bzyct-135-solved-assignment-2024-ss-020cab3d-1c01-486f-9bdf-7506d86b97ee

1. Define the following terms:
   i) Pheromone
   ii) Vitamins $\mathrm{C}$$\mathrm{C}$C\mathrm{C}$\mathrm{C}$
   iii) Allosteric enzyme
   iv) Malpighian tubule

2. a) Discuss the mechanism urine production in nephron.

1. Filtration: The first step in urine production occurs in the glomerulus, a network of capillaries surrounded by Bowman’s capsule. Blood pressure forces water, ions, and small molecules (such as glucose, amino acids, and urea) from the blood in the glomerulus into the Bowman’s capsule, forming the glomerular filtrate. Larger molecules like proteins and blood cells are too big to pass through and remain in the bloodstream.
2. Reabsorption: As the filtrate passes through the various segments of the nephron tubule (proximal convoluted tubule, loop of Henle, distal convoluted tubule), essential substances are reabsorbed back into the bloodstream. For example, in the proximal convoluted tubule, most of the glucose, amino acids, and a significant portion of water and ions are reabsorbed. In the descending limb of the loop of Henle, water is reabsorbed, while in the ascending limb, sodium and chloride ions are reabsorbed. This reabsorption is crucial for maintaining the body’s electrolyte balance and preventing the loss of important nutrients.
3. Secretion: In addition to reabsorption, the nephron also actively secretes certain substances from the bloodstream into the tubular fluid. This process occurs primarily in the distal convoluted tubule and collecting duct. Secreted substances include hydrogen ions, potassium ions, and certain drugs and toxins. Secretion is important for regulating the body’s pH balance and eliminating substances that are not filtered out by the glomerulus.
4. Concentration and Dilution: The final concentration of urine is regulated in the collecting duct, where water reabsorption is adjusted according to the body’s needs. The hormone antidiuretic hormone (ADH) plays a key role in this process. When the body needs to conserve water, ADH increases the permeability of the collecting duct to water, leading to more water reabsorption and concentrated urine. When hydration is adequate, ADH levels decrease, resulting in less water reabsorption and dilute urine.

1. Dehydrogenation: The first step involves the removal of two hydrogen atoms from the fatty acid, forming a trans double bond between the alpha (α) and beta (β) carbon atoms. This reaction is catalyzed by the enzyme acyl-CoA dehydrogenase, and the electrons removed during this process are transferred to the electron carrier molecule FAD, forming FADH2. The product of this reaction is a trans-Δ²-enoyl-CoA.
2. Hydration: In the second step, water is added across the double bond formed in the previous step. This reaction is catalyzed by the enzyme enoyl-CoA hydratase, resulting in the formation of L-β-hydroxyacyl-CoA.
3. Dehydrogenation: The third step involves another dehydrogenation reaction, where the hydroxyl group at the β-carbon is oxidized to a keto group. This reaction is catalyzed by the enzyme β-hydroxyacyl-CoA dehydrogenase, and NAD+ is the electron acceptor, forming NADH + H+. The product of this reaction is β-ketoacyl-CoA.
4. Thiolysis: In the final step, the β-ketoacyl-CoA is cleaved by the enzyme thiolase, which adds a molecule of Coenzyme A (CoA) to the β-carbon, releasing a molecule of acetyl-CoA and leaving behind an acyl-CoA that is two carbons shorter than the original fatty acid. The shortened acyl-CoA can then re-enter the β-oxidation cycle until the entire fatty acid chain is converted into acetyl-CoA units.