Which one of the following statements about enzymes and enzyme-catalyzed
chemical reactions is CORRECT?
a. Spontaneous chemical reactions are relatively fast.
b.Enzymes are always made of protein.
c. Enzymes are typically promiscuous, e.g, an enzyme that catalyzes a reaction
involving a specific sugar can typically catalyze reactions with many other
types of sugars.
d. Enzymes often change shape when they bind their substrate(s). - ANSWER
d. Enzymes often change shape when they bind their substrate(s).
Which one of the following statements concerning enzyme regulation is
FALSE?
a. The allosteric site is never the same as the active site.
b. ATP can be a substrate at the active site of an enzyme or it can bind to the
allosteric site as an inhibitor.
c. Most enzymes regulated by allosteric mechanisms contain one or more
polypeptides (subunits).
d. Many metabolic pathways are regulated by the binding of their end product to
an enzyme that acts in an early step of the pathway, a type of feedback
inhibition. - ANSWER a. The allosteric site is never the same as the active
site.
Which one of the following statements concerning polypeptide(s) or protein(s)
is INCORRECT?
,a. A protein is made up of one or more polypeptides.
b. The primary structure of a polypeptide determines where (along the length of
the polypeptide) secondary structures such as alpha-helices or beta-sheets can
form.
c. Polypeptide synthesis involves addition of amino acid monomers only at the
C- (COOH-) terminus of the polypeptide.
d. The initial, most rapid, folding reactions of a linear polypeptide is driven by
hydrophobic collapse where the nonpolar side chains are more likely to end up
in the interior region of the folded polypeptide. - ANSWER d. The initial, most
rapid, folding reactions of a linear polypeptide is driven by hydrophobic
collapse where the nonpolar side chains are more likely to end up in the interior
region of the folded polypeptide.
Which one of the following statements concerning protein folding in cells is
INCORRECT?
a. The chaperone HSP70 can bind to a nascent polypeptide.
b. Ubiquitin ligase-mediated attachment of ubiquitin to a newly synthesized
polypeptide leads to hydrolysis (breakdown, degradation) of that polypeptide by
the proteasome.
c. The chaperone HSP70 has an ATP-dependent mechanism for delaying the
folding of a newly synthesized polypeptide.
d. Protein folding in cells is highly efficient with more than 95% of all newly
synthesized polypeptides folding into their native, fully functional shapes. -
ANSWER d. Protein folding in cells is highly efficient with more than 95% of
all newly synthesized polypeptides folding into their native, fully functional
shapes.
Which one of the following statements concerning the regulation of enzyme
activity is FALSE?
,a. The enzyme activity of some proteins is regulated by the noncovalent binding
of other proteins, i.e., by protein-protein interaction.
b. A phosphorylated protein (polypeptide) has a phosphate molecule covalently
attached to the side chain of an amino acid (for example, serine) in the
polypeptide.
c. Covalent modification of an enzyme protein by protein kinase-mediated
phosphorylation can cause increases or decreases in catalytic activity,
depending on the protein kinase substrate.
d. A positively-acting allosteric ligand typically remains on the allosteric site of
an enzyme for an extended period of time, thereby providing a kind of memory
and sustaining an active enzyme state. - ANSWER d. A positively-acting
allosteric ligand typically remains on the allosteric site of an enzyme for an
extended period of time, thereby providing a kind of memory and sustaining an
active enzyme state.
Which one of the following statements concerning a plasma membrane (cell
membrane) is CORRECT?
a. Phospholipids move very rapidly by themselves from one layer (leaflet) of
the bilayer to the other.
b. Plasma membrane carbohydrates (polysaccharides) are mostly covalently
attached to lipids, with the combined molecule called a glycolipid.
c. The plasma membrane of bearberry (an arctic tundra plant) has more
unsaturated fatty acids (fatty acids with double bonds) in its phospholipids than
does that of guava (a tropical plant).
d. Most transmembrane proteins move from one surface of the plasma
membrane to the other. - ANSWER c. The plasma membrane of bearberry (an
arctic tundra plant) has more unsaturated fatty acids (fatty acids with double
bonds) in its phospholipids than does that of guava (a tropical plant).
Which one of the following statements regarding transport of solute molecules
across the plasma membrane is INCORRECT?
, a. Movement of oxygen molecules across the plasma membrane does not
require assistance by membrane proteins.
b. Rapid diffusion of water across a plasma membrane requires assistance by
membrane proteins.
c. The sodium-potassium pump actively transports sodium ions (Na+) and
potassium ions (K+) in equal numbers across the plasma membrane of animal
cells.
d. Animal cells use transport proteins to maintain a potassium ion gradient
across their plasma membrane, with higher concentration of K+ inside the cell
than outside. - ANSWER c. The sodium-potassium pump actively transports
sodium ions (Na+) and potassium ions (K+) in equal numbers across the plasma
membrane of animal cells.
Which one of the following statements about ATPases such as HSP70 is
INCORRECT?
a. ATPases are highly specific for ATP as a substrate over the other three
ribonucleotides: CTP, GTP, and UTP.
b. The main function of ATPases in cells is the hydrolysis of ATP to ADP and
inorganic phosphate (Pi).
c. A protein enzyme that catalyzes ATP hydrolysis changes shape when it binds
the ATP substrate molecule.
d. The active site of an ATPase provides a special chemical environment that
increases the probability of adding a water molecule between the last two
phosphates of ATP, thus increasing the rate of its hydrolysis. - ANSWER b.
The main function of ATPases in cells is the hydrolysis of ATP to ADP and
inorganic phosphate (Pi).
Which one of the following statements concerning membrane proteins is
INCORRECT?
chemical reactions is CORRECT?
a. Spontaneous chemical reactions are relatively fast.
b.Enzymes are always made of protein.
c. Enzymes are typically promiscuous, e.g, an enzyme that catalyzes a reaction
involving a specific sugar can typically catalyze reactions with many other
types of sugars.
d. Enzymes often change shape when they bind their substrate(s). - ANSWER
d. Enzymes often change shape when they bind their substrate(s).
Which one of the following statements concerning enzyme regulation is
FALSE?
a. The allosteric site is never the same as the active site.
b. ATP can be a substrate at the active site of an enzyme or it can bind to the
allosteric site as an inhibitor.
c. Most enzymes regulated by allosteric mechanisms contain one or more
polypeptides (subunits).
d. Many metabolic pathways are regulated by the binding of their end product to
an enzyme that acts in an early step of the pathway, a type of feedback
inhibition. - ANSWER a. The allosteric site is never the same as the active
site.
Which one of the following statements concerning polypeptide(s) or protein(s)
is INCORRECT?
,a. A protein is made up of one or more polypeptides.
b. The primary structure of a polypeptide determines where (along the length of
the polypeptide) secondary structures such as alpha-helices or beta-sheets can
form.
c. Polypeptide synthesis involves addition of amino acid monomers only at the
C- (COOH-) terminus of the polypeptide.
d. The initial, most rapid, folding reactions of a linear polypeptide is driven by
hydrophobic collapse where the nonpolar side chains are more likely to end up
in the interior region of the folded polypeptide. - ANSWER d. The initial, most
rapid, folding reactions of a linear polypeptide is driven by hydrophobic
collapse where the nonpolar side chains are more likely to end up in the interior
region of the folded polypeptide.
Which one of the following statements concerning protein folding in cells is
INCORRECT?
a. The chaperone HSP70 can bind to a nascent polypeptide.
b. Ubiquitin ligase-mediated attachment of ubiquitin to a newly synthesized
polypeptide leads to hydrolysis (breakdown, degradation) of that polypeptide by
the proteasome.
c. The chaperone HSP70 has an ATP-dependent mechanism for delaying the
folding of a newly synthesized polypeptide.
d. Protein folding in cells is highly efficient with more than 95% of all newly
synthesized polypeptides folding into their native, fully functional shapes. -
ANSWER d. Protein folding in cells is highly efficient with more than 95% of
all newly synthesized polypeptides folding into their native, fully functional
shapes.
Which one of the following statements concerning the regulation of enzyme
activity is FALSE?
,a. The enzyme activity of some proteins is regulated by the noncovalent binding
of other proteins, i.e., by protein-protein interaction.
b. A phosphorylated protein (polypeptide) has a phosphate molecule covalently
attached to the side chain of an amino acid (for example, serine) in the
polypeptide.
c. Covalent modification of an enzyme protein by protein kinase-mediated
phosphorylation can cause increases or decreases in catalytic activity,
depending on the protein kinase substrate.
d. A positively-acting allosteric ligand typically remains on the allosteric site of
an enzyme for an extended period of time, thereby providing a kind of memory
and sustaining an active enzyme state. - ANSWER d. A positively-acting
allosteric ligand typically remains on the allosteric site of an enzyme for an
extended period of time, thereby providing a kind of memory and sustaining an
active enzyme state.
Which one of the following statements concerning a plasma membrane (cell
membrane) is CORRECT?
a. Phospholipids move very rapidly by themselves from one layer (leaflet) of
the bilayer to the other.
b. Plasma membrane carbohydrates (polysaccharides) are mostly covalently
attached to lipids, with the combined molecule called a glycolipid.
c. The plasma membrane of bearberry (an arctic tundra plant) has more
unsaturated fatty acids (fatty acids with double bonds) in its phospholipids than
does that of guava (a tropical plant).
d. Most transmembrane proteins move from one surface of the plasma
membrane to the other. - ANSWER c. The plasma membrane of bearberry (an
arctic tundra plant) has more unsaturated fatty acids (fatty acids with double
bonds) in its phospholipids than does that of guava (a tropical plant).
Which one of the following statements regarding transport of solute molecules
across the plasma membrane is INCORRECT?
, a. Movement of oxygen molecules across the plasma membrane does not
require assistance by membrane proteins.
b. Rapid diffusion of water across a plasma membrane requires assistance by
membrane proteins.
c. The sodium-potassium pump actively transports sodium ions (Na+) and
potassium ions (K+) in equal numbers across the plasma membrane of animal
cells.
d. Animal cells use transport proteins to maintain a potassium ion gradient
across their plasma membrane, with higher concentration of K+ inside the cell
than outside. - ANSWER c. The sodium-potassium pump actively transports
sodium ions (Na+) and potassium ions (K+) in equal numbers across the plasma
membrane of animal cells.
Which one of the following statements about ATPases such as HSP70 is
INCORRECT?
a. ATPases are highly specific for ATP as a substrate over the other three
ribonucleotides: CTP, GTP, and UTP.
b. The main function of ATPases in cells is the hydrolysis of ATP to ADP and
inorganic phosphate (Pi).
c. A protein enzyme that catalyzes ATP hydrolysis changes shape when it binds
the ATP substrate molecule.
d. The active site of an ATPase provides a special chemical environment that
increases the probability of adding a water molecule between the last two
phosphates of ATP, thus increasing the rate of its hydrolysis. - ANSWER b.
The main function of ATPases in cells is the hydrolysis of ATP to ADP and
inorganic phosphate (Pi).
Which one of the following statements concerning membrane proteins is
INCORRECT?
