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Cellular Respiration. Study your notes as much as possible and keep up with the web site so that you don’t fall behind! If you need help, ask for it!. Aerobic vs. Anaerobic. Introduction. Cellular Respiration Energy stored in food is released
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Cellular Respiration Study your notes as much as possible and keep up with the web site so that you don’t fall behind! If you need help, ask for it! Aerobic vs. Anaerobic
Introduction • Cellular Respiration Energy stored in food is released • Cellular Respiration is the reverse of photosynthesis • During Cellular Respiration: • H atoms from carbohydrates join O, from O2, to form H20 • Biochemical Pathways of carbon forming carbohydrates and organic molecules are broken • Energy stored is available for cellular activities • Carbon is linked to O2 to form CO2
Aerobic Respiration • For most cells, aerobic respiration is the main energy-releasing pathway leading to ATP formation. • Aerobic means with oxygen, reaction cannot take place without the presence of oxygen. • These reactions are different from photosynthesis because they release energy and photosynthesis acquires energy.
Anaerobic Respiration • Anaerobic means without oxygen, reaction can take place without the presence of oxygen • Many bacteria and protistans depend exclusively on anaerobic pathways to make ATP • Animal cells also use anaerobic respiration when cells do not have enough oxygen.
Other Anaerobic Reactions • Alcoholic fermentation, lactate Fermentation, and anaerobic electron transport use an organic or inorganic compound (not oxygen) to accept electrons. Glycolysis • This is a series of reactions splitting the molecule glucose into two pyruvate molecules. • This is the first step for all the previously mentioned reactions.
Overview of Aerobic Respiration • Of all the energy-releasing pathways, aerobic respiration produces the most ATP for each glucose molecule. • C6H12O6 + 6O2 6CO2 + 6H2O • The above equation only gives you the beginning and end. There are three cycles in between the beginning and the end. • Aerobic respiration begins in the cytoplasm of the cell and ends inside the mitochondria
Steps of Gylcolysis • See Handout! • Important things to remember: • Glycolysis is the beginning of aerobic respiration. • The reactions partly break down glucose to form two pyruvate molecules, two NADH, and four ATP. • ONLY TWO ATP are net yielded because two had to be used to get the reactions started in the first place.
Glycolysis Continued • The first steps of this process are energy-requiring. • They proceed only when two ATP molecules each donate energy to the glucose backbone by transferring a phosphate group to it. • The attachments cause the backbone to split forming two molecules of PGAL. • PGAL formation begins the energy-releasing steps of glycolysis.
Each PGAL is converted into an unstable intermediate that gives up a phosphate group to ADP, forming ATP. • The next intermediate in the sequence does the same thing. • Thus a total of four ATP molecules have been formed by substrate-level phosphorylation- the direct transfer of a phosphate group from a substrate of the reactions to ADP. • Meanwhile, hydrogen atoms and electrons that were released from each PGAL are transferred to the coenzyme NAD. • Glycolysis converts a bit of the energy stored in glucose to ATP energy. • Hydrogen and electrons stripped from glucose have been loaded onto a coenzyme, and these have roles in the next stage of reactions.
Preparatory Steps for the Krebs Cycle • Pyruvate leaves the cytoplasm and enters the mitochondria. • Carbon and oxygen atoms depart from pyruvate, in carbon dioxide and water. • Coenzymes accept hydrogen and electrons released during the reactions. • A carbon atom is stripped from each pyruvate molecule, leaving an acetyl group that gets picked up by a coenzyme forming acetyl coenzyme A (acetyl-CoA) • The acetyl group becomes attached to oxaloacetate, the point of entry into the Krebs cycle.
The Krebs Cycle • These reactions serve three functions: 1. Hydrogen and electrons transferred to NAD+ and FAD, form NADH and FADH2 2. Substrate level phosphorylations produce two ATP. 3. Intermediates are rearranged into Oxaloacetate (Cells have only so much and it must be regenerated to keep the cyclic reactions going)
Electron Transport Phosphorylation • Electron Transport systems and neighboring channel proteins run in electrons and unbound hydrogen delivered by coenzymes. • As electrons are transferred through the transport systems, hydrogen ions are tossed into the outer compartment. This sets up a hydrogen concentration and electric gradients across the membrane. • Channel proteins allow hydrogen to follow the gradients, back into the inner compartment. • The flow drives the formation of ATP from ADP and an unbound phosphate. Free oxygen keeps ATP production going. It withdraws electrons from transport systems and combines with hydrogen to form water molecules.
Summary • In aerobic respiration, glucose is completely broken down to carbon dioxide and water. • Coenzymes transfer hydrogen and electrons from substrates to electron transport systems, the operation of which drives ATP formation. • Oxygen is the final electron acceptor. • From start (glycolysis in the cytoplasm) to finish (in mitochondrion), this pathway commonly yields thirty-six ATP for every glucose molecule.
