3- Enzymes

Question 1

What are enzymes?

Answer 1

Proteins that are biological catalysts

Question 2

What is the ‘lock and key’ theory?

Answer 2

That the active site on an enzyme is specific to a substrate and that only a complimentary substrate will be able to bind to it and form a enzyme-substrate complex.

Question 3

What is the ‘induced fit’ theory?

Answer 3

Enzymes active site changes to fit around the substrate

Question 4

Enzyme activity (Rate of reaction) and temperature

Answer 4

• Increase in temp causes increase in enzyme + substrate kinetic energy therefore they successfully collide more frequently and form the enzyme-substrate complex
• Reach optimum temp, activity is at its maximum
• High temperatures cause denaturing of tertiary structure bonds, active site altered so substrate will not bind and no enzyme-substrate complex will form.

Question 5

Enzyme activity (Rate of reaction) and pH

Answer 5

• Enzyme activity peaks at optimum pH
• Ionisation groups at the active site change with the change of pH meaning the substrate will not bind and enzyme-substrate complex will not form

Question 6

Rate of reaction and substrate concentration

Answer 6

• As substrate concentration increases so does the rate of reaction as there are many free active sites to bind to the many substrate particles
• The rate reaches a maximum when the conc of enzymes becomes a limiting factor and there are no free active sites available

Question 7

Rate of reaction and enzyme concentration

Answer 7

• Rate of reaction increases with increase in enzyme concentration as there are more active sites to bind to the substrate and form enzyme-substrate complexs
• The rate plateus when the substrate becomes a limiting factor

Question 8

What is an enzyme inhibitor (general)?

Answer 8

Slows down (reversible) or stops (irreversible) enzyme activity

Question 9

What is a competitive enzyme inhibitor?

Answer 9

Competes to bind to active sites with substrates
Binds to enzyme active site, complimentary in shape
Similar in shape to substrate
Reversible competitive inhibitors lower the rate of reaction but still allow the enzyme to reach its max rate if substrate conch is high enough

Question 10

What is a non competitive inhibitor?

Answer 10

Binds to allosteric site and alters the shape of the active site so it is no longer complimentary to the substrate
When the inhibitor leaves the active site returns to normal
Increasing substrate conc will not effect the rate of reaction

Question 11

Measuring the rate of an enzyme-controlled reaction: How fast product is made:

Answer 11

Use catalase to catalyse the breakdown of hydrogen peroxide into water and oxygen
Boiling tubes of same volume and concentration of hydrogen peroxide and equal volumes of buffer solution - pH the same
Boiling tubes connected to delivery tubes connected to upside-down measuring cylinder submerged in a trough of water
Each boiling tube in a water bath at different temps (10, 20, 30, 40 degrees C)
Use pipette to add equal amounts of catalase to boiling tubes and quickly place bung on
Record how much oxygen is produced in the first minute using stopwatch
Repeat 3 times to find average
Calculate average rate of reaction

Question 12

Measuring the rate of an enzyme-controlled reaction: How fast the substrate is broken down:

Answer 12

Amylase catalyses breakdown of starch to maltose
Spotting tile + dropping pippete + test tube with starch solution and amylase enzyme
Place drop of iodine in potassium iodide in each well of spotting tile
Amylase and starch then mixed together in test tube
Dropping pipette used to drop a sample of the mixture into a well every timed interval and the resulting colour observed
Record how long it takes until the solution no longer turns blue-black and remains browny-orange