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Download Assignment 6 Cell Respiration
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Name Sec. . Score . Working in groups of two to four and armed with a textbook or some other reliable source answer the following questions concerning cellular respiration (Chapter 6). This assignment is worth 30 points with the possible points for each question in parenthesis. Helpful web sites: http://www.biology-pages.info/C/CellularRespiration.html http://www.phschool.com/science/biology_place/biocoach/cellresp/fermentation.html http://www.youtube.com/watch?v=Gh2P5CmCC0M 1. (5) In your own words, describe the overall goal of aerobic cellular respiration and the specific cellular sites of each of the three processes (Glycolysis, Transport step, Krebs cycle, and the ETC) which occur during cellular respiration? The overall goal of aerobic cellular respiration is to liberate energy from the degradation of primarily glucose molecules, but also other nutrient molecules, like amino acids or lipids and to transfer this energy into the molecule called Adenosine Tri-Phosphate (ATP). The processes involved are Glycolysis, the Krebs cycle, and the Electron Transport Chain (ETC) (also called the electron transport system or shuttle (ETS)). Glycolysis occurs as a series of enzymatically driven steps (10) which occur in the cytoplasm of all cells. The Krebs cycle is a series of enzymatically driven steps (8) that occur in the mitochondrial matrix of eukaryotic cells. The ETC is run by a series of reduction/oxidation linked molecules (called cytochromes) found embedded into the inner mitochondrial membrane (imm.). Where would the Glycolytic enzymes, Kreb’s cycle enzymes and ETC cytochromes be found in a prokaryotic cell? 2. (5) Describe the three major events of Glycolysis: Investment, Splitting, and Harvest to include how each of these adds to the efficiency of the breakdown of glucose to pyruvic acid and producing ATP? Glycolysis is designed to take nutrient molecules like glucose and prepare them for complete degradation via the Kreb’s Cycle. To accomplish this goal glycolysis is divided into three phases: Investment, Splitting, and Harvest. The Investment stage of glycolysis involves the attachment of 2 phosphate groups to the glucose by splitting 2 molecules of ATP by an enzyme with the last name of Kinase. This happens twice. The first time is to change a glucose molecule structurally to prevent it from leaking back across the cell membrane via a facilitated diffusion protein channel. The second time is to rearrange the glucose into a fructose that is a balanced molecule with a phosphate group on either end of the 6C fructose molecule to allow for the ease of splitting the molecule into two equal halves by an enzyme called Aldolase. The Splitting stage happens when an enzyme (called aldolase) simply cuts the fructose into two 3 carbon chains called G3P, each with a phosphate group on one end (Remember G3P from the Calvin cycle?). This step (splitting a bond) liberates energy in the form of hydrogen electrons from two hydrogens, which are then removed from the area by a molecule called Nicotinamide Adenine Dinucleotide (NAD+) forming NADH + H+(by an enzyme called Dehydrogenase). So we have removed some energy but it is not yet into a usable ATP molecule. When the electrons are removed and picked up by NAD+ the hydrogen protons chase the NAD+ with the hopes of retrieving their lost electrons (This will happen later during the running of the ETC). A phosphate group (designated as Pi or inorganic phosphate from your diet) in the cell cytosol nearby is attracted to the site which liberated the electrons and Biology& 100 Mr. Brumbaugh 1 Class Assignment 6 attaches itself to the carbon chain to prevent the molecule from simply reforming. This happens twice or once for each of the 3C chains and the resulting molecules have phosphates on either end of their structure once again. The Harvest involves the direct phosphorylation (or Substrate Level Phosphorylation or SLP) of ADP by enzymes that can remove the phosphates from each of the 3 carbon chains and attach them to an Adenosine Di-Phosphate (ADP) forming ATP (by different Kinases). This happens four times so we get a net yield of 2ATP (Why?). We also produce 2 3Carbon pyruvic acid (PAs) molecules that still can be broken down to liberate the rest of the energy in the form of liberated electrons. The net gains from glycolysis are 2ATP’s (4 total but it costs two to start), 2 PAs, and 2NADH + H+’s per glucose. 3. (5) Describe the steps of the transport of pyruvic acid to the Krebs cycle enzymes? The resulting PAs (pyruvic acids) from glycolysis are then transported one at a time to the mitochondrial matrix for further degradation. A problem arises since two mitochondrial membranes have to be crossed in eukaryotic cells. To accomplish this transport a special taxi cab molecule called Co-enzymeA (CoA) was designed to cart the PA, but CoA can only transport a 2C chain molecule (a two seater taxi). To accommodate CoA a CO2 is removed from each PA to form a 2C acetyl group. The liberation of CO2 by Dehydrogenase enzymes also liberates electrons and Biology& 100 Mr. Brumbaugh 2 Class Assignment 6 NAD+ is waiting in the wings to steal electrons from whom? You guessed it hydrogen. This happens twice or once for each PA. The net gains from the transport step are 2CO2’s and 2NADH + H+’s per glucose. 4. (5) Describe the two major divisions of the Krebs cycle: Destroying and Rearranging. In your answer includes how each of these adds to the efficiency of the breakdown of acetic acid and producing ATP? The Krebs cycle can be grossly divided into two halves the splitting or destroying side which destroys each acetyl group by cutting out 2CO2’s and liberating electrons (from?) and the rearranging side to get back to the starting molecule oxaloacetic acid . To start the destruction each acetyl group being transported by CoA is combined to a starting molecule called oxaloacetic acid (OA) to form citric acid (CA) (the other name for the cycle) by the enzyme Citrate Synthase. 2CO2’s are split from the CA by Dehydrogenase enzymes and each time a CO2 is released the electrons from hydrogen are given to NAD+ (think energy) to form NADH + H+. Just like in glycolysis, when the electrons are removed a phosphate (from your diet) can fill the void on the molecule to prevent it from collapsing back on itself and then the phosphate can be enzymatically removed to ADP to form 1ATP (via SLP) (The GTP in the figure below is an intermediate step.). The rearrangement side of the cycle is designed to reform the starting molecule of OA (oxaloacetic acid). To do these steps electrons are stripped from the remaining acetyl group (from whom?) and given not only to an NAD+ to form NADH + H+, but also a different electron carrier molecule called Flavin Adenine Dinucleotide (FAD+) to form FADH2 (This molecule can bind both of the hydrogen atoms hence it is referred to as FADH2). Once we have reformed OA we can begin the cycle with the second acetyl group from the other pyruvic acid from the original glucose. The net gains are 4CO2’s, 6 NADH + H+’s, 2FADH2’s, and 2ATP’s per glucose. Biology& 100 Mr. Brumbaugh 3 Class Assignment 6 5. (5) Describe the electron transport chain, system, or shuttle (ETC or S) in five steps or less. The ETS is a series of oxidation/reduction molecules (called cytochromes) tied together and embedded into the inner mitochondrial membrane. The NADH + H+’s arrive at the beginning of the chain and give the electrons (from whom?) to the first molecule of the chain (reducing it), who passes the electrons to its neighbor reducing the neighbor while oxidizing itself. This electron passing continues through the rest of the transport molecules. The FADH2’s have to drop off their electrons farther down the chain, but the transport mechanism is the same. As the electrons are passed from cytochrome to cytochrome they lose energy and the energy loss is used to pump the hydrogen ion (H+) across the imm. and into the space between the inner and outer mitochondrial membranes. Eventually the electrons are passed to an oxygen atom by the last cytochrome on the inside of the inner membrane (Why do you need to breathe?). As the hydrogen concentration gradient builds up across the imm. the hydrogen’s seek a means to return to their electrons. The hydrogen’s can only return across the imm. via a specific portal called ATP synthase (IcanmakeATPdoggoneitase). As the hydrogen’s pass through the portal, ATP synthase unites ADP with a Pi forming ATP and the hydrogen’s bind with the oxygen to form a water molecule (called metabolic water). Each pair of electron passed through the chain from the NADH + H+’s will yield the production of 3ATP, whereas those from FADH2’s will yield 2ATP. This is called oxidative phosphorylation (OP) via chemiosmosis. Please see the figure on the next page. What is the total ATP production for Aerobic Respiration, Glycolysis only, Kreb’s cycle only, and ETS only? Biology& 100 Mr. Brumbaugh 4 Class Assignment 6 6. (5) Describe Figure 7.11 in the textbook or why is having a complete balanced diet as it applies to your eating habits, attempts to lose or gain weight, or maintaining a healthy life style? I’ll leave this answer for you to ponder after learning the previous material and studying the figure. Biology& 100 Mr. Brumbaugh 5 Class Assignment 6