For a protein to be an integral membrane protein, it would have to be
amphipathic, with at least one hydrophobic region
You have a planar bilayer with equal amounts of saturated and unsaturated phospholipids. After testing the permeability of this membrane to glucose, you increase the proportion of unsaturated phospholipids in the bilayer. What will happen to the membrane'
Permeability to glucose will increase.
According to the fluid mosaic model of cell membranes, phospholipids
can move laterally along the plane of the membrane
The membranes of winter wheat are able to remain fluid when it is extremely cold by
increasing the percentage of unsaturated phospholipids in the membrane
Some regions of the plasma membrane, called lipid rafts, have a higher concentration of cholesterol molecules. At higher temperatures, these regions
are less fluid than the surrounding membrane
Singer and Nicolson's fluid mosaic model of the membrane proposed that membranes
consist of protein molecules embedded in a fluid bilayer of phospholipids
An animal cell lacking oligosaccharides on the external surface of its plasma membrane would likely be impaired in which function?
cell-cell recognition
Which of these are NOT embedded in the hydrophobic portion of the lipid bilayer at all?
peripheral proteins
Why are lipids and proteins free to move laterally in membranes?
There are only weak hydrophobic interactions in the interior of the membrane.
Which component is a peripheral protein?
D
Which component is cholesterol?
E
Which component is a protein fiber of the extracellular matrix?
A
Which component is a microfilament (actin filament) of the cytoskeleton?
C
Which component is a glycolipid?
B
Cell membranes are asymmetrical. Which of the following statements is the most likely explanation for the membrane's asymmetrical nature?
The two sides of a cell membrane face different environments and carry out different functions.
In what way do the membranes of a eukaryotic cell vary?
Certain proteins are unique to each membrane.
Which of the following is a reasonable explanation for why unsaturated fatty acids help keep a membrane more fluid at lower temperatures?
The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.
What kinds of molecules pass through a cell membrane most easily?
small and hydrophobic
Which of the following most accurately describes selective permeability?
Only certain molecules can cross a cell membrane.
Which of the following is a characteristic feature of a carrier protein in a plasma membrane?
It exhibits a specificity for a particular type of molecule.
Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?
CO2
Which of the following allows water to move much faster across cell membranes?
aquaporins
You are working on a team that is designing a new drug. 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
Diffusion
is a passive process in which molecules move from a region of higher concentration to a region of lower concentration
Which of the following processes includes all others?
passive transport
When a cell is in equilibrium with its environment, which of the following occurs for substances that can diffuse through the cell?
There is random movement of substances into and out of the cell.
Which of the following is true of osmosis?
In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration.
Initially, in terms of tonicity, the solution in side A with respect to the solution in side B is
isotonic
After the system reaches equilibrium, what changes are observed?
The water level is higher in side A than in side B.
A patient was involved a serious accident and lost a large quantity of blood. In an attempt to replenish body fluids, distilled water�equal to the volume of blood lost�is added to the blood directly via one of his veins. What will be the most probable res
The patient's red blood cells will swell and possibly burst because the blood has become hypotonic compared to the cells.
At the beginning of the experiment,
side A is hypotonic to side B.
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
Which line in the graph represents the bag that contained a solution isotonic to the 0.6 M solution at the beginning of the experiment?
C
Which line in the graph represents the bag with the highest initial concentration of sucrose?
A
Which line or lines in the graph represent(s) bags that contain a solution that is hypertonic at 50 minutes?
B
Celery stalks that are immersed in fresh water for several hours become stiff. Similar stalks left in a 0.15 M salt solution become 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
What will happen to a red blood cell (RBC), which has an internal ion concentration of about 0.9 percent, if it is placed into a beaker of pure water?
The cell would swell because the water in the beaker is hypotonic relative to the cytoplasm of the RBC.
Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells? The animal cell is in
an isotonic solution, and the plant cell is in a hypotonic solution
In which of the following would there be the greatest need for osmoregulation?
a salmon moving from a river into an ocean
When a plant cell, such as one from a rose stem, is submerged in a very hypotonic solution, what is likely to occur?
The cell will become turgid.
A sodium-potassium pump
move three sodium ions out of a cell and two potassium ions into a cell while consuming an ATP for each cycle
The sodium-potassium pump is called an electrogenic pump because it
contributes to the membrane potential
Which of the following membrane activities requires energy from ATP?
movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid
The voltage across a membrane is called the
membrane potential
Ions diffuse across membranes through specific ion channels down
their electrochemical gradients
Which of the following would increase the electrochemical gradient across a membrane?
a proton pump
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 membrane�
cotransport
In some cells, there are many ion electrochemical gradients across the plasma membrane even though there are usually only one or two proton pumps present in the membrane. The gradients of the other ions are most likely accounted for by
cotransport proteins
Which of the following is most likely true of a protein that cotransports glucose and sodium ions into the intestinal cells of an animal?
A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose.
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.
Several epidemic microbial diseases of earlier centuries incurred high death rates because they resulted in severe dehydration due to vomiting and diarrhea. Today they are usually not fatal because we have developed which of the following?
hydrating drinks with high concentrations of salts and glucose
The force driving simple diffusion is _____, while the energy source for active transport is
the concentration gradient; ATP
An organism with a cell wall would most likely be unable to take in materials through
phagocytosis
White blood cells engulf bacteria using
phagocytosis
Familial hypercholesterolemia is characterized by
defective LDL receptors on the cell membranes
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 offers more selectivity.
In receptor-mediated endocytosis, receptor molecules initially project to the outside of the cell. Where do they end up after endocytosis?
on the inside surface of the vesicle
A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in
lysosomes
In an HIV-infected cell producing HIV virus particles, the viral glycoprotein is expressed on the plasma membrane. How do the viral glycoproteins get to the plasma membrane? They are synthesized
by ribosomes in the rough ER and arrive at the plasma membrane in the membrane of secretory vesicles
What would be observed by live-cell fluorescence microscopy immediately after HIV entry if HIV is endocytosed first, and then later fuses with the endocytotic vesicle membrane?
The red fluorescent dye-labeled lipids will appear in the infected cell's interior.
Three lab groups carried out an experiment to identify the correct molarities for five solutions. Each unknown contained one of the following sucrose concentrations: 0.0 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, and 1.0 M. Each data entry represents the average of 3
Osmosis of water molecules from unknown solution A likely caused the increase in mass observed.
Which of the following is true of metabolism in its entirety in all organisms?
Metabolism consists of all the energy transformation reactions in an organism.
Which of the following is an example of potential rather than kinetic energy?
a molecule of glucose
Most cells cannot harness heat to perform work because
temperature is usually uniform throughout a cell
Which of the following involves a decrease in entropy?
condensation reactions
Which term most precisely describes the cellular process of breaking down large molecules into smaller ones?
catabolism (catabolic pathways)
Anabolic pathways
consume energy to build up polymers from monomers
Which of the following is a statement of the first law of thermodynamics?
Energy cannot be created or destroyed.
For living organisms, which of the following is an important consequence of the first law of thermodynamics?
The organism ultimately must obtain all of the necessary energy for life from its environment.
Living organisms increase in complexity as they grow, resulting in a decrease in the entropy of an organism. How does this relate to the second law of thermodynamics?
As a consequence of growing, organisms cause a greater increase in entropy in their environment than the decrease in entropy associated with their growth.
Which of the following statements is a logical consequence of the second law of thermodynamics?
Every chemical reaction must increase the total entropy of the universe.
Which of the following statements is representative of the second law of thermodynamics?
Cells require a constant input of energy to maintain their high level of organization.
Which of the following types of reactions would decrease the entropy within a cell?
anabolic reactions
Biological evolution of life on Earth, from simple prokaryote-like cells to large, multicellular eukaryotic organisms,
has occurred in accordance with the laws of thermodynamics
The mathematical expression for the change in free energy of a system is ?G =?H - T?S. Which of the following is (are) correct?
?G is the change in free energy.
A system at chemical equilibrium
can do no work
Which of the following is true for all exergonic reactions?
The reaction proceeds with a net release of free energy.
A chemical reaction that has a positive ?G is best described as
endergonic
Chemical equilibrium is relatively rare in living cells. An example of a reaction at chemical equilibrium in a cell would be
a chemical reaction in which both the reactants and products are not being produced or used in any active metabolic pathway at that time in the cell
Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as _____ is to _____
exergonic; endergonic
In solution, why do hydrolysis reactions occur more readily than condensation reactions?
Hydrolysis increases entropy and is exergonic.
Why is ATP an important molecule in metabolism?
It provides energy coupling between exergonic and endergonic reactions.
When 10,000 molecules of ATP are hydrolyzed to ADP and Pi in a test tube, about half as much heat is liberated as when a cell hydrolyzes the same amount of ATP. Which of the following is the best explanation for this observation?
Reactant and product concentrations in the test tube are different from those in the cell.
Which of the following is most similar in structure to ATP?
an RNA nucleotide
Catabolic pathways
supply energy, primarily in the form of ATP, for the cell's work
When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?
It is lost to the environment.
When ATP releases some energy, it also releases inorganic phosphate. What happens to the inorganic phosphate in the cell?
It may be used to form a phosphorylated intermediate.
A number of systems for pumping ions across membranes are powered by ATP. Such ATP- powered pumps are often called ATPases, although they do not often hydrolyze ATP unless they are simultaneously transporting ions. Because small increases in calcium ions
ATPase activity must be pumping calcium from the cytosol to the SR against the concentration gradient.
Which of the following is the most correct interpretation of the figure?
ATP is a molecule that acts as an intermediary to store energy for cellular work.
How do cells use the ATP cycle shown in the figure?
Cells use the cycle to recycle ADP and phosphate.
Which of the following is true of enzymes?
Enzymes increase the rate of chemical reaction by lowering activation energy barriers.
Which of the following is true when comparing an uncatalyzed reaction to the same reaction with a catalyst?
The catalyzed reaction will have the same ?G.
The lock-and-key analogy for enzymes applies to the specificity of enzymes
binding to their substrate
Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's
activation energy
You have discovered an enzyme that can catalyze two different chemical reactions. Which of the following is most likely to be correct?
Either the enzyme has two distinct active sites or the reactants involved in the two reactions are very similar in size and shape.
During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a ?G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the ?G for the new reaction?
-20 kcal/mol
The active site of an enzyme is the region that
is involved in the catalytic reaction of the enzyme
According to the induced fit hypothesis of enzyme catalysis,
the binding of the substrate changes the shape of the enzyme's active site
Increasing the substrate concentration in an enzymatic reaction could overcome which of the following?
competitive inhibition
Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as
a cofactor necessary for enzyme activity
A noncompetitive inhibitor decreases the rate of an enzyme reaction by
changing the shape of the enzyme's active site
You collect data on the effect of pH on the function of the enzyme catalase in human cells. Which of the following graphs would you expect?
C
How might a change of one amino acid at a site, distant from the active site of an enzyme, alter an enzyme's substrate specificity?
by changing the shape of an enzyme
For the enzyme- catalyzed reaction shown in the figure, if the initial reactant concentration is 1.0 micromolar, which of these treatments will cause the greatest increase in the rate of the reaction?
doubling the enzyme concentration
In the figure, why does the reaction rate plateau at higher reactant concentrations?
Most enzyme molecules are occupied by substrate at high reactant concentrations.
Which curves on the graphs may represent the temperature and pH profiles of an enzyme taken from a bacterium that lives in a mildly alkaline hot springs at temperatures of 70�C or higher?
curves 3 and 5
Which temperature and pH profile curves on the graphs were most likely generated from analysis of an enzyme from a human stomach where conditions are strongly acid?
curves 1 and 4
Which of the following terms best describes the forward reaction in the figure?
exergonic, ?G < 0
Which of the following in the figure would be the same in either an enzyme-catalyzed or a noncatalyzed reaction?
d
Which of the following represents the activation energy required for the enzyme-catalyzed reaction in the figure?
b
Succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, which resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the ratio of succinate to malonic acid reduces
Succinate is the substrate, and fumarate is the product.
What is malonic acid's role with respect to succinate dehydrogenase? Malonic acid
is a competitive inhibitor
HIV is the virus that causes AIDS. In the mid-1990s, researchers discovered an enzyme in HIV called protease. Once the enzyme's structure was known, researchers began looking for drugs that would fit into the active site and block it. If this strategy for
competitive inhibition
A series of enzymes catalyze the reaction X ? Y ? Z ? A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. With respect to the enzyme that converts X to Y, subs
an allosteric inhibitor
A series of enzymes catalyze the reaction X ? Y ? Z ? A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. What is substance X?
a substrate
The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as
feedback inhibition
You have isolated a previously unstudied protein, identified its complete structure in detail, and determined that it catalyzes the breakdown of a large substrate. You notice it has two binding sites. One of these is large, apparently the bonding site for
It is probably an enzyme that works through allosteric regulation.
Allosteric enzyme regulation is usually associated with
an enzyme with more than one subunit
Which of the following is an example of cooperativity?
a molecule binding at one unit of a tetramer, allowing faster binding at each of the other three
Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity?
localization of enzymes into specific organelles or membranes
Protein kinases are enzymes that transfer the terminal phosphate from ATP to an amino acid residue on the target protein. Many are located on the plasma membrane as integral membrane proteins or peripheral membrane proteins. What purpose may be served by
They can more readily encounter and phosphorylate other membrane proteins.
Biological systems use free energy based on empirical data that all organisms require a constant energy input. The first law of thermodynamics states that energy can be neither created nor destroyed. For living organisms, which of the following statements
The organism must ultimately obtain all the necessary energy for life from its environment.
In a biological reaction, succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, a substance that resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the amount
Succinate is the substrate, and fumarate is the product in the reaction.