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Define the term enzyme.
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Define the term enzyme.
An enzyme is a protein that acts as a biological catalyst to speed up the rate of a chemical reaction.
What does a catalyst do?
A catalyst speeds up the rate of a chemical reaction without being used up or changed in the reaction.
True or False?
Enzymes are necessary for all living organisms.
True.
Enzymes are necessary for all living organisms to maintain reaction speeds at a rate that can sustain life.
Define the term substrate.
A substrate is the reactant of an enzyme-catalysed reaction.
State the meaning of the term active site.
The active site is the region on an enzyme where a specific substrate attaches for the reaction to be catalysed.
What happens after a reaction has occurred in the active site of an enzyme?
After the reaction has occurred the products leave the enzyme's active site and the enzyme is free to take up another substrate.
True or False?
Enzymes are changed or used up in the reactions they catalyse.
False.
Enzymes are not changed or used up in the reactions they catalyse; they can be recycled and used in further reactions.
Define the term optimum temperature.
The optimum temperature is the temperature at which an enzyme works fastest.
Define the term denatured.
When an enzyme is denatured its active site changes shape and can no longer bind to its specific substrate. This results in a loss of enzyme function.
In a practical that investigates the effect of temperature on rate of reaction in amylase, what is the variable being changed?
The variable being changed (independent variable) is the temperature of the amylase and starch reaction mixture.
In a practical that investigates the effect of temperature on rate of reaction in amylase, what is the purpose of adding iodine solution?
When investigating the effect of temperature on rate of reaction in amylase, iodine is added to detect the presence of starch. When all the starch has been digested into sugar the iodine will no longer turn blue-black.
True or False?
In a practical that investigates the effect of temperature on rate of reaction in amylase, the iodine solution will stop turning blue-black fastest at the optimum temperature.
True.
In a practical that investigates the effect of temperature on rate of reaction in amylase, the iodine solution will stop turning blue-black fastest at the optimum temperature; this is because the enzyme is working at its fastest rate breaking down the starch to sugar.
In a practical that investigates the effect of temperature on rate of reaction in enzymes, what happens to the rate at low temperatures?
In a practical that investigates the effect of temperature on rate of reaction, the rate of reaction will be slow at low temperatures. This is due to low kinetic energy.
In a practical that investigates the effect of temperature on rate of reaction in enzymes, what happens to the rate at high temperatures?
In a practical that investigates the effect of temperature on rate of reaction in amylase, the rate of reaction will decrease to zero at high temperatures. This is because the amylase enzyme has become denatured and cannot break down the starch.
In a practical that investigates the effect of temperature on rate of reaction, which variables should be kept constant?
In a practical that investigates the effect of temperature on rate of reaction the variables that should be kept constant include:
the concentration and volume of starch solution
the concentration and volume of enzyme solution
the pH
In a practical that investigates the effect of temperature on rate of reaction in enzymes, why must the starch and amylase solutions be placed in a water bath at optimum temperature before being used?
In a practical that investigates the effect of temperature on rate of reaction in enzymes, the reactants and enzymes must be placed in a water bath at optimum temperature before being used so that they are brought up to the correct temperature before the investigation.
In a practical investigating the effect of pH on rate of reaction in amylase, why does the iodine solution stop turning blue-black at certain pH levels?
In a practical investigating the effect of pH on rate of reaction in amylase, the iodine solution stops turning blue-black at certain pH levels because the starch is fully broken down by the amylase. This means that there is no longer starch in the solution to turn the iodine blue-black.
In a practical investigating the effect of pH on rate of reaction in amylase, what impact does the optimum pH have on the rate of amylase activity?
In a practical investigating the effect of pH on rate of reaction in amylase, at the optimum pH the iodine solution will stop turning blue-black and remain orange-brown within the shortest time period. This is because the amylase is working at its fastest rate to break down the starch.
In a practical investigating the effect of pH on rate of reaction in amylase, what impact does a very low pH, such as pH2, have on the rate of amylase activity?
In a practical investigating the effect of pH on rate of reaction in amylase, at very low pH values the iodine solution will continue turning blue-black throughout the investigation. This is because the enzymes are denatured so the rate of amylase activity has slowed down/stopped.
What is a buffer solution?
A buffer solution is a solution that resists changes in pH upon the addition of small amounts of an acid or base.
What is the role of a buffer solution when investigating the effect of pH on enzyme activity?
Buffer solutions are used to maintain a specific pH environment for the amylase enzyme. This keeps the pH the same throughout the investigation for each of the pH conditions.
True or False?
The starch and amylase solutions need to be at room temperature to investigate the effect of pH on the activity of amylase.
False.
The starch and amylase solutions should ideally be placed in a water bath at the optimum temperature before being used in the investigation, however it does not need to be the exact optimum as long as the temperature is kept constant throughout.
Define the term specificity in the context of enzymes. (Extended Tier Only)
Enzyme specificity means that enzymes only bind to/catalyse the reaction of one specific substrate. This is because the active site of the enzyme is a complementary shape to the substrate.
What is an enzyme-substrate complex? (Extended Tier Only)
An enzyme-substrate complex is formed when a substrate attaches to the active site of an enzyme.
True or False?
Enzymes can bind to several types of substrate. (Extended Tier Only)
False.
Enzymes are specific to one particular substrate(s) as the active site of the enzyme is a complementary shape to the substrate.
True or False?
The substrate is the same shape as the active site. (Extended Tier Only)
False.
The shapes are opposite to each other to allow them to fit together. This is a called complementary shape.
Why is enzyme activity low at low temperatures? (Extended Tier Only)
Enzyme activity is low at low temperatures due to a lack of kinetic energy. This means that few successful collisions occur between enzyme and substrate molecules and so few enzyme-substrate complexes form.
Why does increasing temperature towards the optimum temperature increase reaction rate? (Extended Tier Only)
Increasing the temperature towards the optimum increases enzyme activity as the molecules have more kinetic energy, leading to more successful collisions with substrate molecules and a faster rate of reaction.
Why does increasing temperature too far beyond the optimum temperature result in a reaction rate that decreases to zero? (Extended Tier Only)
Increasing temperature too far beyond the optimum reduces reaction rate to zero because heat breaks the bonds that hold the enzyme together, causing it to lose its shape and become denatured.
What happens to an enzyme or substrate if its kinetic energy increases? (Extended Tier Only)
If an enzyme or substrate gains kinetic energy it moves around faster.
Why does the rate of an enzyme-controlled reaction decrease as the pH level moves further from the enzyme's optimum pH? (Extended Tier Only)
The rate of an enzyme-controlled reaction decreases as the pH level moves further from the enzyme's optimum because extremes of pH break the bonds that hold the amino acid chain together, denaturing the active site and reducing the rate of reaction.
True or False?
All enzymes denature in acid. (Extended Tier Only)
False.
Different enzymes function well at different pH levels, e.g. enzymes from the stomach have a low optimum pH (around pH 2) because the stomach is an acidic environment.