AP BIOLOGY ENZYMES AND ENERGY
Kinetic energy is the energy of motion
potential energy is stored energy
Oxidation: during a chemical reaction the energy stored in chemical bonds may be used to make new bonds and an atom or molecule that loses an electron is said to be oxidized
Reduction: an atom or molecule that gains an electron is said to be reduced. The reduced form of a molecule has a higher level of energy than the oxidized form
The first law of thermodynamics concerns the amount of energy in the universe. Energy cannot be created or destroyed it can only change from one form to another.
The second law of Thermodynamics concerns transforming potential energy into heat, or random molecular motion during energy transactions. Entropy is increasing! Chemical bonding reduces entropy while heat increases it.
Free energy is the amount of energy available to do work
exergonic reactions: if the products have less free energy than the reactants, the reaction will proceed spontaneously, energy is released, -ΔG
Endergonic reactions: if the products have more free energy than the reactants, the reaction will not proceed spontaneously because they require an input of energy, +ΔG
Activation energy is needed to destabilize existing chemical bonds and initiate a chemical reaction. Reactions with larger activation energies tend to proceed more slowly
Induced fit model: proteins are not rigid. The Binding of a substrate induces the enzyme to adjust its shape slightly, leading to a better induced fit between the enzyme and substrate.
For catalysis to occur within the complex, a substrate molecule must fit precisely into an active site. Substrates bind to the enzyme at active sites, forming an enzyme-substrate complex.
Amino acid side groups of the enzyme end up very close to certain bonds of the substrate. These side groups interact chemically with the substrates distorting a particular Bond and lowering activation energy
Multienzyme Complexes: Multiple enzymes that catalyze different steps in a sequence of reactions are grouped in non-covalently bonded structures
The rate of an enzyme reaction is limited by how often the enzyme collides with its substrate. If a series of sequential reactions occur within a multi-enzyme complex, the product of one reaction can be delivered to the next enzyme without releasing it to diffuse away.
Because the reacting substrate does not leave the complex while it goes through the series of reactions, unwanted side reactions are prevented.
All the reactions that take place within the multi-enzyme complex can be controlled as a unit
By studying the enzyme RnaseP We found that this enzyme was composed of both protein and RNA and further, the RNA was a catalytic molecule. Ribozymes greatly accelerate the rate of a particular biochemical reaction and show substrate specificity. For many years it was thought that RNA was a structural framework for this vital organelle, but it is now clear that ribosomal RNA plays a key role in ribosome function. The ribosome itself is a ribozyme.
Below the optimal temperature, the hydrogen bonds and hydrophobic interactions that determine the enzyme shape are not flexible enough to permit the induced fit that is Optimum for catalysis. Above This temperature, these forces are too weak to maintain the enzyme shape against random movements, leading to denaturation.
If the pH becomes too basic or too acidic the enzyme can denature
Competitive Inhibitors compete with the substrate for the same active site, occupying the active site and thus preventing substrates from binding.
Non-competitive inhibitors bind to the enzyme in a location other than the active site known as the allosteric site, changing the shape of the enzyme and making it unable to bind to the substrate.
During allosteric inhibition, non-competitive Inhibitors bind to a specific portion of the enzyme called an allosteric site. These sites serve as chemical on/off switches, The Binding of a substrate to the site can switch the enzyme between its active and inactive configuration. The allosteric site reduces enzyme activity.
Cofactors: enzyme function is often assisted by additional chemical components known as cofactors. These can be inorganic, metal ions that are often found in the active site participating directly in catalysis.
Coenzyme: When the co-factor is a non-protein organic molecule, it is called a coenzyme. The B vitamins b6 and b12 both function as coenzymes for a number of different enzymes.
Reaction coupling: one reaction gives off energy and another reaction uses that energy to keep doing its job. The energy released by an exergonic reaction is used to drive an endergonic reaction.
Anabolism: chemical reactions that expand energy to build up molecules. Endergonic reactions that require an input of energy
Catabolism: reactions that Harvest energy by breaking down molecules. Exergonic reactions that release energy
Feedback inhibition: for a biochemical Pathway to operate efficiently, its activity must be coordinated and regulated by the cell. It is unnecessary to synthesize a compound when plenty is already present, but doing so would waste energy and raw materials. The regulation of simple biochemical Pathways often depends on a feedback mechanism: the end product of the pathway binds to an allosteric site on the enzyme that catalyzes the first reaction in the pathway. The end product of a biochemical pathway stops or slows down the activity of an enzyme involved in its own production. It helps maintain homeostasis.