Please define the terms, and state the similarities, differences or relationship
ID: 11915 • Letter: P
Question
Please define the terms, and state the similarities, differences or relationships between them in your own words.carbon fixation / RuBP regeneration
Explanation / Answer
Hello!!!!! Hope this answer will help you:) Photosynthesis is the synthesis of organic molecules using the energy of light. For the sugar glucose (one of the most abundant products of photosynthesis) the equation is: 6CO2 + 12H2O -> C6H12O6 + 6H2O + 6O2. Light provides the energy to: * transfer electrons from water to nicotinamide adenine dinucleotide phosphate (NADP+) forming NADPH; * generate ATP. * CO2 combines with the phosphorylated 5-carbon sugar ribulose bisphosphate. * This reaction is catalyzed by the enzyme ribulose bisphosphate carboxylase oxygenase (RUBISCO)(an enzyme which can fairly claim to be the most abundant protein on earth). * The resulting 6-carbon compound breaks down into two molecules of 3-phosphoglyceric acid (PGA). * The PGA molecules are further phosphorylated (by ATP) and are reduced (by NADPH) to form phosphoglyceraldehyde (PGAL). * Phosphoglyceraldehyde serves as the starting material for the synthesis of glucose and fructose. * Glucose and fructose make the disaccharide sucrose, which travels in solution to other parts of the plant (e.g., fruit, roots). * Glucose is also the monomer used in the synthesis of the polysaccharides starch and cellulose. The first step involves the addition of CO2 to a 5-Carbon acceptor [RUBP]. This leads to the production of two 3-Carbon molecules. The next step involves the reduction of the 3-Carbon molecule into a Carbohydrate. The final step is a complex series of reactions, which regenerates the 5-Carbon Acceptor (Ribulose-1-5-bisphosphate [RUBP]). One CO2 is gained with each cycle. Six cycles lead to the formation of a 6-Carbon sugar. The Enzyme that adds CO2 to RUBP is called RUBISCO (Ribulose Bisphosphate Carboxylase/Oxygenase). It is the most abundant protein on the planet. It can represent 40% of the soluble protein in a leaf. RUBISCO has a Dual Function. It can Carboxylate RUBP (above) or it can Oxygenate it. The latter is called Photorespiration. Photorespiration results in the loss of CO2 which negates CO2 fixation! Both of these reactions involve the same active site, and the substrates (CO2 & O2) directly compete with one another. Photorespiration reduces the efficiency of photosynthesis by as much as 50%. It is interesting to note that the dual nature of RUBISCO is universal from orchids to photosynthetic bacteria. The Concentrations of CO2 & O2, plus the Leaf Temperature regulate the Balance between Carboxylation (Carbon Gain) & Oxygenation (Carbon Loss). Carbon Dioxide concentrations are always much lower than Oxygen levels inside leaves and in the atmosphere. Leaf Temperature rises during the day when photosynthesis occurs. This is especially true under dry, sunny conditions. This favors Oxygenation (Photorespiration). The kinetic properties of RUBISCO also favor Oxygenation at high temperatures.