Cell Respiration Assignment Score. Name Sec.. Date. Working by alone or in a group, answer the following questions about Cell Respiration. This assignment is worth 30 points with the possible points for each question in parenthesis. Maybe these web sites will help: http://www.phschool.com/science/biology_place/biocoach/cellresp/intro.html, http://www.youtube.com/watch?v=gh2p5cmcc0m When answering these questions always in the back of your mind think about the basic goal of the process and then add the details as you progress through the process. 1. (4) Cite two reasons why two ATP s are used at the beginning of glycolysis? The problem stems from the fact that the glucose (the usual molecule sent through glycolysis) is moved into the cell via facilitated diffusion and is an unbalanced molecule in terms of shape. So to prevent the glucose from diffusing back out of the cell upon entry an enzyme named HexoKinase adds a phosphate group to the #1 carbon of the sugar (changing its molecular structure) to make glucose 6-phosphate. This change in shape prevents the glucose from diffusing back out of the cell. A second phosphate group is added (another Kinase called PhosphofructoKinase) to the #6 carbon at the opposite end of the glucose to make fructose 1, 6 - biphosphate a balanced molecule so the enzyme Aldolase can cleave the molecule into equal 3C halves. This is called the Investment portion of Glycolysis 2. (6) Draw and label a diagram that would show the steps of the process called Glycolysis (Investment, Splitting, and Harvest) showing the main enzymes involved? The important enzymes which run Glycolysis are the Kinases (enzymes which add phosphate groups to other molecules), Aldolases (able to cut fructose 1, 6 - biphosphate in half because we added the two phosphate groups), Isomerases (able to convert one molecular shape into another), 1
and Enolases (able to split out water molecules to rearrange a molecule). Note how the liberated H + electrons and accompanying ions are picked up by Nicotinamide Adenine Dinucleotide (NAD + ) reducing NAD + to NADH + H +. The important stages of glycolysis are called Investment, Splitting and finally Harvest. Look at the power point slides to get the detail of each of these stages. Where do the products of Glycolysis go to liberate the rest of their energy if possible? 3. (4) Draw and label a diagram that would show the process of transporting pyruvic acid to the mitochondria showing the main players involved? Because of pyruvates (pyruvic acid or P.A.) shape it can t move across the two mitochondrial membranes as is and needs a taxi (called coenzyme A or CoA) to carry the pyruvate to the site of the Kreb s (or citric acid) cycle in the mitochondrial matrix. To accommodate the pyruvate into the cab a Dehydrogenase enzyme (able to break a bond between carbon atoms to release H + and CO2) is able to split off the open carbonyl group from the carbon chain of the pyruvate releasing a CO2 and H + protons. The protons electrons are picked up by an NAD +, which is then reduced to NADH + H + but the H + proton is simply following the NAD + (now neutral since it picked up the two electrons from the hydrogens. The CoA then binds to the remaining 2C acetyl group and carts it to the Kreb s cycle enzymes for further degradation. Where do these products from the Transporting Step go to liberate the rest of their energy if possible? 4. (6) Draw and label a diagram that would show the steps of the process (Destroying and Rebuilding) called the Kreb s cycle showing all the main enzymes involved? The important enzymes which run the Kreb s cycle are Citrate Synthase, a building enzyme (adds the 2C acetyl group from CoA to a 4C oxaloacetic acid). Dehydrogenase (to split out the CO2 to harvest the liberated H + electron that is picked up by NAD + to form NADH + H +, a different Synthase (works between succinyl CoA and succinate), and Fumerase (hydrogenates fumarate to form malate). 2
After the CO2 s are removed an inorganic phosphate (Pi) (shown at the bottom of the cycle) temporarily binds to the intermediate molecule to prevent the molecule from reforming and losing the gained H +. The Pi is then removed to be attached to an ADP to form ATP (a Kinase enzyme does this step) by Direct Phosphorylation (or SLP (Substrate Level Phosphorylation)). Note that the step between succinate and fumarate liberates 2H + that are both picked up but by a different electron carrier called Flavin Adenine Dinucleotide (FAD + ) to form FADH2. Finally the rearrangement that occurs between malate and oxaloacetic acid liberates the final electron from one H + proton and is picked up by NAD + to form NADH + H +. Where do the products of the Kreb s cycle go to liberate the rest of their energy if possible? 5. (6) Draw and label a diagram that would show the process of the Electron Transport System (Chain or Shuttle are other names.) (E.T.S.) showing the main players involved? 3
This is basically a reduction/oxidation keep away of electrons from hydrogen. The electrons are dropped off, by either NADH + H + (each pair of electrons from NADH + H + yields 3ATP) or FADH2 (each pair of electrons from FADH2 yields 2ATP), two at a time. As the electrons are sent down the chain they drop in energy. This allows the E.T.S. (Electron Transport System, Chain, or Shuttle) cytochrome proteins to move H + ions across the inner mitochondrial membrane to build up a concentration gradient (potential energy) across the membrane or between the inner and outer mitochondrial membranes. The gradient is dissipated through a membrane protein complex called ATP synthase (or IcanmakeATPdogoniterase) allowing the H + protons to pass back across the membrane and into the waiting electron arms of ½O2 that received the electrons from the last cytochrome (called cyto. a3) to form H2O (converting potential energy to kinetic energy). This process is called chemiosmosis. This H2O is what is termed metabolic water. Where do the products of the E.T.S. go once their energy has been liberated? 6. (4) Draw and label a diagram that would show the difference between Fermentation and the Lactic Acid Shuttle? Fermentation Lactic Acid shuttle 4
What is the inherent value of either strategy? Is this a waste of time and can it be sustained indefinitely? What kinds of organisms do either process and can you discern any reasons why some organisms do one strategy and others do the other? Where do the products of either strategy go once either process has been completed? So many questions! Who could answer them all or who would want to know the answers? People interested in energy transference and healing. That is whom! 5