Enzymes (Edexcel GCSE Combined Science: Biology): Flashcards
Exam code: 1SC0
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Enzyme
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Cards in this collection (25)
Enzyme
A biological catalyst (a protein) that speeds up the rate of a reaction without being used up.
Active site
The part of an enzyme where the substrate binds; its shape is complementary to the substrate.
Describe the 'lock and key' model of enzyme action.
The substrate fits into the enzyme's active site, like a key in a lock, forming an enzyme-substrate complex.
The reaction takes place and the products are released, leaving the enzyme unchanged.
What is meant by enzyme specificity?
Each enzyme only catalyses one particular reaction, because only a substrate with a complementary shape fits its active site.
The substrate binds to the enzyme at its .
active site
are biological catalysts made of protein.
Enzymes
Describe the effect of temperature on enzyme activity.
As temperature rises, the rate increases because molecules have more kinetic energy and collide more often.
Above the optimum temperature, the active site changes shape (the enzyme denatures) and the rate falls.
Describe the effect of pH on enzyme activity.
Each enzyme has an optimum pH at which it works fastest.
Away from the optimum pH, the active site changes shape (denatures) and the rate falls.
Describe the effect of substrate concentration on enzyme activity.
As substrate concentration increases, the rate increases because there are more collisions with active sites.
Once all the active sites are working as fast as they can, the rate levels off.
Denatured
When an enzyme's active site changes shape so the substrate no longer fits, and the enzyme stops working.
At high temperatures an enzyme is because its active site changes shape.
denatured
Each enzyme works fastest at its pH.
optimum
Outline how to investigate the effect of pH on the activity of amylase.
Use buffer solutions to set different pH values.
Mix amylase with starch at each pH.
Every 30 seconds, test a drop of the mixture with iodine solution.
Record the time taken for the starch to be fully digested (iodine stays orange-brown).
solutions are used to keep each mixture at a set pH.
Buffer
In this practical, how do you know when the starch has all been digested?
The iodine solution stops turning blue-black and stays orange-brown.
In the amylase practical, solution is used to test for the presence of starch.
iodine
How can you calculate the rate of an enzyme reaction?
Rate = 1 ÷ time taken.
(Or: amount of product formed ÷ time taken.)
Starch is fully digested in 50 seconds. What is the rate of reaction?
Rate = 1 ÷ time
= 1 ÷ 50
= 0.02 per second (s⁻¹)
A shorter time for a reaction to finish means a rate.
faster
Rate of reaction can be calculated as 1 ÷ taken.
time
Biological catalyst
A substance (an enzyme) that speeds up the rate of a reaction in a living organism without being used up.
What are the two main roles of enzymes in the body?
Synthesis: building large molecules from smaller ones (e.g. carbohydrates, proteins and lipids).
Breakdown: splitting large molecules into smaller ones.
What do carbohydrates, proteins and lipids break down into?
Carbohydrates → sugars.
Proteins → amino acids.
Lipids → fatty acids and glycerol.
Enzymes are biological that speed up reactions without being used up.
catalysts
Proteins are built from, and broken down into, .
amino acids
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