Topic 2:2 - enzymes Flashcards
what is the key concept surrounding enzymes?
Enzymes are specific for their substrate and increase reaction rates by lowering activation energy. Enzyme function is affected by a range of factors.
what are enzymes?
A type of protein! an enzyme is an organic catalyst, which speeds up a chemical reaction without itself being changed or destroyed.
what structure do enzymes have?
Enzymes are proteins with a tertiary structure hence a 3-D shape.
what type of protein are enzymes?
Enzymes are called globular proteins, to distinguish them from secondary structural proteins which are fibrous.
What is an active site?
The active site is the region on the surface of the enzyme molecule with a particular shape, into which only a specific substrate molecule with a complementary shape will fit.
why is the shape of the active site important?
The shape of the active site of each enzyme is specific to the complementary shape of the substrate.
what binding occurs when a substrate enters an enzymes active site?
Binding is by weak hydrogen bonds.
As the substrate enters the active site attractions cause…
slight changes in the shape of the enzyme and substrate until the fit is perfectly complementary.
why is enzyme-substrate binding helpful?
Binding stresses the chemical bonds in the substrate molecule so they break more easily, thus the required chemical reaction proceeds more quickly.
what happens after a chemical reaction occurs in an enzymes active site?
When products of the chemical reaction are released the active site of the enzyme returns to its original shape to be reused.
What is a chemical reaction?
Chemical reactions involve the breaking of chemical bonds in the molecules of reactants and the formation of new chemical bonds in the molecules of products.
what is activation energy?
Activation energy is the amount of energy required to break the bonds in the reactants and enable the chemical reaction to proceed.
what is the relationship between enzymes and chemical reaction rates?
Enzymes increase reaction rates by lowering the activation energy of chemical reactions.
what are the two types of factors that affect enzyme function? (give examples)
- PHYSICAL e.g temperature
- CHEMICAL e.g pH, co-factors, inhibitors
describe enzyme function at low temperatures
at low temperatures (<20 degrees):
-Molecules move slowly
-Less collisions between substrate and enzyme
-Low reaction rate
describe enzyme function at optimum temperatures
at optimal temperatures (35-40 degrees):
-Many collisions between substrate and enzyme
-Fast rate of reaction
describe enzyme function at extreme high temperatures
at high temperatures (>50 degrees):
DENATURATION
the tertiary structure is destabilised, altering the arrangement of amino acids
the altered arrangement of amino acids results in changes in shape of the active site, so binding cannot occur.
describe how pH affects enzyme function
Each enzyme has an optimum pH that will produce the shape required for its action.
A change in pH alters the charge on the amino acids, which results in a change in the hydrogen bonding within the enzyme molecule such that the SHAPE of the protein CHANGES.
Therefore, if an enzyme is exposed to a pH that is either side of its optimum the reaction rate will be lowered until the enzyme is denatured.
describe how co-factors affect enzyme activity
Some enzymes need other chemicals (e.g. metal ions, non-protein molecules etc.) to be present to function effectively.
Co-factors may bind to complete the active site or bind to the enzyme to alter the shape of the active site.
what are some examples of co-factors that affect enzyme function?
Cu, Fe, Zn, vitamins
briefly describe how inhibitors affect enzyme activity
Chemicals, specific to an enzyme, that inhibit/reduce enzyme activity by preventing substrate binding.
what are the two types of inhibitors that affect enzyme activity?
Competitive inhibitors resemble the shape of the substrate molecule and compete with substrate for enzyme active site (i.e. bind to the active site irreversibly to prevent substrate binding).
Non-competitive inhibitors bind elsewhere to the enzyme (allosteric site) causing the active site to change shape and hence prevent substrate binding (also called allosteric inhibitors).
what are some examples of inhibitors that affect enzyme function?
-most poisons
-DDT
-cyanide
-arsenic
-penicillin
describe how SUBSTRATE concentration impacts enzyme activity
Increasing the substrate concentration, increases the likelihood of collisions between the enzyme and the substrate.
Increase in substrate binding to the active site increases the rate of reaction.
The maximum rate of reaction occurs when the enzyme active sites continuously contain the substrate.
describe enzyme activity when there is low concentrations of substrate molecules
When the substrate is present at low concentrations, the active sites of the enzymes are not filled, and therefore the rate of reaction is slow.
describe enzyme activity when there is a higher concentration of substrate molecules
At higher concentrations, there are more molecules present which results in an increase in the number of collisions that are possible between the enzyme and the substrate. This leads to an increase in substrate binding to the active site and in the rate of reaction.
describe enzyme activity when the saturation point of substrate concentration is reached
The maximum rate of reaction occurs when the enzyme active sites continuously contain the substrate. (all enzymes are being used)
describe how enzyme activity is impacted by ENZYME concentration
Increasing the enzyme concentration, increases the number of molecules of enzyme present, increasing the number of active sites available to bind to the substrate.
Therefore, the likelihood of collision between substrate and active site is increased.
Therefore, as enzyme concentration increases, the rate of reaction will also increase.
(this is limited by availability of substrate)
