enzyme inhibition
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45 Terms
What is reversible enzyme inhibition?
Inhibitor binds noncovalently and can dissociate.
What is competitive inhibition? [HOMEWORK]
Inhibitor resembles substrate and competes for the active site of free E.
Which enzyme form does competitive inhibitor bind? [SLIDES]
Free E only.
What is the competitive inhibitor's relationship to substrate structure? [SLIDES]
Often resembles substrate structurally.
What does competitive inhibition do to apparent KM? [SLIDES]
Increases KM.
What does competitive inhibition do to Vmax? [SLIDES]
Vmax unchanged.
Can increasing [S] overcome competitive inhibition? [SLIDES]
Yes.
Why is Vmax unchanged in competitive inhibition? [HOMEWORK]
At sufficiently high [S], substrate displaces inhibitor and reaches same maximum rate.
How does competitive inhibition affect Michaelis-Menten graph?
Right shift, same Vmax.
Where do competitive inhibition Lineweaver-Burk lines intersect?
Y-axis.
What is the competitive inhibitor example with PABA? [SLIDES]
Sulpha drugs compete with PABA in bacterial folate synthesis.
Why can sulpha drugs selectively affect bacteria? [SLIDES]
Bacteria synthesize folate using PABA; humans do not have that folate-synthesis enzyme.
What enzyme does ibuprofen inhibit? [SLIDES]
Cyclooxygenase (COX).
What pathway do statins inhibit? [SLIDES]
Cholesterol synthesis.
What is uncompetitive inhibition? [SLIDES]
Inhibitor binds only ES complex.
What complex forms in uncompetitive inhibition? [SLIDES]
Inactive ESI dead-end complex.
What happens to KM in uncompetitive inhibition? [SLIDES]
Decreases.
What happens to Vmax in uncompetitive inhibition? [SLIDES]
Decreases.
Can increased [S] overcome uncompetitive inhibition? [SLIDES]
No.
What do uncompetitive Lineweaver-Burk lines look like?
Parallel lines.
What is the mass-action explanation for decreased apparent KM in uncompetitive inhibition? [SLIDES]
ESI formation pulls equilibrium toward ES formation, lowering apparent KM.
What herbicide is the slide example for uncompetitive inhibition? [SLIDES]
Roundup.
What biosynthetic pathway is inhibited by Roundup according to slides?
Aromatic amino acid synthesis in plants.
What is pure noncompetitive inhibition? [SLIDES]
Inhibitor binds E and ES equally at site other than active site.
What happens to Vmax in pure noncompetitive inhibition? [SLIDES]
Decreases.
What happens to KM in pure noncompetitive inhibition? [SLIDES]
Unchanged.
Can increased [S] overcome noncompetitive inhibition? [SLIDES]
No.
Where do pure noncompetitive Lineweaver-Burk lines intersect?
X-axis.
What is the slide's dilution analogy for noncompetitive inhibition? [SLIDES]
Unaffected enzyme behaves normally, but active enzyme concentration is effectively reduced.
What antibiotic is the slide example for noncompetitive inhibition? [SLIDES]
Doxycycline (spelled deoxycycline in slide), inhibits bacterial collagenase in periodontal disease.
What happens to Vmax if effective active enzyme concentration falls?
Decreases.
How does mixed inhibition differ from pure noncompetitive inhibition?
Inhibitor binds E and ES with unequal affinity; Vmax decreases and KM can change.
What inhibition type has KM up and Vmax unchanged?
Competitive.
What inhibition type has KM down and Vmax down?
Uncompetitive.
What inhibition type has KM same and Vmax down?
Pure noncompetitive.
What inhibition type has parallel Lineweaver-Burk lines?
Uncompetitive.
What inhibition type has Lineweaver-Burk Y-axis intersection?
Competitive.
What inhibition type has Lineweaver-Burk X-axis intersection?
Pure noncompetitive.
What inhibition type is overcome by adding substrate?
Competitive.
Which inhibition types cannot be overcome by more substrate?
Uncompetitive and noncompetitive.
Which type of inhibitor binds only ES?
Uncompetitive.
Which type binds only free E at the active site?
Competitive.
Which type binds E and ES equally outside active site?
Pure noncompetitive.
What inconsistency exists in the typed inhibition homework?
A line says competitive KM and Vmax are both same, but the lecture slides explicitly state KM increases and Vmax is unchanged; use the slide's rule and verify with professor.
What is the primary graph recognition shortcut?
Competitive = same Y intercept; uncompetitive = parallel; pure noncompetitive = same X intercept.