Enzymes
What do enzymes NOT change (4)?
Free energy, Keq, ΔG, direction of reaction
What does a lower Km indicate?
Higher substrate affinity
What does the enzyme tyrosinase do in cats?
Increases eumelanin
What are the three types of reversible inhibition and their brief differences? The inhibitor and target enzyme bind through which kind of bond?
1. competitive (inhibitor competes with substrate for free enzyme)
2. uncompetitive (inhibitor binds to ES complex)
3. noncompetitive (inhibitor can bind to the free enzyme or ES complex -pure or mixed)
noncovalent bonds
What stage is considered the first step in protein folding?
Secondary structure
What do enzymes do? How do they do it? What happens to them after a reaction is complete?
Act as catalysts, speed up reactions by lowering activation energy
Active site on enzyme fits into substrate - Induced fit model
Enzymes can be reused
What happens to Km if enzyme concentration is increased?
Nothing
Describe how temperature impacts enzyme activity over time
Enzyme activity increases to a threshold then rapidly declines
What happens to Km and Vmax during competitive inhibition? Why?
Km increases, Vmax stays the same
Takes more substrate to reach half of vmax
Are proteins highly stable structures? Why?
No - they have to remain dynamic enough to undergo folding.
Explain the three relationships between Keq, ΔG˚, and reaction direction (chart from lecture slides).
Keq > 1.0, (-) ΔG˚, forward reaction
Keq = 1.0, 0 ΔG˚, equilibrium
Keq < 1.0, (+) ΔG˚, backwards reaction
An accumulation of this organic molecule causes hangover symptoms
acetaldehyde
Why does enzyme activity diminish at high temperatures?
High temps break weak interactions and denatures enzymes
What happens to Km and Vmax during uncompetitive inhibition? Why?
Km and Vmax both decrease
formation of ES is favored
product formation diminishes
How would you best describe the structural characteristics of α -keratin? (4)
Pairs of α -helices
Form coiled coils
Coiled coils held together by disulfide bridges
Rich in hydrophobic residues
What is the activation energy of a reaction?
The difference in free energy between the substrate and the transition state
What are characteristics of allosteric enzymes that michaelis-menten enzymes do not share (3)?
Cooperative binding
multiple active sites
can undergo T to R transition
How does a change in pH alter the rate of enzymatic activity?
Changes the charge of the enzyme
What happens to Km and Vmax during noncompetitive inhibition? Why?
Km stays the same, Vmax decreases
doesn't alter enzme's substrate affinity
reduces amount of enzyme available to make product
What is urea? What does it affect?
Protein-denaturing agent, disrupts noncovalent interactions (hydrogen bonding, hydrophobic interactions)
If a product has lower free energy than the substrate, what will happen at equilibrium?
ΔG < 0, exergonic, so Keq > 1, reaction will move forward, there will be more product at equilibrium
Describe what the graphs would look like for:
-Rate of reaction
-Michaelis-Menten Model (+ what is Km)
-Lineweaver Burk Plot (+ what is slope and intercepts)
Rate of reaction: [P] vs. time, graph curves and levels off
MM: V0 vs [S], Km = [S] needed to reach Vmax/2
Lineweaver Burk: 1/V0 vs 1/[S], x-intercept = -1/Km, y-intercept = -1/Km, slope = Km/Vmax, linear
What are the optimal pH's for pepsin and chymotrypsin? What does optimal pH mean for enzyme activity? How would this look in a graph?
pepsin - 2
chymotrypsin - 8
optimal pH = max enzyme activity, bell curved graph
What is the difference between pure and mixed inhibitors (noncompetitive inhibition)?
pure - binds to the free enzyme or enzyme substrate complex equally
mixed- binds to the free enzyme or ES complex unequally
A protein has become misfolded and exposed hydrophobic regions that could cause it to aggregate. What class of proteins would help prevent this aggregation? What do they do?
Chaperones - temporarily bind to exposed hydrophobic regions of misfolded/unfolded proteins to prevent them from aggregating and help them regain their proper folded structure.