MCB 150 Test 1
The term "allosteric" means
"other shape (or structure)."
A food company hydrogenated a barrel of fat. The treatment made the fat ______.
less fluid
Researchers can analyze the atomic structure of enzymes during catalysis. In one recent study, investigators found that the transition state included the formation of a free radical and that a coenzyme bound to the active site donated an electron to help stabilize the free radical. How would the reaction rate and the stability of the transition state change if the coenzyme were not available?
(W/OUT THE COENZYME) the free-radical-containing transition state would not be stabilized and the reaction rate would drop dramatically.
Which of the following is true of activation energy? (a) Molecules usually get it from thermal energy. (b) Molecules usually get it by breaking bonds. (c) It's the energy difference between reactants and products. (d)Both (a) and (c). (e): (a), (b), and (c).
(a) Molecules usually get it from thermal energy.
DNA and mRNA differ with respect to ... (c) how many kinds of nucleotides are used to make the polymer. (b) the kinds of purines they contain. (a) the kind of sugar they contain. Both (a) and (b). (d) the ability to make a double helix.
(a) the kind of sugar they contain.
What do fats, steroids, and waxes have in common? (a) Moderate polarity. (b) Low solubility in water. (c) They occur in membranes. Both (a) and (c). Both (b) and (c).
(b) Low solubility in water.
Which statement is characteristic of allosteric effectors? Which statement is characteristic of allosteric effectors? (a) They bind to the active site. (b) Covalent bonds attach them to the enzyme. (c) They may not resemble the enzyme's substrates. Both (b) and (c). (a), (b), and (c).
(c) They may not resemble the enzyme's substrates.
Which statement is true of the transition state? (a) It can break apart to yield either reactants or products. (b) It is extremely unstable and lasts only an instant. (c) It has less potential energy than the reactants but more than the products. (d)Both (a) and (b). (e)Both (b) and (c).
(d) Both (a) It can break apart to yield either reactants or products. and (b) It is extremely unstable and lasts only an instant.
In triglycerides, Tail lengths of ___ to ___ are common. There may be from ___ to ___ double bonds.
16 to 22; 0 to 6
Which method of inactivating an enzyme could most likely be overcome by adding high levels of substrate? A) Competitive inhibition B) Allosteric inhibition C) Phosphorylation D) High temperature
A) Competitive inhibition
Which statement helps to explain how DNA stores hereditary information? A) DNA contains four kinds of nitrogenous bases. B) DNA is made from thousands of kinds of monomers. C) DNA binds a master copy of each kind of protein. D) DNA contains 20 kinds of amino acids. E) DNA is a self-replicating type of protein.
A) DNA contains four kinds of nitrogenous bases.
Which one of the following statements about lipids and biological membranes is incorrect? A) Membrane fluidity is affected by lipid composition but not by temperature. B) Phospholipid bilayers are fluid. C) Ions are not allowed to freely traverse a lipid bilayer. D) For lipid movement, flex is faster than lateral shift. E) Increased temperature can change the membrane from gel phase to fluid phase.
A) Membrane fluidity is affected by lipid composition but not by temperature.
Identify each of the following characteristics that would increase the stability of the plasma membrane of an animal cell. Choose all that apply. A) More saturated fatty acids B) Fewer saturated fatty acids C) Shorter average tail length D) Longer average tail length E) Higher temperature F) Lower temperature G) More cholesterol at low temps H)Less cholesterol at low temps
A) More saturated fatty acids D) Longer average tail length F) Lower temperature H)Less cholesterol at low temps
Which of these is NOT a lipid? A) RNA B) wax C) steroids D) cholesterol E) phospholipid
A) RNA
Why are lipids and proteins free to move laterally in membranes? A) There are only weak hydrophobic interactions in the interior of the membrane. B) Molecules such as cellulose can pull them in various directions. C) Lipids and proteins repulse each other in the membrane. D) The interior of the membrane is filled with liquid water. E) Hydrophilic portions of the lipids are in the interior of the membrane.
A) There are only weak hydrophobic interactions in the interior of the membrane.
What nitrogenous bases are pyrimidines? A) Thymine B) Uracil C) Adenine D) Cytosine E) Guanine
A) Thymine B) Uracil D) Cytosine
When nucleotides polymerize to form a nucleic acid _____. A) a covalent bond forms between the sugar of one nucleotide and the phosphate of a second B) hydrogen bonds form between the bases of two nucleotides C) covalent bonds form between the bases of two nucleotides D) a hydrogen bond forms between the sugar of one nucleotide and the phosphate of a second
A) a covalent bond forms between the sugar of one nucleotide and the phosphate of a second
When a pathway is subject to allosteric feedback inhibition, ... A) an accumulation of effectors slows the pathway. B) the effector is made by another pathway. C) an increase in effector concentration speeds the pathway. D) the last enzyme in the pathway is allosteric. E) the concentration of effectors does not change with time.
A) an accumulation of effectors slows the pathway.
With respect to the outer and inner faces of the lipid bilayer of the cell membrane, the composition of lipids is A) asymmetrical. B) identical. C) not identical but symmetrical. D) highly random and varies throughout the cell. E) a mirror image.
A) asymmetrical.
Of the following lipids, which is found in approximately equal amounts in both the outer and inner portions of the lipid bilayer? A) cholesterol B) glycolipid C) phosphatidylserine D)phophatidylethanolamine E) phophatidylinositol
A) cholesterol
A(n) _____ reaction occurs spontaneously. A) exergonic B) chemical C) endergonic D) kinetic E) anabolic
A) exergonic
The energy for an endergonic reaction comes from a(n) _____ reaction. A) exergonic B) glucose + glucose --> maltose C) ADP + P --> ATP D) synthesis E) anabolic
A) exergonic
The following reaction A --> B + C + heat is a(n) _____ reaction. A) exergonic B) endergonic C) exchange D) dehydration synthesis E) anabolic
A) exergonic
Which of the following increases the strength of the hydrophobic interactions in lipid bilayers and thus makes them less permeable to polar molecules? A) increasing length of the hydrocarbon chains B) increasing temperature C) the presence of double bonds D) removing cholesterol
A) increasing length of the hydrocarbon chains
Based on the composition of cell membranes, the most prominent lipids are A) phospholipids. B) glycolipids. C) cholesterol. D) phytosterol. E) cerebrosides.
A) phospholipids.
Decreasing the saturation of the fatty acid chains on a particular type of phospholipid would result in the formation of _____. A) a bilayer with decreased permeability to CO2 B) glycerol C) more fluid bilayers D) cholesterol
C) more fluid bilayers
Which statement best explains the effect on membrane permeability of cholesterol and/or temperature? A) Adding cholesterol increases permeability because its steroid rings decrease the density of the hydrophobic membrane interior. B) Adding cholesterol reduces permeability because its steroid rings fill gaps in the hydrophobic membrane interior. C) Increasing temperature increases permeability because it increases the strength of hydrophobic interactions in the membrane interior. D) Adding cholesterol increases permeability because its steroid rings increase the density of the hydrophobic membrane interior.
B) Adding cholesterol reduces permeability because its steroid rings fill gaps in the hydrophobic membrane interior.
What is responsible for the increased stability of DNA compared to RNA? A) DNA's secondary structure is more stable because it includes short regions of double helices and looped structures. B) DNA is more resistant to cleavage because it lacks a hydroxyl group on the 2' carbon. C) DNA's secondary structure is more stable because of hydrophobic interactions and hydrogen bonds that form between complementary bases of the two sugar-phosphate backbones. D) DNA is more resistant to cleavage because it has a hydroxyl group on the 2' carbon.
B) DNA is more resistant to cleavage because it lacks a hydroxyl group on the 2' carbon. AND C) DNA's secondary structure is more stable because of hydrophobic interactions and hydrogen bonds that form between complementary bases of the two sugar-phosphate backbones.
Which statement most accurately explains how allosteric regulation can change an enzyme's catalytic activity? A) In allosteric inhibition, a regulatory molecule binds to a location other than the active site, resulting in a change in enzyme shape that allows the active site to bind substrate. B) In allosteric activation, a regulatory molecule binds to a location other than the active site, resulting in a change in enzyme shape that allows the active site to bind substrate. C) In allosteric inhibition, a regulatory molecule binds to the active site, blocking substrate binding. D) In allosteric activation, a regulatory molecule binds to the active site, allowing substrate binding.
B) In allosteric activation, a regulatory molecule binds to a location other than the active site, resulting in a change in enzyme shape that allows the active site to bind substrate.
What is the fate of the phosphate group that is removed when ATP is converted to ADP? A) It is broken down into one phosphorus and four oxygen atoms. B) It is acquired by a reactant in an endergonic reaction. C) It is acquired by a reactant in an exergonic reaction. D) It is used to convert an ATP into an AQP. E) It is acquired by a reactant in a spontaneous reaction.
B) It is acquired by a reactant in an endergonic reaction.
Which type of control agent never speeds an enzyme's action? A) Allosteric effector B) Substrate analog C) Regulatory protein D) Protein kinase E) None of the above.
B) Substrate analog
You have just discovered an organism that lives in extremely cold environments. Which of the following would you predict to be true about the phospholipids in its membranes, compared to phospholipids in the membranes of organisms that live in warmer environments? A) The membrane phospholipids of cold-adapted organisms will have more saturated hydrocarbon tails. B) The membrane phospholipids of cold-adapted organisms will have more unsaturated hydrocarbon tails. C) The membrane phospholipids of cold-adapted organisms will have longer hydrocarbon tails.
B) The membrane phospholipids of cold-adapted organisms will have more unsaturated hydrocarbon tails.
Dr. Haxton told one of his students, "To move in the bloodstream, fats need the help of phospholipids." What would a good student say? A) You have it backwards. Fats help phospholipids to travel. B) Yes. Nonpolar molecules aren't compatible with water. C) Sorry, Dr. Haxton! Help comes from cholesterol, not phospholipids. D) Right. Fats are too polar to travel alone in water. E) Not so. Fats are small enough to travel easily without help.
B) Yes. Nonpolar molecules aren't compatible with water.
Which of the following factors would tend to increase membrane fluidity? A) a relatively high protein content in the membrane B) a greater proportion of unsaturated phospholipids C) a greater proportion of saturated phospholipids D) a greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses E) a lower temperature
B) a greater proportion of unsaturated phospholipids
Which of the following would decrease membrane fluidity? A) an increase in the number of C-C double bonds of fatty acids in the membrane B) increased level of saturation of fatty acids C) a shorter chain length of fatty acids D) an increase in the number of transmembrane proteins
B) increased level of saturation of fatty acids
RNA nucleotides contain __________ than DNA nucleotides. A) less phosphorus B) more oxygen C) different purines D) less oxygen E) None of the above.
B) more oxygen
Where would you most likely find an integral membrane protein? A) on the inside surface of the cell membrane B) spanning the cell membrane, with parts of the protein visible from both the inside and the outside of the cell C) on the outside surface of the cell membrane D) floating freely in the cytoplasm
B) spanning the cell membrane, with parts of the protein visible from both the inside and the outside of the cell
The presence of many C-C and C-H bonds causes fats to be ... (a) rich in energy. (b) insoluble in water. (c) low in energy. Both (a) and (b). Both (b) and (c).
Both (a) and (b).
Triglycerides vary with respect to the number of ... (a) hydrocarbon tails. (b) C atoms in the tails. (c) double bonds in the tails. Both (b) and (c). All of the above.
Both (b) and (c).
Which type of control agent exerts noncompetitive inhibition? (a) Substrate analog (b) Protein kinase (c) Allosteric effector Both (b) and (c). (a), (b), and (c).
Both (b) and (c).
What nitrogenous bases are purines? A) Thymine B) Uracil C) Adenine D) Cytosine E) Guanine
C) Adenine E) Guanine
Which statement most accurately describes the relationship between the permeability and fluidity properties of phospholipid bilayers and their structure? A) Bilayers are most permeable but least fluid when they consist of shorter, unsaturated hydrocarbon tails. B) Bilayers are most permeable and most fluid when they consist of longer, unsaturated hydrocarbon tails. C) Bilayers are most permeable and most fluid when they consist of shorter, unsaturated hydrocarbon tails. D) Bilayers are most permeable and most fluid when they consist of longer, saturated hydrocarbon tails.
C) Bilayers are most permeable and most fluid when they consist of shorter, unsaturated hydrocarbon tails.
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's permeability to glucose? A) Permeability to glucose will stay the same. B) Permeability to glucose will decrease. C) Permeability to glucose will increase. D) You cannot predict the outcome. You simply have to make the measurement.
C) Permeability to glucose will increase.
Which of the following is a covalent modification that can affect enzyme activity? A) pH B) Allosteric activation C) Phosphorylation D) Competitive inhibition
C) Phosphorylation
Which of the following is true of membrane lipids? A) Both the head group and the tail are hydrophobic. B) They contain a hydrophobic head group and a hydrophilic tail. C) They contain a hydrophilic head group and a hydrophobic tail. D) Both the head group and the tail are hydrophilic.
C) They contain a hydrophilic head group and a hydrophobic tail.
In the reaction that builds a fat,________ groups react with ________ groups. A) phosphate; amino B) sulfhydryl; carboxyl C) hydroxyl; carboxyl D) hydroxyl; phosphate E) carboxyl; amino
C) hydroxyl; carboxyl
The membranes of winter wheat are able to remain fluid when it is extremely cold by _____. A) decreasing the number of hydrophobic proteins in the membrane B) increasing the percentage of cholesterol molecules in the membrane C) increasing the percentage of unsaturated phospholipids in the membrane D) using active transport E) cotransport of glucose and hydrogen
C) increasing the percentage of unsaturated phospholipids in the membrane
What is energy coupling? A) the use of an enzyme to reduce EA B) the hydrolysis of ATP to ADP + P C) the use of energy released from an exergonic reaction to drive an endergonic reaction D) a barrier to the initiation of a reaction E) a description of the energetic relationship between the reactants and products in an exergonic reaction
C) the use of energy released from an exergonic reaction to drive an endergonic reaction
Which statement most accurately explains why ATP hydrolysis is highly exergonic? A)ATP contains the carbohydrate ribose which stores a large amount of chemical energy. B)Energy is released when a phosphate group is added. C)There is a large drop in potential energy because charge repulsion is reduced D)There is a large increase in potential energy because charge repulsion is reduced.
C)There is a large drop in potential energy because charge repulsion is reduced
Arrange the following molecules in the correct order, from least likely to most likely to pass across a purified phospholipid bilayer? (Be sure to use the "<" symbol between your answers.) H2O N2 Cl- C6H12O6
Cl- < C6H12O6 < H20 <N2
In cells, what is usually the immediate source of energy for an endergonic reaction? A) ADP B) sugar C) as spontaneous reactions, endergonic reactions do not need an addition of energy D) ATP E) glucose
D) ATP
When allosteric effector X binds to enzyme #1, the enzyme stops working. Nevertheless, the speed of the reaction can be altered by adjusting the concentration of X. How? A) When X detaches from an enzyme, the enzyme regains full activity. B) There are many copies of the enzyme. C) X easily escapes from the allosteric site. D) All of the above. E) None of the above.
D) All of the above. Because X leaves an enzyme easily and lets the enzyme go back to work, there are always some working enzymes. The concentration of X determines how many copies are working at each moment. This wouldn't be true if the enzymes couldn't recover.
If you mechanically shook a mixture of phospholipids and water, what would you expect to see when you observe the solution using an electron microscope? A) Most lipids will have completely dissolved in solution because they are partially polar. B) The lipids and water will have separated into two distinct layers because the lipids are partially nonpolar. C) All the lipids will have formed planar bilayer membranes. D) Some lipids will have formed tiny vesicles filled with water.
D) Some lipids will have formed tiny vesicles filled with water.
Which of the following statements about the 5' end of a polynucleotide strand of RNA is correct? A) The 5' end has phosphate attached to the number 5 carbon of the nitrogenous base. B) The 5' end has a hydroxyl group attached to the number 5 carbon of ribose. C) The 5' end has a carboxyl group attached to the number 5 carbon of ribose. D) The 5' end has a phosphate group attached to the number 5 carbon of ribose.
D) The 5' end has a phosphate group attached to the number 5 carbon of ribose.
You are attempting to re-create the mouse/human hybrid cell fusion experiment described in your screencasts. You believe you are performing the procedure the same as it was initially performed, but it takes only half the time for the fluorescent proteins to evenly distribute. Which one of the following statements most likely describes the reason for the difference in your data? A) The labeled cells were taken out of the refrigerator and used immediately, instead of being allowed to come to room temperature. B) Different colored fluorescent labels were used, and the difference in wavelength needed to produce the fluorescence impeded the movement of the labeled proteins. C) More of the phospholipids in this procedure were saturated than in the original experiment. D) The phospholipids in this procedure had a shorter average fatty acid tail length than in the original experiment. E) None of the above statements provide a likely explanation for the difference in experimental data between your experiment and the original experiment.
D) The phospholipids in this procedure had a shorter average fatty acid tail length than in the original experiment.
Which of the following scenarios would you predict to be responsible for activating this enzyme? A) The sugar cleaves the enzyme so it is now in an active conformation. B) The sugar phosphorylates the enzyme, triggering a conformational change. C) The sugar binds to the active site and competes with the normal substrate. D) The sugar binds to the enzyme and changes the conformation of the active site.
D) The sugar binds to the enzyme and changes the conformation of the active site.
How are the structures of RNA and DNA similar? A) Adenine pairs with thymine in both. B) They both have the same tertiary structure. C) They both contain the sugar ribose. D) Their sugar-phosphate backbones are formed by phosphodiester linkages.
D) Their sugar-phosphate backbones are formed by phosphodiester linkages.
Which of the following can change the shape of an enzyme? A) pH B) phosphorylation C) temperature D) all of the above
D) all of the above
A "mystery molecule" was isolated in a laboratory and scientists found that the molecule readily crossed artificial membranes. Which of the following molecules can be ruled out as the "mystery molecule?" A) O2 B) CO2 C) H2O D) chloride ion
D) chloride ion Charged molecules do not cross membranes on their own because it is energetically unfavorable for them to break their interactions with water and enter the hydrophobic interior of the membrane. Thus, a chloride ion cannot be the mystery molecule that easily crossed membranes.
The movement of molecules through a plasma membrane channel protein is always _____. A) "paid for" by an expenditure of cellular energy B) against the molecule's electrochemical gradient C) toward the inside of the cell D) down the molecule's electrochemical gradient
D) down the molecule's electrochemical gradient
In fat synthesis,________ and fatty acids combine to make fats plus________. A) phosphate; glycerol B) esters; phosphate C) glucose; phosphate D) glycerol; water E) esters; water
D) glycerol; water
In cooperativity, ... A) two or more enzymes are needed to bind one control agent. B) two enzymes cooperate to produce a control agent. C) two enzymes share a binding site for a control agent. D) if one substrate is bound, the next binds more easily. E) two control agents must bind to affect enzyme action.
D) if one substrate is bound, the next binds more easily.
Nucleotides are joined by a _____ to form the DNA and RNA polymers that function in the cell. A) base-phosphate linkage B) sugar-base linkage C) sugar-base-phosphate linkage D) sugar-phosphate linkage
D) sugar-phosphate linkage
The most unsaturated fats have ... A) the longest hydrocarbon tails. B) the highest ratio of H to C. C) the shortest hydrocarbon tails. D) the most double bonds. E) the fewest double bonds.
D) the most double bonds.
What region of a steroid is hydrophilic? A) the methyl (-CH3) groups B) the ring structures C) the long hydrocarbon chain D) the terminal hydroxyl group
D) the terminal hydroxyl group
Which of the following interactions that were previously described as protein-stabilizing forces are also likely to act among the hydrocarbon tails of fatty acids in a lipid bilayer? Choose all that apply. A) Disulfide linkages B) Hydrogen bonds C) Ionic bonds D) van der Waals forces E) Covalent bonds
D) van der Waals forces
Which of the following statements is a logical consequence of the second law of thermodynamics? A) Energy can be transferred or transformed, but it cannot be created or destroyed. B) If there is an increase in the energy of a system, there must be a corresponding decrease in the energy of the rest of the universe. C) Every energy transfer requires activation energy from the environment. D) If the entropy of a system increases, there must be a corresponding decrease in the entropy of the universe. E) Every chemical reaction must increase the total entropy of the universe.
E) Every chemical reaction must increase the total entropy of the universe.
When ATP releases some energy, it also releases inorganic phosphate. What happens to the inorganic phosphate in the cell? A) It is secreted as waste. B) It enters the nucleus and affects gene expression. C) It is added to water and excreted as a liquid. D) It is used only to regenerate more ATP. E) It may be used to form a phosphorylated intermediate.
E) It may be used to form a phosphorylated intermediate.
Which of the following is a chemical reaction? A) Changing a carbon atom to a nitrogen atom by radioactive decay. B) Dissolving a lump of sugar in a cup of coffee. C) Making a hydrogen bond between a water molecule and a sugar molecule. D) Melting ice. E) None of the above.
E) None of the above.
What do DNA, proteins, and fats have in common? A) They contain phosphorus. B) They contain nitrogen. C) They are polar. D) They are polymers. E) They contain carbonyl groups.
E) They contain carbonyl groups.
The reaction ADP + P --> ATP is a(n) _____ reaction. A) hydrolysis B) exergonic C) spontaneous D) chemical E) endergonic
E) endergonic
Which fact is most important in explaining how molecules convert thermal energy to activation energy (EA)? A)Potential energy increases when molecules make bonds. B)Thermal energy is a form of potential energy. C)Distortion decreases a molecule's potential energy. D)Potential energy decreases when molecules make bonds. E)Distortion increases a molecule's potential energy.
E)Distortion increases a molecule's potential energy.
Which of the following is a chemical reaction? A)Changing a carbon atom to a nitrogen atom by radioactive decay. B)Dissolving a lump of sugar in a cup of coffee. C)Making a hydrogen bond between a water molecule and a sugar molecule. D)Melting ice. E)None of the above.
E)None of the above.
Which of the following hypothetical nucleotide abbreviations indicate molecules that are not biologically relevant? Choose all that apply, and your options will not necessarily appear in the order you see them on the main screen. A) dATP B) UMP C) CTP D) dCTP E) ADP F) dUTP G) TTP H) dGTP
F)dUTP G)TTP
In feedback control, the first enzyme of a pathway is often ________, and a final product of the pathway is the enzyme's allosteric inhibitor.
allosteric
Information is stored in the sequence of nitrogenous bases along the DNA polymer. The bases include two kinds of ________ and two kinds of __________.
pyrimidines; purines
Because the competitor and the substrate are competing for the same site, high substrate levels can outcompete the inhibitor and help _________________________.
restore enzyme activity
Sugar wise, RNA uses ______; DNA uses ________. The polymer names reflect this difference: RNA is short for Ribonucleic acid; DNA is short for deoxyribonucleic acid.
ribose; deoxyribose
Hydrogenation removes double bonds, so the tails can __________.
straighten
