BIO SEM 1 Final- Unit 1 Flashcards

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.

Bacteriophages are viruses that infect bacteria. In an experiment, bacteriophages were labeled with either radioactive phosphorus or radioactive sulfur. The labeled bacteriophages were incubated with bacteria for a brief amount of time and then removed. The infected bacteria cells were found to contain significant amounts of radioactive phosphorus but not radioactive sulfur.

Based on the results of the experiment, which of the following types of molecules did the bacteriophages most likely inject into the bacteria cells?

A. Simple carbohydrate

B. Amino acid

C. DNA

D. Polypeptide

Which of the following is responsible for the cohesive property of water?

A. Hydrogen bonds between the oxygen atoms of two adjacent water molecules

B. Covalent bonds between the hydrogen atoms of two adjacent water molecules

C. Hydrogen bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule

D. Covalent bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule

E. Hydrogen bonds between water molecules and other types of molecules

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.

If 30% of the nucleotides in a single-stranded RNA molecule are adenine, then what percent are expected to be thymine?

A. 0%

B. 20%

C. 30%

D. 70%

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.

Which of the following correctly illustrates a dipeptide and an amino acid in the optimal position to form a tripeptide?

A

B

C

D

A researcher measured the temperature at which two different samples of double-stranded DNA denature (separate into single strands). Sample 1 denatured at a significantly lower temperature than sample 2 did. Based on the data, the researcher claims that the DNA in sample 2 is composed of a higher percentage of guanine and cytosine than the DNA in sample 1 is.

Which of the following best supports the researcher’s claim?

A. The bonds between guanine and cytosine are covalent bonds, which require more energy to disrupt than those between adenine and thymine.

B. Guanine-cytosine pairs denature at a higher temperature because they have more hydrogen bonds between them than adenine-thymine pairs do.

C. Adenine-thymine pairs require less energy to separate because adenine and thymine are both single-ring bases.

D. Guanine-cytosine pairs require more energy to separate because one is a purine and one is a pyrimidine.

High levels of certain plant nutrients in runoff can lead to rapid growth of algae (an algal bloom) in aquatic ecosystems. These algal blooms are generally followed by algal death and decomposition, which consumes large amounts of dissolved oxygen in the water and results in oxygen levels insufficient to support aerobic respiration. This process is known as eutrophication. The amount of algae present in a body of water can be estimated from the amount of chlorophyll a in a sample of the water. A researcher studying eutrophication collected samples at different times of the year in a freshwater ecosystem. The samples were analyzed for total nitrogen and chlorophyll a concentration (Figure 1) as well as total phosphorus and chlorophyll a concentration (Figure 2).

Which of the following best explains how higher concentrations of nitrogen and phosphorus contribute to eutrophication?

A. An increase in the population of algae results in more nitrogen and phosphorus in the water, causing severe eutrophication.

B. Both bacteria and algae require nitrogen and phosphorus, so the algae must grow faster to compete with bacteria.

C. Nitrogen and phosphorus stimulate oxidative phosphorylation, which consumes the available oxygen in the water.

D. Algae require nitrogen and phosphorus to build macromolecules, so higher concentrations of these nutrients can result in algal blooms.

This group of questions consists of five lettered headings followed by a list of phrases or sentences. For each phrase or sentence, select the one heading to which it is most closely related. Each heading may be used once, more than once, or not at all.

This group of questions refers to the following groups of biological compounds.

(A) Proteins
(B) Carbohydrates
(C) Nucleic acids
(D) Lipids
(E) Steroids

Used to carry the genetic code

A. Proteins

B. Carbohydrates

C. Nucleic acids

D. Lipids

E. Steroids

Which of the following best describes the hydrolysis of carbohydrates?

A. The removal of a water molecule breaks a covalent bond between sugar monomers.

B. The removal of a water molecule forms a covalent bond between sugar monomers.

C. The addition of a water molecule breaks a covalent bond between sugar monomers.

D. The addition of a water molecule forms a covalent bond between sugar monomers.

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.

A feature of organic compounds NOT found in inorganic compounds is the presence of

A. ionizing chemical groups

B. electrons

C. carbon atoms covalently bonded to each other

D. oxygen

E. hydrogen bonds

Which of the following best explains why a cell’s plasma membrane is composed of two layers of phospholipids rather than just a single layer?

A. Having two oppositely oriented layers of phospholipids allows only the hydrophilic heads to interact with water inside and outside of the cell.

B. Having two oppositely oriented layers of phospholipids allows the hydrophilic heads to repel water both inside and outside of the cells.

C. Having two identically oriented layers of phospholipids gives cells more protection from the exterior environment than just a single layer would.

D. Having two identically oriented layers of phospholipids allows for the production of vacuoles while still maintaining a protective barrier.

The amino acid in Figure 1 is found in a region of a polypeptide that folds away from water. Which part of the amino acid most likely contributes to the hydrophobic behavior of this region of the polypeptide?

A. Amine (NH2) group

B. Carboxyl (COOH) group

C. Methyl (CH3) group

D. Hydrogen (H) atom

Which of the following best describes the process by which gas from the atmosphere is obtained by plants and used to build lipids?

A. Gas is fixed by plants as part of the sulfur cycle.

B. Gas is fixed by plants as part of the nitrogen cycle.

C. Gas is directly obtained by plants as part of the carbon cycle.

D. Gas is directly obtained by plants as part of the magnesium cycle.

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.

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.

The synthesis of protein or carbohydrate polymers always produces which of the following as a byproduct?

A. ATP

B. Oxygen

C. Carbon dioxide

D. Urea

E. Water

The sequences for two short fragments of DNA are shown above. Which of the following is one way in which these two segments would differ?

A. Segment 1 would not code for mRNA because both strands have T, a base not found in RNA.

B. Segment 1 would be more soluble in water than segment 2 because it has more phosphate groups.

C. Segment 1 would become denatured at a lower temperature than would segment 2 because A-T base pairs have two hydrogen bonds whereas G-C base pairs have three.

D. Segment 1 must be from a prokaryote because it has predominantly A-T base pairs.

A culture of Spirogyra (an autotrophic alga) is maintained in a water solution containing dissolved carbon dioxide and a source of phosphates but lacking nitrogen compounds. A researcher determines the rates of synthesis of several organic compounds found in the Spirogyra before and after several weeks in the water solution. Which of the following graphs best illustrates a likely result of the experiment?

Ultraviolet (UV) radiation can damage DNA by breaking weak bonds. Which of the following best explains how this occurs?

A. UV radiation disrupts the double helix structure by breaking the covalent bonds between the nitrogenous base pairs.

B. UV radiation disrupts the double helix structure by breaking the hydrogen bonds between the nitrogenous base pairs.

C. UV radiation is able to break DNA strands in two by breaking covalent bonds between the sugar-phosphate backbone molecules.

D. UV radiation is able to break DNA strands in two by breaking hydrogen bonds between the sugar-phosphate backbone molecules.

A student analyzed a viral genome and found that the genome had the following nucleotide composition.

• 28% adenine

• 20% thymine

• 35% cytosine

• 17% guanine

Which of the following best describes the structure of the viral genome?

A. Double-stranded DNA

B. Single-stranded DNA

C. Double-stranded RNA

D. Single-stranded RNA

Which of the following is most directly responsible for water’s unique properties?

A. It contains oxygen atoms.

B. It contains hydrogen atoms.

C. It is an ionic compound.

D. It forms hydrogen bonds.

E. It is nonpolar.

Based on Figure 1, the amino acids in region A are most likely to have which of the following characteristics?

A. Most amino acids will be hydrophobic because they interact most favorably with the phospholipid tails.

B. Most amino acids will be hydrophilic because they interact most favorably with the phospholipid heads.

C. Most amino acids will be ionic amino acids because they interact most favorably with the phospholipid tails.

D. Most amino acids will be polar amino acids because they interact most favorably with the phospholipid heads.

A researcher analyzed four different samples of macromolecules, where all macromolecules in each sample are of the same type. The researcher measured the percent of carbon, oxygen, hydrogen, nitrogen, phosphorus, and sulfur atoms in each sample. The results are shown in Table 1.

Which of the following claims is best supported by the data in Table 1 ?

A. Sample A contains nucleic acids.

B. Sample B contains protein.

C. Sample C contains nucleic acids.

D. Sample D contains protein.

Scientists examined the folded structure of a purified protein resuspended in water and found that amino acids with nonpolar R groups were primarily buried in the middle of the protein, whereas amino acids with polar R groups were primarily on the surface of the protein. Which of the following best explains the location of the amino acids in the folded protein?

A. Polar R groups on the surface of the protein can form ionic bonds with the charged ends of the water molecules.

B. Polar R groups are too bulky to fit in the middle of the protein and are pushed toward the protein’s surface.

C. Nonpolar R groups that cannot form hydrogen bonds with water are pushed into the middle of the protein.

D. Nonpolar R groups from different parts of the protein form covalent bonds with each other to maintain the protein’s structure.

A chemical binds to a protein composed of a single polypeptide chain and prevents the formation of an alpha helix that is typically formed in the absence of the chemical. Which of the following best describes the effect the chemical has on the structure of the protein?

A. The primary structure held together by covalent bonds is affected.

B. The secondary structure held together by hydrogen bonds is affected.

C. The secondary, tertiary, and quaternary structures are affected.

D. All levels of protein structure are affected.