ch 9 respiration and fermentation

ch 9 respiration and fermentation - HARVESTING CHEMICAL...

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HARVESTING CHEMICAL ENERGY: Biology 1A Chapter 9 Living is Hard Work! Moving, making proteins, transporting molecules and reproducing takes lots of energy Where do cells get their energy from? Heterotrophs can ONLY gain energy by oxidizing organic molecules obtained outside themselves. o Glucose is a common energy source. o in general, molecules with lots of hydrogen atoms are good food sources, because they can be oxidized (release electrons and possibly protons) Autotrophs can store energy in organic molecules (e.g. photosynthesis) and then use these organic molecules later. To gain energy from complex molecules, cells use two General Processes: o FERMENTATION (does not require O 2 ) Glycolysis usually follows o AEROBIC RESPIRATION (requires O 2 ) Catabolic Metabolic Paths How does a cell harvest chemical energy to generate energy for cellular work (aka ATP )??? o Molecules and chemical bonds store energy (“Food” is made of complex molecules). o Respiration and fermentation are processes cells use to break chemical bonds and transfer energy to ATP. How is energy captured? When complex molecules are hydrolyzed into simpler forms, energy is released. o The energy must be recaptured in a form useful to the cell, or it will be lost as heat. o Cells control catabolic reactions carefully, harnessing energy into other molecules whenever possible. o This is a step-wise process, and energy is transferred with electrons. Cell has max amt of control REDOX: Oxidation-reduction reactions : o Coupled Oxidation and Reduction rxns o Many reactions result from the transfer of electrons from one atom or molecule to another.
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o Energy is released when electrons move closer to an electronegative atom. (exergonic reaction) An electron is more stable (less energetic) when near an electronegative atom. o AH 2 + B --> BH 2 + A o One molecule (A) is oxidized (loss of e - ), while the other (B) is reduced (gains e - ). Protons may also be transferred along with electrons. NOTE: Electrons are not soluble in aqueous solutions, so they must be directly transferred from one molecule to another. Protons are soluble (in the form of H 3 O + ). o Oxidizing agent = electron acceptor, becomes reduced (B) o Reducing agent = gives up electron, becomes oxidized (A) o LEO (loses electrons oxidation) o GER (gains electrons reduction) o OAR (oxidizing agent becomes reduced) o Oxygen is a VERY STRONG oxidizing agent Energy is transferred in REDOX reactions : o delta G is negative (exothermic!) cell will try to recapture that energy into some other form o Transferred electrons carry energy o Rearranging bonds may also release energy o Molecules that carry the right size energy “package” were favored by evolution ATP like 20 dollar bill… o NAD + , FAD + , and NADP + are important oxidizing agents in cells
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This note was uploaded on 04/15/2008 for the course BIS 1A taught by Professor Gearhart during the Spring '07 term at UC Davis.

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ch 9 respiration and fermentation - HARVESTING CHEMICAL...

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