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Lec 17 Cellular Respiration.docx

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University of Lethbridge
BIOL 1010
Igor Kovalchuk

Cell Metabolism Lecture 17 Organism live at the expense of free energy - The maximum amount of usable energy that can be harvested from a particular reaction is the system’s free energy change from initial to the final state - This change in free energy (ΔG) is given by the Gibbs-Helmholtz equation at constant temperature and pressure: ΔG= ΔH-TΔS An energy profile of a reaction Comparison of passive and active transport - In passive transport, a substance diffuses spontaneously down its concentration gradient with no need for the cell to expend energy. - Hydrophobic molecules and very small uncharged polar molecules diffuse directly across the membrane. - Hydrophilic substances diffuse through transport proteins in a process called facilitated diffusion - In active transport, a transport protein moves substances across the membrane “uphill” against their concentrations gradients - Active transport requires an expenditure of energy usually supplied by ATP. An electrogenic pump - Proton pumps are examples of membrane proteins that store energy by generating voltage (charge separation) across substances - Using ATP for power, a proton pump translocates positive charge in the form of hydrogen ions. - The voltage and H+ gradient represent a dual energy source that can be tapped by the cell to drive other processes, such as the uptake of sugar and other nutrients. - Proton pumps are the main electrogenic pumps of plants, fungi and bacteria. Co-transport - An ATP-driven pump stores energy by concentrating a substance (H+, in this case) on one side of the membrane. - As the substance leaks back across the membrane through specific proteins, it escorts other substances into the cell. - The proton pump of the membrane is indirectly driving sucrose accumulation by a plant cell, with the help of a protein co- transports the two solutes. Energy flow and chemical recycling in ecosystems - The mitochondria of eukaryotes (including plants) use the organic products of photosynthesis as a fuel for cellular respiration, which also consumes the oxygen produced by photosynthesis. - Respiration harvests the energy stored in organic molecules to generate ATP, which powers most cellular work. - The waste products of respiration, carbon dioxide, and water, are the very substances that chloroplasts use as raw materials for photosynthesis - Thus, the chemical elements essential to life are recycled. But energy is not; it flows into an ecosystem as sunlight and leaves it as heat. How ATP drives cellular work - Phosphate-group transfer is the mechanism responsible for most types of cellular work - Enzymes shift a phosphate group (P) from ATP to some other molecule and this phosphorylated molecule undergoes a change that performs work. - For example, ATP drives active transport by phosphorylating specialized proteins built into membrane; - drives mechanical work by phospolyating motor proteins, such as the ones that move organelles along cytoskeleton “tracks” in the cell; - And drives chemical work by phosphorlyating key reactants - The phoshorylated molecules lose the phosphate groups as work is performed leaving ADP and inorganic phosphate as products - Cellular respiration replenishes the ATP supply by powering the phosphorlyation of ADP. Cellular respiration and fermentation are catabolic - Fermentation an ATP producing catabolic pathway in which both electron donors and acceptors are organic compounds o Can be an anaerobic process o Results in
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