2.4 enzyme definitions Flashcards
Activation energy
The amount of energy needed for a reaction to happen
Active site
A specific region on an enzyme where the substrate binds and the reaction takes place.
Amylase
An enzyme that catalyses the extracellular breakdown of starch
Catalase
An enzyme that catalyses the intracellular breakdown of hydrogen peroxide into oxygen and water
Coenzyme
A type of cofactor that is bound loosely to an enzyme with weak interactions
Cofactors
A non-protein molecule that is needed for the effective functioning of an enzyme.
Competitive inhibitor
A molecule which binds to the active site of an enzyme and prevents the substrate from binding, decreasing its activity as they compete with substrate for
the enzyme.
Cyanide (CN-)
A metabolic poison which acts as an irreversible inhibitor of cytochrome oxidase and hence preventing respiration.
End-product inhibition
A method of enzyme inhibition where the product of an enzyme controlled reaction can bind to the enzyme and prevent it from working.
Enzyme
A biological catalyst used to speed up the rate of biochemical reactions without being used up or permanently altered.
Enzyme-product complex
The temporary complex formed after the enzyme has catalysed the reaction but before the products have left the active site of the enzyme.
Enzyme-substrate complex
The temporary complex formed when the substrate binds to the active site of the enzyme.
Extracellular reaction
A reaction that occurs outside of cells
Inactive precursor
An inactive form of an enzyme that cannot carry out its function until it is activated
Induced fit hypothesis
A model of enzyme action that describes how once a specific substrate binds to the active site, the enzyme undergoes subtle conformational changes to fit the substrate better.
Intracellular reaction
A reaction that occurs within cells
Lock and key hypothesis
A model of enzyme action that describes how the enzyme will only fit a substrate that has the correct complementary shape to the active site
Metabolism
The sum of all the chemical reactions taking place in a cell
Non-competitive inhibitor
An inhibitor which binds to a different part of an enzyme known as the allosteric site and prevents the enzyme from functioning as it changes the shape of the active site therefore preventing the binding of the substrate
Prosthetic group
A type of cofactor that is permanently bound to an enzyme with strong interactions.
Substrate specificity
The ability of an enzyme to catalyse only a specific reaction or set of reactions which have substrates complementary to the active site of the enzyme
Temperature coefficient (Q10)
A method of calculating an increase in reaction rate after a 10C temperature increase - calculated using the following equation
Q10 = R2/R1
Trypsin
An enzyme that catalyses the extracellular breakdown of proteins
what are the factors affecting the rate of enzyme-controlled reaction
enzyme concentration
substrate concentration
temperature
Explain how enzyme concentration affects the rate of reaction
the rate of reaction increases as enzyme concentration increases as there are more active sites for substrates to bind to, however increasing the enzyme concentration beyond a certain point has no effect on the rate of reaction as there are more active sites than substrates so substrate concentration becomes the limiting factor
Explain how substrate concentration affects the rate of a reaction
As concentration of substrate increases, rate of reaction increases as more enzyme-substrate complexes are formed. However, beyond a certain point the rate of reaction no longer increases as enzyme concentration becomes the limiting factor
Explain how temperature affects the rate of a reaction
Rate of reaction increases up to the optimum temperature, which is the temperature at which enzymes work at their maximum rate. Rate of reaction
decreases above the optimum temperature and if it goes to high the enzymes may denature as the active sights will change shape
What is an inhibitor
a substance which slows down or stops a reaction by affecting the binding of substrate to the enzymes. Inhibitors can either be reversible or irreversible
Give an example of an irreversible inhibitor
heavy metal ions such as mercury and silver which cause disulphide bonds within the protein structure to break, as a result causing the shape of the active site to change, thus affecting protein activity
What is a reversible inhibitor
a substance which binds to the active site through hydrogen bonds and weak ionic interactions therefore they do not bind permanently and can be reversed by the addition of excess substrate.
what is an irreversible inhibitor
A substance that covalently bonds to a particular group at the active site. The inhibitor-enzyme bond is so strong that the inhibition cannot be reversed by the addition of excess substrate.
give examples of an inhibitor
Many drugs are inhibitors:
penicillin which is used to fight bacterial infections, it is an inhibitor of enzyme transpeptidase which plays an important role in cell wall formation.
Ritonavir which is an antiretroviral drug used to treat
HIV which inhibits HIV protease which is responsible for assembly of new viral particles and spread of infection.
what happens to the amount of product formed when a competitive inhibitor is present
remains the same
what happens to the rate of product formed when a competitive inhibitor is present
decreases - the higher the concentration of competitive inhibitor the lower the reaction rate
how do you outcompete a competitive inhibitor
increasing the substrate reverses the effect of competitive inhibitors by outcompeting them
what are the types of reversible inhibitors
competitive and non competitive
how do you out compete a non competitive inhibitor
you can’t - Increasing the concentration of substrate has no effect
what are the 3 types of cofactors
coenzymes
activators
prosthetic groups
what are most coenzymes
vitamin derived, examples include NAD derived from niacin, which acts as a hydrogen acceptor.
what is an activator
inorganic metal ions which temporarily binds to the enzyme and alters its active site, making the reaction more feasible.
give an example of an activators
magnesium ion is an important activator which is involved in processes such as shielding negative charge.
give an example of a prosthetic group
haemoglobin contains a prosthetic haem group which contains iron, permanently bound to the molecule,
which allows oxygen to bind and form haemoglobin
