Cellular Respiration/Photosynthesis

• Catabolic pathways break glucose own into simpler molecules, releasing energy to build ATP. Is the catabolism of glucose exergonic
• Fermentation results from the partial catabolism of glucose. Aerobic respiration is the full catabolism of glucose, releasing as much energy as possible for ATP construction
• Fermentation results from the partial catabolism of glucose
• Aerobic respiration is the full catabolism of glucose, releasing as much energy as possible for ATP construction
• Cellular aerobic respiration converts organic molecules and oxygen to carbon dioxide and water, with a large energy release
• Redox reactions are chemical reactions where electrons are transferred between reactants
• If all the energy is released all at once, it cannot be harvested efficiently
• A cell’s first electron transfer in controlled energy harvest moves H (electros + proton) from glucose to NAD+
• There is only a small amount of energy loss in the electron transfer from glucose to NAD+. NAD+ and NADH can cycle back and forth easily, so they are convenient molecules to act as electron recipients, and NADH can pass electrons along in the next steps
• NADH is now carrying a high potential energy, in the form of the electrons it got from glucose. NADH passes it electrons to a series of several carrier molecules in multiple small redox reactions
• O2 ultimately receives the electrons (and partner protons) at the end of this chain
• If H2 plus half of an O2 are released too quickly, explosive things happen
• Electrons are passed from NADH through several intermediates. This releases small amounts of energy at each transfer
• Coupling controlled small exergonic reactions with other reactions result in endergonic ATP synthesis
• Energy from glucose, first step is glycolysis and it occurs in all living cells. Three phases are energy investment phase, cleavage phase, and energy payoff phase
• In the energy investment phase, each P contributed by an ATP bumps G up a little bit, helping glucose get over the activation energy hump
• Kinase is an enzyme that catalyzes the transfer of a phosphate group from high-energy, phosphating donating molecules to other substrates
• Isomerase is an enzyme that convert one isomer to another
• Dehydrogenase is an enzyme that transfers hydrogen atoms from organic compounds to electron acceptor, thereby oxidizing the organic compounds
• Glycolysis starts with 1 glucose, invest 2 ATP, end with 2 pyruvate, 4 ATP, 2 NADH
• When a compound donates (loses) electrons, that compound becomes oxidized (OIL)
• When a compound accepts (gains) electrons, that compound becomes reduced (RIG)
• In glycolysis, the carbon-containing compound that functions as the electron donor is glucose
• Once the electron donor in glycolysis gives up its electrons, it is oxidized to a compound called a pyruvate
• NAD+ is the compound that functions as the electron acceptor in glycolysis
• The reduced form of the electron acceptor in glycolysis is NADH
• Among the products of glycolysis, the compound that contain energy that can be used by other biological reactions are pyruvate, ATP, and NADH
• A bond must be broken between an organic molecule and phosphate before ATP can form
• One of the substrates is a molecule derived from the breakdown of glucose
• The citric acid cycle starts with 2 carbons from acetyl CoA, where it then has 6 carbons in citrate to 6 carbons isocitrate, then to 5 carbons for alpha-ketoglutarate (loses CO2 and NAD+ -> NADH), then again to 4 carbons for succinyl CoA (loses CO2 and NAD+ -> NADH), then 4 carbons for succinate (ADP +Pi -> ATP loses CoA), 4 carbons fumarate (FAD -> FADH2), 4 carbons malate (NAD+ -> NADH), then 4 carbons oxaloacetate
• Pyruvate is oxidized to CO2 and NAD+ is reduced to NADH and FAD is reduced to FADH2
• The citric acid cycle is is a cyclic pathway rather than a linear pathway because it is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two carbon compound
• Although possible to oxidize the two carbon acetyl group of acetyl CoA to two molecules of CO2, it is much more difficult than adding the acetyl group to a four carbon acid to form a six carbon acid (citrate). Citrate can then be oxidized sequentially to release two molecules of CO2
• In mitochondrial electron transport, the direct role of O2 is to function as the final electron acceptor in the electron transport chain
• O2 only has a place at the end of cellular respiration during electron transport chain as the final electron acceptor. Oxygen has a high affinity for electrons which contributes to the formation of a proton gradient and synthesizing ATP
• Oxidative phosphorylation is a cellular process that harnesses the reduction of oxygen to generate high energy phosphate bonds in the form of ATP
• Anaerobic conditions would stop the rate of electron transport and ATP synthesis
• Fewer protons are pumped across the inner mitochondrial membrane when FADH2 is the electron donor than when NADH is the electron donor (which explains why more ATP is made per molecule of NADH)
• Gramicidin causes membranes to become very leaky to protons, so that a proton gradient cannot be maintained and ATP synthesis stops. However, the leakiness of the membrane has no effect on the ability of electrons to move along the electron transport chain. Thus, the rates of electron transport and oxygen uptake remain unchanged
• Photosynthesis produces oxygen