Exam 2
Cooking oil and gasoline (a hydrocarbon) are not amphipathic molecules because they _____. A) do not have a polar or charged region B) do not have a nonpolar region C) have hydrophobic and hydrophilic regions D) are highly reduced molecules
A) do not have a polar or charged region
If cells are grown in a medium containing radioactive 32P-labeled phosphate, which of these molecules will be labeled? A) proteins B) cellulose C) amino acids D) nucleic acids E) glucose
E) glucose
Which line in the graph represents the bag with the highest initial concentration of sucrose? A) A B) B C) C D) D E) E
A) A
The work of Bartel's group on the ribozyme RNA replicase supports which conclusion? A) An RNA world could produce molecules that could self-replicate. B) Natural selection requires human oversight. C) DNA must have come before RNA. D) Life cannot come from nonlife.
A) An RNA world could produce molecules that could self-replicate.
Compare proteins to nucleic acids. Which of the following is true? A) Both have primary and secondary structure. B) Both contain sulfur. C) Both take on structural roles in the cell. D) Both have monomers, which contain phosphorus.
A) Both have primary and secondary structure.
Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly? A) CO2 B) an amino acid C) glucose D) K+ E) starch
A) CO2
DNA is the main hereditary material of all life. However, DNA lacks one important characteristic for the first forms of life. Why have researchers rejected the idea that DNA was found in the first life form? A) It does not function as a catalyst. B) It is not stable enough to have withstood early Earth's harsh atmosphere. C) DNA only has four types of bases. Therefore, DNA cannot adapt and evolve. D) The type of sugar found in DNA is too complicated to have been present early in Earth's history.
A) It does not function as a catalyst.
What is the most important factor in explaining why osmosis occurs spontaneously? A) It leads to an increase in entropy. B) It leads to a decrease in entropy. C) The process is exothermic. D) The process is endothermic.
A) It leads to an increase in entropy.
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 increase. B) Permeability to glucose will decrease. C) Permeability to glucose will stay the same. D) You cannot predict the outcome. You simply have to make the measurement.
A) Permeability to glucose will increase.
DNA double helices are soluble in water but insoluble in alcohol. How do these physical properties reflect the chemical structure of the DNA molecule? A) The charged phosphate groups and sugars of DNA are hydrophilic. B) The purine and pyrimidine bases are hydrophilic. C) The 5 prime to 3 prime polarity of DNA makes it soluble in water but not in alcohol. D) The charged R-groups of DNA are hydrophilic.
A) The charged phosphate groups and sugars of DNA are hydrophilic.
Why is it that RNA can catalyze reactions but DNA cannot? A) The sugar of RNA is much more reactive than the sugar of DNA. B) The bases of RNA are much more reactive than the bases of DNA. C) The phosphate groups of RNA are much more reactive than the phosphate groups of DNA. D) The primary structure of RNA is fundamentally different than the primary structure of DNA.
A) The sugar of RNA is much more reactive than the sugar of DNA.
Which aspect of phospholipids is most important to the formation of bilayers? A) They are amphipathic. B) Their size is large, relative to cholesterol. C) Their size is small, relative to fats. D) Their hydrocarbon tails can consist of fatty acids or isoprene subunits.
A) They are amphipathic.
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) a hydrogen bond forms between the sugar of one nucleotide and the phosphate of a second C) covalent bonds form between the bases of two nucleotides D) hydrogen bonds form between the bases of two nucleotides
A) a covalent bond forms between the sugar of one nucleotide and the phosphate of a second
Which of the following factors would tend to increase membrane fluidity? A) a greater proportion of unsaturated phospholipids B) a greater proportion of saturated phospholipids C) a lower temperature D) a relatively high protein content in the membrane E) a greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses
A) a greater proportion of unsaturated phospholipids
Which of the following crosses lipid bilayers the slowest? A) a sodium ion B) a small, polar molecule like water C) a large, polar molecule like glucose D) a small, nonpolar molecule like oxygen (O2)
A) a sodium ion
Which of the following is a large organic molecule that is NOT assembled by polymerization of a few kinds of simple subunits? A) a steroid B) cellulose C) DNA D) an enzyme E) a contractile protein
A) a steroid
A membrane protein that spans the phospholipid bilayer one or more times is _____. A) a transmembrane protein B) an associated protein C) a peripheral protein D) an integrin E) a glycoprotein
A) a transmembrane protein
Both DNA and RNA _____. A) are information-containing molecules B) show primary, secondary, tertiary, and quaternary structure C) are highly reactive catalysts in cells D) naturally occur as a double helix
A) are information-containing molecules
Lipids _____. A) are insoluble in water B) are made from glycerol, fatty acids, and nitrogen C) contain less energy than proteins and carbohydrates D) are made by dehydration reactions E) contain sulfur polymers
A) are insoluble in water
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 _____. A) cotransport proteins B) ion channels C) pores in the plasma membrane D) passive diffusion across the plasma membrane E) cellular metabolic reactions that create or destroy ions
A) cotransport proteins
The presence of cholesterol in the plasma membranes of some animal cells _____. A) enables the membranes to stay fluid when cell temperature drops B) enables the cell to remove hydrogen atoms from saturated phospholipids C) enables the cell to add hydrogen atoms to unsaturated phospholipids D) makes the cell membrane less flexible, allowing it to sustain greater intracellular pressure E) reduces mutations to genetic material inside the cell
A) enables the membranes to stay fluid when cell temperature drops
The membranes of winter wheat are able to remain fluid when it is extremely cold by _____. A) increasing the percentage of unsaturated phospholipids in the membrane B) increasing the percentage of cholesterol molecules in the membrane C) decreasing the number of hydrophobic proteins in the membrane D) cotransport of glucose and hydrogen E) using active transport
A) increasing the percentage of unsaturated phospholipids in the membrane
Use the following information when answering the corresponding question(s). Rhodopsins are light-sensitive molecules composed of a protein (opsin) and retinal (derivative of vitamin A). Opsin is a membrane protein with several α-helical segments that loop back and forth through the plasma membrane. There are two classes of rhodopsins. According to Oded Beje, one class has relatively slow dynamics (a photocycle of approximately 0.5 second) and is well suited for light detection. The second class has faster dynamics (a photocycle of approximately 0.02 seconds) and is well suited for chemiosmosis: pumping of protons or chloride ions across cell membranes. Oded Beje was the first, in September 2000, to report on a rhodopsin (proteorhodopsin) found in the domain Bacteria. [SOURCE: O. Beje et al., Science 289 (2000): 1902.] 40) Refer to the paragraph on Rhodopsins. Which of the following best describes this particular protein? A) integral B) peripheral C) external D) internal
A) integral
The text states that ribonucleotides can diffuse through some types of liposomes. It is likely that the lipids present early in chemical evolution had short chains. Would liposomes formed from these types of lipids be more or less permeable to ribonucleotides than if early cells formed from long-chained lipids? A) more permeable B) less permeable C) same permeability
A) more permeable
Nucleic acids are polymers made up of which of the following monomers? A) nucleotides B) sugars C) amino acids D) nitrogenous bases
A) nucleotides
Use the following information when answering the corresponding question(s). Shu-ichi Nakano reported in Science in February 2000 that "The RNA enzyme (ribozyme) from hepatitis delta virus catalyzes self-cleavage of a . . . [chemical] . . . bond." This reaction is inherently slow due to the formation of an unfavorable negative charge on the ribozyme. The author goes on to show that this self-cleavage is made faster by joining it with an acid-base reaction that neutralizes the negative charge. Nakano's model describes a positively charged cytosine base on the ribozyme acting as the acid, and magnesium hydroxide acting as the base. Specifically, the cytosine donates its proton (H+) to neutralize the unstable negative charge that would have formed on the ribozyme. Is Nakano's quote from Science consistent with the textbook's claim that RNA is a good candidate for the first life form? A) yes B) no
A) yes
Refer to Nakano's quote from Science. If the cytosine is positively charged (+) before self-cleavage, what would its charge be after self-cleavage? A) + (positive) B) - (negative) C) 0 (neutral) D) no way to predict
B) - (negative)
If one strand of a DNA molecule has the sequence of bases 5'ATTGCA3', the other complementary strand would have the sequence _____. A) 5'TAACGT3' B) 5'TGCAAT3' C) 5'UAACGU3' D) 3'UAACGU5' E) 5'UGCAAU3'
B) 5'TGCAAT3'
Which line or lines in the graph represent(s) bags that contain a solution that is hypertonic at 50 minutes? A) A and B B) B C) C D) D E) D and E
B) B
In what way do the membranes of a eukaryotic cell vary? A) Phospholipids are found only in certain membranes. B) Certain proteins are unique to each membrane. C) Only certain membranes of the cell are selectively permeable. D) Only certain membranes are constructed from amphipathic molecules. E) Some membranes have hydrophobic surfaces exposed to the cytoplasm, while others have hydrophilic surfaces facing the cytoplasm.
B) Certain proteins are unique to each membrane.
Which of the following is a characteristic feature of a carrier protein in a plasma membrane? A) It is a peripheral membrane protein. B) It exhibits a specificity for a particular type of molecule. C) It requires the expenditure of cellular energy to function. D) It works against diffusion. E) It has no hydrophobic regions.
B) It exhibits a specificity for a particular type of molecule
Why do researchers think the first self-replicating molecule was RNA? A) RNA is the only type of molecule that can catalyze a chemical reaction. B) RNA can carry information and catalyze chemical reactions. C) Self-replicating molecules of RNA exist today, in human cells. D) Fossil evidence of such a molecule was recently discovered.
B) RNA can carry information and catalyze chemical reactions.
What is the difference between a ribonucleotide and a deoxyribonucleotide? A) Ribonucleotides contain a phosphate group. B) Ribonucleotides have a hydroxyl group on the 2 carbon of their sugar subunit. C) Ribonucleotides contain a sugar with five carbon atoms. D) Ribonucleotides have a hydrogen atom on the 1 carbon of their sugar subunit.
B) Ribonucleotides have a hydroxyl group on the 2 carbon of their sugar subunit.
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) The lipids and water will have separated into two distinct layers because the lipids are partially nonpolar. B) Some lipids will have formed tiny vesicles filled with water. C) All the lipids will have formed planar bilayer membranes. D) Most lipids will have completely dissolved in solution because they are partially polar.
B) 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 end has a hydroxyl group attached to the number 5 carbon of ribose. B) The end has a phosphate group attached to the number 5 carbon of ribose. C) The end has phosphate attached to the number 5 carbon of the nitrogenous base. D) The end has a carboxyl group attached to the number 5 carbon of ribose. E) The end is the fifth position on one of the nitrogenous bases.
B) The end has a phosphate group attached to the number 5 carbon of ribose.
DNAase is an enzyme that catalyzes the hydrolysis of the covalent bonds that join nucleotides together. What would first happen to DNA molecules treated with DNAase? A) The two strands of the double helix would separate. B) The phosphodiester bonds between deoxyribose sugars would be broken. C) The purines would be separated from the deoxyribose sugars. D) The pyrimidines would be separated from the deoxyribose sugars. E) All bases would be separated from the deoxyribose sugars.
B) The phosphodiester bonds between deoxyribose sugars would be broken.
Enzymes that break down DNA catalyze the hydrolysis of the covalent bonds that join nucleotides together. What would happen to DNA molecules treated with these enzymes? A) The two strands of the double helix would separate. B) The phosphodiester linkages of the polynucleotide backbone would be broken. C) The purines would be separated from the deoxyribose sugars. D) The pyrimidines would be separated from the deoxyribose sugars. E) All bases would be separated from the deoxyribose sugars.
B) The phosphodiester linkages of the polynucleotide backbone would be broken.
Steroid hormones are large communication molecules that are modified cholesterol molecules. How do you think they enter a cell? A) Their size probably allows them to diffuse through the plasma membrane. B) Their lipid nature probably allows them to diffuse through the plasma membrane. C) Their protein structure probably allows them to diffuse through the plasma membrane. D) They must require a protein transporter, because the plasma membrane is completely impermeable to molecules.
B) Their lipid nature probably allows them to diffuse through the plasma membrane.
Steroids are considered to be lipids because they _____. A) are essential components of cell membranes B) are not soluble in water C) are made of fatty acids D) are hydrophilic compounds E) contribute to atherosclerosis
B) are not soluble in water
What is the structural feature that allows DNA to replicate? A) sugar-phosphate backbone B) complementary pairing of the nitrogenous bases C) disulfide bonding (bridging) of the two helixes D) twisting of the molecule to form an α-helix E) three-component structure of the nucleotides
B) complementary pairing of the nitrogenous bases
Which of the following are pyrimidine nitrogenous bases? A) guanine and adenine B) cytosine and uracil C) thymine and guanine D) ribose and deoxyribose E) adenine and thymine
B) cytosine and uracil
Based on the figure above, which of these experimental treatments would increase the rate of sucrose transport into the cell? A) decreasing extracellular sucrose concentration B) decreasing extracellular pH C) decreasing cytoplasmic pH D) adding an inhibitor that blocks the regeneration of ATP E) adding a substance that makes the membrane more permeable to hydrogen ions
B) decreasing extracellular pH
One of the primary functions of RNA molecules is to _____. A) transmit genetic information to offspring B) function in the synthesis of proteins C) make a copy of itself, thus ensuring genetic continuity D) act as a pattern or blueprint to form DNA E) form the genes of higher organisms
B) function in the synthesis of proteins
Which of the following are purine nitrogenous bases? A) cytosine and guanine B) guanine and adenine C) adenine and thymine D) thymine and uracil E) uracil and cytosine
B) guanine and adenine
In the acid-base reaction described in the preceding paragraph about Nakano's research on RNAs, a proton (H+) is being transferred. What is acting as the proton acceptor? A) cytosine B) magnesium hydroxide C) the virus D) cytosine, magnesium hydroxide, or the virus
B) magnesium hydroxide
A phospholipid is a _____. A) nonpolar lipid molecule that is made polar by the addition of a phosphate B) nonpolar lipid molecule that is made amphipathic by the addition of a phosphate C) polar lipid molecule that fully interacts with water D) polar lipid molecule that fully repels water
B) nonpolar lipid molecule that is made amphipathic by the addition of a phosphate
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.. 30) Refer to the figure. At the beginning of the experiment, A) side A is hypertonic to side B. B) side A is hypotonic to side B. C) side A is isotonic to side B. D) side A is hypertonic to side B with respect to glucose. E) side A is hypotonic to side B with respect to NaCl.
B) side A is hypotonic to side B.
Recall the Bartel lab group experiment to create a ribozyme from scratch. If they had created exact copies of each ribozyme (rather than creating copies with a few differences), the ribozymes would have _____. A) become more efficient with each round of selection B) stayed the same with each round of selection C) become less efficient with each round of selection D) stopped catalyzing reactions after just a few rounds of selection
B) stayed the same with each round of selection
What region of a steroid is hydrophilic? A) the methyl (-CH3) groups B) the terminal hydroxyl group C) the ring structures D) the long hydrocarbon chain
B) the terminal hydroxyl group
Ions diffuse across membranes through specific ion channels down _____. A) their chemical gradients B) their concentration gradients C) the electrical gradients D) their electrochemical gradients E) the osmotic potential gradients
B) their concentration gradients
Under what circumstances does membrane transport require energy? A) wherever large molecules are moved within a cell B) whenever a solute is moved against its electrochemical gradient C) whenever an ion moves through a phospholipid bilayer membrane D) whenever oxygen moves through a phospholipid bilayer membrane
B) whenever a solute is moved against its electrochemical gradient
If a DNA sample were composed of 10% thymine, what would be the percentage of guanine? A) 10 B) 20 C) 40 D) 80 E) It is impossible to tell from the information given.
C) 40
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 in the cytosol can trigger a number of different intracellular reactions, cells keep the cytosolic calcium concentration quite low under normal conditions, using ATP-powered calcium pumps. For example, muscle cells transport calcium from the cytosol into the membranous system called the sarcoplasmic reticulum (SR). If a resting muscle cell's cytosol has a free calcium ion concentration of 10-7 while the concentration in the SR is 10-2, then how is the ATPase acting? A) ATPase activity must be powering an inflow of calcium from the outside of the cell into the SR. B) ATPase activity must be transferring i to the SR to enable this to occur. C) ATPase activity must be pumping calcium from the cytosol to the SR against the concentration gradient. D) ATPase activity must be opening a channel for the calcium ions to diffuse back into the SR along the concentration gradient. E) ATPase activity must be routing calcium ions from the SR to the cytosol, and then to the cell's environment.
C) ATPase activity must be pumping calcium from the cytosol to the SR against the concentration gradient.
Which of the following is the best explanation for why cholesterol decreases the permeability of biological membranes? A) Cholesterol binds to the outside surface of a membrane, thus blocking the movement of solutes. B) Because cholesterol is amphipathic, it forms tiny vesicles that trap solutes. C) Because cholesterol is amphipathic, it fits in between the phospholipids and blocks diffusion through the membrane. D) Cholesterol has four rings in its structure that can sequester (trap) solutes.
C) Because cholesterol is amphipathic, it fits in between the phospholipids and blocks diffusion through the membrane.
Five dialysis bags constructed of membrane, which is permeable to water and impermeable to sucrose, were filled with various concentrations of sucrose and then placed in separate beakers containing an initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the bags were massed (weighed) and the percent change in mass of each bag was graphed. 32) 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? A) A B) B C) C D) D E) E
C) C
Which of the following statements best summarizes the differences between DNA and RNA? A) DNA encodes hereditary information, whereas RNA does not. B) The bases in DNA contain sugars, whereas the bases in RNA do not contain sugar. C) DNA nucleotides contain a different sugar than RNA nucleotides. D) DNA contains the base uracil, whereas RNA contains the base thymine. E) The bases in DNA contain sulfur, whereas the bases in RNA do not contain sulfur.
C) DNA nucleotides contain a different sugar than RNA nucleotides.
Which of the following is true of osmosis? A) Osmosis only takes place in red blood cells. B) Osmosis is an energy-demanding or "active" process. C) In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration. D) In osmosis, solutes move across a membrane from areas of lower water concentration to areas of higher water concentration.
C) In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration. hypotonic to hypertonic
Gramicidin is an antibiotic that increases the permeability of bacterial cell walls to inorganic ions. What is the most likely mode of action of gramicidin? A) It acts by active transport. B) It causes membranes to fuse with one another. C) It forms a channel in the membrane. D) It removes electrical charges from solutes.
C) It forms a channel in the membrane.
Nucleic acids have a definite polarity, or directionality. Stated another way, one end of the molecule is different from the other end. How are these ends described? A) One end has a hydroxyl group on the 2 carbon; the other end has a hydrogen atom on the 2 carbon. B) One end contains a nitrogenous base; the other end lacks it. C) One end has an unlinked 3 carbon; the other end has an unlinked 5 carbon. D) One end has one phosphate group; the other end has two phosphate groups.
C) One end has an unlinked 3 carbon; the other end has an unlinked 5 carbon.
If 14C-labeled uracil is added to the growth medium of cells, what macromolecules will be labeled? A) phospholipids B) DNA C) RNA D) both DNA and RNA E) proteins
C) RNA
Which of the following is a difference between RNA and DNA? A) RNA is single-stranded and DNA is usually triple-stranded. B) DNA contains adenine and RNA does not. C) RNA has ribose sugar and DNA has deoxyribose sugar. D) RNA is made from nucleotide monomers and DNA is made from amino acid monomers.
C) RNA has ribose sugar and DNA has deoxyribose sugar.
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 longer hydrocarbon tails. B) The membrane phospholipids of cold-adapted organisms will have more saturated hydrocarbon tails. C) The membrane phospholipids of cold-adapted organisms will have more unsaturated hydrocarbon tails.
C) The membrane phospholipids of cold-adapted organisms will have more unsaturated hydrocarbon tails.
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 result of this transfusion? A) It will have no unfavorable effect as long as the water is free of viruses and bacteria. B) The patient's red blood cells will shrivel up because the blood has become hypotonic compared to the cells. C) The patient's red blood cells will swell and possibly burst because the blood has become hypotonic compared to the cells. D) The patient's red blood cells will shrivel up because the blood has become hypertonic compared to the cells. E) The patient's red blood cells will burst because the blood has become hypertonic compared to the cells.
C) The patient's red blood cells will swell and possibly burst because the blood has become hypotonic compared to the cells.
In the context of chemical evolution, DNA's structure is interesting because it suggests a possible copying mechanism. What about DNA's structure facilitates copying? A) It has the same number of purines and pyrimidines. B) The nitrogenous bases are located on the inside of the double helix. C) The strands of the double helix are complementary. D) DNA always goes from 5 prime to 3 prime.
C) The strands of the double helix are complementary.
Which of the following descriptions best fits the class of molecules known as nucleotides? A) a nitrogenous base and a phosphate group B) a nitrogenous base and a sugar C) a nitrogenous base, a phosphate group, and a sugar D) a phosphate group and an adenine or uracil E) a sugar and a purine or pyrimidine
C) a nitrogenous base, a phosphate group, and a sugar
For a protein to be an integral membrane protein, it would have to be _____. A) hydrophilic B) hydrophobic C) amphipathic, with at least one hydrophobic region D) completely covered with phospholipids E) exposed on only one surface of the membrane
C) amphipathic, with at least one hydrophobic region
Which of the following includes all of the pyrimidines found in RNA and DNA? A) cytosine and uracil B) cytosine and thymine C) cytosine, uracil, and thymine D) cytosine, uracil, and guanine
C) cytosine, uracil, and thymine
Phospholipids and triglycerides both _____. A) contain serine or some other organic compound B) have three fatty acids C) have a glycerol backbone D) have a phosphate
C) have a glycerol backbone
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_____. A) and the salt solution are both hypertonic to the cells of the celery stalks B) and the salt solution are both hypotonic to the cells of the celery stalks C) is hypotonic and the salt solution is hypertonic to the cells of the celery stalks D) is hypertonic and the salt solution is hypotonic to the cells of the celery stalks E) is isotonic and the salt solution is hypertonic to the cells of the celery stalks
C) is hypotonic and the salt solution is hypertonic to the cells of the celery stalks
Which of the following membrane activities requires energy from ATP? A) facilitated diffusion of chloride ions across the membrane through a chloride channel B) movement of water into a cell C) movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid D) movement of glucose molecules into a bacterial cell from a medium containing a higher concentration of glucose than inside the cell E) movement of carbon dioxide out of a paramecium
C) movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid
Use the following information when answering the corresponding question(s). Shu-ichi Nakano reported in Science in February 2000 that "The RNA enzyme (ribozyme) from hepatitis delta virus catalyzes self-cleavage of a . . . [chemical] . . . bond." This reaction is inherently slow due to the formation of an unfavorable negative charge on the ribozyme. The author goes on to show that this self-cleavage is made faster by joining it with an acid-base reaction that neutralizes the negative charge. Nakano's model describes a positively charged cytosine base on the ribozyme acting as the acid, and magnesium hydroxide acting as the base. Specifically, the cytosine donates its proton (H+) to neutralize the unstable negative charge that would have formed on the ribozyme. Which of the following chemical bonds do you think Nakano is referring to in his quote? A) peptide B) glycosidic C) phosphodiester D) ionic
C) phosphodiester
Which of the following types of molecules are the major structural components of the cell membrane? A) phospholipids and cellulose B) nucleic acids and proteins C) phospholipids and proteins D) proteins and cellulose E) glycoproteins and cholesterol
C) phospholipids and proteins
Bartel's research group showed that an RNA replicase ribozyme could be created by _____. A) carefully synthesizing a novel ribozyme monomer by monomer based on the sequence of known ribozymes B) creating large numbers of random RNA segments and testing each one to see if any replicase activity was present C) starting with random components and allowing selection to result in molecules that were better and better at replicating D) examining protein replicases and reverse-engineering an RNA molecule capable of doing the same job
C) starting with random components and allowing selection to result in molecules that were better and better at replicating
Which of the following pairs of base sequences could form a short stretch of a normal double helix of DNA? A) 5'-purine-pyrimidine-purine-pyrimidine-3' with 3'-purine-pyrimidine-purine-pyrimidine-5' B) 5'-AGCT-3' with 5'-TCGA-3' C) 5'-GCGC-3' with 5'-TATA-3' D) 5'-ATGC-3' with 5'-GCAT-3' E) All of these pairs are correct.
D) 5'-ATGC-3' with 5'-GCAT-3'
Which component is a peripheral protein? A) A B) B C) C D) D E) E
D) D
In an experiment involving planar bilayers, a solution of table salt (sodium and chloride ions in water) is added on the left side of the membrane while pure water is added on the right side. After 30 minutes the researchers test for the presence of ions on each side of the membrane. The right side tests negative for ions. What can you conclude? A) The experiment failed. B) The water somehow blocked the movement of ions across the membrane. C) The left side would probably also test negative for ions. D) Ions cannot cross planar bilayers.
D) Ions cannot cross planar bilayers.
RNA and proteins combine in cells to form structures called ribosomes. Ribosomes contain the active site for peptide bond formation. Based on their chemical structures, do you think protein or RNA molecules actually form the active site within the ribosome? A) protein, because RNA cannot catalyze reactions B) RNA, because proteins cannot catalyze a reaction that involves another protein C) proteins, because only proteins can catalyze a reaction that involves another protein D) It could be either, because both molecules have catalytic properties.
D) It could be either, because both molecules have catalytic properties.
You have a polymer of DNA with 10 adenine bases followed by 10 cytosine bases. If that strand bonded to a strand of 20 thymine bases, how would the double helix shape vary from a typical DNA double helix? A) The double helix would be longer than normal. B) The double helix would be shorter than normal. C) One strand of the double helix would be longer than the other strand. D) The width of the double helix would vary along the length of the strand.
D) The width of the double helix would vary along the length of the strand.
Why are lipids and proteins free to move laterally in membranes? A) The interior of the membrane is filled with liquid water. B) Lipids and proteins repulse each other in the membrane. C) Hydrophilic portions of the lipids are in the interior of the membrane. D) There are only weak hydrophobic interactions in the interior of the membrane. E) Molecules such as cellulose can pull them in various directions.
D) There are only weak hydrophobic interactions in the interior of the membrane.
Refer to the figure. If you examine side A after three days, you should find _____. A) a decrease in the concentration of NaCl and glucose and an increase in the water level B) a decrease in the concentration of NaCl, an increase in water level, and no change in the concentration of glucose C) no net change in the system D) a decrease in the concentration of NaCl and a decrease in the water level E) no change in the concentration of NaCl and glucose and an increase in the water level
D) a decrease in the concentration of NaCl and a decrease in the water level
Which of the following crosses lipid bilayers the fastest? A) a sodium ion B) a small, polar molecule like water C) a large, polar molecule like glucose D) a small, nonpolar molecule like oxygen (O2)
D) a small, nonpolar molecule like oxygen (O2)
Which of the following best describes DNA's secondary structure? A) beta-pleated sheet B) double parallel helical strands C) turn-loop-turn D) double antiparallel helical strands
D) double antiparallel helical strands
Which of the following increases the strength of the hydrophobic interactions in lipid bilayers and thus makes them less permeable to polar molecules? A) the presence of double bonds B) increasing temperature C) removing cholesterol D) increasing length of the hydrocarbon chains
D) increasing length of the hydrocarbon chains
Refer to the following paragraph and accompanying figure to answer the following questions. : Since structure correlates well with function, look for new ways to probe the complex structure of proteins in order to understand what they do and how they do it. One of the most powerful techniques in existence today is X-ray crystallography. The main difficulty with this technique is getting the protein to crystallize. Once crystallized, the protein is bombarded with X-rays to create a pattern that can be analyzed mathematically to determine the three-dimensional structure of the protein. This analysis has been performed by Palczewski (2000) on the protein rhodopsin, which is a light-sensitive protein found in species ranging from ancient bacteria (archaea) to humans. The structure (schematically shown above, where each letter represents an amino acid) is characterized by a single polypeptide chain with several α-helical segments that loop back and forth across the cell membrane. Another notable feature is the disulfide bond (-S-S-) that can be seen at the bottom of the third transmembrane segment. [Figure adapted from K. Palczewski et al., Science 289 (2000): 739.] 36) Which term best describes the type of membrane protein in the figure? A) peripheral B) external C) internal D) integral
D) integral
When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are _____. A) peripheral proteins B) phospholipids C) carbohydrates D) integral proteins E) cholesterol molecules
D) integral proteins
Which of the following affects the osmolarity of a solution? I) concentration of cations II) concentration of anions III) concentration of water A) only I B) only III C) only I and II D) only II and III E) I, II and III
D) only II and III
Which of the following processes includes all others? A) osmosis B) diffusion of a solute across a membrane C) facilitated diffusion D) passive transport E) transport of an ion down its electrochemical gradient
D) passive transport
Some viruses consist only of a protein coat surrounding a nucleic acid core. If you wanted to radioactively label the nucleic acids separately from the protein, you would use radioactive _____. A) sulfur B) carbon C) nitrogen D) phosphorus
D) phosphorus
Lipids that form membranes have what kind of structure? A) completely nonpolar, because they are lipids B) completely polar, which allows them to dissolve in water C) polar heads and nonpolar tails; the nonpolar tails interact with water D) polar heads and nonpolar tails; the polar heads interact with water
D) polar heads and nonpolar tails; the polar heads interact with water
Where would you most likely find an integral membrane protein? A) on the inside surface of the cell membrane B) on the outside surface of the cell membrane C) floating freely in the cytoplasm D) spanning the cell membrane, with parts of the protein visible from both the inside and the outside of the cell
D) spanning the cell membrane, with parts of the protein visible from both the inside and the outside of the cell
What is/are the variable structure(s) of a nucleotide? A) the phosphate group B) the sugar C) the base D) the sugar and the base
D) the sugar and the base
What feature of single nucleotides provides the energy needed for polymerization when nucleic acids are formed? A) their methyl groups B) their sugar groups C) their nitrogenous bases D) their phosphate groups
D) their phosphate groups
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) Sodium and glucose compete for the same binding site in the cotransporter. B) Glucose entering the cell down its concentration gradient provides energy for uptake of sodium ions against the electrochemical gradient. C) Sodium ions can move down their electrochemical gradient through the cotransporter whether or not glucose is present outside the cell. D) The cotransporter can also transport potassium ions. E) A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose.
E) A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose.
Which of the following allows water to move much faster across cell membranes? A) the hydrophobic interior of a cell membrane B) the sodium-potassium pump C) ATP D) peripheral proteins E) aquaporins
E) aquaporins
The difference between the sugar in DNA and the sugar in RNA is that the sugar in DNA _____. A) is a six-carbon sugar and the sugar in RNA is a five-carbon sugar B) can form a double-stranded molecule C) is an aldehyde sugar and the sugar in RNA is a keto sugar D) is in the α configuration and the sugar in RNA is in the β configuration E) contains one less oxygen atom
E) contains one less oxygen atom
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—more acidic outside the cell than inside the cell. Phosphate transport is an example of _____. A) passive diffusion B) facilitated diffusion C) active transport D) osmosis E) cotransport
E) cotransport
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. Using this information, which transport mechanism is most probably functioning in the intestinal cells? A) simple diffusion B) phagocytosis C) active transport pumps D) exocytosis E) facilitated diffusion
E) facilitated diffusion
When biological membranes are frozen and then fractured, they tend to break along the middle of the bilayer. The best explanation for this is that _____. A) the integral membrane proteins are not strong enough to hold the bilayer together B) water that is present in the middle of the bilayer freezes and is easily fractured C) hydrophilic interactions between the opposite membrane surfaces are destroyed on freezing D) the carbon-carbon bonds of the phospholipid tails are easily broken E) the hydrophobic interactions that hold the membrane together are weakest at this point
E) the hydrophobic interactions that hold the membrane together are weakest at this point
