Biolchem 415 1st EditionExam # 3 Study Guide Lectures: 22 - 32Lecture 22 (March 13)What is photosynthesis? How does it work?Photosynthesis the process that takes light energy and creates ATP and NADPH. It occurs in the chloroplast. Chlorophyll drives the reaction by absorbing light. The energy from the light is harnessed by two photosystems. The energy from the light excites electrons in photosystem II enough that it jumps to photosystem one and results in the oxidation of water to oxygen. To get from photosystem II photosystem I the electron must flow through a cytochrome system. Again light excites the electron and it reduces NADPH  NADP+. This creates a proton gradient that can be used to generate ATP. What is the Calvin Cycle? What is the rate-limiting step?The Calvin Cycle uses NADPH and ATP generated during photosynthesis to incorporate CO2 into carbohydrates. It is considered to be a “dark reaction” and occurs in the stroma of the chloroplast. The rate-limiting step is the trapping of CO2 into ribulose 1,5-bisphosphate by RuBisCO. It produces 3-phosphoglycerate. Stage 2 of the Calvin Cycle requires the NADPH and ATP. It produces glycerate 3-phosphate and fructose 6-phosphate. These products can wither enter the metabolism, be stored as sucrose or starch, OR replenish ribose 5-phosphate, which is the next stage of the calvin cycle. The regeneration of ribose 5-phosphate is the rearrangement of fructose 6-phosphate and glyceraldehyde 3-phosphate. These are transketolase and transaldolase reactions. What is the Pentose Phosphate Pathway? The PPP operates in all organisms and occurs in the cytosol. It generates NADPH, ribose, and “uncommon” sugars and occurs in two phases. The first phase involves two oxidative steps and is regulated by NADP+ levels. First is the rate limiting step catalyzed by glucose 6-dehydrogenase. It converts glucose 6-phosphate to 6-phosphoglucono-δ-lactone. This step oxidizes NADP+  NADPH. Next 6-phosphoglucono-δ-lactone is converted to 6-phosphogluconate by lactonate. The last step of the first phase is the reaction catalyzed by 6-phosphogluconate dehydrogenase that produces ribulose 5-phosphate and CO2. The second phase of the PPP consists of sugar interconversions catalyzed by transketolase and transaldolase. This phase produces ribose and “uncommon” sugars. Why is NADPH important?NADPH is required for synthetic reactions and protection against oxidative stress. With out NADPH to do this oxidative stress could lead to cell death. Lecture 23 (March 16) How do fatty acids provide energy to tissues?Fatty acids are stored in adipose tissue as triacylglycreols. These are processed in three stages inorder to provide energy to tissues: mobilization, processing in target tissues/cells, and energy generation in the mitochondria. Mobilization occurs when the triacylglycerides are degraded into fatty acids and glycerol by triacylglycerol lipase. This is stimulated by energy need signaling hormones like epinephrine through 7TM receptors with messengers like adenol cyclase by the modification of the enzyme perilipin and the lipase. The products of this reaction are carried to tissues through the blood stream by carriers like serum albumin. Glycerol can enter gluconeogenesis or glycolysis. Fatty acids are made into energy through oxidation in the mitochondria. Explain how fatty acids are used to create energy.Fatty acids are oxidized to create energy in the mitochondria. First they must be activated for transport into the mitochondria. They are activated by the addition of Coenzyme A on the outer mitochondrial membrane. This reaction produces acyl CoA and it requires ATP. Acyl CoA cannot cross the mitochondrial membrane and therefore it used carnitine to carry it across. Acylcarnitine can cross the membrane and acyl CoA is reconstituted in the mitochondria. Oxidation of the fatty acid has 4 steps. First is an oxidation reaction catalyzed by acyl CoA dehydrogenase. It oxidizes FAD FADH2 and forms a trans double bond. Second is a hydration by enol CoA hydratase. This introduces an –OH at the double bond for the next step. Third is the oxidation of the –OH by hydroxyacyl CoA dehydrogenase. This step yields a keto group and NADH. Last is a thiolysis by β-ketothiolase. 3-ketoacyl CoA is cleaved by the thiol group of CoA toacetyl Coa and acyl(n-2) CoA. This four step process is repeated until the saturated acyl CoA is completely degraded. One fatty acid chain can produce up to 106 ATP. How does the oxidation of unsaturated fatty acids differ from the oxidaition of saturated fatty acids?Oxidation of unsaturated fatty acids require additional steps and enzymes in order to move the double bonds. The β-oxidation occurs normally until a double bond is reached. At this point Isomerase shifts the position of the double bond into can odd numbered position. Isomerase andreductase are required to metabolize these double bonds. What are ketone bodies?Ketone bodies occur when fatty acid oxidation exceeds the capacity of TCA cycle and acetyl CoA is diverted to for these Ketone bodies via HMG-CoA via the liver. Ketone bodies can be used as energy sources during times of starvation. However, they are also deadly metabolites which canlead to acidosis, ketosis, coma, and eventual death.Lecture 24 (March 18)How are fatty acids synthesized?Fatty acid synthesis occurs in three stages. First acetyl CoA is transferred from the mitochondria to the cytosol by citrate. This is catalyzed by citrate translocase and costs 1 ATP. This step also produces one NADPH for every acetyl CoA transported. Next it is activated to form malonyl CoA. This is the commited step of the process. This is catalyzed by acetyl CoA carboxylase with a biotin cofactor and requires ATP. The last stage is the repetitive addition of 2C units to the fatty acid chain through a four-part reaction: condensation, reduction, dehydration, and reduction. During condensation the acetyl ACP and malonyl ACP are condensed to form acetoacetyl ACP and CO2. It is catalyzed by ketoacyl synthase. The first reduction is that of NADPH  NADP+ when acetoacetyl ACP is transformed to D-3-hydroxbutyryl ACP by the enzyme β-ketoacyl ACP reductase. The dehydration, catalyzed by 3-hydroxyacyl ACP dehydratase, results in crotonyl ACP. The final reduction is catalyzed by enoyl ACP reductase and occurs at the double bond in crotonyl ACP. NADPH is again reduces and Butyryl ACP is produced. The new acyl(n+2) ACP