Unit Two “Energy Acquisition” “How Cells Harvest Energy from Food”

Energy in Food Energy is obtained from Glucose for use in building ATP via the removal of electrons from the Glucose molecule “Cellular Respiration” is defined as the oxidation (loss of electrons) of food to obtain energy Cellular Respiration is quite different from “Respiration” (breathing), however, the two are related in that “Respiration” supplies Oxygen to the cells so they can carry out “Cellular Respiration”

Energy in Food It is important to note that both plants and animals participate in Cellular Respiration, and therefore, both have Mitochondria, the organelle where ATP production occurs The main difference between plants and animals is that plants synthesize Glucose from smaller molecules,whereas animals need to consume food matter in order to obtain Glucose The above is why plants are called “Producers” and animals are called “Consumers”

Cellular Respiration and its Stages Cellular Respiration is accomplished in three stages: –A–A–A–A) Glycolysis: production of ATP that takes place in the cytoplasm of cells, and does not require Oxygen (occurs in the Cytoplasm) –B–B–B–B) Acetyl-CoA formation and Krebs Cycle: production of large amounts of ATP that takes place in the Mitochondria, and does require Oxygen (occurs in the Mitochondria) –C–C–C–C) Electron Transport Chain: NADH and FADH2 release electrons that fuel the movement of protons across inner mitochondrial membrane; result in the addition of phosphate to ADP to generate lots of ATP (occurs in the Mitochondria)

Chemical Reaction for Cellular Respiration Glucose + Oxygen  Carbon Dioxide + Water + Energy C6H12O6 + 6O2  6 CCCC OOOO HHHH 2222 OOOO + eeee nnnn eeee rrrr gggg yyyy

Stage 1 of Cellular Respiration –A–A–A–A) Glycolysis: production of ATP that takes place in the cytoplasm of cells, and does not require Oxygen 1. 2 Phosphates from 2 ATP’s are added to Glucose 2. The “Phosphorylated” Glucose is split in two, forming 2 three-carbon sugar phosphates 3. In a series of reactions, both three-carbon sugars phosphate groups are converted to “Pyruvate” 4. The above Pyruvate forming process liberates Hydrogen so it can bond with NAD+ to form NADH, and 2 ATP’s are formed from each Pyruvate

Glycolysis

Stage 2 of Cellular Respiration –B–B–B–B) Acetyl-CoA formation and Krebs Cycle: production of approximately 4 ATP’s that occurs in the Mitochondria and does require Oxygen 1. A Carbon is removed from Pyruvate and departs as a carbon dioxide molecule 2. The 2 carbon fragment that remains after the removal of one Carbon joins to a structure called “Coenzyme A” (CoA) forming a compound known as “Acetyl-CoA”

Stage 2 of Cellular Respiration 3. If the cell has ample amounts of ATP, then Acetyl-CoA is funneled into fat synthesis; if the cell does not have ample amounts of ATP, then Acetyl-CoA is directed toward ATP production via the Krebs Cycle 4. The Krebs Cycle begins when a 2 Carbon fragment is transferred from Acetyl-CoA to a 4 Carbon molecule to form a 6 Carbon molecule 5. The 6 carbon molecule has Carbon and Hydrogen removed twice to form NADH from NAD+, while the removed Carbons bond with Oxygen to form Carbon Dioxide (byproduct)

Stage 2 of Cellular Respiration 6. Finally, the resulting 4 Carbon molecule loses more Hydrogens via oxidation to form FADH2 and NADH 7. This final 4 Carbon molecule is the starting material needed to begin Cellular Respiration again

Krebs Cycle

Step 3 of Cellular Respiration C) Electron Transport Chain: formation of approximately 30 ATP’s that occurs in the Mitochondria in the presence of oxygen C) Electron Transport Chain: formation of approximately 30 ATP’s that occurs in the Mitochondria in the presence of oxygen 1. NADH and FADH 2 transfer high energy electrons to molecules embedded in inner mitochondrial membrane 2. Once they’ve donated electrons, NAD+ and FAD move back to Krebs Cycle 3. Electrons fuel a proton pump that results in the addition of a phosphate group to an ADP to form ATP; this happens approximately 30 times!

Electron Transport Chain

Cellular Respiration Summary 3 Main stages 3 Main stages –Glycolysis: occurs in Cytoplasm, can be aerobic or anaerobic and generates a net of 2 ATP’s –Formation of Acetyl-CoA and Krebs(Citric Acid) Cycle: occurs in Mitochondria, must be aerobic and generates approximately 4 ATP’s –Electron Transport Chain: occurs in Mitochondria, must be aerobic and generates approximately 30 ATP’s

Other Cellular Food The focus to now has been the conversion of Carbohydrates (Glucose) into other molecules thereby liberating energy for use by cells There are other categories of macromolecules that can serve as the “Raw Materials” for subsequent energy production (Chapter 4) Proteins (Amino Acids) and Lipids (Fatty Acids) undergo chemical changes to convert them into molecules that can be inserted into either stage of Cellular Respiration

Cellular Respiration Overview h h tttt tttt pppp :::: //// //// wwww wwww wwww.... pppp hhhh ssss cccc hhhh oooo oooo llll.... cccc oooo mmmm //// ssss cccc iiii eeee nnnn cccc eeee //// bbbb iiii oooo llll oooo gggg yyyy ____ pppp llll aaaa cccc eeee //// bbbb iiii oooo cccc oooo aaaa cccc hhhh //// cccc eeee llll llll rrrr eeee ssss pppp //// iiii nnnn tttt rrrr oooo.... hhhh tttt mmmm llll h tttt tttt pppp ssss :::: //// //// wwww wwww wwww.... yyyy oooo uuuu tttt uuuu bbbb eeee.... cccc oooo mmmm //// wwww aaaa tttt cccc hhhh ???? vvvv ==== jjjj bbbb GGGG ____ cccc ffff GGGG uuuu QQQQ