Cellular Respiration - Harvesting Chemical Energy Add anything with *** to your handout Cellular respiration – breaking down food to make ATP using oxygen as a final electron acceptor *** Gas exchange done in lungs functions to maintain levels of gas in your body due to this process (take in/use oxygen and make/release carbon dioxide)

Cellular Respiration - Harvesting Chemical Energy Plants and animals both use products of photosynthesis (glucose) for metabolic fuel. *** So plants have mitochondria too. Remember that photosynthesis is merely an autotrophs way of getting food. Heterotrophs: must take in energy from outside sources, cannot make their own e.g. animals When we take in glucose (or other carbs), proteins, and fats-these foods don’t come to us the way our cells can use them. We must break them down to make ATP.

Cellular Respiration Overview Transformation of chemical energy in food into chemical energy cells can use: ATP These reactions proceed the same way in plants and animals. Process is called cellular respiration Overall Reaction: C6H12O6 + 6O2 → 6CO2 + 6H2O *** Notice that this is the exact opposite of photosynthesis Why do we need this process (or why don’t we just break down our food all at once?)

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Cellular Respiration Stages Stage 1: Glycolysis Series of reactions which break the 6-carbon glucose molecule down into two 3-carbon molecules called pyruvate in the cytoplasm *** Process is an ancient one-all organisms from simple bacteria to humans perform it the same way Notice this occurs in the cytoplasm so mitochondria are not required (so bacteria can do it) Yields 2 ATP and 2 NADH molecules for every one glucose molecule broken down, BUT *** For eukaryotic organisms, the main purpose of this stage is to break down glucose to pyruvate *** NADH is electron carrier like NADPH in photosynthesis (think P for photosynthesis to differentiate the 2) After this point, life diverges into two forms and two pathways. Anaerobic cellular respiration (aka fermentation) Aerobic cellular respiration

***(Whole slide) Anaerobic Cellular Respiration Some organisms thrive in environments with little or no oxygen Marshes, bogs, gut of animals, sewage treatment ponds No oxygen used = anaerobic All prokaryotic organisms do only this level of cellular respiration as they do not have mitochondria for the next 2 steps Results in no more ATP, final steps in these pathways serve ONLY to regenerate NAD+ so it can return to pick up more electrons and hydrogens in glycolysis. End products are ethanol and CO2 (single cell fungi (yeast) in beer/bread) or lactic acid (muscle cells) Why wouldn’t every species want to use this type of respiration?

Aerobic Cellular Respiration Oxygen required=aerobic 2 more sets of reactions which occur in a specialized structure within the cell called the mitochondria 1. Kreb’s Cycle (Citric Acid Cycle) 2. Electron Transport Chain

Step 2 of Cellular Respiration: Citric Acid Cycle (*** Kreb’s Cycle) Completes the breakdown of glucose Takes the pyruvate (3-carbons) and breaks it down, the carbon and oxygen atoms end up in CO2 and H2O *** Occurs in mitochondrial matrix Hydrogens and electrons are stripped and loaded onto NAD+ and FAD to produce NADH and FADH2 *** FADH2 also an electron carrier ** Production of only 2 more ATP so main purpose of this stage is to produce electrons carriers (NADH and FADH2) for next stage

3RD Step of Cellular Respiration: Oxidative Phosphorylation ( 3RD Step of Cellular Respiration: Oxidative Phosphorylation (** Production of ATP in first 2 stages called “substrate” level b/c doesn’t use oxygen) Electron carriers loaded with electrons and protons from the Kreb’s cycle move to this chain-like a series of steps (staircase). (What are these “electron carriers”?) *** As electrons drop down stairs, energy released to pump H+ ions into the INTERMEMRANE SPACE. This is called the Electronic Transport Chain and is similar to the ETC used in chloroplasts for photosynthesis. These H+ ions flow back into the MITOCHONDRIAL MATRIX through the ATP Synthetase (remember chemiosmosis) to create a total of 32 or 34 ATP Oxygen waits at bottom of staircase, picks up electrons and protons and in doing so becomes water. This is the reason why breathe harder and faster whenever we are exercising. Also the reason why you can see moisture when you breathe on a window.

Why oxygen? ***Oxygen is the most electronegative (what did this word mean) element in living organisms. This means that the electrons can “fall” through more molecules releasing more kinetic energy. Combining hydrogen to oxygen at the end of the ETC makes water (which is why you can see moisture if you breathe on glass).

Electron Transport Chain and Chemiosmosis Similarities and differences for mitochondria and chloroplasts

Energy Tally 36 ATP for aerobic vs. 2 ATP for anaerobic Glycolysis 2 ATP Kreb’s 2 ATP Electron Transport 32 ATP 36 ATP Anaerobic organisms can’t be too energetic but are important for global recycling of carbon

Glucose (carbs) are not the only macromolecule that can be used in cellular respiration. Proteins and fats can also be broken down for energy as well.