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Flashcards in 3- Enzymes Deck (12):

What are enzymes?

Proteins that are biological catalysts


What is the 'lock and key' theory?

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.


What is the 'induced fit' theory?

Enzymes active site changes to fit around the substrate


Enzyme activity (Rate of reaction) and temperature

- 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.


Enzyme activity (Rate of reaction) and pH

- 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


Rate of reaction and substrate concentration

- 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


Rate of reaction and enzyme concentration

- 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


What is an enzyme inhibitor (general)?

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


What is a competitive enzyme inhibitor?

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


What is a non competitive inhibitor?

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


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

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


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

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