Chapter 8
1. Explain the role of catabolic and anabolic pathways in cellular metabolism.
Catabolic pathways release energy by breaking down complex molecules to simpler compounds. Anabolic pathways consume energy to build complicated molecules from simpler ones.
2. Distinguish between kinetic and potential energy.
Kinetic energy is associated with the relative motion of objects. Potential energy is the energy that matter possesses because of its location or structure.
3. Explain the first and second laws of thermodynamics in your own words.
1st Law of Thermodynamics: conservation of energy; energy is transferred and transformed, not created or destroyed.
2nd Law of Thermodynamics: transformation increases entropy (randomness/disorder)
4. List the three main kinds of cellular work. Explain in general terms how cells obtain the energy to do cellular work.
- Chemical work: the pushing of endergonic reactions
- Transport work: the pumping of substances across membranes against the direction of spontaneous movement.
- Mechanical work: the contraction of muscle cells and the movement of chromosomes during cellular reproduction.
Cells manage their energy resources to do this work through energy coupling, the use of an exergonic process to drive an endergonic one.
5. Describe the structure of ATP and identify the major class of macromolecules to which ATP belongs.
ATP contains the sugar ribose, with the nitrogenous base adenine and a chain of three phosphate groups bonded to it. ATP is also one of the nucleoside triphosphates used to make RNA.
6. Explain how ATP performs cellular work.
When ATP hydrolyzes there is a release of energy and this energy is used to perform the three types of cellular work.
7. Describe the function of enzymes in biological systems.
An enzyme catalyzes a reaction by lowering the activation energy barrier, enabling the reactant molecules to absorb enough energy to reach the transition state, even at moderate temperatures. This eliminates the need to use heat to speed up the reaction because high temperatures can also denature proteins and kill cells.
8. Explain how enzyme structure determines enzyme specificity.
9. Explain the induced-fit model of enzyme functions.
Enzyme changes shape to bond with the substrate
10. Explain how temperature, pH, cofactors, and enzyme inhibitors can affect enzyme activity.
The rate of an enzyme reaction increases with increasing temperature up to a point. After that point, the rate of the reaction will drop. The same thing occurs with pH. The cofactors can be bound tightly or loosely to the enzyme. Coenzymes act as organic helpers and perform a crucial function in catalysis. Competitive inhibitors mimic the substrate. Noncompetitive inhibitors bind to another part of the enzyme altering its shape.
12. Describe the function of enzymes in biological systems.
An enzyme acts as a catalyst, which speeds up reactions. Enzymes are proteins in biological systems used to regulate the metabolism.
Key Terms
Metabolism: The totality of an organism's chemical reactions, consisting of catabolic and anabolic pathways, which manage the material and energy resources of the organism.
Metabolic Pathway: A series of chemical reactions that either builds a complex molecule (anabolic pathway) or breaks down a complex molecule into simpler compounds (catabolic pathway)
Catabolic Pathways: A metabolic pathway that releases energy by breaking down complex molecules to simpler compounds.
Anabolic Pathways: A metabolic pathway that consumes energy to synthesize a complex molecule from simpler compounds.
Bioenergetic: (1) The overall flow and transformation of energy in an organism. (2) The study of how energy flows through organisms.
Energy: The capacity to cause change, especially to do work (to move matter against an opposing force).
Kinetic Energy: The energy associated with the relative motion of objects. Moving matter can preform work by imparting motion to other matter.
Heat/Thermal Energy: The total amount of kinetic energy due to the random motion of atoms or molecules in a bond of matter; also called thermal energy. Heat is energy in its most random form.
Potential Energy: The energy that matter possesses as a result of its location or spatial arrangement (structure).
Chemical Energy: Energy available in molecule's for release in a chemical reaction; a form of potential energy.
Thermodynamics: The study of energy transformations that occur in a collection of matter.
First Law of Thermodynamics: The principle of conservation of energy: energy can be transferred and transformed, but it cannot be created or destroyed.
Entropy: A measure of randomness or disorder.
Seconds Law of Thermodynamics: The principle stating that every energy transfer or transformation increases the entropy of the universe, Ordered forms of energy are at least partly converted to heat.
Free Energy: The portion of a biological system's energy that can perform work when temperature and pressure are uniform throughout the system. *the change in free energy of a system is calculated by the equation G=H-TS, where H is enthalpy [in biological systems, equivalent to total energy] T is also temperature, and S is entropy.
Exergonic Reaction: A spontaneous chemical reaction, in which there is a net realise of free energy.
Endergonic Reaction: A non-spontaneous chemical reaction, in which free energy is absorbed from the surroundings.
Energy Coupling: In cellular metabolism, the use of energy released from an exergonic reaction to drive an endergonic reaction.
ATP (Adenosine Triphosphate): An adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.
Phosphorylated: Referring to a molecule that is covalently bonded to a phosphate group.
Enzyme: A macromolecule serving as a catalyst, a chemical agent that changes the rate of a reaction without being consumed by the reaction.
Catalyst: A chemical agent that increases the rate of a reaction without being consumed by the reaction.
Activation Energy/Free Energy of Activation: The amount of energy that reactants must absorb before a chemical reaction will start; also called free energy of activation.
Substrate: The reactant on which an enzyme works.
Enzyme-Substrate Complex: A temporary complex formed when an enzyme binds to its substrate molecule.
Active Site: The specific portion of an enzyme that binds the substrate by means of multiple weak interactions and that forms the pocket in which catalysis occurs.
Induced Fit: Induced by entry of the substrate, the change in shape of the active site of an enzyme so that it binds more snugly to the substrate.
Cofactors: Any nonprotein molecule or ion that is required for the proper functioning of an enzyme. Cofactors can be permanently bound to the active site or may bind loosely with the substrate during catalysis.
Coenzyme: An organic molecule serving as a cofactor. Most vitamins function as coenzymes in metabolic reactions.
Competitive Inhibitors: A substance that reduces the activity of an enzyme by entering the active site in place of the substrate whose structure it mimics.
Noncompetitive Inhibitors: A substance that reduces the activity of an enzyme by binding to a location remote from the active site, changing the enzyme's shape so that the active site no longer functions effectively.
Allosteric Regulation: The binding of a regulatory molecule to a protein at one site that affects the functions of the protein at a different site.
Cooperativity: A kind of allosteric regulation whereby a shape change in one subunit of a protein caused by substrate binding is transmitted to all the others, facilitation binding of subsequent substrate molecules.
Feedback Inhibition: A method of metabolic control in which the end product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.
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