enzymes Flashcards
what are enzymes?
catalysts that lowers reaction energy (the free energy of activation) but it’s not used up in the reaction
what does lowering the free energy of activation do to the rate of reaction?
-increases the rate of reaction
enzyme and their rate enhancement table
what is the simplest way to lower the reaction energy?
by bringing the substrates together
what are enzyme cofactors?
enzymes that act by bringing substrates together and restrict their rotational freedom
what makes and enzyme an enzyme?
-if it reaches the free energy of activation of a reaction
how are enzymes named?
-adding the suffix- are to the name of the substrate they modify e.g DNase
-the reaction that they catalyse glucose+ATP=Glucose-6-phosphate +ADP, the enzyme for this is hexokinase
-some have arbitrary name e.g trypsin
what is zymogen?
the inactive form of an enzyme
what is a holoenzyme?
a whole enzyme, it is made by an apoenzyme + cofactor
what are the different classes of enzymes?
-oxidoreductases
-transferases
-hydrolases
-lyases
-isomerases
-ligases
what is oxidoreductases?
-the transfer of electrons via oxidation or reduction
A+B ⇌ A + B
what is transferases?
the transfer of chemical groups from one molecule to another
A +BX →AX + B
what is hydrolases?
the cleavage of a substrate using water (hydrolysis)
A + H2O→B + C
what is lyases?
the addition of groups to double bonds or the formation of double bonds following the removal of groups
A →B + C
what is isomerases?
the rearrangement of a single substrate, generating isoforms
ABC → ACB
what is ligases?
the joining of two substrates, often by eliminating water
A + B→ AB
what is the breaking of bonds for hydrolase enzymes?
-the enzyme single bonds are broken through the addition of water
what does the breaking of bonds other than hydrolysis and oxidation lead to?
forming a new double bond or a new ring structure
what is the lock and key structure of enzyme action?
-was created by fisher
-the active site of an unbound enzyme,complementary to the shape of the substrate
what is the induced fit model of enzyme action?
-was created by koshland
-the enzyme changes shape when the substrate binds, the active site is complementary to the shape of the substrate only after the substrate is bound
what is an enzymes active site?
-the 3D arrangement of specific amino acids within enzymes
-usually adjacent pockets-binding and catalytic residues
what is an enzymes active site the source of?
- source of substrate and reaction specificity
-usually only a small part of the substrate enters the active site e.g a chemical group
-there are a range of substrates which all that group
how does pH affect enzyme activity?
-pH needs to be at optimal pH range for normal conformation
-temperature-outside this range there is ionisation if a.a side-chains and change in confirmation
–may denature enzymes
how does temp affect enzyme activity?
-affects the kinetic energy of S,E
-this determines the frequency of S & E interaction
-the rate of reaction increases until E is saturated or becomes denatured
-there is then the presence of inhibitors
how does substrate affect enzyme activity?
-it determines the frequency of S + E interaction
-the rate of reaction increases until E is saturated
