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1. Which activity of living things is a direct result of the strong cohesive and adhesive forces of
water molecules?
A. blood circulating through the blood vessels of an animal
B. water rising through the vascular tissue of a plant
C. glucose, salts, and other compounds dissolving in blood plasma
D. water repelling off the waxy coat on birds' feathers
2. A scientist is investigating the function of Enzyme Z. In a series of experiments, he mixes the
enzyme in an aqueous solution with its substrate and various other compounds. The table shows
the results.
Trial Mixture
Results
1
Enzyme Z + substrate
no reaction
2
Compound A + substrate
no reaction
3
Compound B + substrate
no reaction
4
Enzyme Z + substrate + Compound A
reaction is catalyzed at a fast rate
5
Enzyme Z + substrate + Compound B
no reaction
6
Enzyme Z + substrate + Compound A + Compound
B
reaction is catalyzed at a slow
rate
Which best describes the roles of Compounds A and B in the enzyme's activity?
A.
A is a coenzyme or cofactor; B is a competing substrate that participates in the same
reaction.
B.
A is a regulatory protein that promotes the enzyme's synthesis; B is a regulatory protein
that inhibits the enzyme's synthesis.
C. A is a competing enzyme that catalyzes the same reaction; B is a coenzyme or cofactor.
D. A is a coenzyme or cofactor; B is an inhibitor
3. Every protein has a complex three-dimensional structure and shape that determines its
structure and function. Which set of factors is most responsible for the structure and shape of a
protein that is synthesized at a ribosome?
A.
the percentage of each nitrogen base in the encoding DNA, and the mechanism of
regulation of gene expression
B.
the types of RNA involved in the synthesis (mRNA, tRNA, and rRNA), and the
mechanism of regulation of gene expression
C.
the percentage of each amino acid in the protein, and the osmolarity of the surrounding
fluid
D. the order of amino acids in the protein, and the pH and temperature of the environment
4. The catalytic effect of an enzyme on its substrate is evaluated in the presence of a variety of
substances. Which describes the substance that most strongly decreases the catalytic effect of the
enzyme? Assume that all substances are acting at the same concentration.
A.
a small molecular compound that binds irreversibly to an allosteric site, changing the
shape of the active site
B. a protein that binds the substrate and catalyzes the formation of a different product
C. a protein that catalyzes the formation of the substrate
D. a small molecular compound that binds reversibly to the active site of the enzyme
5. A scientist is investigating phosphoglucose isomerase, one of the enzymes of glycolysis. In
her experiment, she places the enzyme and the reactants in an aqueous solution, then gradually
raises the pH of the solution from mildly acidic to mildly basic. She measures and records the
rate of product formation at each pH.
In the line graph below, which line describes the predicted results of the experiment?
A. Line 2
B. Line 3
C. Line 1
D. Line 4
6. A scientist uses carbon-14 to label the carbon compounds taken in by a colony of bacteria.
Into which set of bacterial compounds will the carbon-14 be incorporated?
A. essentially all compounds that the bacteria synthesizes
B. proteins and nucleic acids only
C. carbohydrates and proteins only
D. carbohydrates, lipids, and nucleic acids only
7. A scientist is investigating the effects of a kinase in a signal transduction pathway. The kinase
acts to add a phosphate group on a protein. In a laboratory experiment, the concentrations of the
kinase, the protein, and the phosphorylated protein are measured and recorded over time. The
line graph shows the results.
What do the three lines represent?
Line 1: substrate
Line 2: enzyme
A.
Line 3: product
Line 1: enzyme
Line 2: substrate
B.
Line 3: product
Line 1: product
Line 2: substrate
C.
Line 3: enzyme
Line 1: product
Line 2: enzyme
D.
Line 3: substrate
8. Water is a liquid across a broad range of temperatures, a solvent of a huge variety of
compounds, and the most common compound in all living things. In contrast are molecules of
similar small size, including carbon dioxide, hydrogen sulfide, and ammonia, all of which have
limited use in living systems. Which set of properties of water is most responsible for its unique
set of roles?
A. the polarity of the water molecule and strong hydrogen bonding
B. strong cohesion and adhesion forces
C. the linear shape of the water molecule and its low reactivity
D. high heat of vaporization and high heat of fusion
9. A gene mutation has the effect of changing tyrosine into valine in the encoded protein. The
role of the protein is to act as an enzyme in a metabolic pathway. Which describes the most
likely effect of the mutation on the enzyme's function?
A.
If the substitution changed the shape of the active site, then the enzyme will be
significantly less functional or nonfunctional.
B. In all circumstances, the enzyme will be significantly less functional or nonfunctional.
C.
Because only one amino acid is altered, enzyme function will be only marginally affected
or unaffected.
D. The enzyme will be maximally functional at a slightly different pH than before.
10. The illustration shows four nucleotides that are linked together in a single strand of DNA.
Each nucleotide consists of three parts: a phosphate group, the sugar deoxyribose, and a nitrogen
base.
For the illustration to show RNA, which set of changes should be made?
I. Change the sugar from deoxyribose to ribose.
II. Replace the phosphate groups with purines and pyrimidines.
III. Change the set of possible nitrogen bases.
A. I, II, and III
B. I and III
C. I only
D. II only
11. Scientists classify amino acids into groups based on their chemical properties. When the
amino acid is joined into a protein, its properties determine its effect on the structure and
function of the protein.
The diagram shows the structure of two amino acids: alanine and phenylalanine. Both are
classified in the same group of amino acids.
When alanine and phenylalanine join together in a protein, a chemical bond forms between
which pair of functional groups?
the carboxylic acid (-COOH) group of one amino acid, and the amine (-NH2) group of the
A.
other amino acid
B. the amine (-NH2) group of alanine and the phenyl (-C6H5) group of phenylalanine
C. the carboxylic acid (-COOH) groups of both amino acids
D. the amine (-NH2) groups of both amino acids
12. DNA transcription occurs in one direction only: from the 5' carbon end to the 3' carbon end.
What advantage does unidirectional transcription provide the cell?
A.
It allows gene transcription to be sequenced according to its position on the DNA
molecule.
B.
It produces functional RNA from one strand of DNA only and avoids nonsensical RNA
from the other strand.
C. It produces functional RNA from both strands of DNA.
D.
It allows RNA to be transcribed in tiny units, called Okazaki fragments, that later are
joined together.
13. Scientists classify amino acids into groups based on their chemical properties. When the
amino acid is joined into a protein, its properties determine its effect on the structure and
function of the protein.
The diagram shows the structure of two amino acids: alanine and phenylalanine. Both are
classified in the same group of amino acids.
Of the following four compounds, which is classified in the same group as alanine and
phenylalanine?
W.
X.
Y.
Z.
A. Y
B. W
C. Z
D. X
14. A protein acts as an enzyme. Which amino acid substitution would be most likely to affect its
function?
A.
Substitution of aspartic acid (an ionic amino acid) for glycine (a nonpolar amino acid) at
the active site of the enzyme.
B.
Substitution of serine for threonine (both polar amino acids) at a locus far away from the
active site of the enzyme.
C.
Substitution of aspartic acid for glutamic acid (both ionic amino acids) at the active site of
the enzyme.
D.
Substitution of glycine for alanine (both nonpolar amino acids) at the active site of the
enzyme.
15. The illustration shows four nucleotides that are linked together in a single strand of DNA.
Each nucleotide consists of three parts: a phosphate group, the sugar deoxyribose, and a nitrogen
base.
In which set of ways do regions of DNA differ from one another?
I. the specific arrangement of phosphate groups and nitrogen base around the ribose ring
II. the number of nitrogen bases bonded to the ribose ring
III. the type of nitrogen base bonded to the ribose ring
A. I and III only
B. III only
C. I only
D. II and III only
Answers
1. B
2. D
3. D
4. A
5. C
6. A
7. D
8. A
9. A
10. B
11. A
12. B
13. D
14. A
15. B
Explanations
1. Cohesion is the attractive force that water molecules exert on one another. Adhesion is the
attractive force between water molecules and a surface. Both forces help explain capillary action,
which is the ability of water molecules to rise up a narrow tube. Vascular plants, which include
nearly all the plants important to animal life, depend on capillary action to lift water from the soil
and roots to leaves, flowers, and fruits.
2. Coenzymes and cofactors do not act as enzymes by themselves. They do not have active sites
and do not bind substrates. Instead, they bind to enzymes to activate their function, typically by
slightly altering the enzyme's shape in a way that allows the substrate to bind to the active site. In
this experiment, the presence of Compound A was necessary for the reaction to occur at a fast
rate, yet neither Compound A nor the enzyme could catalyze the reaction by themselves. This
indicates that Compound A is a cofactor or coenzyme. The results of trial 6 indicate that
Compound B is an inhibitor, meaning it slows the reaction rate.
3. Polypeptides are assembled linearly. Yet polypeptides, as well as the proteins they form, take
on three-dimensional structures due to the specific order of amino acids they contain. Some
amino acids are polar, acidic, or basic. They tend to attract water and group on the outside of the
protein. Other amino acids are nonpolar. They tend to avoid water and group in the interior of the
protein. Links between sulfur atoms also provide a three-dimensional structure. In addition,
environmental factors, such as pH and temperature, can significantly affect the protein's shape.
These factors can change the charge distribution on the acidic and basic amino acids, which in
turn alter the protein's shapes.
4. The choice, "a small molecular compound that binds reversibly to the active site of the
enzyme", describes a competitive inhibitor, in which the inhibitor mimics the substrate and
competes for the binding of the active site. The choice, "a small molecular compound that binds
irreversibly to an allosteric site, changing the shape of the active site", describes a
noncompetitive inhibitor, which binds irreversibly to the enzyme at an allosteric site (a site that
is not the active site). Generally, noncompetitive inhibitors are the more consequential. By
changing the shape of the active site, they completely or nearly completely stop substrates from
binding there.
5. All enzymes function optimally across a very narrow range of pH. When the pH strays beyond
this range, the shape of the protein changes, which is a process called denaturing. Even a small
change in shape to the active site can drastically affect its ability to bind to the substrate.
6. All organisms—regardless of domain, kingdom, or phylum—make and use a tremendous
variety of carbon-based compounds. The four main classes of these compounds are
carbohydrates, proteins, lipids, and nucleic acids. Life would not be possible without carbon.
7. An enzyme is neither consumed nor produced by a reaction, so its concentration remains
constant and is shown by Line 2. The substrate is the compound that enters into the reaction, so
its concentration will decrease over time, as shown by Line 3. The substrate is converted into a
product, so the concentration of the product increases at the same rate that the substrate
concentration decreases. The product is shown by Line 1.
8. In contrast to the linear shape of a molecule of carbon dioxide, the water molecule has a bent
shape. This shape provides the highly electronegative oxygen atom with a slight negative charge,
and the two hydrogen atoms with slight positive charges. The charge distribution is significant
enough that a collection of water molecules is held together by strong hydrogen bonds, which are
intermolecular forces between the hydrogen atom of one molecule and the oxygen atom of
another molecule. The polarity of the water molecule and strong hydrogen bonding explain most
of water's other properties, among them strong cohesion and adhesion forces and high heat of
vaporization and high heat of fusion.
9. As explained by the lock and key model, a substrate binds to the enzyme because the two
compounds fit together precisely, much like a key fits into a lock. The site of the enzyme that
binds the substrate is called the active site, and it may be a very small region of the enzyme.
Nevertheless, because the shape of a protein is a result of its sequence of amino acids, a change
to even one amino acid—regardless of its location in the sequence—can affect the shape of the
active site and alter its ability to bind the substrate.
10. The molecular structure of RNA is remarkably similar to DNA, but there are several
differences. In RNA, the sugar is ribose instead of deoxyribose. Three of the four nitrogen bases
are the same, but uracil replaces thymine. RNA is also single stranded, whereas DNA is double
stranded. RNA molecules also tend to be much shorter than DNA.
11. Every amino acid consists of a carboxylic acid group (-COOH), which is acidic, and an
amino (-NH2) group, which is basic. These two groups readily react with one another to release
water and form a bond, called a peptide bond. In a protein, a series of peptide bonds joins amino
acids together in a linear arrangement.
12. Remember that a molecule of DNA consists of two strands, each with complementary base
pairs. If the one strand contains the sequence AAGCTCG in the 5' to 3' direction, then the
complementary strand contains the sequence TTCGAGC in the 3' to 5' direction. Because DNA
is read in one direction, only one of the strands is transcribed. The cell avoids transcribing the
other strand, which would not translate into a useful protein.
13. Like alanine and phenylalanine, the compound X (glycine) is nonpolar. Notice that all amino
acids have many structures in common: a carboxylic acid group (-COOH), an amino (-NH2)
group, and a central carbon atom. Amino acids differ in the third functional group attached to the
central carbon atom. When this functional group is a hydrocarbon, hydrogen atom, or other
nonpolar constituent, the amino acid is classified as nonpolar. Note that choice Z is glutamic
acid, which is an acidic amino acid. Choice W is oxalic acid, which is not an amino acid because
it lacks an amino group. Choice Y is lysine, a basic amino acid.
14. The shape of a protein is determined, in part, by the interactions of its component amino
acids with the surrounding environment. Amino acids that are polar, acidic, or basic tend to
attract water and group on the outside of the protein. Nonpolar amino acids tend to avoid water
and group in the interior of the protein. The substitution of even a single amino acid, especially
when the substitution affects the polarity of the location, can have drastic effects on the protein
shape, and thus its function. The active site of an enzyme, which is where substrates are bound,
is especially susceptible to this type of change.
15. A single strand of DNA consists of a phosphate-ribose backbone to which nitrogen bases are
attached. The specific bonds and components of the backbone are consistent throughout every
section of DNA. The only difference in the nucleotides is the identity of the nitrogen bases,
which are either adenine, guanine, cytosine, or thymine. The arrangement of these four bases
determines the information that DNA carries.