How Cells Harvest Chemical Energy – Cellular Respiration

Cellular Respiration C6H12O6 + 602  6CO2 + 6H20 Glycolysis A catabolic pathway Oxygen is consumed as a reactant along with organic compounds. Involves three stages: Glycolysis Krebs Cycle Electron Transport Chain

What is Cellular Respiration? The process in which organisms take molecules broken down from food and release the chemical energy stored in the chemical bonds of those molecules. It’s important to remember that food is not the direct source of energy.

The energy that is released from chemical bonds during cellular respiration is stored in molecules of ATP.

What types of organisms undergo cellular respiration? While only autotrophs undergo photosynthesis both Heterotrophs AND Autotrophs Undergo cellular respiration.

What Is ATP? Adenosine Triphosphate Energy used by all Cells Organic molecule containing high-energy Phosphate bonds

Chemical Structure of ATP

What Does ATP Do for You? It supplies YOU with ENERGY!

How Do We Get Energy From ATP? By breaking the high- energy bonds between the last two phosphates in ATP

NADH and FADH2 NAD+ traps electrons from glucose to make NADH (energy stored) Similarly, FAD+ stores energy as FADH2

Where Does Cellular Respiration Take Place? It actually takes place in two parts of the cell: Glycolysis occurs in the Cytoplasm Krebs Cycle & ETC Take place in the Mitochondria

Review of Mitochondria Structure Smooth outer Membrane Folded inner membrane Folds called Cristae Space inside cristae called the Matrix

Diagram of the Process Occurs in Matrix Occurs across Cristae Occurs in Cytoplasm

Glycolysis 1. Means “splitting of sugar” 2. Occurs in the cytosol of the cell 3. Partially oxidizes glucose (6C) into two pyruvate (3C) molecules. 4. Occurs whether or not oxygen is present.

5. An exergonic process, (meaning energy is released) most of the energy harnessed is conserved in the high-energy electrons of NADH and in the phosphate bonds of ATP

Glycolysis Summary Takes place in the Cytoplasm Anaerobic (Doesn’t Use Oxygen) Requires input of 2 ATP Glucose split into two molecules of Pyruvate Also produces 2 NADH and 4 ATP

Formation of Acetyl CoA 1. Junction between glycolysis and Krebs cycle 2. Oxidation of pyruvate to acetyl CoA 3. Pyruvate molecules are translocated from the cytosol into the mitochondrion by a carrier protein in the mitochondrial membrane. 4. A CO2 is removed from pyruvate – making a 2C compound. 5. Coenzyme A is attached to the acetyl group.

Formation of Acetyl CoA

Formation of Acetyl CoA

Krebs Cycle Requires Oxygen (Aerobic) Cyclical series of oxidation reactions that give off CO2 and produce one ATP per cycle Turns twice per glucose molecule Produces two ATP Takes place in matrix of mitochondria

Krebs Cycle Summary Each turn of the Krebs Cycle also produces 3NADH, 1FADH2, and 2CO2 Therefore, For each Glucose molecule, the Krebs Cycle produces 6NADH, 2FADH2, 4CO2, and 2ATP

Electron Transport Chain 1. Located in the inner membrane of the mitochondria. 2. Oxygen pulls the electrons from NADH and FADH2 down the electron transport chain to a lower energy state . 3. Process produces 34 ATP or 90% of the ATP in the body.

Electron Transport Chain 4. Requires oxygen, the final electron acceptor. 5. For every FADH2 molecule – 2 ATP’s are produced. 6. For every NADH molecule – 3 ATP’s are produced. 7. Chemiosmosis – the production of ATP using the energy of H+ gradients across membranes to phosphorylate ADP.

ATP Synthase A protein in the inner membrane in the mitochondria. Uses energy of the ion gradient to power ATP synthesis. For every H+ ion that flows through ATP synthase, one ATP can be formed from ADP

Cellular Respiration in Summary Glycolysis 2 ATP 2 NADH  4-6 ATP (Depends on how this NADH molecule gets to the ETC. To make things simple we will say that these two NADH’s make 4 ATP ) Formation of Acetyl CoA 2 NADH  6 ATP

Cellular Respiration in Summary Krebs Cycle 2 ATP 6 NADH  18 ATP 2 FADH2  4 ATP Grand Total = 36 ATP

What happens to the products of glycolysis when O2 isn’t present?

Anaerobic Pathways Fermentation

Fermentation Occurs when O2 NOT present (anaerobic) Called Lactic Acid fermentation in muscle cells (makes muscles tired) Called Alcoholic fermentation in yeast (produces ethanol) Nets only 2 ATP

Lactic Acid Fermentation Occurs in muscle cells in the body. Lactic acid is a waste product of fermentation that will build up and cause your muscles to “burn” during hard exercise.

Lactic Acid Fermentation Lactic acid fermentation also occurs in some bacteria and molds. Waste products of the fermentation process give cheese different flavors. Yogurt is another product of lactic acid fermentation.

Alcoholic Fermentation Alcoholic fermentation is a process used by many yeasts and plants. Also uses the products of glycolysis (NADH and pyruvic acid) to provide enough NAD+ and ATP for glycolysis to continue.

Alcoholic Fermentation Alcoholic fermentation is used to make bread or dough rise and is also used for beer and wine.

Fermentation Bacteria that rely upon fermentation play a very important role in digestive systems of animals. They breakdown molecules by taking undigested material for their needs. Without these bacteria we’d be unable to fully digest food.

Questions What is the real benefit of fermentation? What is the cellular respiration equation? What factor determines the pathway that pyruvic acid takes after leaving glycolysis? What is the importance of cellular respiration to us? Explain how cellular respiration complements photosynthesis. What is the ultimate end product of cellular respiration?