Question

enzymes are sensitive molecules. they often have a narrow range of conditions under which they operate properly. at low temperatures there is little activity. as temperature is increased, so does the enzyme activity until the point is reached when the temperature is so high it damages the protein (denaturation). this causes the enzyme to stop working. extremes in acidity (ph) can also cause the protein structure of enzymes to denature. poisons often work by causing enzymes to cease functioning. cofactors such as vitamins and trace elements are required for many enzymes to function. in the four graphs below, the rate of reaction or degree of enzyme activity is plotted against each of four factors that affect enzyme performance. answer the questions that relate to each graph:

1. enzyme concentration

(a) describe the change in the rate of reaction when the enzyme concentration is increased (assuming there is plenty of the substrate present):
(b) suggest how a cell may vary the amount of enzyme present in a cell:

1. substrate concentration

(a) describe the change in the rate of reaction when the substrate concentration is increased (assuming a fixed amount of enzyme and ample cofactors):
(b) explain why the rate changes the way it does:

1. temperature

higher temperatures speed up all reactions, but few enzymes can tolerate temperatures higher than 50 - 60°c. the rate at which enzymes are denatured (change their shape and become inactive) increases with higher temperatures.
(a) describe what is meant by an optimum temperature for enzyme activity:
(b) explain why most enzymes perform poorly at low temperatures:

1. acidity (ph)

like all proteins, enzymes are denatured by extremes of ph (very acid or alkaline). within these extremes, most enzymes are still influenced by ph. each enzyme has a preferred ph range for optimum activity.
(a) state the optimum ph for each of the enzymes:
pepsin: __________ trypsin: ________ urease: __________
(b) pepsin acts on proteins in the stomach. explain how its optimum ph is suited to its working environment:

Explanation:

1. (a) When substrate is plentiful, increasing enzyme concentration increases the reaction rate linearly as more enzyme - substrate complexes can form.

(b) A cell can vary enzyme amount by regulating gene expression (transcription and translation of enzyme - encoding genes), or by enzyme degradation and storage.

1. (a) With fixed enzyme and cofactors, as substrate concentration increases, the reaction rate first increases rapidly, then levels off.

(b) Initially, more substrate means more enzyme - substrate complexes form. But as enzyme sites become saturated, adding more substrate has no effect.

1. (a) Optimum temperature is the temperature at which an enzyme has the highest activity, with the best balance between increased reaction rate and enzyme stability.

(b) At low temperatures, molecular motion is slow, reducing the frequency of enzyme - substrate collisions.

1. (a) Pepsin: 1.5 - 2; Trypsin: 7.5 - 8.5; Urease: around 7.

(b) Pepsin's optimum pH of 1.5 - 2 is suited to the acidic environment of the stomach.

Answer:

1. (a) The rate of reaction increases linearly.

(b) By regulating gene expression, enzyme degradation, or storage.

1. (a) The rate first increases rapidly and then levels off.

(b) Initially more substrate forms more complexes, but enzyme sites become saturated.

1. (a) The temperature at which enzyme has highest activity.

(b) Molecular motion is slow, reducing collision frequency.

1. (a) Pepsin: 1.5 - 2; Trypsin: 7.5 - 8.5; Urease: around 7.

(b) Its optimum pH is suited to the acidic stomach environment.