Many proteins are enzymes

Question 1

How do enzymes act as biological catalysts?

Answer 1

each enzyme lowers activation energy of the reaction it catalyses to speed up the rate of reaction

Question 2

What is the induced-fit model of enzyme action?

Answer 2

1. substrate binds to active site (not completely complementary)
2. causes active site to change shape to become complementary
3. forms enzyme-substrate complex
4. causes bonds in substrate to distort lowering activation energy

Question 3

How have models of enzyme action changed over time?

Answer 3

initially lock & key model suggested that active site is completely complementary to one substrate

Question 4

What is the specificity of enzymes?

Answer 4

• specific tertiary structure determine shape of active site which depends on sequence of amino acids
• active site is complementary to specific substrate which induced shape of active site forming enzyme-substrate complex

Question 5

What is the effect of enzyme concentration on the rate of enzyme-controlled reactions?

Answer 5

• as enzyme conc increases rate of reaction increases so more enzyme-substrate complexes form (enzyme conc is limiting factor)
• after a certain point rate of reaction levels off as substrate becomes limiting factor (all substrate in use)

Question 6

What is the effect of substrate concentration on the rate of enzyme-controlled reactions?

Answer 6

-as substrate conc increases the rate of reaction increases forming more E-S complexes (substrate conc is the limiting factor)
- after a certain point rate of reaction levels off as enzyme becomes limiting factor (all enzymes in use)

Question 7

What is the effect of temperature on the rate of enzyme-controlled reactions?

Answer 7

• as temp increases to optimum rate of reaction increases as there is more kinetic energy so more E-S complexes form
• as temp exceeds optimum the rate of reaction decreases because enzyme denatures - H/ionic bonds break changing the shape of the active site so fewer E-S complexes form

Question 8

What is the effect of pH on the rate of enzyme-controlled reactions?

Answer 8

• as pH increases/ decreases past optimum rate of reaction decreases
• enzyme denatures - H/ionic bonds break changing the shape of the active site so fewer E-S complexes form

Question 9

How does the conc of competitive inhibitors effect the rate of enzyme-controlled reactions?

Answer 9

• as conc of competitive inhibitors increases the rate of reaction decreases
• they have a similar shape to substrate so bind to active site, blocking substrate from binding
• fewer E-S complexes form
• increasing substrate conc can reduces effect of inhibitors

Question 10

How does the conc of non-competitive inhibitors effect the rate of enzyme-controlled reactions?

Answer 10

• as conc of non-competitive inhibitors increases the rate of reaction decreases
• they bind to allosteric site changing the shape of active site
• active site is no longer complementary to substrate so fewer E-S complexes form
• increasing substrate conc doesn’t effect rate of reaction as change to active site is permanent