Presentation on theme: "PowerPoint Lectures Campbell Biology: Concepts & Connections, Eighth Edition REECE TAYLOR SIMON DICKEY HOGAN Chapter 5 Lecture by Edward J. Zalisko The."— Presentation transcript:
Figure 5.4 Solute molecule Selectively permeable membrane Water molecule Solute molecule with cluster of water molecules Osmosis H2OH2O Lower concentration of solute Higher concentration of solute More equal concentrations of solute
Cells transform energy as they perform work Cells are miniature chemical factories, housing thousands of chemical reactions. Some of these chemical reactions release energy, and others require energy.
Energy is the capacity to cause change or to perform work. There are two basic forms of energy. 1. Kinetic energy is the energy of motion. 2. Potential energy is energy that matter possesses as a result of its location or structure.
Thermal energy is a type of kinetic energy associated with the random movement of atoms or molecules. Thermal energy in transfer from one object to another is called heat. Light is also a type of kinetic energy; it can be harnessed to power photosynthesis.
Chemical energy is the potential energy available for release in a chemical reaction and the most important type of energy for living organisms to power the work of the cell.
Thermodynamics is the study of energy transformations that occur in a collection of matter. The word system is used for the matter under study. The word surroundings is used for everything outside the system; the rest of the universe.
Two laws govern energy transformations in organisms. Per the first law of thermodynamics (also known as the law of energy conservation), energy in the universe is constant. Per the second law of thermodynamics, energy conversions increase the disorder of the universe. Entropy is the measure of disorder or randomness.
Automobile engines and cells use the same basic process to make the chemical energy of their fuel available for work. In the car and cells, the waste products are carbon dioxide and water. Cells use oxygen in reactions that release energy from fuel molecules. In cellular respiration, the chemical energy stored in organic molecules is used to produce ATP, which the cell can use to perform work.
Chemical reactions either release or store energy Chemical reactions either release energy (exergonic reactions) or require an input of energy and store energy (endergonic reactions).
Exergonic reactions release energy. These reactions release the energy in covalent bonds of the reactants. Burning wood releases the energy in glucose as heat and light. Cellular respiration involves many steps, releases energy slowly, and uses some of the released energy to produce ATP.
An endergonic reaction requires an input of energy and yields products rich in potential energy. Endergonic reactions start with reactant molecules that contain relatively little potential energy but end with products that contain more chemical energy.
Photosynthesis is a type of endergonic process. In photosynthesis, energy-poor reactants (carbon dioxide and water) are used, energy is absorbed from sunlight, and energy-rich sugar molecules are produced.
Chemical reactions either release or store energy A living organism carries out thousands of endergonic and exergonic chemical reactions. The total of an organism’s chemical reactions is called metabolism. A metabolic pathway is a series of chemical reactions that either builds a complex molecule or breaks down a complex molecule into simpler compounds.
Energy coupling uses the energy released from exergonic reactions to drive endergonic reactions, typically using the energy stored in ATP molecules.
ATP drives cellular work by coupling exergonic and endergonic reactions ATP, adenosine triphosphate, powers nearly all forms of cellular work. ATP consists of adenosine and a triphosphate tail of three phosphate groups.
Hydrolysis of ATP releases energy by transferring its third phosphate from ATP to some other molecule in a process called phosphorylation. Most cellular work depends on ATP energizing molecules by phosphorylating them.
A cell uses and regenerates ATP continuously. In the ATP cycle, energy released in an exergonic reaction, such as the breakdown of glucose during cellular respiration, is used in an endergonic reaction to generate ATP from ADP.
Enzymes speed up the cell’s chemical reactions by lowering energy barriers Although biological molecules possess much potential energy, it is not released spontaneously. An energy barrier must be overcome before a chemical reaction can begin. This energy is called the activation energy (because it activates the reactants).
We can think of activation energy as the amount of energy needed for a reactant molecule to move “uphill” to a higher-energy but an unstable state so that the “downhill” part of the reaction can begin. One way to speed up a reaction is to add heat, which agitates atoms so that bonds break more easily and reactions can proceed, but too much heat will kill a cell.
Enzymes function as biological catalysts, increase the rate of a reaction without being consumed by the reaction, and are usually proteins (although some RNA molecules can function as enzymes). Enzymes speed up a reaction by lowering the activation energy needed for a reaction to begin.
For every enzyme, there are optimal conditions under which it is most effective. Temperature affects molecular motion. An enzyme’s optimal temperature produces the highest rate of contact between the reactants and the enzyme’s active site. Most human enzymes work best at 35–40°C. The optimal pH for most enzymes is near neutrality.
Many enzymes require nonprotein helpers called cofactors, which bind to the active site and function in catalysis. Some cofactors are inorganic, such as the ions of zinc, iron, or copper. If a cofactor is an organic molecule, such as most vitamins, it is called a coenzyme.
Enzyme inhibition can regulate enzyme activity in a cell A chemical that interferes with an enzyme’s activity is called an inhibitor. Competitive inhibitors block substrates from entering the active site and reduce an enzyme’s productivity.
Noncompetitive inhibitors bind to the enzyme somewhere other than the active site, change the shape of the active site, and prevent the substrate from binding.
Passive transport (requires no energy) Active transport (requires energy) Diffusion Facilitated diffusion Higher solute concentration Lower solute concentration Osmosis Higher free water concentration Solute Water Lower free water concentration Higher solute concentration ATP Lower solute concentration