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Principles of Biochemistry, 5/E



Laurence A. Moran, University of Toronto
Robert A Horton, North Carolina State University
Gray Scrimgeour, University of Toronto
Marc Perry, University of Toronto

ISBN-10: 0321707338
ISBN-13:  9780321707338
Publisher:  Prentice Hall
Copyright:  2012


Principles of Biochemistry, 5e (Moran/Horton/Scrimgeour/Perry/Rawn)
Chapter 7   Coenzymes and Vitamins


1) Active holoenzymes are formed from ________ in the presence of ________.
A) cofactors; proteins
B) proteins; cofactors
C) apoenzymes; cofactors
D) apoenzymes; proteins
E) apoenzymes; inactive holoenzymes
Answer:  C
Page Ref: 7-Introduction

2) Because coenzymes are specific for the chemical groups that they accept and donate, they are referred to as
A) cofactors.
B) reactive centers.
C) activator ions.
D) group-transfer reagents.
E) All of the above.
Answer:  D
Page Ref: 7-Introduction

3) Ca++ or Mg++ are most likely to be part of ________, while Zn++ or Fe++ are present in ________.
A) metal-activated enzymes; metalloenzymes
B) metalloenzymes; metal-activated enzymes
C) cofactors; coenzymes
D) coenzymes; cofactors
E) apoenzymes; holoenzymes
Answer:  A
Page Ref: Section 7-1

4) The metal ions in metalloenzymes are firmly bound at the active site of the enzyme.  The ion may be bound to side chains of amino acids or may be part of a ________ group such as those found in catalase and cytochromes.
A) sulfur clusters
B) phosphate
C) vitamin
D) heme
Answer:  D
Page Ref: Section 7-1

 
5) The role of zinc in the mechanisms of carbonic anhydrase is to
A) maintain the configuration of the holoenzyme.
B) bind to three histidine residues.
C) produce a nucleophilic attack on the substrate.
D) promote ionization of bound water.
E) produce an electrophilic attack on the substrate.
Answer:  D
Page Ref: Section 7-1
6) What is the role of the magnesium ion in kinases that require the magnesium-ATP complex to donate phosphoryl groups?
A) Maintain the configuration of the holoenzyme.
B) Shield the charged phosphate groups of ATP.
C) Produce an electrophilic attack on the substrate.
D) Promote ionization of bound water.
E) Produce ionization of the substrate to be phosphorylated.
Answer:  B
Page Ref: Section 7-1

7) An ion commonly found in metalloenzymes and which can undergo reversible oxidation and reduction is
A) Ca++.
B) Mg++.
C) S-.
D) Fe++.
E) All of the above.
Answer:  D
Page Ref: Section 7-1

8) Which does not return to its original form after each catalysis?
A) Prosthetic groups.
B) Cosubstrates.
C) Metalloenzyme.
D) None of the above.  They all return to their original forms.
Answer:  D
Page Ref: Section 7-2

9) Unlike coenzymes that are prosthetic groups, ________ are altered in the course of an enzyme reaction and dissociate from the active site.
A) isozymes
B) cosubstrates
C) metalloenzymes
D) holoenzymes
Answer:  B
Page Ref: Section 7-2

 
10) S-adenosylmethionine (SAM) is formed from the amino acid methionine so that
A) methyl groups can be formed.
B) it can react with nucleophilic acceptors.
C) it can donate methyl groups in many biosynthetic reactions.
D) All of the above.
E) B and C.
Answer:  E
Page Ref: Section 7-3
11) ATP is involved in
A) transferring a phosphate group to other compounds.
B) forming S-adenosylmethionine.
C) transfer of its AMP moiety to another compound.
D) All of the above.
E) A and C only.
Answer:  D
Page Ref: Section 7-3

12) A nucleotide-sugar coenzyme involved in carbohydrate metabolism (UDP-glucose) is formed when UTP reacts with a glucose molecule. More UTP is made available for additional reactions by the transfer of a phosphate group from
A) another carbohydrate.
B) ATP.
C) ADP.
D) UTP.
E) UDP.
Answer:  B
Page Ref: Section 7-3

13) NAD and NADP dependent dehydrogenases catalyze substrates by transferring ________ to C-4 of NAD+ and NADP+.
A) one electron
B) two electrons
C) one electron and one proton
D) two electrons and one proton
E) two electrons and two protons
Answer:  D
Page Ref: Section 7-4

14) The "+" sign in NAD+ indicates that
A) this is the reduced form of the coenzyme.
B) the nitrogen atom has a positive charge.
C) the entire molecule is positively charged.
D) it can bind to negatively charged proteins only.
Answer:  B
Page Ref: Section 7-4

15) What structure is shown?

A) NADH
B) NAD+
C) FMN
D) FAD
Answer:  B
Page Ref: Section 7-4

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