biomolecules - enzymes Flashcards
What are enzymes?
globular proteins which act as catalysts
what are catalysts?
alter the rate of a chemical reaction by lowering the activation energy without undergoing a change themselves
What conditions must be in place for a chemical reaction to take place?
-molecules must collide with sufficient energy.
-energy of products must be less than that of substrates.
-requires a minimum amount of energy needed to activate the reaction (activation energy).
What is the structure of an enzyme?
-globular proteins so have a 3D shape that is the results of their sequence of amino acids (primary protein structure).
-A specific region of the enzyme is functional, known as the active site, which is made up of a smaller number of amino acids.
-the molecule on which the enzyme acts on is called the substrate.
-The substrate fits into the active site and forms an enzyme-substrate complex, which is held together by bonds formed between certain amino acids.
Describe the induced fit model of enzyme action.
- The active site forms as the enzyme and substrate interact. the proximity of the substrate ( a change in the environment of the enzyme ) leads to a change in the enzyme that forms the functional active site. The enzyme is flexible and can mould around the the substrate.
What are the 2 changes we most frequently measure when measuring an enzyme-catalysed reaction?
- the formation of the products of the reaction
- this disappearance of the substrate
What is the effect of the temperature on enzyme action?
-A rise in temperature increases the kinetic energy of molecules.
-Molecules move around more rapidly and frequency of collisions is increased
-More enzyme-substrate complexes formed and so the rate of reaction increases
-If temperature gets too high (usually around 60 degrees) , the enzyme becomes denatured and can no longer function
What is the effect of pH on enzyme action?
-Each enzyme has an optimum pH at which it works fastest.
-A change in pH away from the optimum affects the rate of enzyme action
- If change in pH is extreme , the enzyme can become denatured
-A change in pH alters the charges on the amino acids that make up the active site of the enzyme, therefore, the substrate can no longer become attached so enzyme-substrate complex cannot be formed
-Depending on how significant the change in pH is, it may cause bonds maintaining the enzyme’s tertiary structure to break, changing the shape of the active site.
What is the effect on enzyme concentration on the rate of reaction?
Once an active site on an enzyme has acted on a substrate, it is free to repeat the procedure on another substrate molecule. This means enzymes, being catalysts, are not used up in the reaction and therefore work efficiently at very low concentrations.
-As long as there is an excess of substrate, an increase in the amount of enzyme increases the rate of reaction. If you increase conc of enzyme, some of the excess substrate can now be acted upon and rate of reaction increases.
-However, if the substrate is limiting, then any increase in enzyme concentration will have no effect on the rate of reaction.
What is the effect of substrate concentration on the rate of enzyme action?
if the concentration of enzyme is fixed and substrate concentration is slowly increased, the rate of reaction increases. This is because, at low substrate concentrations, the enzyme molecules have only a limited number of substrate molecules to collide with, and therefore the active sites of enzymes are not working to full capacity. As more substrate is added, the active sites gradually become filled, until they are all working as fast as they can. The rate of reaction is at maximum. After that, adding more substrate will have no effect on the rate of reaction.
What are enzyme inhibitors and what are the 2 types?
-Substances that directly or indirectly interfere with the functioning of the active site and so reduce its activity:
-Competitive inhibitors - which bind to the active site of the enzyme
-Non-competitive inhibitors - which bind to the active site at a position other than the active site .
What is the effect of the concentration of competitive inhibitors on the rate of reaction?
Competitive inhibitors have a molecular shape similar to that of the substrate , allowing them to occupy the active site of an enzyme. They compete with the substrate for the available active sites.
-If the substrate conc is increased, the effect of the inhibitor is reduced. the inhibitor is not permanently bound to the active site and so, when it leaves, another molecule can take its place ( either a substrate or inhibitor molecule depending on how much of each type is present) . Eventually all substrate molecules will occupy an active site.
-The greater the conc of inhibitor, the longer this will take.
What is the effect of non-competitive inhibitors on the rate of enzyme reaction ?
-Non-competitive inhibitors attach themselves to the enzyme at a binding site which is not the active site. The inhibitor changes the shape of the enzyme and thus the shape of the active site in a way that substrate molecules can no longer occupy it, and so the enzyme cannot function.
-As the substrate and inhibitor are not competing for the same site, an increase in substrate concentration does not decrease the effect of the inhibitor.
