Cellular Energy Photosynthesis & Respiration Part 2: Cellular Respiration

How are photosynthesis and respiration linked?

Energy Why do living things need energy? ATP – Adenosine Triphosphate Reproduction Repair Growth and development Movement ATP – Adenosine Triphosphate The most usable form of chemical energy in the body. ATP is made during cellular respiration. A molecule of ADP (adenosine diphosphate) is joined with a phosphate group to make ATP (an anabolic reaction). ATP has a great deal of energy in it because of the 3 phosphate groups. These groups are all negative. It takes a lot of energy to hold the 3 negative groups next to each other. When 1 phosphate is separated from the group of 3, ATP is converted back into ADP and energy that was in the bond is released (a catabolic reaction).

Cellular Respiration It is the process that converts the chemical energy stored in the bonds of glucose into chemical energy cells can use (ATP); produces 36-38 ATP Equation: Reactants: The 6 O2 molecules come from the air. They were put there by photosynthetic organisms. The C6H12O6 comes from being generated during photosynthesis. Autotrophs will use the food that they made. Heterotrophs will consume the glucose. Products: The CO2 and the H2O are released into the atmosphere. Most of the energy in glucose is going to be lost as heat (~60%) while some (~40%) is transformed into ATP for the organism to use. Occurs in the CYTOPLASM and the MITOCHONDRIA First step occurs in the cytoplasm (Glycolysis); 2nd (Krebs Cycle) and 3rd (Electron Transport Chain) steps occur in the mitochondria (In eukaryotic) Utilized by ALL aerobic eukaryotic organisms (plants, algea, animals) If an organism is anaerobic, it will perform glycolysis and then fermentation C6H12O6 + 6O2 ---> 6CO2 + 6H2O + energy (ATP + heat)

Glycolysis – 4 ATP (Net gain 2 ATP) This is the first step in cellular respiration. It does not require oxygen to occur (anaerobic). This step occurs in the cytoplasm of cells. Here, glucose will undergo a series of reactions that converts the molecule into two 3-carbon molecules called pyruvic acid (pyruvate). The process will require the use of 2 ATP molecules. The process will make 4 ATP molecules. Therefore, the net gain from glycolysis is 2 ATP molecules. The process also make 2 molecules of NADH from 2 molecules of NAD+. Reactants: Glucose + 2 ATP + 2 NAD + Products: 2 Pyruvic Acids + 4 ATP + 2 NADH If an organism is going to use oxygen, an aerobic organism, they will take the 2 molecules of pyruvic acid to the mitochondria for the Krebs cycle. If an organism does not use oxygen, an anaerobic organism, they will continue in the cytoplasm using fermentation.

Anaerobic Respiration: Fermentation – 0 ATP No ATP is made during the process of fermentation. The entire purpose of fermentation is regenerate NAD+ to perform glycolysis again. Alcoholic Fermentation Lactic Acid Fermentation Occurs in your muscle cells when oxygen is not available Glucose is broken down by glycolysis, making 2 pyruvic acid molecules and 2 NADH molecules. Through the use of the energy in NADH, pyruvate is further broken down and produces the waste product of lactic acid, which causes muscle soreness. The NADH is converted back into NAD+ to be used again in glycolysis. Used by single-celled organisms, such as yeast cells Glucose is broken down by glycolysis, making 2 pyruvic acid molecules and 2 NADH molecules. Through the use of the energy in NADH, pyruvate is broken down into CO2 and ethyl alcohol. The NADH is converted back into NAD+ to be used again in glycolysis.

Cellular Respiration – Major Steps After glycolysis, aerobic organisms that have access to oxygen, will use the Krebs cycle and the electron transport chain. Prokaryotes: Happens in the cytoplasm and the cell membrane Eukaryotes: Happens in the mitochondria Krebs Cycle: The oxidation of glucose that began in glycolysis is completed. Electron Transport Chain (ETC): NADH and FADH2 (energy carriers) are used to make ATP. Oxygen is used at this step.

Mitochondrion Organelle where aerobic respiration occurs (oxygen is needed). The Krebs cycle happens in the matrix (fluid) of the mitochondria. The ETC happens in the inner membrane of the mitochondria. The inner membrane is highly folded. It is called the cristae. The cristae allow for more electron transport chains to be in the mitochondria in a smaller space.

Kreb’s Cycle (Citric Acid Cycle) – 2 ATP Happens in the matrix of the mitochondria. Pyruvic acid diffuses through the double membrane into the matrix. Here, the 2 pyruvic acid molecules will undergo a series of reactions. The end result is that the pyruvic acid is broken down into 6 CO2. Reactants: 2 Pyruvic Acid + 8 NAD+ + 2 FAD + 2 ADP Products: 6 CO2 + 8 NADH + 2 FADH2 + 2 ATP Only produced 2 ATP in this step. Most of the energy of glucose is now trapped in the energy carriers FADH2 and NADH.

The Electron Transport Chain – 34 ATP Embedded in the inner membrane of the mitochondria. Electrons in the NADH and FADH2 have a lot of energy. The electrons transfer into the chain. As they pass through the chain, they use their energy to pull H+ out of the matrix creating a concentration gradient. This drives chemiosmosis to create ATP by using ATP synthase located in the membrane. At the end, the electrons that were moving through the chain are accepted by a molecule of O. They also combine with two molecules of H+ and makes water. The energy in NADH and FADH2 make 34 ATP molecules in this step.

The Importance of Oxygen It is the final acceptor of the electrons as they move through the chain. If the electrons had no where to go, then they would build up in the chain, and the chain could not work again.

The End At the end, 36-38 molecules of ATP have been made. About 40% of the energy in glucose is converted into ATP by the end of all 3 processes. (20x more efficient than glycolysis alone). The remaining energy is being lost as heat. Cellular Respiration: Photosynthesis C6H12O6 + 6 O2 --> 6 CO2 + 6 H2O + energy 6 CO2 + 6 H2O + light energy ---> C6H12O6 + 6 O2