Enzymes Flashcards
What are enzymes?
1)They accelerate the rate of a biochemical reaction
2)Enzymes are not used up (or consumed) in the reaction
3)Enzymes contain one (or more) active site(s), that is/are used for the catalysis reaction
4)Names of enzymes usually end with a suffix ‘ase’
What is an Active site?
(Enzyme catalyzed reaction)
The active site is a pocket in the 3-D structure of the enzyme that binds to the substrate and converts it into product
Side Chains
(Enzyme catalyzed reaction)
1)Side chains of amino acids residues on the active site hold the substrate in the correct position by reversible non-covalent interactions
2)The side chains also mediate the catalysis of the reaction
3)Enzymes bind to substrate to form enzyme-substrate intermediate first. The reaction is catalyzed and the product is released
The Lock and Key Model
1)The substrate (key) fits exactly into the shape of the active site (lock).
2)The substrate binds to the enzyme and reacts.
3)(Likened to inserting a key into a lock).
The Induced Fit Model
1)Initially, the substrate does not fit exactly into the shape of the active site.
2)But the active site adjusts its shape for the substrate to
bind and react.
Characteristics of enzyme catalyzed reactions
1)Enzyme catalyzed reactions are specific
2)The enzyme only binds either to:
-a specific biological substrate
or
-a specific group of similar substrates
(e.g. peptidase break peptide bonds of all proteins)
What is activation energy?
A fixed amount of energy required for a chemical reaction to initiate
Activation energy of reactions
1)Since substrates and products are different substances, they have different energy values
2)Activation energy hinders the transition from one energy values to another
3)It does not affect the energy values of the substrates and products
4)An enzyme/catalyst lowers the activation energy of a reaction by providing an alternative path
-Less energy is thus required for the reaction to proceed
5)Enzymes lower activation energy by forming a transition state with the substrate = the enzyme substrate complex (ES)
-Enzymes help a reaction to proceed more readily, thus increasing the reaction rate
-An enzyme reduces the activation energy of a reaction, but does not eliminate it completely
Factors affecting enzyme activity
a)Environmental factors
-Enzymes are proteins!
-Therefore factors we learned that can affect protein conformation will also affect enzyme activities
b)Presence of inhibitors
-Substances that stop enzyme activity
c)Cofactors and coeznymes
-Molecules that are essential for an enzyme to function
a)Environmental factors that affect enzyme activity
-Factors that influence protein structure will influence enzyme activity
Factors:
1)Temperature
2)pH
3)Detergents
4)Organic solvent
5)salt
6)Mechanical agitation
7)Presence of reducing agents (Beta-mercaptoethanol or DDT)
-Conformation of the enzyme active site is important for it’s function
-When enzymes are exposed to the factors that will cause protein denaturation, the enzymes lose their conformation and therefore their activity
Effect of temperature on enzyme activity
1)Higher temperature helps to overcome the activation energy
-increased the kinetic energy of molecules, or causes the molecules to vibrate/ collide more vigorously
2)Hence, as temperature increases, rate of reaction also increases
3)However, when the temperature becomes too high, the enzyme will start to denature. This causes enzyme activity to decrease
4)Therefore, there exists an optimal temperature for every enzyme where it can function optimally
(optimum temperature for most human enzymes is generally around 25-40 degrees celsius)
Effect of pH on enzyme activites
-Different enzymes work optimally at different pH ranges
1)Each enzyme usually has maximum activity at an optimal pH
2)At the optimal pH, the protein structure exists as the most stable structure for maximum activity
3)When the pH is higher or lower than the optimal
-changes in concentration of hydrogen ions or hydroxide ions
-changes in the charges on the enzyme
-this disrupts the non-covalent interactions on the enzyme, and eventually results in denaturation of the enzyme when the change become too large
b)Inhibitors
1)Inhibit enzyme’s activity by either affecting the binding between enzyme and substrate or by affecting the enzyme itself
2)Since inhibitors inhibits enzymes, they are often also toxic to cells
Use of inhibitors
1)In enzyme research
2)In nature
Example: believed to be a defense mechanism against predators
3)In medicine
Example: inhibitors to kill cancer cells
Types of Reversible inhibitor
-Reversible inhibitor’s action can be controlled by changing the amount of inhibitors available
1)Competitive inhibitors
2)Non-competitive inhibitors
