Which of the following types of bonds is most likely responsible for the unusual base pairing shown in Figure 3 that results in the formation of a triplex DNA structure?
answer
hydrogen Explanation: The unusual base pairing shown in Figure 3 is most likely responsible for the formation of a triplex DNA structure. This type of bond is formed when two DNA strands are held together by hydrogen bonds. The hydrogen bonds are formed between the bases on the two strands. The bases that are most commonly involved in triplex formation are thymine and cytosine.
question
A mutation in the gene coding for a single-polypeptide enzyme results in the substitution of the amino acid serine, which has a polar R group, by the amino acid phenylalanine, which has a nonpolar R group. When researchers test the catalysis of the normal enzyme and the mutated enzyme, they find that the mutated enzyme has much lower activity than the normal enzyme does.
Which of the following most likely explains how the amino acid substitution has resulted in decreased catalytic activity by the mutated enzyme?
a. The substitution decreased the mass of the enzyme so that the mutated enzyme binds more weakly to the substrate than the normal enzyme does.
b. The substitution altered the secondary and tertiary structure of the enzyme so that the mutated enzyme folds into a different shape than the normal enzyme does.
c. The substitution caused many copies of the mutated enzyme to cluster together and compete for substrate to bind.
d. The substitution caused the directionality of the enzyme to change such that the amino terminus of the normal enzyme has become the carboxy terminus of the mutated enzyme.
answer
b. The substitution altered the secondary and tertiary structure of the enzyme so that the mutated enzyme folds into a different shape than the normal enzyme does Explanation: The substitution most likely caused the secondary and tertiary structure of the enzyme to change such that the mutated enzyme folds into a different shape than the normal enzyme does.
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A typical bag of fertilizer contains high levels of nitrogen, phosphorus, and potassium but trace amounts of magnesium and calcium. Which of the following best matches the fertilizer component with the molecule in which it will be incorporated by organisms in the area?
a. Nitrogen will be incorporated into nucleic acids.
b. Phosphorus will be incorporated into amino acids.
c. Potassium will be incorporated into lipids.
d. Magnesium will be incorporated into carbohydrates.
answer
a. Nitrogen will be incorporated into nucleic acids. Explanation: A. Nitrogen will be incorporated into nucleic acids.Nucleic acids are large molecules that are essential for all known forms of life. Nucleic acids are made up of smaller units called nucleotides. Nitrogen is a key component of nucleotides, and thus it will be incorporated into nucleic acids when organisms in the area use fertilizer.B. Phosphorus will be incorporated into amino acids.Amino acids are the building blocks of proteins. Proteins are essential for all known forms of life. Phosphorus is a key component of amino acids, and thus it will be incorporated into amino acids when organisms in the area use fertilizer.C. Potassium will be incorporated into lipids.Lipids are a type of molecule that includes fats, oils, and waxes. Lipids are essential for all known forms of life. Potassium is a key component of lipids, and thus it will be incorporated into lipids when organisms in the area use fertilizer.D. Magnesium will be incorporated into carbohydrates.Carbohydrates are a type of molecule that includes sugars, starches, and cellulose. Carbohydrates are essential for all known forms of life. Magnesium is a key component of carbohydrates, and thus it will be incorporated into carbohydrates when organisms in the area use fertilizer.
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If 30% of the nucleotides in a single-stranded RNA molecule are adenine, then what percent are expected to be thymine?
answer
0 Explanation: If 30% of the nucleotides in a single-stranded RNA molecule are adenine, then 60% are expected to be thymine. This is because adenine always pairs with thymine, and thymine always pairs with adenine.
question
Amylase is an enzyme that converts carbohydrate polymers into monomers. Glycogen synthase is one of the enzymes involved in converting carbohydrate monomers into polymers.
Which of the following best explains the reactions of these enzymes?
a. Amylase aids in the removal of a water molecule to break covalent bonds whereas glycogen synthase aids in the addition of a water molecule to form covalent bonds.
b. Amylase aids in the addition of a water molecule to break covalent bonds whereas glycogen synthase aids in the removal of a water molecule to form covalent bonds.
c. Amylase aids in the addition of a water molecule to form covalent bonds whereas glycogen synthase aids in the removal of a water molecule to break covalent bonds.
d. Amylase aids in the removal of a water molecule to form covalent bonds whereas glycogen synthase aids in the addition of a water molecule to break covalent bonds.
answer
b. Amylase aids in the addition of a water molecule to break covalent bonds whereas glycogen synthase aids in the removal of a water molecule to form covalent bonds. Explanation: The answer is b. Amylase aids in the addition of a water molecule to break covalent bonds whereas glycogen synthase aids in the removal of a water molecule to form covalent bonds.
question
A common test for liver function involves sprinkling sulfur powder onto a sample of urine (mostly water with dissolved bodily waste). Sulfur powder sprinkled on a sample from an individual with impaired liver function will sink because the urine contains a high level of bile salts, while the sulfur powder sprinkled on normal urine samples will float.
Which of the following best explains why bile salts cause the sulfur powder to sink?
a. Bile salts decrease the surface tension of the urine sample.
b. Bile salts increase the water potential of the urine.
c. Bile salts increase the density of the urine sample.
d. Bile salts decrease the strength of the covalent bonds within a water molecule.
answer
a. Bile salts decrease the surface tension of the urine sample. Explanation: Bile salts are amphipathic molecules, meaning that they have both hydrophilic and hydrophobic regions. When bile salts are sprinkled onto a urine sample, the hydrophilic regions of the bile salts interact with the water molecules in the urine, while the hydrophobic regions of the bile salts interact with the sulfur powder. The interaction between the bile salts and the sulfur powder causes the sulfur powder to sink because the bile salts decrease the surface tension of the water molecules, which makes it easier for the sulfur powder to sink through the water.
question
The diagram shows how water can adhere to the xylem in the stems of plants, which contributes to water movement in the plant. Which of the following best explains how water is able to move upward from the roots of a plant, through its xylem in the stem, and out to the leaves?
a. Water is polar, and the walls of the xylem are nonpolar. Water molecules have the ability to form hydrogen bonds with one another but not with the xylem walls.
b. Water is nonpolar, and the walls of the xylem are polar. Water molecules are able to form hydrogen bonds with the xylem walls, and they are pulled up the xylem.
c. Water and the xylem are both nonpolar. Water molecules have the ability to form hydrogen bonds with one another but not with the xylem walls.
d. Water and the xylem are both polar. Water molecules have the ability to form hydrogen bonds with each other and with the walls of the xylem.
answer
d. Water and the xylem are both polar. Water molecules have the ability to form hydrogen bonds with each other and with the walls of the xylem. Explanation: The correct answer is d. Water and the xylem are both polar. Water molecules have the ability to form hydrogen bonds with each other and with the walls of the xylem.
question
Humans produce sweat as a cooling mechanism to maintain a stable internal temperature. Which of the following best explains how the properties of water contribute to this physiological process?
a. The high specific heat capacity of water allows the body to absorb a large amount of excess heat energy.
b. The high heat of vaporization of water allows the body to remove excess heat through a phase change of water from liquid to gas.
c. The high surface tension of water contributes to the physical process by which water leaves the body.
d. The high melting temperature of water allows the body to remove excess heat through a phase change of water from solid to liquid.
answer
b. The high heat of vaporization of water allows the body to remove excess heat through a phase change of water from liquid to gas. Explanation: The best answer is b. The high heat of vaporization of water allows the body to remove excess heat through a phase change of water from liquid to gas.
question
Describe how amino acids are categorized by their chemical properties.
answer
categorized by the chemical properties of the R groups Explanation: Amino acids are categorized by their chemical properties in a few different ways. One way is by their side chain, or R group. There are 20 different amino acids that are commonly found in proteins, and each one has a different side chain. The side chain can be hydrophobic, or water-hating, which means it will not interact with water molecules. Examples of hydrophobic amino acids are glycine and alanine. The side chain can also be hydrophilic, or water-loving, which means it will interact with water molecules. Examples of hydrophilic amino acids are lysine and arginine.Another way that amino acids are categorized by their chemical properties is by their charge. Amino acids can be uncharged, positively charged, or negatively charged. Uncharged amino acids have side chains that are neutral, meaning they neither attract nor repel water molecules. Positively charged amino acids have side chains that are positively charged, meaning they attract water molecules. Negatively charged amino acids have side chains that are negatively charged, meaning they repel water molecules.
question
The researcher hypothesizes that the FXR1 gene codes for a protein that binds to mRNAs that encode some of the proteins that damage arteries. Individuals with a particular mutation of the FXR1 gene tend to have high levels of these proteins. Based on this information, predict how the FXR1 protein most likely interacts with the mRNAs
answer
The FXR1 protein most likely interacts with the mRNAs by inhibiting, or suppressing, mRNA's in order to prevent for them to be translated by ribosomes in order to prevent the production of the amino acid sequence that produces the artery damaging proteins. Explanation: that encode these damaging proteins.The FXR1 protein most likely interacts with the mRNAs that encode these damaging proteins by binding to them. This would prevent the proteins from being made, and therefore would reduce the amount of damage that they can do to arteries.
question
A scientist designed an experiment to test an artificial membrane that mimics the phospholipid bilayer of a cell.
The scientist built a tube that was divided by an artificial membrane and filled with distilled water. The scientist put a known amount of a protein into the water on one side of the membrane. After some time, the scientist measured the concentration of the protein on either side of the membrane but found that there had been no change.
Which of the following experimental changes would allow the scientist to observe transport of a solute across the artificial membrane?
a. Increase the solute concentration in the solution
b. Use a small, nonpolar solute instead of a protein
c. Increase the temperature of the solution
d. Add artificial aquaporins to the membrane
answer
b. Use a small, nonpolar solute instead of a protein Explanation:that encode these damaging proteins.The FXR1 protein most likely interacts with the mRNAs that encode these damaging proteins by binding to them. This would prevent the proteins from being made, and therefore would reduce the amount of damage that they can do to arteries.
question
Which of the following describes the most likely location of cholesterol in an animal cell?
a. Embedded in the plasma membrane
b. Dissolved in the cytosol
c. Suspended in the stroma of the chloroplast
d. Bound to free ribosomes
answer
a. Embedded in the plasma membrane Explanation: Cholesterol is most likely located in an animal cell embedded in the plasma membrane. Cholesterol is a type of lipid, and lipids are amphipathic molecules, meaning they have both hydrophobic and hydrophilic regions. The hydrophobic region of a lipid is insoluble in water, while the hydrophilic region is soluble in water. The plasma membrane is made up of a phospholipid bilayer, with the hydrophobic regions of the lipids facing each other and the hydrophilic regions facing the cytosol. Cholesterol is thought to help stabilize the plasma membrane by filling in the spaces between the hydrophobic regions of the lipids.
question
Carbon dioxide most likely enters a cell through which of the following processes?
a. Facilitated diffusion through membrane proteins
b. Active transport through membrane proteins
c. Simple diffusion through the membrane
d. Active transport through aquaporins
answer
c. Simple diffusion through the membrane Explanation: Carbon dioxide most likely enters a cell through facilitated diffusion through membrane proteins. This is because carbon dioxide is a small molecule that can easily diffuses through the cell membrane. Additionally, facilitated diffusion does not require energy from the cell, which is important for cells that are not actively dividing.
question
Which of the following describes why a glucose transporter is needed to move glucose into the cell?
a. Glucose is nonpolar and requires ATP to move across the membrane.
b. Glucose molecules are polar and need to move from low concentration to high concentration.
c. Glucose molecules are charged, and charged molecules are only ever actively transported.
d. Glucose is large and polar and cannot pass through the phospholipid bilayer.
answer
d. Glucose is large and polar and cannot pass through the phospholipid bilayer. Explanation: Glucose is a sugar molecule that is essential for cellular metabolism. It is transported across cell membranes by special proteins called glucose transporters. Glucose transporters are needed because glucose molecules are too large and polar to pass through the phospholipid bilayer of the cell membrane. Additionally, because glucose is essential for cellular metabolism, it must be transported from areas of low concentration (outside the cell) to areas of high concentration (inside the cell).
question
Which of the following is evidence that eukaryotes and prokaryotes share a common ancestor?
a. All eukaryotes and prokaryotes contain linear DNA.
b. All eukaryotes and prokaryotes contain ribosomes.
c. All eukaryotes and prokaryotes use organic molecules as an energy source.
d. All eukaryotes and prokaryotes are capable of mitosis.
answer
b. All eukaryotes and prokaryotes contain ribosomes. Explanation: All of the options given are evidence that eukaryotes and prokaryotes share a common ancestor. Linear DNA, ribosomes, and the use of organic molecules as an energy source are all features that are shared by both eukaryotes and prokaryotes. Additionally, both eukaryotes and prokaryotes are capable of mitosis, which is another way of saying that they are both capable of cell division.
question
Which of the following is the strongest evidence supporting the endosymbiont hypothesis?
a. Mitochondria have their own DNA and divide independently of the cell.
b. Mitochondria can carry out hydrolytic reactions on organic molecules.
c. Mitochondria have a highly folded membrane.
d. Mitochondria are found in both plants and animals.
answer
a. Mitochondria have their own DNA and divide independently of the cell. Explanation: The strongest evidence in support of the endosymbiont hypothesis is that mitochondria have their own DNA and divide independently of the cell. This is evidence that mitochondria were once free-living organisms that were taken up by other cells and now exist in a symbiotic relationship with them.
question
1. Which of the following best explains why larger grapes have a different rate of water absorption per gram of mass than smaller grapes do?
a. The rate is slower because smaller grapes have a larger surface-area-to-volume ratio than the larger grapes do.
b. The rate is slower because larger grapes have a larger surface-area-to-volume ratio than the smaller grapes do.
c. The rate is slower because smaller grapes can expand more than larger grapes to hold excess water.
d. The rate is slower because larger grapes have more volume to hold excess water than smaller grapes do.
answer
a. The rate is slower because smaller grapes have a larger surface-area-to-volume ratio than the larger grapes do. Explanation: The rate of water absorption is slower for larger grapes because they have a smaller surface-area-to-volume ratio than the smaller grapes do. This means that the larger grapes have less surface area exposed to the water, so the water has less opportunity to enter the grape. The smaller grapes can expand more than the larger grapes to hold excess water, so the smaller grapes absorb water more quickly.
question
A student placed a semipermeable membrane inside a U-shaped channel with two chambers, as shown. The membrane permits the movement of water but not salt. The student wants to vary the rate of osmosis that occurs across the membrane. Which of the following experimental designs will result in the fastest net rate of water movement into chamber A?
a. Placing salt water in chamber A and distilled water in chamber B
b. Placing distilled water in both chambers
c. Placing distilled water in chamber A and salt water in chamber B
d. Placing salt water in both chambers
answer
a. Placing salt water in chamber A and distilled water in chamber B Explanation: The student wants to vary the rate of osmosis that occurs across the membrane. The faster the net rate of water movement, the higher the rate of osmosis.The experimental design that will result in the fastest net rate of water movement into chamber A is placing distilled water in chamber A and salt water in chamber B. This will create a higher concentration gradient across the membrane, resulting in a higher rate of osmosis.
question
A mutation in the upland cotton plant causes the development of chloroplasts with a single outer membrane and no internal membranes. Which of the following would most likely be observed in chloroplasts of cotton plants with this mutation?
a. They would be unable to remove waste products, because internal transport proteins would not be present.
b. They would be unable to generate the ATP and NADPH needed to make sugars, because these processes occur on membranes within the chloroplast.
c. They would be unable to take up carbon dioxide, because CO2 is transported into the chloroplast in membrane-bound vesicles.
d. They would be unable to move within the cell, because only organelles with double membranes are mobile.
answer
b. They would be unable to generate the ATP and NADPH needed to make sugars, because these processes occur on membranes within the chloroplast. Explanation: The most likely observation in chloroplasts of cotton plants with this mutation would be that they would be unable to generate the ATP and NADPH needed to make sugars, because these processes occur on membranes within the chloroplast.
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