Question

Biochm 265: Please explain the below to me cause I cant find the answer in my notes. This is not for points but study.

17) What are the Urea cycle components and locations in general

18) Explain Anerobic vs. aerobic respiration

19) NAD+, NADH, NADP+, NADPH. NADH is used for catabolism mainly, while NADPH is used for biosynthesis.

20) Coupling of unfavorable process to favorable process, feature Alcohol dehydrogenase.

Answer 1

17.The urea cycle takes place primarily in the liver and also in the kidneys to a lesser extent. The urea cycle is a cycle of biochemical reactions that produces urea from ammonia. The conversion from ammonia to urea in urea cycle is accomplished through five main reactions. Following are the five reactions and the components of urea cycle along with the location where the reactions are taking place.

1. NH₃ + HCO₃^? + 2ATP => carbamoyl phosphate + 2ADP + P_i (This reaction is catalyzed by carbamoyl phosphate synthetase I (CPS1), and takes place in mitochondria)

2. carbamoyl phosphate + ornithine => citrulline + P_i (This reaction is catalyzed by ornithine transcarbamoylase (OTC), zinc, biotin, and takes place in mitochondria)

3. citrulline + aspartate + ATP => argininosuccinate + AMP + P_i (This reaction is catalyzed by arginino succinate synthetase (ASS), and takes place in cytosol)

4. arginino succinate => arginine + fumarate ( This reaction is catalyzed by arginino succinate lyase (ASL), and takes place in cytosol)

5. arginine + H₂O => ornithine + urea (This reaction is catalyzed by arginase 1 (ARG1), manganese, and takes place in cytosol)

18. Aerobic respiration takes place in the presence of oxygen whereas anaerobic respiration takes place without the use of oxygen. Through aerobic respiration a large amount of energy is produced while through anaerobic respiration a smaller amount of energy is produced. In an aerobic respiration- carbon dioxide and water are produced as the waste products. On the other hand in an anaerobic respiration alcohol or lactic acid or other compounds are produced.

The chemical equation corresponding to aerobic respiration is C6H12O6 + 6O2 ? 6CO2 + 6H2O (glucose + oxygen -> carbon dioxide + water). While the chemical equation corresponding to anaerobic respiration is C6H12O6 -> 2C3H6O3 (Glucose -> Lactic acid).

19. The role of NADH is mostly used in catabolic reactions, where NAD⁺ is needed as an oxidizing agent. NADH is produced in catabolic reactions and is later used in the electron transport chain to obtain energy by converting NADH back to NAD+.

The role of NADPH is mostly used in anabolic reactions or biosynthesis, where NADPH is needed as a reducing agent. The phosphate group in NADPH doesn't affect the redox abilities of the molecule, as it is too far away from the part of the molecule involved in the electron transfer. The phosphate group lets the enzymes to discriminate between NADH and NADPH, which allows the cell to regulate both independently. NADPH is used in biosynthesis of cholesterol, fatty acids, transmittor substances and nucleotides etc.

20. D -3-Phosphoglycerate dehydrogenase (SerA) is a key enzyme in l-serine biosynthesis. The coupling of dehydrogenation of d-3-phosphoglycerate to 3-phosphohydroxypyruvate (energetically unfavorable) and the reduction of 2-ketoglutarate to d-2-hydroxyglutarate (d-2-HG) (energetically favorable) by D -3-Phosphoglycerate dehydrogenase (SerA). This is an example of how nonenergetically favorable and energetically favorable reactions are linked together to allow metabolic processes to proceed, and the one that also features a dehydrogenase.