Biochem

An uncatalyzed reaction has a rate of 4.2 x 10-7 sec-1. When an enzyme is added the rate is 3.2 x 104 sec-1. Calculate the rate enhancement caused by the enzyme. 7.6 x 10^10 3.2 x 10^4 1.3 x 10-2 7.4 x 10-3 cannot be determined

7.6 x 10^10

With respect to oxygen saturation, hemoglobin is _____saturated at the pO2 of the lungs and ________saturated at the pO2 of the tissue.

>90% ; between 30 and 70%

Which allosteric effector has the greatest ability to stabilize the deoxy state of hemoglobin? BPG CO2 O2 H+ all of the above have equal ability

A

Which of the following explains the conversion of hemoglobin subunits from deoxy to oxy state? all four subunits switch simultaneously each subunit switches only upon oxygen binding to the particular subunit both α subunits simultaneously switch first followed by both β subunits both β subunits simultaneously switch first followed by both α subunits none of the above

A

A well-designed enzyme active site provides which of the following features? A. Complementarity of shape and chemical nature to the substrate(s). B. Proximity and correct orientation of substrates and catalytic groups. C. Complementarity of shape and chemical nature to the transition state. Both A and B but NOT C are correct. A, B and C are all correct.

A, B and C are all correct.

What is the N-Terminal residue of the peptide AYSDG?

Alanine

Substrates and reactive groups in an enzyme's active site must be precisely aligned in order for a productive reaction to occur. Why, then, is some conformational flexibility also a requirement for catalysis? Conformational flexibility allows for substrate access to the active site. Conformational flexibility allows for product release from the active site. Conformational flexibility facilitate access to the transition state. All of these answers are correct.

All of these answers are correct

What amino acid residue present in the specificity pocket allows trypsin to bind to peptides containing Arg or Lys? Val Asp Lys Ser His

Asp

A plot of the binding of oxygen to myoglobin as a function of pO2 gives a _____ shape; a similar plot for hemoglobin gives a _____ shape. sigmoidal; sigmoidal hyperbolic; sigmoidal hyperbolic; hyperbolic sigmoidal; hyperbolic hyperbolic; exponential

B

In a motor protein, ATP is used to convert chemical energy to electrical energy. alter the conformation of the protein. cause coiled coils to uncoil. lengthen actin filaments or microtubules.

B

Which of the following represents the longest distance traveled by a kinesin-vesicle complex? movement of a glucose filled vesicle to the membrane of a liver cell movement of a neurotransmitter vesicle down the axon of a nerve cell movement of a lipid-filled vesicle within an intestinal cell none of the above movement of a mitochondria in a cardiac cell

B

Proteins such as hemoglobin are known as _____ proteins since binding of a molecule to one site alter binding to other sites. ligand-activated allosteric induced-fit cooperative none of the above

B.

Which of the following is one way in which metal ions participate in the catalytic process? By shielding positive charge. By making water molecules more basic. By binding to substrates to orient them properly for reaction. By mediating oxidation-reduction reactions through irreversible changes in the metal's oxidation state.

By binding to substrates to orient them properly for reaction.

Collagen has an unusual amino acid composition because collagen genes are highly prone to mutations. some amino acids are unstable in the extracellular matrix. only certain residues can form a triple helix. certain residues must interact with vitamin C.

C

During the formation of microfilaments, which of the following occurs? ATP binds to F-actin F-actin polymerizes, becoming G-actin ATP hydrolysis is catalyzed by F-actin polymerization proceeds quickly at first, then slows after about ten actin monomers have polymerized none of the above

C

Kinesin is known as a processive motor because it repeatedly binds and hydrolyzes ATP. it uses a linear microtubule as a molecular track. it remains attached to its track after each reaction cycle. after the first few reaction cycles, it moves more quickly.

C

The changes in cell shape that allow crawling are mainly the result of the fraying of intermediate filaments. microtubules binding to colchicine or taxol. actin filament assembly and disassembly. GTP hydrolysis to GDP + Pi.

C

Which of the following occurs in hemoglobin upon oxygen binding? the heme Fe2+ is pulled out of the plane of the heme group the His coordinated to the heme Fe2+ is pushed away from the heme group the central cavity between the four subunits is decreased in size hemoglobin changes from the R state to the T state all of the above occur

C

A protonated side chain in an enzyme's active site can function as a base to catalyze a reaction. can donate a proton during catalysis. acts as a nucleophile during catalysis. can mimic the reactivity of a metal ion.

Can donate a proton during catalysis

Which of the following amino acids has a thiol group in its side chain?

Cys

Hemoglobin's oxygen-binding curve is sigmoidal because O2 must first be released from myoglobin. each O2-binding site in hemoglobin operates independently. hemoglobin has four O2-binding sites. O2 binding shifts hemoglobin to a high-affinity conformation.

D

The helical structure of collagen contains _____. three right-handed helices wound around each other in a right-handed triple helix three right-handed helices wound around each other in a left-handed triple helix three left-handed helices wound around each other in a left-handed triple helix three left-handed helices wound around each other in a right-handed triple helix none of the above

D

Which of the following correctly describes the sequence of events in the myosin-actin cycle? myosin release from actin, myosin binds to another actin subunit, ATP binds to myosin, stretched myosin returns to original conformation, release of Pi and ADP myosin release from actin, ATP binds to myosin, myosin binds to another actin subunit, stretched myosin returns to original conformation, release of Pi and ADP ATP binds to myosin, myosin release from actin, myosin binds to another actin subunit, stretched myosin returns to original conformation, release of Pi and ADP ATP binds to myosin, myosin release from actin, myosin binds to another actin subunit, release of Pi and ADP, stretched myosin returns to original conformation myosin release from actin, ATP binds to myosin, myosin binds to another actin subunit, release of Pi and ADP, stretched myosin returns to original conformation

D

When oxygen is bound to the heme group of myoglobin, it is coordinated between _____ and _____. F8 His; Fe3+ of heme E7 His; Fe3+ of heme F8 His; Fe2+ of heme E7 His; Fe2+ of heme none of the above

D.

At a pH above its pKa, the phenolic group of tyrosine is _______

Deprotonated and negatively charged

Which of the following fibers is correctly paired with the protein that forms the fiber? microfilaments: actin microtubule: tubulin extracellular support fibers: collagen intermediate filaments: keratin all of the above

E

While the composition of hemoglobin in adult humans is α2β2, in the developing fetus, _____ is observed α2ζ2 α2δ2 α2ε2 ζ2ε2 α2γ2

E

Which statement best describes the model of "induced fit"? Enzyme-substrate binding induces an increase in the reaction entropy. Enzyme-substrate binding induces formation of the transition state, which reduces the free energy of the reaction. Enzyme-substrate binding induces enzyme specificity. Enzyme-substrate binding induces a conformational change in the enzyme, such that the binding site better conforms to the shape of the substrate.

Enzyme-substrate binding induces a conformational change in the enzyme, such that the binding site better conforms to the shape of the substrate.

The catalytic ability of enzymes is extraordinarily sensitive to changes in their precise 3D structure, and heat easily disrupts the weak, non-covalent forces that stabilize a protein's 3D structure. Why does heat inactivate enzymes? Heat causes dissociation of essential cofactors from the active site. Heat disrupts the weak, non-covalent interactions that determine protein 3-D structure. Heat decreases the free energy change of a reaction, making it less favourable. Heat breaks the peptide bonds that link the amino acid residues together.

Heat disrupts the weak, no-covalent interactions that determine protein 3-D structure

Which of the following best describes the peptide backbone in the b-sheet? A. Highly extended B. Bent C. Rigid D. Coiled

Highly Extended

A plot of the binding of oxygen to myoglobin as a function of pO2 gives a _____shape; a similar plot for hemoglobin gives a ______ shape.

Hyperbolic; sigmoidal

How do the standard amino acids differ from one another

In the identity of the R group (side chain)

Enzymes that perform group elimination reactions to form double bonds are called: lyases. hydrolases. transferases. isomerases. ligases.

Lyases

Which of the following statements concerning standard amino acids is incorrect? A. standards amino acids are called essential amino acids B. They are all alpha-amino acids C. None of the standard amino acids are chiral D. There are three main categories of amino acids

None of the standard amino acids are chiral

A rigid planar structure consisting of about 40% double bond character is characteristic of a ________.

Peptide Bond

What term describes a small, circular molecule of DNA that can be used to transfer genetic material from one organism to another?

Plasmid

The individual hemoglobin subunits and myoglobin share similar____structure but have rather different______structure.

Secondary and tertiary; primary

The first step in the folding of disordered polypeptide chains into stable proteins is the formation of

Secondary structural elements

An enzyme's specificity refers to what substrates the enzyme acts on. whether the enzyme occurs in some or all organisms. how quickly the enzyme can catalyze a reaction. whether the enzyme's name reveals its function.

What substrates the enzymes acts on

Of the following ions, which would be most likely to participate in metal ion catalysis? Ag+ Ba2+ K+ Na+ Zn2+

Zn2+

What is the prominent type of secondary structure observed in myoglobin?

a-helices

A zymogen is a substance that inhibits an enzyme. an inactive precursor of an enzyme. an enzyme that activates another enzyme. the evolutionary ancestor of an enzyme.

an inactive precursor of an enzyme.

An enzyme that forms a covalent bond with its substrate during the course of a reaction is considered to undergo _____. acid-base catalysis covalent catalysis electrophilic catalysis metal ion catalysis none of the above

covalent catalysis

The ability for an enzyme to change its shape upon substrate binding represents the concept of _____. lock and key induced fit proximity and orientation effects covalent catalysis none of the above

induced fit

Different enzymes that catalyze the same reaction are known as _____. transferases isomerases allosteric enzymes holoenzymes isozymes

isozymes

His 57 in chymotrypsin's active-site functions only as an acid-base catalyst. only as a covalent catalyst. as both an acid-base and a covalent catalyst. as neither an acid-base nor a covalent catalyst.

only as an acid base catalyst

Heme is considered a ________

prosthetic group

Enzymes are classified according to the order in which they were discovered. the type of organism that makes them. the type of reaction they catalyze. their location in a cell.

the type of reaction they catalyze.