Question

Enolase is an enzyme that catalyzes one reaction in glycolysis in all organisms that carry out this process. The amino acid sequence of enolase is similar but not identical in the organisms. Researchers purified enolase from Saccharomyces cerevisiae, a single-celled eukaryotic yeast that grows best at 37°C, and from Chloroflexus aurantiacus, a bacterium that grows best at the much higher temperature of 55 C. The researchers compared the activity of purified enolase from the two organisms by measuring the rate of the reaction in the presence of varying concentrations of substrate and a constant amount of each enzyme at both 37°C and 55°C (a) Depending on the organism, the optimal pH for enolase to catalyze its reaction is between 6.5 and 8.0. Describe how a pH below or above this range is likely to affect enolase and its catalytic ability(b) Identify the appropriate negative control the researchers most likely used when measuring the reaction rate in the presence of each organism's enolase. (c) The researchers predict that for any particular concentration of substrate, the C. aurantiacus enolase- catalyzed reaction is more rapid at 55°C than at 37°C. Provide reasoning to justify the researchers' prediction.

Answer 1

Answer and Explanation:

(a) Depending on the organism, the optimal pH for enolase to catalyze its reaction is between 6.5 and 8.0. Describe how a pH below or above this range is likely to affect enolase and its catalytic ability

Enzymes are special types of protein that work on substrates to facilitate chemical reactions. They make these reactions faster. Enzymes also have optimum temperatures and pH. These factors affect protein folding, specificity of substrate binding and enzymatic activity.

pH is a measure of the alkalinity or acidity of a solution. High pH's are alkaline, while low ones are acidic. Enolase works best at an average to slightly alkaline pH (between 6.5 and 8.0).

pH changes the R group  ionization of amino acids making up the protein. The altered charges affect the hydrogen bonding and thus the shape of the enzyme may change; substrate may not adequately bind to this shape.

• At lower pH, the enzyme activity slows  
• At higher pH, the enzyme is denatured. Denaturation changes the structure and the enzymes are completely unable to attach to the substrate.

(b) Identify the appropriate negative control the researchers most likely used when measuring the reaction rate in the presence of each organism's enolase.

The researchers most likely used a buffer solution containing all reagents, without the enzyme enolase, as a negative control. A negative control is usually indicative of any contaminants that may affect the result obtained from the experiment.

• Negative controls should show no results from the assay.
• Thus, if another molecule is capable of converting 2-phosphoglycerate or 2-PGphosphoenolpyruvate PEP, its activity would be detected.

(c) The researchers predict that for any particular concentration of substrate, the C. aurantiacus enolase- catalyzed reaction is more rapid at 55°C than at 37°C. Provide reasoning to justify the researchers' prediction.

As the temperatures increase, the number of collisions of the molecules increases, and so does the reaction rate.  This makes it more likely that the substrate would collide and bind with the active site. Beyond its optimal temperature, enolase would become denatured and the activity of the enzymes declines.

Recall, denaturation changes the structure and the enzymes are completely unable to attach to the substrate i.e. The attachment precision of the enzyme's active site to the substrate is impaired.

Higher activation energy found in C. aurantiacus would mean more energy is supplied to increase the number of collisions and reaction rate before denaturation occurs.