Cellular respiration

• Living cells require energy from outside sources.
• Some animals, such as the giant panda, obtain energy by eating plants, and some animals feed on other organisms that eat plants.
• Energy flows into an ecosystem as sunlight and leaves as heat.
• Photosynthesis generates O2 and organic molecules, which are used in cellular respiration.
• Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work.
• The breakdown of organic molecules is exergonic.
• Fermentation is a partial degradation of sugars that occurs without O2.
• Aerobic respiration consumes organic molecules and O2 and yields ATP.
• Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2.
• The citric acid cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn.
• The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle.
• The NADH and FADH2 produced by the citric acid cycle relay electrons extracted from food to the electron transport chain.
• The acetyl group of acetyl CoA joins the citric acid cycle by combining with oxaloacetate, forming citrate.
• The citric acid cycle has eight steps, each catalyzed by a specific enzyme.
• The citric acid cycle, also known as the Krebs cycle, takes place within the mitochondrial matrix.
• The mitochondrion is the site of the citric acid cycle, also known as Tricarboxylic acid cycle or Kreb’s Cycle.
• Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration.
• Carbohydrates, fats, and proteins are all consumed as fuel, but it is helpful to trace cellular respiration with the sugar glucose: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy (ATP + heat).
• The mitochondrion was coined by Carl Benda in 1898.
• The term “mitochondria” is derived from the Greek words “mitos” meaning thread and “chondros” meaning granule.
• The transfer of electrons during chemical reactions releases energy stored in organic molecules.
• Chemical reactions that transfer electrons between reactants are called oxidation - reduction reactions, or redox reactions.
• In oxidation, a substance loses electrons, or is oxidized.
• In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced).
• The electron donor is called the reducing agent.
• The electron receptor is called the oxidizing agent.
• Electrons from organic compounds are usually first transferred to NAD+, a coenzyme.
• O2 pulls electrons down the chain in an energy-yielding tumble.
• Glycolysis harvests chemical energy by oxidizing glucose to pyruvate.
• Cellular respiration has three stages: Glycolysis, the citric acid cycle, and oxidative phosphorylation.
• In cellular respiration, glucose and other organic molecules are broken down in a series of steps.
• Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration.
• The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions.
• In the energy investment phase of glycolysis, Glucose is converted to 2 ADP + 2 Pi and 2 ATP are used, resulting in 4 ATP formed.
• NAD+ functions as an oxidizing agent during cellular respiration.
• Glycolysis occurs in the cytoplasm and has two major phases: the energy investment phase and the energy payoff phase.
• Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP.
• A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation.
• The electron transport chain passes electrons in a series of steps instead of one explosive reaction.
• In the energy payoff phase of glycolysis, 4 ADP + 4 Pi are converted to 2 NAD+ + 4 e- + 4 H+, resulting in 2 NADH + 2 H+ produced.