Exam #3 Practice Questions Flashcards
Which of the following amino acids would NOT provide a nucleophilic center for covalent catalysis?
Cysteine Serine Alanine Lysine Glutamic Acid
Alanine
In the chymotrypsin reaction mechanism, ___ is involved in covalent catalysis.
A. Asp 102 B. Ser 195 C. His 57 D. His 102 E. Asp 195
Ser 195
In the catalytic triad common to many serine proteases, ___ increases the basicity of ___, thus allowing deprotonation of ___ to serve as a nucleophile.
A. Ser-His-Asp B. Ser-His-His C. His-Ser-Asp D. Asp-His-Ser E. Cys-His-Ser
D. Asp-His-Ser
Which of the following is false regarding serine proteases?
A) they employ metal ion catalysis
B) They contain a catalytic triad of His, Ser, and Asp residues
C) They cleave simple organic ester bonds near larger residues
D) They employ general acid-base catalysis
A) they employ metal ion catalysis
An enzyme that has the maximum activity at pH 4 may indicate the involve of ___ amino aid in acid-base catalysis.
A) Lysine B) Cysteine C) Arginine D) Histidine E) Glutamic Acid
E) Glutamic Acid
All are characteristics of allosteric enzymes except:
A) They obey Michaelis-Menton kinetics
B) Effectors may show stimulatory or inhibitory activity.
C) They have multiple subunits
D) The regulatory effect by altering conformation and interaction of subunits
E) Binding one subunit impacts the binding of substrate to other subunits
A) They obey Michaelis-Menton kinetics
Proinsulin is converted to insulin by:
A) Proteolytic excision of a specific peptide
B) Allosteric binding of glucose
C) None of the above
D) Removal of phosphate by converter enzymes
E) Phosphorylation to the active form
A) Proteolytic excision of a specific peptide
Heme is a porphyrin prosthetic group that coordinates __ at four positions.
A) Fe 1+
B) Fe
C) Fe 2+
D) Fe 3+
C) Fe 2+
Which of the following is generally true for catabolism, but not anabolism?
A) A net production of energy results from degradation of large molecules
B) Pathways are compartmentalized within eukaryotic cells
C) All reactions are reversible
D) Energy may be required some, but not all intermediate steps
A) A net production of energy results from degradation of large molecules
All are coenzymes with an adenine nucleotide portion except:
A) NADH B) FADH2 C) Coenzyme A D) ATP E) FMNH2
E) FMNH2
What is a characteristic difference between FAD and NAD+?
NAD+ transfers two electrons while FAD can transfer one or two.
What does not contribute to a large negative delta G of ATP?
A) Phosphate hydrolysis B) All of the above contribute C) Smaller solvation energy D) Resonance stabilization E) Electrostatic repulsion
B) All of the above contribute
__ can bypass the regulatory step at 3-FTK to enter glycolysis which may be a contributing factor to obesity.
Fructose
All are allosteric regulators of phosphofructokinase-1 except:
A) Citrate by inhibition B) Beta-D-fructose-2,6-bisphosphate by stimulation C) glucose-6-phosphate by inhibition D) ATP by inhibition E) AMP by stimulation
C) glucose-6-phosphate by inhibition
All are true for 2,3-bisphosphoglycerate (2,3-BPG) except:
A) A kinase converts 2,3-BPG to 3-phosphoglycerate
B) 2,3-BPG is involved in unloading oxygen from hemoglobin
C) 2,3-BPG is synthesized from 1,2-BPG
D) Erythrocytes typically have high levels of 2,3-BPG
E) Bisphosphoglycerate mutase is an isomerase
A) A kinase converts 2,3-BPG to 3-phosphoglycerate