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
Reactant
what is going to react
Reactions in our body
enzymes catalyse every reaction in our body
Enzymes
Proteins
Biological catalysts in metabolic reactions
Specific (only a selective substrate they function with)
Contain an active site
Activity is affected by temperature, pH, and substrate concentration
Substrate
molecule that an enzyme reacts with
Lock and key
A substrate will fit into an enzymes active site like a lock and a key
No other substrate will work with an enzyme
Each enzyme has a special shape with an area, the active site onto which the substrate molecules bind
Very few amino acids form the active site making it a small component of a large molecule
How enzymes work
Biological catalysts that speed up the rate of metabolic reactions without being used up themselves.
Catabolism
Reactions where larger molecules are broken down into smaller molecules by enzymes
Anabolism
Reactions where small molecules are built up into larger more complex molecules by enzymes
Induced fit hypothesis
Modern interpretations suggest that in the presence of a substrate, the active site of an enzyme may change in order to fit the substrates shape
The enzyme will wrap around the substate
Denaturing of Enzymes
Denaturing is the loss of biological properties (enzymes can no longer speed up the rate of reaction)
Structure can be altered/denatured in extreme temperature and pH
The active site is altered and changes shape which disables the ability for a substrate to bind to it therefore it cannot act as a catalyst
Enzymes have an optimum temperature where it is the most efficient and when the temperature is higher than the optimum temperature the enzymes may denature stopping the reaction
Enzymes have an optimum pH where it is the most efficient. pH level that is too high or too low will lead to the denaturing of enzymes
Enzyme Graph
Uncatalysed reaction/reaction without enzyme should be higher than the catalysed reaction
Height from peak of the graph to the beginning of the reaction is the activation energy. Enzymes catalyse reactions by lowering activation energy so catalysed graph should have smaller activation energy
Start of reaction is at the peak
Smart and end at the same place
If the graph is under the original beginning of the graph, it is exothermic reaction which is releasing heat and thermal energy, if it is above it is an endothermic reaction which absorbs heat and thermal energy
The y-axis of the start of the graph to the end of the graph is the overall change in energy
Free energy (all energy involved with reaction) against course of reaction
Energy needed in enzymes
Chemical reactions need energy to start them off called activation energy
Energy is needed to break the existing chemical bonds inside molecules
In the body, enzymes lower the activation energy of a reaction and so reduce the input of energy needed and allow reactions to take place at lower temperature
What is an enzyme?
A protein catalyst which speeds up the rate of the reaction without undergoing any change itself
What do enzymes bind with?
They bond specifically to a substrate molecule and convert it to a product molecule. They are not used up in a reaction and so can be recycled.
What do enzymes do?
Enzymes reduce the amount of energy required to begin the reactions
What is the structure of an enzyme?
Enzymes are made of proteins that have been folded so that they have a specific active site which binds to its substrate.
How does enzyme action happen?
Enzyme and substrate are available
Substrate binds with enzyme
Substrate is converted to product
Products are released
How is the enzyme affected by temperature?
Enzymes work best at 37 degrees
However at high temperatures the enzymes protein structure is permanently changed so that the substrate can no longer bind to the active site.It becomes denatured
What is the optimal temperature?
The temperature at which the enzyme works best at
How is the enzyme affected by the pH?
Each enzyme works best at a particular pH
Enzymes can dénature by extreme pH changes.
What pH does trypsin work in?
8
What pH does pepsine work in?
2
What pH does catalase work in?
7
What does heat do to enzymes?
More collisions between enzymes and substrate
When do enzymes work the best?
At optimum pH and optimum temperature
How can enzyme activity be changed?
By altering pH and temperature
What happens when the temperature is above the optimum temp?
It denatures the enzyme
What happens if the temperature is below the optimum temp
The enzyme can be inactive
What happens if the pH is above the optimum
It will denature the enzyme and if below it can be inactive
Enzymes are biological catalysts. What does this mean?
They can speed up chemical reactions and break down or build up molecules. Enzymes do not take part in the reactions they catalyse
What is a substrate
A chemical that enzymes act upon
Each Enzyme acts on a specific substrate. What does this mean
They are specialised for certain substrates. E.g amylase always acts on starch and it could never act on a protein or fat molecules
Explain how enzymes fit into substrates
They fit into the active site of the substrate. E.g lock and key
What are the types of digestive enzymes
Charbohydrases
Proteases
Lipases
Starch reaction:
Starch digested by amylase –> maltose
Amylase- salivary or pancreatic
Reaction for maltose
Maltose digested by maltase –> glucose
Reaction for protein
Protein digested by proteases –> amino acids
Proteases e.g pepsin
Reaction for protein
Protein digested by proteases –> amino acids
Proteases e.g pepsin
Reaction for lipids
Lipids digested by Lipases –> fatty acids & glycerol
Reaction for hydrogen peroxide
H2O2 (hydrogen peroxide) digested by catalase –> water + oxygen
What is the order of consumption?
Ingestion -> digestion -> absorption -> assimilation -> egestion
What is ingestion
The process by which food material is taken into the body, the material is taken into the mouth and chewed up into smaller pieces by teeth
What is digestion
Can be either mechanical (teeth) or chemical (enzymes). It is the process by which larger complex molecules are broken down into smaller more simple molecules
What is absorption
The process by which the smaller molecules produced by digestion are passed into the blood supply of the ileum. The molecules pass across to the blood by diffusion and defines by active transport
What is assimilation?
The process by which the small molecules absorbed into the blood are passed into body cells and are then used to make the chemicals needed by the body. For example the amino acids from a plant protein can be arranged to make muscle protein in your body
What is egestion
The process by which undigested material (fibre) and dead cells and bacteria are removed from the body. E.g faeces POOO
What are enzymes made of?
Proteins
Catalyst-
Substances that increase the rate of chemical reaction without being changed by the reaction
Enzymes-
proteins that are biological catalyst that speed up chemical reactions
Enzymes have a specially designed
active site where a
particular substrate is broken
down.
antibodies have a specific antigen that they can
bind to on the pathogen body
enzymes either
break larger molecules into smaller ones
build large molecules from smaller ones
convert one small molecule to another
facts about enzymes
they are biological catalysts
they speed up reactions
they are proteins
they are reusable
can be denatured
influenced by PH and temperature
Lock and key hypothesis
enzymes are specific to its one specific substrate
- the shape of the active site matches the shape of the substrates, allowing two molecules to bind during chemical reactions
- active site specifically matches the shape of substrate
-1) substrate enters active site enzyme and the enzyme-substrate and bonds in substrate and weakened and then products are formed
starch is chemically digested by
amylase
starch is chemically digested by amylase and the product is
maltose ( two glucose molecu;es) the maltose is further broken down by maltase to get two single units of glucose
fats are chemically digested by
lipase
fats are chemically digested by lipase and the products are
fatty acids and glycerol
proteins are chemically digested in the stomach by
pepsin into peptide and is then digested by trypsin to get amino acids
A successful reaction between a substrate and an enzyme depends on :
1) optimal pH
2) optimum temperature
3) orientation of the enzyme and the substrate
why does ph matter in an enzyme and substrate reaction
some enzymes work best in acidic conditions and some in basic conditions and
some in neutral conditions. Wrong pH damages enzymes
why does temperature matter in an enzyme and substrate reaction
for human enzymes is 37 - 40* C - lower than this, enzymes are
inactivated. Higher than this enzymes start to denature
○ Enzymes are folded into a shape that accepts the substrate molecule. This is determined
by the sequence of amino acids that form it
○ As you approach the optimum temp, enzymes gain kinetic energy, and so collisions with
substrates are more frequent. As a result, the rate of reaction is highest
○ As you go beyond the optimum temp, bonds holding enzymes break down, the shape of
the active site changes. So it is denatured
Denaturing
change in a protein that results in a loss (usually permanent) of its biological
properties.
A catalyst
is a substance that increases the rate of a chemical reaction and is not changed by the reaction.
Enzymes
proteins that are involved in all metabolic reactions, where they function as biological catalysts.
Enzymes increase the reaction rate to the
necessary reaction rate to sustain life.
Enzymes and substrate
collide. Enzyme and substrate fit together. Substate binds
with Enzymes active site. Enzyme substrate complex forms. Because enzyme is Complementary to its substrate. This results in the formation of a product.
Enzymes are specific
Substate fits into the active site of an enzyme. Therefore, the
shape of the enzyme and substrate must be complementary
If the temperature is increased
enzymes gain kinetic energy and enzymes move
faster, the frequency of effective collisions increases. If the temperature increases above the optimum temperature, the enzyme loses its shape and the enzyme denatures. The substrate no longer fits into the enzyme’s active site. And the enzyme can not catalyze the reaction anymore.
If the temperature is decreased
enzymes lose kinetic energy and move slower,
frequency of effective collisions decrease. Therefore, the rate of reaction decrease.
Enzymes do not denature in this process.
Extreme pH can also
denature the enzyme
