Lecture 7 - Enzyme Catalysis and Kinetics Flashcards
What are enzymes?
proteins (composed of amino acids) that act as catalyst
How are enzymes named?
by adding the suffix “ase” to the reacting catalyzed or the substrate transformed of a mixture
What are the 6 major classifications of enzymes?
- oxidases
- transferases
- hydrolyses
- lyases
- isomersases
- ligases
catalyze oxidation/reduction reactions
oxidases
catalyze the transfer of functional groups from one molecule to another
transferases
hydrolases
catalyze hydrolysis reactions
lyases
catalyze the cleavage of bonds often resulting in a new double bond or ring structure’
or
catalyze the addition of groups to double bonds
catalyze the isomer isomerization reactions; the structural rearrangement of a molecule
isomerases
catalyze reactions in which two molecules are joined together
ligases
ex. DNA ligase
What is the active site?
the region of the enzyme that bonds the substrate
it contains the residuals (amino acids) that directly participate in making or breaking of bonds
The active site takes up a relatively _____ part of the total volume of the enzyme.
small or large?
small
The active site is a 3D entity formed by groups of different parts of the _____ _____ chain.
amino acid
What are two examples of non-protein comments required by some enzymes for activity.
- coenzymes
2. prosthetic groups
coenzymes
serve in the transfer of electrons, elements, and functional groups
can associate at different times
Name one coenzyme.
ex. NADH, electron carrier
These associate tightly to their enzymes, usually permanently.
prosthetic groups
These associate loosely to their enzymes.
coenzymes
Name an example of a prosthetic group.
Heme group in the cytochromes
cytochromes undergo redox reactions through 4 electron transfers
State the Michaelis-Menton (M-M) equation and define each term.
V = Vmax [S]
_______
[S] + Km
V = rate of catalysis (# of moose of product former per _) Vmax = maximum rate of catalysis [S] = substrate concentration Km = Michaelis-Menton coefficient or half reaction coefficient
What does the Michaelis-Menton (M-M) kinetics/model (or saturation kinetics) predict?
it accounts for the kinetics of simple enzyme catalyzed reactions
What is the assumption about V at low [S]?
At low [S], V increases directly proportional to [S]
the rate is first order with respect to [S]
What is the assumption about V at high [S]?
enzymes become saturated with the substrate, the rate no longer increases
*the rate is zero order with respect to [S].
At high [S], V = ___.
Vmax
Km
Michaelis-Menton coefficent; the substrate concentration when V is half o its max value (Vmax)
when V = Vmax/2, [S] = Km
Km represents the affinity between the _____ and the _____.
substrate, enzyme
A low Km indicates
a strong affinity
*Vmax is reached at lower substrate concentrations
A high indicates
a poor affinity
A (high/low) Km is most ideal. Why?
Low because, enzymes are not overly saturated by the substrate.
___ and ___ can be determined from rates of catalysis of different substrate concentrations; the Michaelis-Menton equations is used.
Km and Vmax
competitive inhibition
a chemical, similar in structure to the normal substrate, competes with the substrate for the active site of the enzyme
e.g. DCE/VE
How can competitive inhibition be overcome?
by increasing the concentration of the substrate
non-competitive inhibition
inhibitors do not compete with the substrate for the active site
- instead the interact with another part of the enzyme
Does increasing the substrate concentration effect non-competitive inhibitors?
no
