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In this collection there will be a bunch of questions to help students review.

This collection will be useful for all chemistry, medical, pharmacy students

Study Set Content:
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Questions with Answers- Proteins & Enzymes 

A.

 

A peptide with 12 amino acids has the following amino acid composition: 
2 Met, 1 Tyr, 1 Trp, 2 Glu, 1 Lys, 1 Arg, 1 Thr, 1 Asn, 1 Ile, 1 Cys 

 

Reaction of the intact peptide with fluorodinitrobenzene followed by acid hydrolysis creates a 
derivative of Ile.    
A specific cleavage of the intact peptide produces fragments with the following sequences: 
 

 

 

  Glu-Cys-Asn-Met-Lys 
  Met-Glu-Thr-Arg-Trp 
 

 

Ile-Tyr                                                                                       (Questions 1-5) 

 
1._____         Which reagent was used for the specific cleavage?  

a)

 

chymotrypsin 

b)

 

trypsin 

c)

 

V8 protease 

d)

 

cyanogen bromide 

 
2._____         Which amino acids would be released when the intact peptide was treated first with           
                        V8 protease followed by treatment with cyanogen bromide? 
                        a)         Glu and Met 
                        

b)

         

Glu and Lys 

                        c)         Met and Lys 
                        d)         Glu, Met, and Lys 
 
3._____ 

Which treatment would result in the release of Lys and Arg from the intact peptide? 

                        a)        trypsin 
                        b)        trypsin followed by dansyl chloride 
                        

c)        trypsin followed by carboxypeptidase 

                        d)        trypsin followed by mild acid 
                          
4._____ 

If this intact peptide is sequenced using the Edman degradation, which step will  

                         be part of the procedure? 

a) 

The Edman reagent will react with all 12 amino acids simultaneously. 

 

  b)         Lithium borohydride will react with an 

α

-carboxyl group. 

 

 

c) 

Phenylisothiocyanate will react with an 

α

-amino group. 

d) 

Strong acid will be used to cleave off one modified amino acid. 

 

5._____ 

If this peptide is normally part of a multimeric protein composed of four identical  

                        subunits, what procedure might be needed prior to performing the Edman  
                        degradation?  

a)

 

The four subunits should be separated and sequenced individually. 

b)

 

Two specific cleavages should be done to create two sets of fragments. 

c)

 

Peptide bonds should be broken using hydrazine. 

d)

 

Disulfide bonds should be reduced with mercaptoethanol. 

 
______________________________________________________________________________ 

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B.

 

A peptide has the following amino acid composition: 

2 Met, 2 Phe, 2 Glu, 1 Arg, 1 Lys, 1 Val, 1 Leu, 1 Gly, 1 Ser 

 

         Reaction of the intact peptide with dansyl chloride followed by acid hydrolysis creates a       
         derivative of Met. 
 
         A specific cleavage of the intact peptide produces fragments with the following sequences: 
 

 

 

 

 

Fragment A:    Glu-Gly-Lys-Phe    

                        Fragment B:    Met-Ser-Leu-Arg    
 

 

Fragment C:    Met-Val-Glu-Phe                   (Questions 6-10) 

 
 
6._____         Which reagent was used for the specific cleavage? 
                        a)         cyanogen bromide  
                        b)         V8 protease 

                        c)         chymotrypsin 

                        d)         trypsin 
 
7._____ 

Which reagent would break only one peptide bond in the intact peptide? 

                        a)         cyanogen bromide  
                        b)         V8 protease 
                        c)         chymotrypsin 
                        

d)         trypsin 

 
8._____         Which amino acid would be released if the intact peptide was treated with a  
                       combination of trypsin and chymotrypsin? 
                        a)         Lys 

                        b)         Phe 

                        c)         Glu 
                        d)         Met 
                          
9._____ 

What information do these result give about the sequence of the peptide? 

a)        The sequence is: Met-Val-Glu-Phe-Glu-Gly-Lys-Phe-Met-Ser-Leu-Arg 

                        b)        The sequence is: Met-Ser-Leu-Arg-Met-Val-Glu-Phe-Glu-Gly-Lys-Phe 
                        c)        The sequence is: Met-Val-Glu-Phe-Met-Ser-Leu-Arg-Glu-Gly-Lys-Phe 

d)        The sequence is: Met-Ser-Leu-Arg-Glu-Gly-Lys-Phe-Met Val-Glu-Phe 
 

10._____ 

 This peptide is one polypeptide chain of a multimeric protein that contains two              

                         non-identical subunits. What problem might be seen when analyzing the primary  
                         structure of the protein if the subunits were not separated? 
 

a) Fluorodinitrobenzene 

might 

react 

with two different amino acids. 

 b) 

Carboxypeptidase might not react with the C-terminals.  

                         c) 

Mercaptoethanol might not reduce disulfide bonds. 

 d) 

Lithium borohydride might cleave peptide bonds randomly. 

_____________________________________________________________________________ 

 
 

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C.

 

Protein A is an 

α

-keratin while Protein B is a transport protein. (Questions 11-15) 

 

 

11._____ 

Which characteristic could be shared by Protein A and Protein B? 
a) 

Both could be fibrous proteins containing multiple polypeptide chains. 

  b) 

Both 

could 

be 

globular 

proteins with similar primary structures. 

 

 

c) 

Both could contain disulfide bridges linking methionine residues. 

 

 

d) 

Both could contain hydrogen bonds between peptide bond atoms. 

 
12._____ 

When comparing Protein A to a 

β

-keratin 

  a) 

 

the 

α

-keratin has a parallel structure while the 

β

-keratin has an antiparallel  

                                     structure.                                 
                        

b)          the 

α

-keratin has a compact structure while the 

β

-keratin has a more  

                                     extended structure. 

 

 

c) 

 both have similar secondary structures that are low-energy states for the  

                                     proteins.   
 

 

d)          both contain hydroxyproline which functions as a prosthetic group. 

  
13._____ 

When comparing Protein B to collagen, 

a) 

both are stabilized by van der Waals interactions. 

b)         both are stabilized by extensive regions of left-handed coils. 
c) 

both contain regions of random secondary structures. 

d) both 

contain 

α

-helices as well as 

β

-pleated sheets. 

 
14._____ 

Which interaction is likely to occur in Protein B? 

 

a) 

A hydrophobic interaction could form between the R-groups of Val and  

                                    Leu. 

                         b) 

A hydrogen bond could form between the R-groups of Ser and Phe. 

 c) 

A salt bridge could form between the R-groups of Arg and His. 

                         d) 

An ionic bond could form between the R-groups of Gln and Trp. 

 

15._____          When comparing Protein A to Protein B,  
                        a)         both could be denatured by using heat to break amide bonds. 
                        b)         both could have primary structures that form with the help of chaperones. 

                        c)         both have conformations stabilized by numerous non-covalent bonds. 

                        d)         both contain the same proportions of hydrophilic and hydrophobic R-                     
                                    groups. 
 

 

 
 
 
 
 
 
 
 

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D.

 

Protein A is a structural component while Protein B is an enzyme. The secondary structures 
of both proteins are studied. (Questions 16-19) 

 

 

16._____ 

Which could be characteristics of Protein A and Protein B? 

 

 

a) 

Protein A could have a low energy conformation while Protein B could  

                                    have a high energy conformation. 
                        b) 

Protein A could be a globular protein while Protein B could be a fibrous  

                                    protein. 

c) 

Protein A could contain mainly 

α

-helix while Protein B could contain 

equal amounts of 

α

-helix and 

β

-sheet. 

 

 

d) 

Protein A could be a type of collagen while Protein B could be a type of  

                                     keratin. 
 
17._____ 

Which could be found within the structure of Protein B? 

 

                        

 

 

a) 

A disulfide bond could form between two prosthetic groups. 

 

 

b) 

A salt bridge could form between two chaperones. 

                        c) 

Protein B could contain areas of random secondary structure stabilized by 
van der Waals forces.  

                        

d) 

Protein B could contain areas of repeating secondary structure stabilized 
by hydrogen bonds. 

 
18._____ 

Which is a characteristic of both an 

α

-helix and a 

β

-pleated sheet? 

a) 

Both can be anti-parallel structures. 

b) 

Both form interactions involving the oxygens of peptide bonds. 

c)         Both are found only within multimeric proteins. 
d) 

Both are denatured when heat breaks peptide bonds. 

 
19._____ 

Which is a difference between an 

α

-helix and a 

β

-pleated sheet? 

 

 

a) 

An 

α

-helix is a right-handed structure containing disulfide bonds while a                 

                                    

β

-pleated sheet is a left-handed structure containing ionic bonds. 

b) An 

α

-helix has a relatively extended spiral shape while a 

β

-pleated sheet has 

a relatively compact zig-zag shape. 

c) An 

α

-helix has non-covalent bonds between amino acids near each other 

in the sequence while a 

β

-pleated sheet has non-covalent bonds between 

amino acids far apart in the sequence. 

  d) 

An 

α

-helix contains mainly amino acids with polar R-groups while a 

β

                                    pleated sheet contains mainly amino acids with non-polar R-groups. 
_____________________________________________________________________________ 
 
 
 
 
 
 
 
 
 

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E.      Two proteins, myoglobin and hemoglobin, are compared. (Questions 20-30) 
 
 
20._____ 

Which characteristics are shared by these two proteins? 

 

 

a) 

They both are globular proteins containing the common amino acids,  

                                     porphyrin, and iron. 

 

 

b) 

They both have closely related primary, secondary, tertiary, and  

                                     quaternary structures. 
 

 

c) 

They both are composed of multiple subunits each of which contains a  

                                     heme prosthetic group. 

 

 

                        d) 

They both have similar molecular weights and bind one oxygen molecule  

                                     per protein molecule. 
 
21._____ 

Which is a property of protein tertiary structure? 
a) 

Tertiary structures usually contain hydrocarbon R-groups in the interior of 
the protein where they can form hydrogen bonds. 

b) 

Tertiary structures usually contain hydroxyl R-groups on the exterior of 
the protein where they can favorably interact with water. 

c) 

A protein’s tertiary structure can be predicted if the amino acid sequence is 
known by performing the Edman degradation. 

d) 

A protein’s tertiary structure can be maintained by covalent salt bridges and 
non-covalent disulfide bridges.  

 
22._____ 

Which is a characteristic of protein quaternary structure?   

 

a) 

A protein composed of identical subunits has quaternary structure but not 
tertiary structure. 

                         b)        A protein composed of non-identical subunits contains two polypeptide 

chains with opposite charges. 

                         c) 

The quaternary structure of a multimeric protein always includes covalent 
crosslinks between the subunits. 

 

d) 

The quaternary structure of a multimeric protein always depends upon the 
primary structure of the subunits. 

 
23._____ 

Which is a property of tertiary structure and quaternary structure? 
a) 

Both structures are stabilized by numerous covalent hydrophobic and 
hydrophilic interactions. 

b) 

Both structures have specific shapes that depend upon the amino acid 
sequence of the protein.   

c) 

Both structures form so that polar amino acid R-groups are found mainly in 
the interior of the protein.  

d) 

Both structures must contain multiple 

α

-helices and 

β

-pleated sheets 

connected by turns. 

 
 
 
 
 
 

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24._____ 

Which property is shared by both myoglobin and hemoglobin? 

 

a) 

Both are saturated with oxygen at low oxygen concentrations.  

 

b) 

Both display cooperative binding when transporting oxygen. 

 

c) 

Both contain strands of 

β

-pleated sheet with a zig-zag shape.  

                         

d) 

Both contain segments of 

α

-helix with a spiral shape. 

 
25._____ 

Which occurs when a hemoglobin molecule binds oxygen?  

 

a) 

Oxygen molecules in the lungs bind irreversibly to the protein’s heme 
groups. 

                         

b) 

The second oxygen molecule binds more easily than the first oxygen 
molecule. 

 c) 

The 

α

 subunits bind oxygen while the 

β

 subunits control cooperativity. 

 

d) 

Ionic bonds form between subunits which changes the quaternary structure. 

 

26._____ 

Which change occurs when a hemoglobin subunit binds oxygen? 

 

a) 

A histidine residue changes position within the subunit. 

 

b) 

An iron atom is removed from a porphyrin group. 

 

c) 

The oxygen binds to amino acids within a segment of 

α

-helix. 

                         d)        The oxygen causes a covalent crosslink to form within the subunit.  
 
27._____ 

Which occurs when a hemoglobin molecule binds oxygen in the lungs?  

 

a) 

Each iron-porphyrin group can reversibly bind four oxygen molecules. 

 

b) 

Salt bridges between subunits break as the first oxygen binds. 

                         c) 

The first oxygen molecule binds more easily than the last oxygen molecule. 

 

d) 

Cooperative binding of oxygen causes the four subunits to dissociate.  

 
28. _____          When myoglobin is denatured using heat 
                          a)        its amino acid composition will change.   
                          b)        its amino acid sequence will change. 

                          c)        its tertiary structure will change. 

                          d)        its C-terminal will change. 
 
29._____ 

When hemoglobin is treated with urea and 

β

-mercaptoethanol 

                          a)        its molecular weight will be unchanged. 
                          b)        its quaternary structure will be unchanged. 
                          

c)        its primary structure will be unchanged.   

                          d)        its conformation will be unchanged. 
 
30._____          Protein Z functions as an oxygen transport protein, and shares 60% of its primary 

structure with myoglobin while the other 40% is different. Which is likely to be a 
characteristic of Protein Z? 

                         a)        It probably contains one heme group that can bond two oxygen molecules. 
                         b)        It probably contains both 

α

 subunits and 

β

 subunits. 

                         c)        It probably could function even if a mutation changes one of the amino 

acids in part of the primary structure that is shared with myoglobin. 

                         

d)        It probably could function even if a mutation changes one of the amino 

acids in part of the primary structure that is different from myoglobin. 

_______________________________________________________________________________ 

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F.       Enzyme X and Enzyme Y are both involved in monosaccharide metabolism. Enzyme X uses  
          glucose as a substrate while Enzyme Y uses fructose as a substrate.  At pH=7.0, Enzyme X    
          has a Vmax of 10 

μ

M/s while Enzyme Y has a Vmax of 20 

μ

M/s. Both enzymes have a K

M

   

          of  3.0 mM for their respective substrates.(Questions 31-37) 
 

 

 

 

 

 

 

 

31._____ 

Which aspects of its reaction will be changed by Enzyme Y? 

 

 

 a) 

the activation energy of the reaction and the energy of the product 

 b) 

the rate of the reaction and the energy of the transition state 

 c) 

the equilibrium position of the reaction and the energy of the substrate 

 d) 

the reversibility of the reaction and the energy of the active site 

 

32._____           When its reaction is carried out at pH = 2.0, the Vmax of Enzyme X is 1.0 

μ

M/s 

because 

 

a) 

the enzyme is inhibited by its product at low pH. 

 

b) 

the enzyme is saturated with substrate at low pH. 

 

c) 

the enzyme is able to stabilize the transition state at low pH. 

 

d) 

the enzyme is partially denatured as R-groups protonate at low pH. 

 
33._____ 

When the reaction is carried out at pH = 7.0 and the substrate concentration is 
equal to the K

M

 value 

 

a) 

X will produce more product than Y. 

 

b) 

Y will produce more product than X. 

 

c) 

X and Y will produce the same amount of product. 

 

d) 

X and Y will both work at their Vmax value. 

 
34._____ 

Enzyme Y can also use the monosaccharide galactose as a substrate with a K

M

 of 

8.0 mM. Which will be a characteristic of Y as it binds galactose compared to its 
binding to fructose? 

 

a) 

Y will form more non-covalent bonds with galactose. 

 

b) 

Y will form more covalent bonds with galactose. 

 

c) 

Y will have an active site that is less complementary to galactose. 

 

d) 

Y will undergo a greater conformational change as it binds galactose. 

 
35._____            Which interaction is likely to occur as Enzyme X carries out its reaction? 
                         

a)       A hydrogen bond could form between a serine R-group in the active site  

                                    and a carbonyl group in the transition state.  

b)

 

An ionic bond could form between a glutamate R-group in the active site and 
a carboxyl group in the substrate. 

c)

 

A hydrophobic interaction could form between an asparagine R-group in the 
active site and a methyl group in the substrate. 

d)

 

A hydrogen bond could form between a valine R-group in the active site and 
a hydroxyl group in the transition state. 

 
 
 
 
 

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36._____ 

Which kinetic property would Enzyme X display as it binds its normal substrate 
and catalyzes its reaction? 

 

a) 

It could have an initial velocity independent of [S] when [S] < K

M

 

b) 

It could have a K

M

 value that decreases as [S] decreases from 3.0 mM to  

                                     0.3 mM. 
 

c) 

It could double the rate of its reaction as [S] increases from 3.0 mM to      

                                    30 mM. 

 

d) 

It could have a Vmax value that is dependent on [S] when [S] < K

M

 
37.______ 

Enzyme Y is allosterically inhibited by ribose and also inhibited by covalent 
modification with phosphate. Which is a characteristic of its regulation? 

                         a) 

Y can covalently bind both ribose and phosphate to specific amino acids 
within the protein. 

 

b) 

Y can establish an equilibrium with either ribose or phosphate to reduce    

                                     the activity of the enzyme. 
 

c) 

Y can bind both ribose and phosphate to a regulatory subunit with the help 
of extra enzymes. 

                         

d) 

Y can undergo reversible conformational changes when either ribose or  

                                     phosphate binds to the enzyme. 

_____________________________________________________________________________ 
 

G.

 

The reactions of two enzymes, Enzyme A and Enzyme B, are studied at pH = 7.0. Both 
enzymes produce glucose and have the same V

max

. Enzyme A has a K

of 2.0 mM while 

Enzyme B has a K

of 5.0 mM. (Questions 38-44) 

 
 
38. ______      Which characteristic will be shared by these two enzymes? 
                        a)         Both will increase the rate of their reaction by increasing the energy of the  
                                    substrate molecules. 

b)

 

Both will properly orient the substrate for their reaction by forming   

            covalent bonds with the substrate. 

c)

 

Both will decrease the activation energy of their reaction by being    

           complementary to the transition state. 

d)

 

Both will shift the equilibrium of their reaction by lowering the energy  

           level of the product.  

 
39. ______       Which property will Enzyme A likely have in common with most other  
                          enzymes? 

                          a)        It can bind the substrate reversibly using specific amino acids. 

b)

 

 It can contain a dozen active sites each of which can bind a substrate  

            molecule. 

                          c)        It can undergo a small change in primary structure as the substrate binds.  

        d)        It can be required in stoichiometric amounts in order to bind the correct  
                   substrate.  

    
 
 

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40. ______       When Enzyme B carries out its reaction with a substrate concentration of 5.0   
                         mM, the reaction velocity gradually decreases 5 minutes after the reaction starts.   
                         What could cause this change in reaction rate? 
                          a)        Enzyme B catalyzes an irreversible reaction. 
                          b)        Enzyme B becomes saturated with substrate. 

                          c)        Enzyme B is inhibited by its product. 

                          d)        Enzyme B is working at its V

max 

value. 

 
41. ______       Which will occur when Enzyme A and Enzyme B both carry out their reaction at  
                          pH = 7.0? 

                          a)        Enzyme A will produce more glucose than Enzyme B when [S] = 5.0 mM. 

                          b)        Enzyme B will produce more glucose than Enzyme A when [S] = 5.0 mM.                 
                          c)        V

o

 for Enzyme A will double as [S] increases from 5.0 mM to 10.0 mM.                  

                          d)        V

o

 for Enzyme B will double as [S] increases from 5.0 mM to 10.0 mM.                           

 
42. ______        Which kinetic property will be shared by Enzyme A and Enzyme B?   
                          a)        Their K

M

  values will decrease as the substrate concentration decreases. 

                          b)        Their V

max

 values will increase as the substrate concentration increases. 

                          c)        Their K

M

  values will depend upon the concentration of the enzymes.                   

                          d)        Their V

max

 values will depend upon the slowest step of their reaction  

                                      mechanisms.

         

 
43.  ______       The substrate for Enzyme A is a sugar phosphate while the substrate for Enzyme B  
                          is a sugar alcohol. Which amino acid is likely to be found in the active site of both  
                          enzymes? 
                          a)       leucine 
                          b)       tryptophan 
                          c)       aspartate 

                          d)       glutamine 

 
44. ______        Enzyme A is an allosteric enzyme inhibited by galactose while Enzyme B is a  
                          covalently modified enzyme inhibited by phosphate. Which will occur during their  
                          regulation? 

a)

 

Enzyme B will become more inhibited as the concentration of phosphate  
increases. 

b)

 

Enzyme A will become more inhibited as the concentration of galactose   
increases. 

c)

 

Both enzymes will undergo an irreversible conformational change as their  
regulating molecule binds. 

d)

 

Both enzymes will bind their regulating molecule to a specific active site  
on a catalytic subunit. 

_______________________________________________________________________________ 

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