Mode of Action of Enzymes (Cambridge (CIE) AS Biology): Flashcards
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Define enzyme.
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Cards in this collection (32)
Define enzyme.
An enzyme is a biological catalyst that increases the rate of a reaction and remains unchanged at the end of the reaction.
What type of protein are all enzymes?
All enzymes are globular proteins.
Define intracellular enzyme.
An enzyme that catalyses reactions inside the cell in which it is made.
Define extracellular enzyme.
An enzyme that is secreted from the cell to catalyse reactions outside the cell.
Give one example of an extracellular enzyme and where it acts.
Amylase — secreted into the gut, where it digests starch outside cells.
Enzymes are globular proteins that act as biological .
Enzymes are globular proteins that act as biological catalysts.
True or False?
Enzymes are used up during the reactions they catalyse.
False.
Enzymes remain unchanged at the end of a reaction and can be reused.
Define active site.
A region on an enzyme with a specific shape to which the substrate binds.
Define enzyme-substrate complex.
The structure formed when a substrate binds to the active site of an enzyme.
Define activation energy.
The minimum energy needed for a reaction to take place.
How do enzymes speed up reactions?
They lower the activation energy of the reaction.
What is meant by enzyme specificity?
Each enzyme catalyses only one type of reaction, because its active site is complementary to only one substrate.
Enzymes speed up reactions by lowering the energy.
Enzymes speed up reactions by lowering the activation energy.
Why is an enzyme specific to only one substrate?
The shape of its active site is complementary to only that substrate's shape.
Define the lock-and-key hypothesis.
A model in which the substrate is complementary in shape to the active site and fits into it like a key into a lock.
Define the induced-fit hypothesis.
A model in which the active site is not exactly complementary at first, but changes shape slightly to fit closely around the substrate.
How does the induced-fit hypothesis differ from the lock-and-key hypothesis?
In lock-and-key, the active site is already complementary to the substrate.
In induced-fit, the active site moulds/changes shape around the substrate as it binds.
In the induced-fit model, what happens to the active site when the substrate binds?
It changes shape to fit more closely around the substrate, forming an enzyme-substrate complex.
In the hypothesis, the active site changes shape to fit the substrate.
In the induced-fit hypothesis, the active site changes shape to fit the substrate.
True or False?
In the lock-and-key hypothesis, the active site changes shape when the substrate binds.
False.
That describes the induced-fit hypothesis. In lock-and-key, the active site is already complementary to the substrate.
What are the two general ways to measure the progress of an enzyme-catalysed reaction?
Measure the rate of formation of product, or the rate of disappearance of substrate.
How can the activity of catalase be measured?
By measuring the rate of formation of product — the volume of oxygen produced from the breakdown of hydrogen peroxide.
How can the activity of amylase be measured?
By measuring the rate of disappearance of substrate — how quickly starch is broken down.
Define enzyme activity.
The rate at which an enzyme converts substrate into product.
Catalase activity can be measured by collecting the gas produced.
Catalase activity can be measured by collecting the oxygen gas produced.
When using amylase and starch, how can the end of the reaction be detected?
When iodine solution no longer turns blue-black, showing that all the starch has been digested.
Define colorimeter.
A device that measures the absorbance (or transmission) of light passing through a coloured solution.
When is a colorimeter useful for measuring the progress of an enzyme-catalysed reaction?
When the reaction involves a colour change.
How does a colorimeter measure the progress of such a reaction?
It measures the change in absorbance of light as the colour of the solution changes over time.
Why is a calibration curve produced before using a colorimeter?
To convert absorbance readings into a concentration of product or substrate.
A colorimeter measures the of light passing through a coloured solution.
A colorimeter measures the absorbance of light passing through a coloured solution.
True or False?
A colorimeter can be used to follow any enzyme-catalysed reaction.
False.
A colorimeter can only follow reactions that involve a colour change.
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