Week 1 Flashcards
Describe how a reaction will proceed if delta G is negative.
spontaneously in the forward direction
Describe how a reaction will proceed if delta G is positive.
spontaneously in the reverse direction
When entropy is less than 0, order____________.
increases
ΔGo’
change in free energy under standard conditions of 25 degrees Celsius and pH of 7.0 with equimolar substrates and products
Keq=
[product] / [substrate]
What will happen to ΔG if the [product] decreases?
the reaction becomes more energetically favorable
Describe three ways enzymes decrease activation energy and increase reaction rates.
- provide proximity and orientation of reactants
- ensure specificity of substrates and products
- stabilize the transition complex
True or False: Enzymes change the ΔG of a reaction.
False
Vmax [S]
v= —————————————–
Km + [S]
identify and explain the elements of this equation
v= rate or velocity of the reaction (amount of product / unit of time)
Vmax= maximum reaction rate at an infinite substrate concentration where all enzyme is bound to substrate
[S]= concentration of substrate
Km= Michaelis constant, the [S] at which v= 1/2Vmax
True or False: enzymes increase reaction rates (v)
true
Name four isoforms of pyruvate kinase and where they are found in the body.
PK-M1: most tissues
PK-M2: embryonic tissue, cancer
PK-L: liver
PK-R: Red blood cells
Describe the affect of an allosteric activator and an inhibitor on the reaction rate curve in the Michaelis-Menten graph.
Activator: shifts curve to the left and changes curve from sigmoid to hyperbola, increasing the rate of reaction.
Inhibitor: shifts curve to the right, decreasing the reaction rate.
What type of enzyme inhibitor increases Km but does not change Vmax?
Competitive Inhibitor
Describe the characteristics of a competitive enzyme inhibitor.
Molecules that bind at the substrate binding site(s) and prevent substrate binding. Substrate analogs and some transition state analogs are competitive inhibitors. Competitive inhibitors increase Km, but do not change Vmax.
Describe the characteristics of a noncompetitive enzyme inhibitor.
Molecules which bind an enzyme and inhibit its activity without inhibiting substrate binding. Suicide inhibitors and some transition state analogs are in this class. Noncomptetive inhibitors decrease Vmax, but do not change Km
create covalent bonds—permanent for the life of the enzyme
Describe the characteristics of a allosteric enzyme inhibitor.
Molecules which bind an enzyme distant from the substrate binding site and cause a conformational change which alters the substrate binding site and prevents substrate binding. Allosteric inhibitors function primarily on oligomeric enzymes, and can not be described by Michaelis-Menten kinetics.
Both Km and Vmax may be changed.
For the reaction A–>B the ∆G is negative. This reaction:
- will proceed spontaneously in the forward direction, A–> B.
- will proceed spontaneously in the reverse direction, B –>A.
- is at equilibrium.
1.will proceed spontaneously in the forward direction, A–> B.
For the reaction: 1 mol H2 + ½ mol O2 –> 1 mol H2O:
- order increases (ΔS > 0)
- order increases (ΔS < 0)
- order decreases (ΔS > 0)
- order decreases (ΔS < 0)
2.order increases (ΔS < 0)
The ΔG0’ for formation of water from oxygen and hydrogen is -238 kJ/mol. The ΔG0’ for dissolving table salt in water is -9 kJ/mol. Which reaction(s) will proceed spontaneously?
Both
There are different isoforms of hexokinase expressed in different tissues. Erythrocyte (red blood cells) hexokinase has a Km of 0.05 mM glucose. Hepatic (liver) glucokinase has a Km of 5.0 mM glucose.A 36 year old male fasted for four days, and his serum glucose concentration was 4.5 mM. What tissue is phosphorylating glucose most rapidly?
Red Blood cells (lower Km)
Penicillin is an antibiotic that targets glycoprotein transpeptidase, an enzyme essential for cross linking the bacterial cell wall. Penicillin’s structure is similar to transpeptidase’s natural substrate when it is in its highest energy state during the reaction. Penicillin also becomes covalently bound to to the enzyme’s active site, permanently disabling the enzyme. How would you describe penicillin?
- non-competitive inhibitor
- competitive inhibitor
- transition state analog
- heavy metal
- suicide inhibitor
1.non-competitive inhibitor (?)
Cancer cells generally proliferate faster than normal cells, and thus have a greater requirement for nucleotides than normal cells. Drugs that block pathways for nucleotide synthesis are generally more lethal to cancer cells than normal cells.Methotrexate is a cancer drug that resembles folate, the natural substrate for dihydrofolate reductase and a precursor of dTTP. Methotrexate increases the Km of dihydrofolate reductase without changing its Vmax.What kind of drug is methotrexate?
- non-competitive inhibitor
- competitive inhibitor
- transition state analog
- heavy metal
- suicide inhibitor
2.competitive inhibitor (?)
