components of a biological membrane together?

covalent interactions between the phospholipid and protein components of the membrane; This is not an important interaction because there are rarely covalent bonds between the phospholipids and integral membrane proteins.

Transport of potassium ions into an animal cell by the sodium-potassium pump requires

energy from ATP.

What is the function of tyrosine-kinase receptors?

enzymatic phosphorylation of tyrosine in the receptor protein; Tyrosine-kinase receptors upon phosphorylation may interact with relay proteins within the cell.

Glucose diffuses slowly through artificial phospholipid bilayers. The cells lining the small intestine, however, rapidly move large quantities of glucose from the glucose-rich food into their glucose-poor cytoplasm. Based on this information, which transport mechanism is most likely responsible for glucose transport in the intestinal cells?

facilitated diffusion

Cystic fibrosis is a genetic disease in humans in which the CFTR protein, which functions as a chloride ion channel, is missing or nonfunctional in cell membranes. The CFTR protein belongs to what category of membrane proteins?

hydrophilic channels

The sodium-potassium pump generates the following concentration gradients across the plasma membrane:

low [Na+] and high [K+] inside the cell and high [Na+] and low [K+] outside.

What is the voltage across a membrane called?

membrane potential

In the figure, the dots in the space between the two structures represent which of the following?

neurotransmitters

Familial hypercholesterolemia is characterized by extremely high levels of cholesterol in the blood, which results from

nonfunctional or missing LDL receptors on cell membranes.

The secretion of a signal molecule by a cell into the local environment, followed by a response by a number of cells in the immediate vicinity, is an example of

paracrine signaling.

The difference between pinocytosis and receptor-mediated endocytosis is that

pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis is highly selective.

The primary function of transcription factors is

regulate gene expression

In general, a signal transmitted via a phosphorylation cascade

results in a conformational change in each phosphorylated protein.

When a neuron responds to a particular neurotransmitter by opening gated ion channels, the neurotransmitter is serving as which part of the signal pathway?

signal molecule

You are working on a team that is designing a new drug. In order for this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would be a factor that determines whether the molecule selectively enters the target cells?

similarity of the drug molecule to other molecules transported by the target cells

Submerging a plant cell in distilled water will result in

the cell becoming turgid.

Submerging a red blood cell in a hypertonic solution will result in

the cell wall shriveling.