5. Enzymes Flashcards
Enzyme definitions
Are biological catalysts that speed up the rate of a chemical reaction without being changed or used up in the reaction. Are also proteins
What is a biological catalyst?
BIOLOGICAL because they are made in living cells
- CATALYSTS because they speed up the rate of chemical reactions without being changed
Why are enzymes necessary?
Enzymes are necessary to all living organisms as they maintain reaction speeds of all metabolic reactions (all the reactions that keep an organism alive) at a rate that can sustain life
What is special about enzymes?
Enzymes are specific to one particular substrate, as the enzyme is a complementary shape to the substrate
What is a substrate?
molecule/s that get broken down or joined together in the reaction
What causes an enzyme to become specific?
Enzymes are specific to one particular substrate(s) as the active site of the enzyme, where the substrate attaches, is a complementary shape to the substrate.
This is because the enzyme is a protein and has a specific 3-D shape
What is enzyme specificity known as?
lock and key hypothesis
What is it called when the substrate moves into the enzyme’s active site?
they become known as the enzyme-substrate complex
What happens after the reaction has occurred?
the products leave the enzyme’s active site as they no longer fit it and it is free to take up another substrate
Describe process of how enzymes work
Enzymes and substates randomly move about in solution
When an enzyme and its complementary substrate randomly collide – with the substrate fitting into the active site of the enzyme – an enzyme-substrate complex forms, and the reaction occurs.
A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions.
What is the enzymes specific shape held in place by?
Enzymes are proteins and have a specific shape, held in place by BONDS
Why is the specific shape important?
This is extremely important around the active site area as the specific shape is what ensures the substrate will fit into the active site and enable the reaction to proceed
When do enzymes work fastest?
Enzymes work fastest at their ‘optimum temperature’ – in the human body, the optimum temperature is 37⁰C
What happens to enzymes when they’re heated to high temperatures?
Heating to high temperatures (beyond the optimum) will break the bonds that hold the enzyme together and it will lose its shape -this is known as denaturation
Why is denaturation such a problem?
Substrates cannot fit into denatured enzymes as the shape of their active site has been lost
Is denaturation reversible?
- Denaturation is irreversible – once enzymes are denatured they cannot regain their proper shape and activity will stop
What happens to enzymes when you increase the temperature from 0 degrees to the optimum?
Increasing the temperature from 0⁰C to the optimum increases the activity of enzymes as the more energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction
What do low temperatures do to enzymes?
This means that low temperatures do not denature enzymes, they just make them work more slowly
What is the general optimum PH for enzymes? What are some exceptions?
The optimum pH for most enzymes is 7
some that are produced in acidic conditions, such as the stomach, have a lower optimum pH (pH 2)
some that are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9)
What can happen to enzymes if the pH is too high or too low?
If the pH is too high or too low, the bonds that hold the amino acid chain together to make up the protein can be destroyed
What happens when the conditions move too far away from the optimum pH of the enzyme?
Moving too far away from the optimum pH will cause the enzyme to denature and activity will stop
What happens to enzyme activity when the conditions move too far away from the optimum pH of the enzyme?
This will change the shape of the active site, so the substrate can no longer fit into it, reducing the rate of activity
What is an enzymes that digests starch and what is it turned into?
Amylase is an enzyme that digests starch (a polysaccharide of glucose) into maltose (a disaccharide of glucose).
Describe procedure for Investigating the Effect of Temperature on Amylase
Starch solution is heated to a set temperature
Iodine is added to wells of a spotting tile
Amylase is added to the starch solution and mixed well
Every minute, droplets of solution are added to a new well of iodine solution
This is continued until the iodine stops turning blue-black (this means there is no more starch left in the solution as the amylase has broken it all down)
Time taken for the reaction to be completed is recorded
Experiment is repeated at different temperatures
The quicker the reaction is completed, the faster the enzyme is working
Describe procedure for Investigating the Effect of pH on Amylase
Place single drops of iodine solution in rows on the tile
Label a test tube with the pH to be tested
Use the syringe to place 2cm3 of amylase in the test tube
Add 1cm3 of buffer solution to the test tube using a syringe
Use another test tube to add 2cm3 of starch solution to the amylase and buffer solution, start the stopwatch whilst mixing using a pipette
After 10 seconds, use a pipette to place one drop of mixture on the first drop of iodine, which should turn blue-black
Wait another 10 seconds and place another drop of mixture on the second drop of iodine
Repeat every 10 seconds until iodine solution remains orange-brown
Repeat experiment at different pH values – the less time the iodine solution takes to remain orange-brown, the quicker all the starch has been digested and so the better the enzyme works at that pH
What is a catalyst (1 mark)?
A catalyst is a substance that increases the rate of a chemical reaction and is not changed by the reaction.
What is an enzyme (1 mark).
An enzyme is a protein that functions as a biological catalyst.
Why are enzymes important (1 mark)?
Enzymes are necessary to all living organisms as they maintain reaction speeds of all metabolic reactions at a rate that can sustain life.
Describe enzyme action with reference to
the complementary shape of an enzyme and
its substrate and the formation of a product (3 marks).
Enzymes are specific to one particular substrate as the enzyme is a complementary shape to the substrate. The enzyme changes the substrate into new molecules called products.
Describe the effect on enzyme activity when the temperature is up to the enzyme’s optimum (4 mark).
As temperature increases to the optimum, the kinetic energy of the enzyme and substrate increases, causing more collisions between the enzyme and substrate. This causes the formation of more enzyme-substrate complexes, leading to an increase in enzyme activity.
Describe the effect on enzyme activity when the temperature is above the optimum (3 marks).
At very high temperatures above the optimum, the enzymes become denatured and the active site changes shape. This decreases the rate of reaction as enzyme-substrate complexes cannot form.
Describe the effect on enzyme activity when the temperature is below the optimum (3 mark).
At low temperatures, enzyme activity is low because the enzyme and substrate molecules have less kinetic energy so there are fewer collisions between them.
Describe the effect on enzyme activity when deviating from the optimum pH (4 marks).
Deviating from the optimum pH (too high or too low) causes the enzyme’s active site to become denatured. Hence, it can no longer form enzyme-substrate complexes, leading to a decrease in enzyme activity.
Explain the specificity of enzymes in terms of the
complementary shape and fit of the active site
with the substrate (3 marks).
Enzymes are specific because different enzymes have different shaped active sites. The shape of an enzyme’s active site is complementary to the shape of its specific substrate or substrates. This means they can fit together.
Explain enzyme action with reference to the
active site, enzyme-substrate complex, substrate
and product (5 marks).
A substrate enters the active site of the enzyme. This forms the enzyme-substrate complex. The reaction then occurs, converting the substrate into products and forming an enzyme products complex. The products then leave the active site of the enzyme.
What are the five properties of enzymes?
Enzymes are proteins and proteins can be tested by using the Biuret test.
Each enzyme matches the complementary shape of a substrate.
Enzymes can be used again and again because they are unchanged in a reaction.
Enzyme are influenced by temperature.
Enzymes are influenced by pH.
What is the lock and key hypothesis/model?
The lock and key hypothesis states that the substrate fits perfectly into the active site of an enzyme
What is the active site?
A specific region of an enzyme where the substrate binds and the reaction takes place.
Define denaturation.
A permanent change in the shape of an enzyme’s active site that prevents the binding of a substrate.
Is denaturation reversible?
Denaturation is irreversible.
State the optimum temperature for enzyme activity in plants and humans.
In the human body, the optimum temperature is 37⁰C.
In plants, the optimum temperature is 28⁰C to 30⁰C.
State the optimum pH for the activity of the enzyme pepsin and amylase/trypsin.
The optimum pH for pepsin in the stomach is pH 2.0
The optimum pH for amylase and trypsin is pH 7.5
Finish the following equations: Enzymes are in CAPITAL LETTERS.
hydrogen peroxide ➡ _______ ➡ water and _______
____ ➡ AMLYLASE ➡ maltose ➡ ________ ➡ glucose.
protein ➡ ______ ➡_________➡ TRYPSIN ➡ ______ acids (proteases).
____/_____ ➡ TRIPASE ➡ fatty acids and _______
hydrogen peroxide ➡ CATALASE ➡ water and oxygen.
starch ➡ AMLYLASE ➡ maltose ➡ MALTASE ➡ glucose.
protein ➡ PEPSIN ➡ peptides ➡ TRYPSIN ➡ amino acids (proteases).
fats/lipids ➡ LIPASE ➡ fatty acids and glycerol.
Diagrams:
Know what a pH scale looks such as what is weak/strong acid and weak/strong alkali.
Catalyst
speeds up the rate of reaction
Product
result of reaction
