Cellular Respiration BIOLOGY

What is Cellular Respiration? Step-by-step breakdown of high-energy glucose molecules to release energy Takes place day and night in all living cells Occurs in stages, controlled by enzymes

Where does it occur? In the Cell Mitochondrion Outer Membrane Inner Membrane

Different types of Cellular Respiration Anaerobic respiration Usually occurs when there is no oxygen available When partially breaking down glucose, this process releases a very small amount of energy. Aerobic respiration Occurs in the presence of oxygen When chemically breaking down glucose completely, this process releases large amounts energy

Stage 1: Glycolysis means "splitting sugars" ….6 carbon glucose is split into two 3 carbon molecules (pyruvate) Occurs in the cytoplasm of cells With or Without O2 not required (anaerobic) Some ATP produced Net yield = 2 ATPs

The Krebs Cycle (a.k.a. citric acid cycle) Occurs in the mitochondria O2 required (aerobic) CO2 (waste) Some ATP produced Net yield = 2 ATPs

SUMMARY OF THE KREBS CYCLE 6 NADH GLYCOLYSIS 2 FADH2 CoA Krebs cycle acetyl coenzyme A CO2 2 ATP electron transport chain 1. oxaloacetic acid citric acid NAD+ NADH NADH NAD+ 2. 6. CO2 a-ketoglutaric acid malic acid Figure: 07-08 Title: Summary of the Krebs cycle. Caption: The Krebs cycle is the major source of electrons that are transported to the electron transport chain by the electron carriers NADH and FADH2. For each molecule of glucose, two molecules of acetyl coenzyme A enter the Krebs cycle. Through a series of reactions, a total of 6 NADH, 2 FADH2, and 2 ATP are produced per glucose molecule. (From counting the number of NADH and FADH2 around the cycle, it would appear that only 3 NADH and 1 FADH2 are produced, but remember that one molecule of glucose results in two “trips” around the cycle, as two molecules of acetyl coenzyme A will enter the Krebs cycle for every molecule of glucose that is metabolized.) 3. CO2 FADH2 FAD+ NAD+ NADH 5. ADP 4. a-ketoglutaric acid derivative succinic acid ATP

Electron Transport Chain series of electron carriers in the membrane of the mitochondria Occurs in the inner membrane of mitochondria O2 required (aerobic) A lot of ATP produced Net yield = 32 ATPs Krebs Cycle

ELECTRON TRANSPORT CHAIN GLYCOLYSIS mitochondrion KREBS CYCLE inner membrane ELECTRON TRANSPORT CHAIN 32 ATP inner compartment O2 H2O outer compartment outer compartment ATP SYNTHESIS H+ H+ H+ H+ H+ inner membrane H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ Figure: 07-09 Title: The electron transport chain. Caption: The movement of electrons through the ETC powers the process that provides the bulk of the ATP yield in respiration. The electrons carried by NADH and FADH2 are released into the ETC and transported along its chain of molecules. The movement of electrons along the chain releases enough energy to power the pumping of hydrogen ions (H+) across the membrane into the outer compartment of the mitochondrion. It is the subsequent energetic “fall” of the H+ ions back into the inner compartment that drives the synthesis of ATP molecules by the enzyme ATP synthase. H+ H+ NADH H+ ATP synthesis NAD+ 2 H+ + 1/2 O2 ADP + P inner compartment H2O ATP ELECTRON TRANSPORT CHAIN

Cellular Respiration Review…... Q. Where does each Stage occur? 3 Stages: Stage 1: Glycolysis O2 not required (anaerobic) Some ATP produced Stage 2: Krebs Cycle O2 required (aerobic) Stage 3: Electron Transport System Much ATP produced A. Cytoplasm of the cell 2 ATPs Mitochondrion (matrix) 2 ATPs A. Mitochondrial innermembrane TOTAL: 36ATP 32 ATPs

GLYCOLYSIS 2 energy tokens GLYCOLYSIS mitochondrion cytosol (ATP) - reactants products glucose GLYCOLYSIS 2 ATP Insert 1 Glucose 2 energy tokens 2 NADH GLYCOLYSIS mitochondrion cytosol (ATP) glucose derivatives - carbon dioxide 2 NADH 2 energy tokens carbon dioxide - KREBS CYCLE KREBS CYCLE - - 6 NADH 2 ATP 2 FADH2 Figure: 07-04a-b Title: Overview of energy harvesting. Caption: a. In metaphorical terms. Just as the video games in some arcades can use only tokens (rather than money) to make them function, so our bodies can use only ATP (rather than food) as a direct source of energy. The energy contained in food is transferred to ATP in three major steps: glycolysis, the Krebs cycle, and the electron transport chain. Though glycolysis and the Krebs cycle contribute only small amounts of ATP directly, they also contribute electrons (on the left of the token machine) that help bring about the large yield of ATP in the electron transport chain. b. In schematic terms. As with the arcade machine, the starting point in this example is a single molecule of glucose, which again yields ATP in three major sets of steps: glycolysis, the Krebs cycle and the electron transport chain (ETC). These steps can yield a maximum of 36 molecules of ATP: 2 in gylcolysis, 2 in the Krebs cycle, and 32 in the ETC. As noted, however, glycolysis and the Krebs cycle also yield electrons that move to the ETC, aiding in its ATP production. These electrons get to the ETC via the electron carriers NADH and FADH2, shown on the left. Oxygen is consumed in energy harvesting, while water and carbon dioxide are produced in it. Glycolysis takes place in the cytosol of the cell, but the Krebs cycle and ETC take place in the cellular organelles called mitochondria. - - 32 energy tokens - ELECTRON TRANSPORT CHAIN ELECTRON TRANSPORT CHAIN - 32 ATP Oxygen Water

Aerobic Respiration Oxygen combines with glucose to convert it into energy Releasing carbon dioxide and water as waste products. glucose + oxygen  carbon dioxide + water + lots of heat energy

Anaerobic Respiration Occurs if there is a lack of oxygen available for aerobic respiration Glucose is incompletely broken down In this type of respiration a lot less energy is produced and most of it is lost as heat.

Anaerobic Energy Production: Fermentation Lactic Acid Formed mainly by animal muscle cells Occurs in some unicellular organisms Glucose  lactic acid + a tiny amount of heat energy Alcoholic Fermentation Yeast cells, Bacteria Glucose  alcohol + carbon dioxide + a tiny amount of heat energy

Summary: Aerobic & Anaerobic Similarities: Glucose is broken down. Carbon dioxide is released. Energy is liberated. Differences: Aerobic respiration Anaerobic respiration Lots of energy released Little energy is released Water is the end product Lactic Acid or alcohol is the end product Glucose is completely broken down Glucose is partially broken down Is dependent on oxygen Is not dependent on oxygen