Many Proteins Are Enzymes (3.1.4.2)

Question 1

What is the activation energy?

Answer 1

• The energy required for a chemical reaction to take place

Question 2

What are enzymes?

Answer 2

• Proteins that act as biological catalysts
• They speed up chemical reactions by providing an alternative reaction pathway of lower activation energy, increasing the rate of reaction

Question 3

What is the lock and key hypothesis?

Answer 3

• Suggests that the enzyme’s active site has a specific, rigid shape that is complementary to its substrate
• Only substrates that perfectly fit the active site can bind and form an enzyme-substrate complex

Question 4

What is the induced fit model?

Answer 4

• Suggests that the active site of the enzyme is not initially complementary to the substrate, but it changes shape to better fit the substrate
• As the enzyme changes shape a strain is placed on bonds within the substrate molecule, forming an enzyme-substrate complex, thus lowering the activation energy

Question 5

What is the effect of enzyme concentration?

Answer 5

• The rate of reaction increases as the enzyme concentration increases as there are more active sites for the substrates to bind to
• However, increasing the enzyme concentration beyond a certain point has no effect on the rate of reaction as there are more active sites than substrates so substrate concentration becomes the limiting factpr

Question 6

What is the effect of substrate concentration?

Answer 6

• The rate of reactions increases as the substrate concentration increases as more enzyme-substrate complexes are formed
• However, increasing the substrate concentration beyond a certain point has no effect on the rate of reaction as all the active sites are occupied at one time so enzyme concentration becomes the limiting factor

Question 7

What is the effect of temperature?

Answer 7

• As the temperature increases, the rate of reaction rises, due to increased kinetic energy, resulting in more frequent collisions and more enzyme-substrate complexes are formed

Question 8

What is the effect of pH?

Answer 8

• Enzymes are only active over a narrow pH range. At lower or higher pHs than the optimum, denaturation can occur
• Changes in pH alter hydrogen and ionic bonds in the enzyme’s tertiary structure, altering the active site and preventing substrate binding

Question 9

What are competitive inhibitors?

Answer 9

• The inhibitor has a similar structure to the substrate
• Binds to active site
• Blocks the substrate from binding, preventing enzyme-substrate complexes from forming
• Reduces the rate of reaction

Question 10

What are non competitive inhibitors?

Answer 10

• Different shape to the substrate
• Attaches to the enzyme at a site other than the active site
• Changes tertiary structure of enzyme
• So active site and substrate no longer complementary so no substrate can bind