Chapter 5

Active transport requires an input of energy and can also generate voltages across membranes. Based on this information, which of the following statements is true? The sodium/potassium pump hydrolyzes ATP and results in a net charge of +1 outside the cell membrane. Active transport can use ATP as its energy source and ensures that there is no voltage across the cell membrane. Active transport moves solutes down their concentration gradients and always uses ATP as the source of energy to do this. Active transport uses channel proteins and ensures that the interior of the cell is always positive compared to the exterior of the cell. The source of energy for active transport of a solute up its gradient can be ATP or a concentration gradient of a second solute. This second gradient of solutes maintains no net difference in voltage across the membrane

a

Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the membrane would carbohydrates most likely be found? on the outside (external) surface of the membrane in the interior of the membrane on the inside (cytoplasmic) surface of the membrane on both hydrophilic surfaces of the membrane but not in the hydrophobic interior Carbohydrates are rarely associated with plasma membranes.

a

Lipid-soluble signaling molecules, such as testosterone, cross the membranes of all cells but affect only target cells because __________. intracellular receptors are present only in target cells only target cells retain the appropriate DNA segments only in target cells is testosterone able to initiate a phosphorylation cascade most cells lack the Y chromosome required only target cells possess the cytosolic enzymes that transduce the testosterone

a

Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because __________. they amplify the original signal manyfold the number of molecules used is small and fixed they counter the harmful effects of phosphatases they are species specific they always lead to the same cellular response

a

The cellular response of a signal pathway that terminates at a transcription factor would be _____. the synthesis of mRNA the activation of an inactive enzyme alteration of the cytoskeleton a change in the chemical composition of the cytosolic environment the activation of a metabolic pathway

a

The concentration of solutes in a red blood cell is about 2%, but red blood cells contain almost no sucrose or urea. Sucrose cannot pass through the membrane, but water and urea can. Osmosis would cause red blood cells to shrink the most when immersed in which of the following solutions? a hypertonic sucrose solution a hypotonic sucrose solution a hypertonic urea solution a hypotonic urea solution pure water

a

Which of the following cell structures exhibits selective permeability between a cell and its external environment? the plasma membrane mitochondria chloroplasts endoplasmic reticulum lysosomes

a

Which of the following molecules is most likely to passively diffuse across the plasma membrane? carbon dioxide glucose sodium ion DNA hemoglobin

a

A mutation in the active site of adenylyl cyclase that inactivates it would most likely lead to _____. an increase in the amount of cAMP present in the cell lower activity of protein kinase A higher activity of protein kinase A reduced binding of adenylyl cyclase to protein kinase A increased binding of adenylyl cyclase to the G protein that activates it

b

Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the plasma membrane would cholesterol most likely be found? on the outside (external) surface of the membrane in the interior of the membrane on the inside (cytoplasmic) surface in the interior and on the inside surface, but not on the outside surface on either surface of the membrane, but not in the interior of the membrane

b

In eukaryotic cells, which of the following is a second messenger that is produced as a response to an external signal such as a hormone? glycogen cyclic AMP tRNA epinephrine glucose

b

In what way do the membranes of a eukaryotic cell vary? Only certain membranes are constructed from amphipathic molecules. Certain proteins are unique to each kind of membrane. Only certain membranes of the cell are selectively permeable. Phospholipids are found only in certain membranes. Some membranes have hydrophobic surfaces exposed to the cytoplasm, while others have hydrophilic surfaces facing the cytoplasm

b

Second messengers tend to be water-soluble and small. This accounts for their ability to _____. rapidly cross the plasma membrane rapidly move throughout the cell by diffusion pass quickly from cell to cell move from substrate to substrate during a phosphorylation cascade cross the nuclear membrane and interact with DNA

b

The source of phosphate for a phosphorylation cascade is _____. cAMP ATP protein kinase GTP protein phosphatase

b

Which of the following correctly describes a general property of all electrogenic pumps? pump sodium out of the cell and potassium into the cell create a voltage difference across the membrane can pump a large variety of solutes across a membrane against their concentration gradient a cell with an interior that is positively charged relative to the outside of the cell a cell with a high internal concentration of protons

b

Which of the following factors would tend to increase membrane fluidity? a relatively high protein content in the membrane a greater proportion of unsaturated phospholipids a greater proportion of saturated phospholipids a lower temperature a greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses

b

Which of the following structural arrangements of the components in biological membranes is most consistent with membrane's property of selective permeability? proteins sandwiched between two layers of phospholipid proteins embedded in two layers of phospholipid a layer of protein coating a layer of phospholipid phospholipids sandwiched between two layers of protein a phospholipid bilayer with proteins scattered on the surfaces of the membranes

b

Which of the following would be least likely to diffuse through a plasma membrane without the help of a transport protein? a large nonpolar molecule a large polar molecule dissolved gases such as oxygen or carbon dioxide a small nonpolar molecule Any of the above would easily diffuse through the membrane.

b

A G protein is active when _____. GDP replaces GTP it is bound by its ligand and transported to the nucleus GTP is bound to it it is phosphorylated by protein kinase Ca2+ binds to a G-protein-linked receptor

c

A single plant cell is placed in an isotonic solution. Salt is then added to the solution. Which of the following would occur as a result of the salt addition? The added salt would enter the cell, causing the cell to take up water and swell. Water would enter the cell by osmosis, and the cell would swell. Water would leave the cell by osmosis, causing the volume of the cytoplasm to decrease. There would be no osmotic movement of water in response to the added salt. The added salt makes the solution hypotonic compared to the cell. Water will enter the cell by osmosis.

c

ATPgammaS is a form of ATP that cannot be hydrolyzed by enzymes. If this compound was introduced to cells so that it replaced the normal ATP present in the cell, which of the following would you predict? an increase in the numbers of phosphorylated proteins in the cell an increase in anabolic cellular reactions a decrease in phosphorylated proteins in the cell an increase in cell division Two of the listed responses would be expected.

c

Cells A and B are the same size, shape, and temperature, but cell A is metabolically less active than cell B; cell B is actively converting oxygen to water in cellular respiration. Oxygen will diffuse more rapidly into cell _____ because _____. A ... the diffusion gradient there is shallower A ... its membrane transport proteins will not be saturated B ... the diffusion gradient in cell B is steeper B ... the oxygen molecules inside cell B have a higher kinetic energy B ... the gradient of oxygen is oriented in the opposite direction compared to cell A

c

Consider the transport of protons and sucrose into a plant cell by the sucrose-proton cotransport protein. Plant cells continuously produce a proton gradient by using the energy of ATP hydrolysis to pump protons out of the cell. Why, in the absence of sucrose, don't protons move back into the cell through the sucrose-proton cotransport protein? Protons cannot move through membrane transport proteins. Protons are freely permeable through the phospholipid bilayer, so no transport protein is needed for protons. The movement of protons through the cotransport protein cannot occur unless sucrose also moves at the same time. In the absence of sucrose, the ATP-powered proton pump does not function, so there is no proton gradient. Protons, unlike other substances, do not diffuse down their concentration gradient.

c

Early work on signal transduction and glycogen metabolism by Sutherland indicated that _____. the signal molecule combined directly with a cytosolic enzyme to form an active quaternary structure the signal molecule worked equally well with intact or disrupted cells the signal molecule did not interact directly with the cytosolic enzyme, but required an intact plasma membrane before the enzyme could be activated the cell-signaling pathway involves two separate steps: transduction and response epinephrine is involved in response to stress

c

Phosphorylation _____. always inactivates a protein activates G-protein-linked receptors can either activate or inactivate a protein is accomplished by protein phosphatases always activates a protein

c

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 leads to Ras being sent to the endomembrane system a mutation that means Ras cannot bind to GTP a mutation that means Ras cannot hydrolyze GTP to GDP a mutation that means GDP is constantly bound to Ras a mutation in which Ras cannot bind to its GPCR

c

Receptors for signal molecules _____. all work via protein kinases are never found in the nucleus of a cell may be found embedded in the plasma membrane, or found within the cytoplasm or nucleus all work by opening ion channels are only found associated with the plasma membrane

c

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 possess enzymes that immediately degrade the molecules as they enter the cell. Nontarget cells lack the inactive enzymes that the signal molecules activate. Nontarget cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cell's nucleus. The signal molecules diffuse from the cell before an effective concentration can be achieved. In nontarget cells, these signal molecules cross the membranes of the endoplasmic reticulum and are captured by vesicles.

c

The general name for an enzyme that transfers phosphate groups from ATP to a protein is _____. protein dehydrogenase protein phosphatase protein kinase peptidase protein cyclase

c

The internal solute concentration of a plant cell is about 0.8 M. To demonstrate plasmolysis, it would be necessary to suspend the cell in what solution? distilled water 0.4 M 0.8 M 1.0 M 150 mM.

c

What did Sutherland discover about glycogen metabolism in liver cells? Glucagon breaks down glycogen to glucose in liver cells. The hormone that breaks down glycogen into glucose enters the liver cell. The hormone epinephrine binds to a specific receptor on the plasma membrane of the liver cell. Glucose is produced from glycogen when epinephrine binds to a cytoplasmic protein. A cytoplasmic receptor triggers the signal transduction pathway that produces glucose from glycogen.

c

Which of the following pairs correctly matches a membrane transport process to its primary function? phagocytosis ... secretion of large particles from the cell by fusion of vesicles with the plasma membrane exocytosis ... the movement of water and solutes out of the cell by vesicle fusion with the plasma membrane pinocytosis ... the uptake of water and small solutes into the cell by formation of vesicles at the plasma membrane osmosis ... passive diffusion of water and small solutes across a membrane None of the above is correct.

c

Which of the following statements about cotransport of solutes across a membrane is correct? Cotransport involves the hydrolysis of ATP by the transporting protein. A cotransport protein is most commonly an ion channel. Cotransport proteins allow a single ATP-powered pump to drive the active transport of many different solutes. The sodium-potassium pump is an example of a cotransport protein. In cotransport, both solutes that are being transported are moving down their chemical gradients.

c

Which of the following statements about diffusion is true? It is very rapid over long distances. It requires expenditure of energy by the cell. It is a passive process. It occurs when molecules move from a region of lower concentration to a region of higher concentration. It always requires integral proteins of the cell membrane.

c

Nitric oxide is unusual among animal signal molecules in that it _____. enters the cell via a protein channel acts by directly binding to DNA binds to membrane receptors and cytoplasm receptors is a gas activates proteins by removing phosphate

d

Steroid hormones can enter a cell by simple diffusion. Therefore steroids _____. are not an example of signaling molecules do not bind to receptors directly bind to DNA do not initiate cell signaling by interacting with a receptor in the plasma membrane act by phosphorylating DNA

d

The plasma membrane is referred to as a "fluid mosaic" structure. Which of the following statements about that model is true? The fluid aspect of the membrane is due to the behavior of phospholipids, and the mosaic aspect is due to the presence of carbohydrates. The fluid aspect of the membrane describes its structure at normal temperatures, and the mosaic aspect describes the behavior of the membrane as the temperature is lowered. The mosaic aspect of the membrane is due to the glycosylation of inner leaflet phospholipids. The fluid aspect of the membrane is due to the lateral and rotational movement of phospholipids, and embedded proteins account for the mosaic aspect. Only phospholipids are capable of moving in the membrane.

d

What event would activate a G protein? hydrolysis of GTP to GDP hydrolysis of GDP to GTP phosphorylation of GDP to GTP replacement of GDP with GTP phosphorylation of GTP to GDP

d

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 _____. neurotransmitter transcription factor protein kinase local regulator G protein

d

Which of the following enables a cell to pick up and concentrate a specific kind of molecule? passive transport facilitated diffusion osmosis receptor-mediated endocytosis channel proteins

d

Which of the following is false in regard to facilitated diffusion? Facilitated diffusion requires a concentration gradient. Facilitated diffusion can occur through protein channels. Facilitated diffusion can occur using transport proteins. Facilitated diffusion requires the hydrolysis of ATP. Facilitated diffusion can move ions across membranes.

d

Which of the following processes and organelle(s) accounts for the replacement of lipids and proteins lost from the plasma membrane? endocytosis and Golgi active transport and the rough endoplasmic reticulum receptor-mediated endocytosis and smooth ER and Golgi exocytosis and smooth and rough ER flip-flop of phospholipids from one side of the plasma membrane to the other and the Golgi

d

Which of the following processes includes all the others? facilitated diffusion diffusion of a solute across a membrane osmosis passive transport transport of an ion down its electrochemical gradient

d

Which of the following statements about the role of phospholipids in the structure and function of biological membranes is correct? Phospholipids are completely insoluble in water. Phospholipids form a single sheet in water. Phospholipids form a structure in which the hydrophobic portion faces outward. Phospholipids form a selectively permeable structure. They are triacylglycerols, which are commonly available in foods.

d

Which of the following statements concerning carbohydrates associated with the plasma membrane is correct? Carbohydrates are only found associated with the membranes of prokaryotic cells. The carbohydrate composition of most eukaryotic plasma membranes is quite similar. Carbohydrates on the plasma membrane are typically short chains of between two and five monosaccharides. Membrane carbohydrates function primarily in cell-cell recognition. Carbohydrates associated with the plasma membrane are located on both surfaces of the membrane.

d

Which of these statements describes some aspect of facilitated diffusion? Facilitated diffusion is another name for osmosis. Facilitated diffusion of solutes occurs through phospholipid pores in the membrane. Facilitated diffusion requires energy to drive a concentration gradient. Facilitated diffusion of solutes may occur through channel or transport proteins in the membrane. There is only one kind of protein pore for facilitated diffusion.

d

A cell has a membrane potential of -100 mV (more negative inside than outside) and has 1,000 times more calcium ions outside the cell than inside. Which of the following best describes a mechanism by which Ca2+ enters the cell? movement of Ca2+ into the cell through an ion channel down its concentration gradient passive diffusion of Ca2+ into the cell down its electrochemical gradient cotransport of Ca2+ into the cell with Cl- movement of Ca2+ into the cell through a carrier protein down its electrical gradient facilitated diffusion of Ca2+ into the cell down its electrochemical gradient

e

A nursing infant is able to obtain disease-fighting antibodies, which are large protein molecules, from its mother's milk. These molecules probably enter the cells lining the baby's digestive tract via which process? osmosis passive transport exocytosis active transport endocytosis

e

Green olives may be preserved in brine, which is a 30% salt solution. How does this method of preservation prevent microorganisms from growing in the olives? Bacterial cells shrivel up in high salt solutions, causing the cell to burst. High salt concentration lowers the pH, thus inhibiting bacterial metabolism. High salt concentration raises the pH, thus inhibiting bacterial metabolism. A 30% salt solution is hypotonic to the bacteria, so they gain too much water and burst. A 30% salt solution is hypertonic to the bacteria, so they lose too much water and plasmolyze.

e

Steroid hormones can enter a cell by simple diffusion. Therefore steroids _____. move up a concentration gradient and are nonpolar move up a concentration and are polar move down a concentration gradient and are polar move through a channel, down a gradient, and are nonpolar None of the listed responses is correct.

e

Testosterone does not affect all cells of the body because _____. testosterone cannot cross the plasma membrane not all cells in the body have membrane receptors for testosterone it is a local regulator it affects only cells that have ion-channel receptors not all cells have cytoplasmic receptors for testosterone

e

Which of the following functional processes is not a consequence of the association of proteins with biological membranes? enzymatic activity cell-cell recognition intercellular joining cell-cell communication energy, carbon, and nitrogen storage

e

Which of the following is a correct difference between active transport and facilitated diffusion? Active transport involves transport proteins, and facilitated diffusion does not. Facilitated diffusion can move solutes against a concentration gradient, and active transport cannot. Active transport can move solutes in either direction across a membrane, but facilitated diffusion can only move in one direction. Facilitated diffusion involves transport proteins, and active transport does not. Active transport requires energy from ATP, and facilitated diffusion does not.

e

Which of the following statements about passive transport is correct? Passive transport operates independently of diffusion. Passive transport operates independently of the concentrations of the moving solute. In passive transport, solute movement stops when the solute concentration is the same on both sides of the membrane. Passive transport does not occur in the human body. Passive transport permits the solute to move in either direction, but the net movement of the population of solute occurs down the concentration gradient of the molecule.

e

Which statement(s) about the sidedness of the plasma membrane is/are correct? Parts of proteins that are exposed on the cytoplasmic side of the endoplasmic reticulum are also exposed on the cytoplasmic side of the plasma membrane. The asymmetrical distribution of membrane proteins, lipids, and carbohydrates across the plasma membrane is determined as the membrane is being constructed. Every integral membrane protein has a specific orientation in the plasma membrane. The two lipid layers may differ in specific lipid composition. All of the listed responses are correct.

e

cAMP usually directly activates _____. phosphodiesterase receptor tyrosine kinases G proteins adenylyl cyclase protein kinase A

e