Enzymes

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What are all the reactions in every living cell collectively known as?
Metabolism
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What are the 2 ways in which enzymes can work and give examples for each
Intercellularly e.g. helicase and DNA, Extracellularly e.g. digestive enzymes
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What are enzymes?
Biological catalysts that speed up chemical reactions without being changed itself.
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What is the protein nature of enzymes?
They are globular proteins, they have a complex tertiary structure
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What factor to do with the amino acids also determine the enzyme's shape?
Hydrophobic R groups project inwards and hydrophilic groups project outwards
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What is the cavity in an enzyme called?
The active site
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What is formed when the enzyme binds with the substrate?
An enzyme-substrate complex
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What is the lock and key theory?
Just as a key fits into a lock in a very precise way, so do the substrates into the active site.
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What is the induced fit theory?
The active site is more flexible than was once thought. It is now believed that the active site is like a soft glove. The active site adjusts to make a close fit around the substrate. If they are too different then they obviously won't fit
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What do all exogonic reactions need?
An input of energy to start the reaction called the activation energy
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How do enzymes speed up reactions?
They lower the amount of activation energy needed to start a reaction
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What are the effects of increasing temperature at temperatures below the optimum temperature?
As temp. increases so does the kinetic energy of the molecules, there are more successful collisions between enzyme active site + substrate and more enzyme-substrate complexes are made = more product made in a given time
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What are the effects of increasing temperature at temperatures above the optimum temperature?
The atoms within the enzyme vibrate excessively, this weakens bonds and eventually breaks the hydrogen bonds holding the enzyme in its specific shape
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What are the effects of increasing temperature at temperatures above the optimum temperature? Pt.2
This means the active site is altered so the substrate fits in less easily and rate of reaction decreases. If temp. continues to increase, the enzyme will suffer irreversible alteration and it will be denatured
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Why would more product be formed at 60'C in the first 5 minutes than 25'C and 37'C?
At 60'C the enzyme and substrate have more kinetic energy = more successful collisions = more enzyme-substrate complexes are formed = rate increases = more product formed in a given time
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Why is less product made overall at 60'C?
The enzymes gradually denature and so not all of the substrate is made into a product
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What is pH a measure of?
H+ ion concentration which is a measure of acidity and alkalinity
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If the pH deviates from the enzyme's optimum, what bonds are broken and what does this result in?
The hydrogen and ionic bonds, the active site will change shape slightly
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What does small deviations in pH cause?
Temporary denaturation
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What does large deviations in pH cause?
Permanent denaturation
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What effect does increasing substrate concentration have on rate of reaction
As substrate conc. increases, the reacting medium becomes more crowded so there are more successful collisions between the active sites and the substrate = more enzyme-substrate complexes and more product is formed in given time
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Above a certain substrate concentration, why wouldn't there be a further increase in rate and why would a graph be shown to be leveling of?
Above the critical amount of substrate conc. all of the available active sites will become filled so any more substrate molecules will have to wait.
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Above the critical amount of substrate concentration, what is limiting the rate of reaction?
Enzyme concentration
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What is the effect of increasing enzyme concentration?
(Explain increasing substrate conc.)
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How can pH be altered?
Using a buffer
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How can different concentrations of enzymes be created?
By diluting the original enzyme sample
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What would you do in a control experiment to show the results are due to an enzyme?
An identical experiment should be carried out using boiled and cooled enzymes.
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What are enzyme inhibitors?
These are substances that reduce the rate of reaction or stop it all together by combining with the enzyme to form enzyme-inhibitor complexes
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How do competitive inhibitors work?
They compete with the substrate for the active site by blocking it directly
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How do non-competitive inhibitors work?
They attach to part of the enzyme away from the active site, but alter the enzyme's shape so an enzyme-substrate complex cannot be formed
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What do competitive inhibitors have in comparison to the active site?
A similar shape
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How can the effect of a competitive inhibitor be reduced?
By increasing the concentration of the substrate
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What is the name of the site where the non-competitive inhibitors bind?
Allosteric site
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Why wouldn't increasing the substrate concentration have an effect on the non-competitive inhibitor?
Because the non-competitive inhibitors are not structurally similar to the substrate molecules or the active site
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What does the graph for a competitive inhibitor show?
It shows the inhibitor slows the rate of reaction but as conc. of the substrate increases the effect of the inhibitor becomes less and rate increases.
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What does the graph for a non-competitive inhibitor show?
A non-competitive inhibitor 'knock out' a fixed amount of the enzyme, the maximum rate of reaction is lowered because there are less enzymes
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What is end-product inhibition?
This is where, to keep the levels of substances constant in a series of reactions, the end-product becomes an inhibitor for the first reaction with in turn slows or stops its production.
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What is end-product inhibition called?
Negative Feedback
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What is an immobilised enzyme?
These are enzymes that have been fixed to or trapped in another unreactive and cannot move freely within the substrate
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What are some ways in which enzymes can be immobilised?
Bound to a solid surface e.g. a gel membrane, held behind a selectively-permeable membrane or alginate beads
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What must immobilisation involve?
Binding to non-catalytic parts of the enzyme molecule (Not the active site)
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What are the advantages of immobilised enzymes?
They can be easily recovered for re-use and do not contaminate the product, they are more stable at higher temperatures, they can tolerate a wider range of pH values so several enzymes can be used at once, used for longer periods of time
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Why do immobilised enzymes allow the rate of reaction to be controlled more carefully?
They can be more easily added to and removed from reactors
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What are disadvantages of immobilisation?
The rate of reaction can decrease because the immobilisation process can affect the shape of the enzyme molecule, the rate of reaction maybe slowed because the enzyme has reduced kinetic energy as it is separated from the substrate by a membrane
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Why do enzymes immobilised inside alginate beads tend to reduce the rate?
The substrate has to diffuse into the bead before binding with the active site of the enzyme
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What are biosensors?
Biosensors make use of immobilised enzymes to detect specific molecules in a mixture
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How do biosensors measure the quantity of a substance?
By converting chemical energy into electrical signal
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What is the use of the membrane in biosensors?
When a substrate is fed into the biosensor, a partially permeable membrane allows the substance to be detected to pass through but not any other molecule
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Once the substrate has passed through the membrane of the biosensor, what happens next?
The substance binds with the immobilised enzymes to made a product, the product stimulates a transducer or an electrode which converts the chemical energy to electrical impulses which are read on a display
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What are the advantages of the use of immobilised enzymes in biosensors?
They are rapid, they are specific, they can accurately measure the quantities present
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What are the uses of biosensors?
Medical diagnosis e.g. diabetes because they can detect the amount of glucose in the blood or urine
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What properties must enzymes in biosensors have?
They must be able to be fixed in an unreactive solid, they must be specific to the test, they need to be able to withstand changes in temperature in pH
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Card 2

Front

What are the 2 ways in which enzymes can work and give examples for each

Back

Intercellularly e.g. helicase and DNA, Extracellularly e.g. digestive enzymes

Card 3

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What are enzymes?

Back

Preview of the front of card 3

Card 4

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What is the protein nature of enzymes?

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Card 5

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What factor to do with the amino acids also determine the enzyme's shape?

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