Metabolism: Energy and Enzymes Chapter 6 Metabolism: Energy and Enzymes
6.1: Cells and the flow of energy Energy: the ability to do work or bring about change Organisms need a constant supply of energy to maintain organization and carry out metabolic activities Flow of energy: fig. 6.1
Forms of Energy Kinetic: energy of motion (a ball rolling down a hill) Potential: stored energy (the food we eat has potential energy) Chemical: chemical composition of substances makes them possess energy, such as lipids, carbs, etc. Mechanical: a type of kinetic in which an organism is using it’s chemical energy and converting it (ie. An organism walking)
Laws of Thermodynamics These two laws explain why energy flows in ecosystems and cells Energy starts from the sun, and flows, it does not cycle. Some of the sun’s energy is dissipated as heat but most of it is used by plants for photosynthesis and animals when they eat. Eventually all solar energy is dissipated as heat.
First Law of Thermodynamics Law of conservation of energy: energy cannot be created or destroyed, only changed from one form or another See picture on p. 102, solar energy being used by a plant to convert carbon dioxide and water into carbohydrates, and energy being lost as heat
Second Law of Thermodynamics Energy cannot be changed from one form to another without a loss of usable energy See picture on p. 103, carbohydrates being used for muscle contraction and some of the energy being lost as heat
Cells and entropy Entropy: a relative amount of disorganization Processes that occur in cells naturally tend to move toward entropy. See fig. 6.2 and consider the ‘messy room’ analogy: a neat room is more organized but less stable than a messy room (it’s easier to mess up), while a messy room is more stable but less organized (harder to clean up)
ENTROPY
6.2 Metabolic Reactions and Energy Transformations Metabolism: the sum of all chemical reactions that occur in the body Reactants: substances in a chemical reaction that begin the reaction Products: the result of the reaction In the reaction on the right, circle the reactants and draw a square around the products Direct combination or synthesis, in which 2 or more chemical elements or compounds unite to form a more complex product: N2 + 3 H2 → 2 NH
Free energy The amount of energy available, still ‘free’ to do work, after a chemical reaction has occurred From Wikipedia, “the Gibbs free energy ΔG equals the work exchanged by the system with its surroundings, less the work of the pressure forces, during a reversible transformation of the system from the same initial state to the same final state.“
Exergonic Reactions When there is a negative ΔG, therefore energy is released. Cellular respiration is an exergonic reaction
Endergonic reaction The ones in which ΔG is positive and energy is absorbed Examples: protein synthesis, nerve conduction, muscle contraction
Adenosine Triphosphate (ATP) The common energy currency of cells, when cells require energy, they ‘spend’ ATP The more active an organism, the greater its demand for ATP It is constantly being generated from ADP (adenosine diphosphate) and a molecule of inorganic phosphate Glucose breakdown during cellular respiration provides the energy for the buildup of ATP in mitochondria
Structure of ATP
Coupled Reactions When reactions are both exergonic and endergonic; energy is first released by an exergonic reaction and in turn used to drive an endergonic reaction See fig. 6.4: first ATP is broken down to get energy and then that energy is used in muscle contraction
Functions of ATP Uses of ATP in living systems: Chemical: ATP provides the cell energy to synthesize macromolecules Transport: ATP provides energy for cells to transport molecules across membranes Mechanical: enables muscle contraction, cells to move, cell division, etc….
For next time(MONDAY) We will finish ch. 6 notes READ chapter 6!!! On page 112 do ‘reviewing ch. #1-7 Study session MON after school for one hour! TEST (chapters 2-6) TUES Come tomorrow to randomly choose your take home essay, due TUES