Cellular Respiration

Cellular Respiration “The Big Picture” By: Calin, Rebecca, Jason, and Ashley

Energy • • Energy enables life • • Living organisms have evolved into structures that efficiently harness free energy from their environment • • Convert energy to useable forms • • Power the endergonic processes of life

Organisms There are 3 different types of organisms: • Photoautotrophs • Heterotrophs • Chemoautotrophs

Photoautotrophs • -Organisms that can build all the organic compounds required for life from simple inorganic materials, using light in the process • • Through photosynthesis • • Are dominant autotrophs

Heterotrophs • Organisms that feed on other organisms to obtain chemical energy • • Includes all animals and fungi, most protest and bacteria • • Rely on autotrophs • •obtain energy and building materials by eating autotrohs

Chemoautotrophs • Organisms that can build all the organic compounds required for life from simple inorganic materials without using light energy • • Usually found in extreme environments • •Volcanoes, sulfur springs, and salt flats • •The first organisms on Earth got their energy • this way because there was not enough organic • material to use and photosynthesis had not • yet developed

Organisms and Energy • • All organisms use glucose (C6H12O6) as a primary source of energy (except Chemoautotrophs) • • Organisms break the covalent bonds and rearrange them into new and more stable configurations • •Through a series of redox reactions • •Redox reactions result in the transfer of electrons from glucose to oxygen • •Glucose is oxidized to carbon dioxide • •Oxygen is reduced to water: • C6H12O6(aq) + 6O2(g) 6CO2(g) + 6H2O(l) + energy via heat and ATP

Aerobic Cellular Respiration • Harvesting energy from organic compounds using oxygen • C6H12O6 (aq) + 6O2 (g)  6CO2 (g) + 6H2O (l) + energy via heat and ATP • • Accomplished through a series of about 20 reactions where the product of one reaction is the reactant of the next • • Redox reactions that use oxygen as the oxidizing agent • • Exergonic processes that release free energy • http://www.youtube.com/watch?v=3aZrkdzrd04

Oxidation C6H12O6 (aq) + 6O2 (g)  6CO2 (g) + 6H2O (l) • Hydrogen atoms carry electrons away from carbon atoms in glucose to oxygen atoms • Hydrogen forms covalent bonds with oxygen, and the shared electron pairs occupy positions closer to the oxygen nuclei • Occurs because oxygen has a higher EN value • As electrons move from less EN carbon atoms in glucose to highly EN oxygen atoms, they lose potential energy • This creates a decrease in free energy and an overall exergonic process

Oxidation (Cont’d.) • The attachment of the remaining oxygen atoms to carbon atoms, forming six carbon dioxide, CO2, molecules also constitutes as oxidation • The previous explanation only accounts for half the combustion process. • When the carbon atoms are bound, the highly electronegative oxygen atoms draw the shared electron pairs to themselves. • The transfer of hydrogen atoms to oxygen results in the attachment of oxygen atoms with carbon to place the electrons in a more stable configuration • Results in a release of free energy.

Aerobic Oxidation • Aerobic oxidation of glucose generally involves the movement of valence electrons from a higher free energy state in glucose, C6H12O6, to a lower free energy state in carbon dioxide, CO2, and water, H2O. • Causes decrease in potential energy and increase in entropy - yielding 2870 kJ of free energy per mole of glucose (approximately 180g) **in conditions of 25° and 101.3kPa

Free Energy • In a living cell, free energy released from the combustion of glucose is also lost as heat and light • Cells have evolved to trap about 34% of the energy by moving the positions of electrons in certain molecules to higher free energy states (e.g. ATP) •Readily available sources to power endergonic processes.

Activation Energy All reactions occur only if the necessary activation energy is provided. This rule is demonstrated in the process of aerobic respiration: • The reactants are stable compounds: • The oxygen atoms in the O2 molecules attract the electrons in the H-C bonds in the glucose • At room temperature (25 degrees Celsius) and normal body temperature (37 degrees Celsius), oxygen is not a strong enough oxidizer to take the electrons from these bonds. • The need for activation energy prevents spontaneous combustion and allows control of oxidation processes.

Activation Energy (Cont’d.) • The activation energy required for the combustion of glucose is relatively high. • Within a living cell, enzymes are used to catalyze the aerobic respiration process: • Enzymes are used to lower the amount of activation energy needed • Enzymes allows the reaction to take place at a rate that is consistent with the needs of the cell • The available free energy is transferred to energy-carrying molecules (such as ATP) } Largeactivation energy } Free energy transferred via heat and light • Series of reactions, each with relatively small activation energy • Free energy transferred via energy carrier molecules

ObligateAerobes • Organisms that obtain energy by oxidizing organic substances using oxygen • Include most plants animals, fungi, protists, and bacteria Humans Field Mushrooms Mycobacterium tuberculosis

Obligate Anaerobes • Organisms that obtain energy by oxidizing inorganic substances • Cannot live in the presence of oxygen • Final electron acceptors include NO2, SO4, CO2, and Fe3+ Clostridium tetani (tetanus) Clostridium botulinum (food poisoning) Clostridium perfringens (gas gangrene)

Facultative Anaerobes • Organisms that obtain energy by oxidizing inorganic substances with or without oxygen • Tolerate aerobic and anaerobic conditions Salmonella enteritidis (food poisoning) Escherichia coli (Dysentery) Vibrio cholerae (cholera)

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Cellular Respiration