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