Chapter 5: Cellular Respiration: Releasing Chemical Energy

5.1 Metabolism & Cell Respiration Metabolism involves synthesis (consumes energy) & decomposition (releases energy). ATP = the major energy carrier in metabolism ATP is made during decomposition & is used during biosynthesis (links the 2 processes).

5.1 Metabolism & Cell Respiration

5.1 Metabolism & Cell Respiration Cell Respiration – a decomposition pathway; a series of reactions that release energy as they break down sugars & other substances into CO2 & H2O Each step is catalyzed by an enzyme. Releases the energy by oxidizing the sugars/other substances. Some of that energy is conserved as ATP, which is used to power life processes

5.1 Metabolism & Cell Respiration Aerobic respiration – occurs in the presence of OXYGEN; O2 is the oxidizing agent that receives the electrons Anaerobic respiration – occurs WITHOUT OXYGEN; substrate is only partly decomposed, releasing less energy with a Nitrogen or Sulfur compound replacing the oxygen

Aerobic vs. Anaerobic Respiration

5.1 Metabolism & Cell Respiration Raw materials for respiration = sugars, fats, & proteins; we’ll concentrate on GLUCOSE primarily Glucose Production Produced when animals digest carbs or glycogen; gets transported in blood Produced when plants break down sucrose & starch; main transport carb = sucrose

5.1 Metabolism & Cell Respiration Summarized Reaction: 1 C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy Oxidizing 1 glucose – releases more energy than a single reactions needs, so glucose is NOT useful as a direct source of energy To release all the energy in glucose at once would waste most of the energy, so it’s done in a series of small steps

5.1 Metabolism & Cell Respiration Car Analogy When all energy in glucose When the energy is released released at once slowly in a controlled manner

5.2 Stages of Aerobic Respiration Three Major Stages: Glycolysis – Enzymes split glucose into two 3-carbon molecules – called pyruvate (uses some ATP & releases a small amount ATP) Krebs cycle – carbon molecules are completely oxidized to CO2 (releases a few more ATP) Electron Transport System – regenerates a supply of NAD+, releasing p+& e- , which are transferred to oxygen, forming water

5.2 Stages of Aerobic Respiration When something is oxidized (lose e-), something else has to be reduced (gain e-). Glucose is oxidized; NAD+ (Nicotinamide adenine dinucleotide) is reduced to NADH – similar to NADP+  NADPH in photosynthesis NAD+  NADH Occurs in the Glycolysis & Krebs cycle

5.2 Stages of Aerobic Respiration Another molecule that gets reduced: FAD (flavin adenine dinucleotide)  FADH2 Happens in Krebs Cycle Hydrogen carriers in cells: NADH, NADPH (only photosynthesis), & FADH2 At end of ETS: NADH & FADH2 reduce oxygen to form water (releasing energy to form ATP).

5.2 Stages of Aerobic Respiration Most ATP is synthesized in the 3rd step: the Electron Transport System Oxygen is the final e- acceptor, so stages 2 and 3 CANNOT proceed without oxygen – they are considered aerobic.

5.2 Stages of Aerobic Respiration

Your assignment…. I have photocopied section 5.3 from your books, but have left out the pictures of the 1st step of respiration: Glycolysis You are going to read/highlight the descriptions of the major steps of this stage and then try to draw what is occuring….. For Example:

If we did this for the Calvin cycle last unit, the book says, “At a, the beginning of the cycle, a molecule of carbon dioxide combines with the 5 carbon sugar-phosphate RuBP….This produces an unstable 6 carbon molecule that….”