The effect of temperature and pH on enzyme activity 2.4.4 & 2.4.5 Flashcards
(23 cards)
What happens to the catalysed reactions when temperature is increased?
Kinetic energy increases - therefore;
- Successful collisions increase
- Formation of ES & EP complexes increase
- Product formation will increase
- Reaction will increase
At what temperature level is the rate of reaction at its maximum?
At the OPTIMUM temperature
What occurs if temperatures exceed the correct level?
Due to heavier vibrations;
- Weaker bonds (hydrogen) break, therefore the tertiary structure alters
- Active site shape changes
- Substrate can no longer fit, no ES complexes
- Rate of reaction decreases
- Enzyme is DENATURED
Which enzymes have a low optimum temperature?
Psychrophilic bacteria
Which enzymes have a high optimum temperature?
Thermophilic bacteria
Why can some enzymes have a higher optimum temperature?
Enzymes, such as thermophilic bacteria, have heat stable proteins which contain more disulphide bonds. These bonds do not break with heat and so keep the protein molecule stable.
What is Q10?
A ratio known as the temperature coefficient
What does the Q10 describe?
What happens to the rate of reaction as temperature increases by 10°C.
What is the formula for Q10?
(Rate of reaction at temperature T + 10°C) divided by (Rate of reaction at temperature T)
When does the Q10 relationship not apply?
Above optimum temperature.
What is the average value of Q10 in a test tube?
2 - which means that for every 10°C rise in temperature the rate of reaction is doubled.
What does a change in pH refer to?
A change in hydrogen ion concentration.
Are there more or less hydrogen ions in a low pH (acid)?
More hydrogen ions
When is the active site at its right shape?
At a certain hydrogen ion concentration - the optimum pH.
What is a buffer?
Something that resists changes in pH.
How does a buffer work?
These chemicals can donate or accept hydrogen ions.
What effect do increased hydrogen ions have on the charges on the active site?
Increased hydrogen ions alter the charges on the active site as more protons will cluster around negatively charged groups - which can interfere with the binding of the substrate molecule.
What pH range do enzymes work in?
A very narrow range
Describe renaturation
Small changes away from the optimum pH will slow the rate of reaction - however if pH is restored the hydrogen bonds can be restored
Describe denaturation
When enzymes are permanently changed
What is the optimum pH of intracellular enzymes?
Close to pH 7.
What is the optimum pH of extracellular enzymes?
They have different values, e.g. pepsin in the stomach = pH 1-2, whereas amylase in saliva = pH 7-8.
