BIOCHEM EXAM 2
The theory that proposes a somewhat flexible enzyme conformation capable of changing shape to accommodate substrate binding and catalysis is the
Induced fit theory
Aspirin works as a fever reducer by
Inhibiting an enzyme used to synthesize the eicosanoids
An enzyme that catalyzes the reversible conversion of glucose to fructose is classified as a/an________
Isomerase
Which of the following is often true of the active site of an enzyme?
It consists of specific amino acids which not adjacent to each other
hemoglobin and glycoproteins are two examples of proteins that contain a prosthetic group. what is a prosthetic group
a nonprotein group bonded to a protein to create a functional unit
Glucokinase catalyzes the transfer of phosphate from ATP to glucose and no other substrates. This limited activity is called
absolute specificity
two cysteine residues in a protein canf orm
disulfide bonds
The names of enzymes are often derived from which of the following?
both a and b the type of reaction they catalyze the substrate on which they act
Acetylcholinesterase belongs to which group of enzymes?
hydrolases
Sucrase is an example of an enzyme that displays absolute specificity. What does the term "absolute specificity" indicate about an enzyme?
it catalyzes the reaction of only a single substrate
which of the following is often true of the active site of an enzyme
it consists of amino acids which are not adjacent to each other
what is the classification of an enzyme that catalyzes the joining of two molecules
ligase
In which type of inhibition does the inhibitor bind to a site different from the active site?
noncompetitive inhibition
aromatic amino acid most often found in the interior of a properly folded protein
nonpolar
To which class of enzymes would you assign an enzyme that carries out the dehydrogenation of its substrate?
oxidoretuctases
which of the following statements concerning protein structure is not true
secondary structure describes the peptide bonds joining the amino acids together in the protein chain
The Km of an enzyme
All of the above Is the substrate concentration that results in one half Vmax Is an indication of enzyme affinity for substrate Is a concentration term (moles/liter) Is a constant for the enzyme
Which of the following is a type of secondary structure?
All of the above α-helix β-pleated sheet Turn
When an enzyme is saturated it
All of the available enzyme molecules are bound with substrate, and the reaction rate approaches a maximum
Which of the following pairs of amino acids can form a salt bridge?
Aspartate and arginine
A negative allosteric effector is a small biological molecule that binds to specific site(s) on an enzyme to
Decrease its activity Switch the enzyme to the low affinity T state
Which of the following is true of the solubility of proteins in water?
None of the above
In which of the following do both amino acids have a nonpolar side chain
Phenylalanine and alanine
Which statement is incorrect about prions?
PrPc is the "infectious" particle
which of the following is incorrect about prions
PrPc is the "infectious" particle
If the following section of a polypeptide folds into an α-helix, to which other amino acid(s) is the leucine (leu) residue hydrogen bonded? ala-ser-val-asp-glu-leu-gly-glu-met-asp-arg-ile
Ser & asp
The quaternary structure of proteins is/are defined by
The interaction between protein subunits
What is an apoenzyme?
The protein only part of an enzyme
For enzyme-catalyzed reactions, what happens as the concentration of the substrate is increased
The rate increases until it reaches a maximum, constant value
Which of the following is true of the atoms in the peptide bond of a protein
They are all in same plane
Which of the following is true of isozymes?
They are different forms of the same enzyme found in different tissues
Which of the following is true of enzymes?
They decrease the activation energy of the chemical reactions
which of the following is true of enzymes
They lower the activation energy of a chemical reaction
Aspartate transaminase belongs to which group of enzymes?
Transferases
the Km is
all of the above a constant equal to the substrate concentration when the rxn rate is half its max value gives an approximation of enzyme affinity for its substrate
an increase in the concentration of the enzyme LDH can be used to detect
all of the above liver disease heart attack leukemia
which of the folowing can denature a protein
all of the above: heat significant changes in pH detergents mechanical agitation
In living cells, nucleotides serve as
all the above (precursors for nucleic acid synthesis, enzyme cofactors, intracellular signals, carriers of metabolic energy)
A small biological molecule that binds to a specific site on an enzyme and once bound increases or decreases the activity of the enzyme is a
allosteric effector
what are two most common types of secondary structures in proteins
alpha helices and b-pleated sheets
a positive allosteric effector is a small biological molecule that binds to specific sites on an enzyme to
b and c increase its activity switch the enzyme to high affinity R state
Under physiological conditions allosteric enzymes are controlled by
binding a positive or negative regulator at a specific allosteric site
Which protein contains hydroxylysine and hydroxyproline?
collagen
which structural protein is found in bone, tendon, and skin
collagen
In which type of inhibition is it possible to restore enzyme activity by adding additional substrate?
competitive inhibition
which of the following best describes the type of bonding between an irreversible inhibitor and an enzyme
covalent
what is the water-soluble vitamin from which NAD+ is made
niacin
which of the following pairs of elements are present in proteins but not most carbohydrates
nitrogen and sulfur
aromatic amino acid most often found on the exterior of a properly folded protein
polar
Which level of protein structure is not affected by denaturation?
primary
compareed to an uncatalyzed rxn, an enzyme catalyzed rxn
produces a single product
Proteolytic digestive enzymes are often produced in an inactive form. What is the name that refers to the inactive form of an enzyme?
proenzyme
amino acid often found in a turn or a bend
proline
what is the term for a molecule that is similar in structure and charge distribution to the substrate in an enzyme catalyzed reaction
reversible inhibitor
What adjective describes an enzyme that is able to catalyze a reaction of D-glucose, but not L-glucose?
sterospecific
what adjective describes an enzyme that is able to catalyze a reaction of D-glucose but not L glucose
sterospecific
during an enzyme catalyzed reaction, _________ are converted to __________
substrate products
amino acids are the building blocks of proteins. which of the following statments concerning amino acids is false?
the amino acids that make up human proteins are only the essential amino acids
Tuftsin is a tetrapeptide that stimulates and promotes the destruction of tumor cells. its primary structure is Thr-Lys-Pro-Arg. which of the following is not a valid interpretation of its primary structure
the amino group of arginine is not joined to any other amino acid
which of the following statements concerning enzymes is false?
the reactant in an enzyme-catalyzed reaction is called a cofactor
amino acid containing an aromatic ring in the side chain
tyrosine
which vitamin is required for the hydroxylation of proline and lysine amino acids in collagen
vitamin C
Which vitamin is required for the hydroxylation of proline and lysine amino acids in collagen
vitamin c
How many different amino acids are commonly found in the proteins?
20
in the a-helical structure of proteins, how many amino acid residues are there in one complete full turn of the helix
3.6
How many polypeptide chains make up hemoglobin?
4
Enzymes are classified into how many different major groups
6
Most globular proteins have
A combination of all of these Only α-helical structures Only non-regular non repeating structure Predominantly β-sheet structure
Which of the following contributes to the stabilization of protein tertiary structure?
All of the above Hydrophobic interactions between amino acid side chains Hydrogen bonds between amino acid side chains Salt bridges between amino acid side chains Disulfide bonds between appropriately positioned cysteine residues
An allosteric enzyme in its relaxed (R) state
All of the above Has high affinity for its substrate Has a low Km for its substrate Is very active
According to the induced-fit model of enzyme action, the enzyme active site
Adjusts the shape of the substrate to fit the transition state
What was a commonly heard explanation when the enemy aircraft overflew the trenches in World War I?
"Oh Poop!"
Which of the following is commonly associated with reversible covalent modification?
Both a & b Phosphorylation Dephosphorylation
Enzymes are usually named by indicating
Both a & b The type of reaction they catalyze The substrate on which they act
Hemoglobin delivers more oxygen to metabolically active tissues because metabolically active tissues directly produce
CO2
Hemoglobin delivers more oxygen to metabolically active tissues because metabolically active tissues produce
CO2
Which of the following correctly describes the relationship between the primary structure of a protein and protein function?
Changing one amino acid may or may not affect protein function
What is the term used when the product of the reaction acts as a competitive toward the enzyme that produced it?
Feedback inhibition
Hexokinase catalyzes the transfer of phosphate from ATP to glucose, mannose, or fructose. This limited activity is called
Group specificity
Secondary structure is stabilized by which of the following?
Hydrogen bonding between the carbonyl oxygen of the peptide bond and the amido hydrogen of the peptide bond
Which of the following is true of a protein at a pH below its isoelectric point
It will have a positive charge
To which class of enzymes would you assign an enzyme that carries out the addition of one substrate across a double bond in a second substrate
Lyases
Hemoglobin is considered an allosteric protein because
a & b It is a multimeric (multisubunit) protein The oxygen binding kinetics is sigmoidal
proteins are made of _________ which contain__________-
a amino acids a carbon and an amine
most globular protiens contain
a combination of all of these b-sheets a-helices regular non repeating structures
ymogens are activated when
a hydrolase removes one or more small peptides
which of the following describes how an enzyme can affect the transition state in an enzyme catalyzed reaction
all of the above by modifying the local pH by accepting or donating H ions by placing stress on a bond in the substrate, making it easier to break by bringing two reactants together in close proximity and in a suitable orientation for reaction
the formation of a peptide bond is best described as which of the following
dehydration reaction
Heavy metals denature proteins by
disrupting salt bridges
what is one of the first steps in an enzyme catalyzed reaction?
formation of an enzyme substrate complex
which of the following amino acids are found in large amounts in collagen
glycine and proline
amino acids or their components are not necessary for the biosynthesis of which of the following
glycogen
Which of the α-amino acids does not contain a chiral carbon?
glysine
Which of the following denaturing agents affects disulfide bonds?
heavy metals
What type of attractive force is responsible for maintaining the secondary structure of a protein?
hydrogen bonds between carbonyl and amine groups of peptide bonds