Exam 2 Questions

Question 1

How does the cabonic anhydrase reaction work?

Answer 1

This reaction happens spontaneously, right to left, whenever you open a bottle of soda. But it happens a million times faster with the enzyme present.

Question 2

What do protease enzymes give at the end of their reaction?

Answer 2

Protease enzymes are protein cutting enzymes. They hydrolyze the peptide bond (amide bond) to give carboxyl and amino groups.

Proteases belong to the Hydrolase group because they add H2O to cleave a molecule.

Question 3

What do esterase enzymes give after their reaction?

Answer 3

Another kind of hydrolase would be an esterase – which hydrolyzes an ester into acid plus alcohol.

Question 4

From the figure which one is Thrombin and which one is Trypsin?

Answer 4

Here are two highly specific protease enzymes. On top we see Trypsin, which cleaves “to the right” of K or R.

Below we see Thrombin, the blood clotting enzyme, which is specific for the R-G peptide bond.

Question 5

Every change of _____ kcal corresponds to a tenfold change in Keq.

The energetic standard is ATP hydrolysis to ADP + Pi. That yields _____ kcal/mol.

Answer 5

1. 36kcal
   - 7.3kcal

Question 6

What does the Gibbs Free energy Equation state?

If its ________, the reaction will go forward.

Answer 6

Delta G = Gibbs Free Energy change. R = gas constant, 1.987 calories/ degree K x mole. T = absolute temperature, Kelvins.

Delta G nought = Standard Free Energy Change, Delta G nought prime = Standard Free Energy at pH 7.

• If its negative, the reaction will go forward
• G= G + RTln[p/R] C/[A][B]^2

Question 7

What does this graph represent?

Which line is catalyzed and which line is not?

Give a reaction that would give this curve

Answer 7

This is the “Michaelis Menten” enzyme, which generally has a single subunit and a single active site.

This graph really illustrates 2 things. One, the red line is the enzyme-catalyzed reaction, the black line is the un-catalyzed reaction. Both of them can go to completion but the catalyzed reaction is much faster.

SO it is a binary reaction like Myoglobin + Oxygen.

(Enzyme is either bound (ES) or free (E), there are only 2 states, so the curve is a rectangular hyperbola like the MB curve.)

Question 8

What determines the rate for a reaction?

Answer 8

This graph shows that it is not the Free Energy Change for a reaction that determines the rate. Rather it is the “Delta G double dagger” or the activation energy that determines the rate.

This ties in with the Arrhenius equation that shows heating a reaction makes it run faster – the extra energy helps the reaction get over the activation barrier.

Question 9

Where is the maximal velocity in this graph?

Answer 9

The Vmax is an “asymptote” which all hyperbolas have.

This is another “Michaelis Menten Enzyme” graph. There are other enzymes that have graphs more like Hemoglobin.

Question 10

Describe the E + S= ES process

What do the letters stand for?

What forces make the E and S come together?

Vformation=

Vbreakdown=

Answer 10

The first event in an enzyme reaction is the formation of an Enzyme Substrate Complex (E + S => ES)

This is an older model called the Fischer Lock and Key. It has some truth to it, often there is shape complementarity between the active site and the substrate

Also the weak forces help E bind to S, including hydrogen bonds, hydrophobic forces, charge interactions, van der Waals etc.

Vformation= k1[E][S]

Vbreakdown= k-1 [ES] + k2 [ES]

Question 11

What is the The Michaelis Menten Equation?

What do low and high km’s represent?

Answer 11

V = Vmax ([S]/([S] + Km))

Low Km implies tight binding between E and S, High Km implies loose binding (and often slower reactions)