Work inside a cell e.g. catalase that breaks down hydrogen peroxide
Extracellular enzymes
Are secreted outside the cell where it functions e.g. amylase and trypsin break down large food molecules outside the cell so that the small products can be absorbed
Tertiary structure
The 3D shape of an enzyme that is necessary for it to function
Specificity
An enzyme only carries out one reaction because of the shape and charge distribution in the active site
Active site
A cleft on an enzyme where the substrate binds
Lock and key hypothesis
The shape of the substrate is complementary to the shape of the active site so they can bind together and form an enzyme substrate complex
Induced fit hypothesis
As the substrate binds into the active site the enzyme changes shape around the substrate forming a transition complex that puts strain on the bonds in the substrate molecule
Enzyme product complex
Once the reaction has occurred the enzyme product complex becomes an enzyme product complex and then the product is released
Activation energy
The energy needed to carry out the reaction, this is much lower when an enzyme is involved because it provides and alternate reaction pathway
Transition state
The substrate is converted into the product through an intermediate form in an alternate reaction pathway
Low/high pH
The quantity of H+ and OH- ions around the enzyme affects the 3D shape of the active site and affects how well a substrate can bind, if the change in pH is extreme then the enzyme will denature.
Low temperature
The frequency of collisions is lowered which results in fewer enzyme substrate complexes being formed, the enzyme is not denatured.
High temperature
Very frequent collisions between molecules cause vibrations within the enzyme that causes hydrogen bonds to be broken, this changes the shape of the active site and the enzyme is denatured.
Enzyme concentration
The rate of reaction increases because more active sites are available, so more enzyme substrate complexes can form until the concentration of substrate is limiting
Substrate concentration
The rate of reaction increases because the substrate can bind into empty active sites forming more enzyme substrate complexes until the enzymes become saturated
Serial dilution
A solution is diluted repeatedly making very low concentrations
Coenzymes
are non-protein biological molecules that bind with the substrate and are often changed during the reaction.
Cofactors
a substance that increases enzyme activity
Inorganic ion cofactor
This binds the enzyme during the reaction affecting the charge of the active site and increases the likelihood of substrate binding
Prosthetic group
A permanent but non-protein component of an enzyme that is necessary for it to function
Coenzyme example
NAD from vitamin B3
Cofactor for amylase
Cl-
Prosthetic group for carbonic anhydrase
Zn2+
Enzyme inhibitor
Reduces the rate of enzyme controlled reactions
Competitive inhibitor
Binds to the active site and reduces the rate of substrate binding (by blocking it), this is overcome at very high substrate concentrations and the maximum rate can still be achieved
Non-competitive inhibitor
Bind away from the active site (allosteric site) this affects the shape of the active site preventing the substrate from binding. The maximum rate of reaction is lowered.
Reversible inhibitors
An inhibitor that binds temporarily to the enzyme, often a competitive inhibitor
Non-reversible inhibitors
An inhibitor that binds permanently to the enzyme preventing the enzyme from working.
Metabolic poison
An enzyme inhibitor that prevents an essential enzyme reaction from occurring this may result in the accumulation of a toxic product
Inhibitors as medicines
An enzyme inhibitor can be used to stop or reduce enzyme reactions that are having adverse effects on a patient
Product inhibition
The product of a reaction binds to an enzyme in an enzyme pathway, preventing an earlier reaction so that this product does not accumulate.
Inactive precursor
A protein that will be converted into an active form only when required such as prothrombin into thrombin in the blood clotting cascade.