At the end of summary you will find a animated tutorials. Each tutorial has four elements: an introduction that describes the topic to be illustrated and puts it into a broader context, a detailed animation that clearly illustrates the topic (there are a few tutorials that include simulations or other types of content, rather than animations), a conclusion that summarizes what you should have learned from the animation, and a quiz on the topic covered
Energy and Energy Conversions
- Energy is the capacity to do work. Potential energy is the energy of state or position; it includes the energy stored in chemical bonds. Kinetic energy is the energy of motion (and related forms such as electric energy, light, and heat).
- Potential energy can be converted to kinetic energy, which can do work.
- Living things, like everything else, obey the laws of thermodynamics. The first law of thermodynamics tells us that energy cannot be created or destroyed. The second law of thermodynamics tells us that the quantity of energy available to do work (free energy) decreases and unusable energy (associated with entropy) increases.
- Changes in free energy, total energy, temperature, and entropy are related by the equation ΔG = ΔH – TΔS.
- Exergonic reactions release free energy and have a negative ΔG. Endergonic reactions take up free energy and have a positive ΔG. Endergonic reactions proceed only if free energy is provided.
- The change in free energy (ΔG) of a reaction determines its point of chemical equilibrium, at which the forward and reverse reactions proceed at the same rate. For exergonic reactions, the equilibrium point lies toward completion (the conversion of all reactants into products).
ATP: Transferring Energy in Cells[wp_campaign_1]
- ATP (adenosine triphosphate) serves as an energy currency in cells. Hydrolysis of ATP releases a relatively large amount of free energy.
- The ATP cycle couples exergonic and endergonic reactions, transferring free energy from the exergonic to the endergonic reaction. See Animated Tutorial
Enzymes: Biological Catalysts
- The rate of a chemical reaction is independent of ΔG, but is determined by the size of the energy barrier. Catalysts speed reactions by lowering the energy barrier.
- Enzymes are biological catalysts, proteins that are highly specific for their substrates. Substrates bind to the active site, where catalysis takes place, forming an enzyme-substrate complex.
- At the active site, a substrate can be oriented correctly, chemically modified, or strained. As a result, the substrate readily forms its transition state, and the reaction proceeds. See Animated Tutorial.
Molecular Structure Determines Enzyme Function[wp_campaign_2]
- The active site where substrate binds determines the specificity of an enzyme. Upon binding to substrate, some enzymes change shape, facilitating catalysis.
- Some enzymes require cofactors to carry out catalysis. Prosthetic groups are permanently bound to the enzyme. Coenzymes are not usually bound to the enzyme. They can be considered substrates, as they are changed by the reaction and then released from the enzyme.
- Substrate concentration affects the rate of an enzyme-catalyzed reaction.
Metabolism and the Regulation of Enzymes
- Metabolism is organized into pathways in which the product of one reaction is a reactant for the next reaction. Each reaction in the pathway is catalyzed by an enzyme.
- Enzyme activity is subject to regulation. Some inhibitors react irreversibly with enzymes and block their catalytic activity. Others react reversibly with enzymes, inhibiting their action only temporarily. A compound closely similar in structure to an enzyme’s normal substrate may competitively inhibit the action of the enzyme. See Animated Tutorial
- Allosteric regulators bind to a site different from the active site and stabilize the active or inactive form of an enzyme. Many such enzymes have multiple subunits. See Animated Tutorial
- For allosteric enzymes, plots of reaction rate versus substrate concentration are sigmoid, in contrast to plots of the same variables for nonallosteric enzymes.
- The end product of a metabolic pathway may inhibit the allosteric enzyme that catalyzes the commitment step of that pathway.
- Enzymes are sensitive to their environment. Both pH and temperature affect enzyme activity.
Animated Tutorials on this section
