Enzymes Flashcards
What are the features of enzymes?
highly specific unchanged after the reaction do not affect position of equilibrium increase rate of reaction usually proteins may require cofactors
Why are we interested in enzymes?
many inheritable genetic disorders include changes to enzyme function
overactive enzymes can cause disease
measurement of enzyme activity can be useful for diagnosis
some drugs work by inhibiting enzymes
What are the features of an active site?
occupies a small part of the enzymes
formed of amino acids from different parts of the primary sequence
clefts/crevices that usually exclude water
complementary shape to substrates
bind substrates by multiple weak bonds
Name the 2 hypotheses for substrate binding
lock and key or induced fit
What is Vo?
The initial rate of reaction
What is the Michaelis-Menten equation?
Vo = (Vmax.[S])/(Km + [S])
It predicts the plot of Vo versus [S] will be a rectangular hyperbola
The model proposes that a specific complex between the enzyme and the substrate is a necessary intermediate in catalysis.
What is Vmax?
The maximal rate when all enzyme active sites are saturated with substrate
What is Km?
Km is the substrate concentration that gives half the maximal velocity
What do Km values indicate?
They give a measure of the affinity of an enzymes for its substrate.
What does a high Km indicate?
The enzyme has a low affinity for its substrate as it has taken a high concentration of substrate to reach half the maximal velocity.
What does a low Km indicate?
The enzyme has a high affinity for its substrate as it has only taken a small concentration of substrate to reach half the maximal velocity.
What is 1 unit in terms of enzymes?
The amount of enzyme that converts 1 micro molar of product per minute under standard conditions.
In what ways can you classify inhibitors?
irreversible, reversible, competitive and non-competitive
What are the features of competitive inhibitors?
bind at the active site affect Km (as inhibitor competes with substrate) doesn't affect Vmax (as adding enough substrate will always overcome the effect of the inhibitor)
What are the features of non-competitive inhibitors?
bind at a different site affects Vmax (as it decreases the turnover number of the enzyme - less ESC formed) doesn't affect Km (as the affinity of an enzyme for its substrate is not changed)
