Enzymes

Amylase found in germinating seeds is incubated with starch at 25 degrees Celsius and pH 2. When a sample is removed after five minutes and mixed with a solution of iodine in potassium iodine solution, the mixture turns to a blue black colour. The MOST likely explanation for this observation is

• all the starch has been hydrolyzed to maltose

• a specific inhibitor of the amylase is present

• amylase does not catalyze the hydrolysis of starch at 25 degrees Celsius

• the pH is too low for the reaction to process quickly

Rate of an enzyme catalyzed reaction with and without inhibitors is shown.

Identify graphs I - II - III respectively.

• Competitive inhibitor - Non-competitive inhibitor - No inhibitor

• Competitive inhibitor - No inhibitor - Non-competitive inhibitor

• No inhibitor - Competitive inhibitor - Non-competitive inhibitor

• No inhibitor - Non-competitive inhibitor - Competitive inhibitor

Which of the following graphs BEST illustrates the effect of temperature on a enzyme controlled reaction?

• 
• 
• 
• 

Which of the following pairs of statements explains the mode of action of enzymes?

• I and II

• II and III

• II and IV

• III and IV

The diagram represents the activation energy for an enzyme catalyzed and an uncatalyzed reaction. The activation energy for an enzyme-catalyzed reaction is represented by the region labelled

• I

• II

• III

• IV

The graph shows the time course of the activity of the enzyme sucrase at various temperatures. At which of the following temperatures does the enzyme work at the FASTEST rate?

• 10 degrees Celsius

• 25 degrees Celsius

• 37 degrees Celsius

• 60 degrees Celsius

Pepsin is an enzyme found in the human alimentary system. Which of the following curves BEST represents the action of pepsin?

• I

• II

• III

• IV

The graph shows the relationship between enzyme concentration and the rate of an enzyme catalyzed reaction. Which of the following statements BEST describes the rate of an enzyme catalyzed reaction?

• The rate is directly proportional to the enzyme concentration

• The rate is inversely proportional to the enzyme concentration

• The rate had reached equilibrium

• The rate is affected by the enzyme concentration

Chymotrypsin is an enzyme that is found in the human alimentary canal. It is active over an active range of alkaline pH values. Which of the activity curves represent the activity of chymotrypsin?

• I and II only

• I and IV only

• II and III only

• III and IV only

The graph shows the effect of increasing substrate concentration on the rate of an enzyme - catalysed reaction. Which of the labelled curves BEST represents the presence of a competitive inhibitor?

• I

• II

• III

• IV