Define the following terms:
i) Pheromone
ii) Vitamins C\mathrm{C}
iii) Allosteric enzyme
iv) Malpighian tubule
Answer:
i) Pheromone: Pheromones are chemical substances produced and released into the environment by an animal, especially an insect or mammal, that affect the behavior or physiology of others of the same species. Pheromones are used for communication among individuals and can trigger various behaviors such as attracting mates, marking territory, or signaling danger.
ii) Vitamin C: Vitamin C, also known as ascorbic acid, is an essential nutrient that plays a crucial role in various bodily functions. It is a powerful antioxidant that helps protect cells from damage caused by free radicals. Vitamin C is also important for the synthesis of collagen, which is a key component of connective tissue and is necessary for wound healing. Additionally, it aids in the absorption of iron from plant-based foods and supports the immune system.
iii) Allosteric Enzyme: An allosteric enzyme is a type of enzyme whose activity is regulated by the binding of an effector molecule at a site other than the enzyme’s active site. This binding causes a conformational change in the enzyme, which can either enhance (activate) or inhibit its catalytic activity. Allosteric regulation is a crucial mechanism for controlling metabolic pathways in cells.
iv) Malpighian Tubule: Malpighian tubules are excretory and osmoregulatory organs found in some arthropods, including insects and arachnids. They are slender, tube-like structures that extend from the digestive tract and absorb waste products, such as uric acid, from the hemolymph (the invertebrate equivalent of blood). The wastes are then concentrated and excreted as solid pellets or dissolved in water, depending on the organism’s need to conserve water. Malpighian tubules play a vital role in maintaining the internal chemical balance and osmotic pressure of these organisms.
a) Discuss the mechanism urine production in nephron.
Answer:
The production of urine in the nephron, the functional unit of the kidney, involves three main processes: filtration, reabsorption, and secretion. These processes ensure that essential substances are retained in the body while waste products and excess substances are excreted in the urine. Here’s a detailed overview of these processes:
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.
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.
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.
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.
The final urine, containing waste products and excess ions, flows from the collecting ducts into the renal pelvis, then to the ureter, and finally to the bladder for storage and eventual excretion through the urethra.
b) Explain beta\beta-oxidation pathway of saturated fatty acid breakdown.
Answer:
The β-oxidation pathway is the primary metabolic process for breaking down saturated fatty acids to produce energy. It occurs in the mitochondria of cells and involves the sequential removal of two-carbon units from the fatty acid chain in the form of acetyl-CoA. The pathway consists of four main steps:
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.
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.
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.
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.
Each round of β-oxidation produces one molecule of acetyl-CoA, one molecule of FADH2, and one molecule of NADH. The acetyl-CoA can enter the citric acid cycle (also known as the Krebs cycle) to generate further energy, while the FADH2 and NADH can enter the electron transport chain to produce ATP. This process continues until the entire fatty acid chain is broken down into acetyl-CoA units, providing a significant source of energy for the cell.