📖 Biochemistry
Essential vs. Nonessential Amino Acids
BiochemistryEssential vs. Nonessential Amino Acids
|
Nonessential |
Essential |
|
Alanine |
Arginine* |
|
Asparagine |
Histidine |
|
Aspartate |
Isoleucine |
|
Cysteine |
Leucine |
|
Glutamate |
Lysine |
|
Glutamine |
Methionine* |
|
Glycine |
Phenylalanine* |
|
Proline |
Threonine |
|
Serine |
Tyrptophan |
|
Tyrosine |
Valine |
*The amino acids arginine, methionine and phenylalanine are considered essential for reasons not directly related to lack of synthesis. Arginine is synthesized by mammalian cells but at a rate that is insufficient to meet the growth needs of the body and the majority that is synthesized is cleaved to form urea. Methionine is required in large amounts to produce cysteine if the latter amino acid is not adequately supplied in the diet. Similarly, phenyalanine is needed in large amounts to form tyrosine if the latter is not adequately supplied in the diet.
BIOLOGICAL BUFFER SYSTEMS
BiochemistryBIOLOGICAL BUFFER SYSTEMS
Cells and organisms maintain a specific and constant cytosolic pH, keeping biomolecules in their optimal ionic state, usually near pH 7. In multicelled organisms, the pH of the extracellular fluids (blood, for example) is also tightly regulated. Constancy of pH is achieved primarily by biological buffers : mixtures of weak acids and their conjugate bases
Body fluids and their principal buffers
Body fluids Principal buffers
Extracellular fluids {Biocarbonate buffer Protein buffer }
Intracellular fluids {Phosphate buffer, Protein }
Erythrocytes {Hemoglobin buffer}
Parathyroid Hormone
BiochemistryParathyroid Hormone
Parathyroid hormone (PTH), parathormone or parathyrin, is secreted by the chief cells of the parathyroid glands.
It acts to increase the concentration of calcium (Ca2+) in the blood, whereas calcitonin (a hormone produced by the parafollicular cells of the thyroid gland) acts to decrease calcium concentration.
PTH acts to increase the concentration of calcium in the blood by acting upon the parathyroid hormone 1 receptor (high levels in bone and kidney) and the parathyroid hormone 2 receptor (high levels in the central nervous system, pancreas, testis, and placenta).
Effect of parathyroid hormone in regulation of serum calcium.
Bone -> PTH enhances the release of calcium from the large reservoir contained in the bones. Bone resorption is the normal destruction of bone by osteoclasts, which are indirectly stimulated by PTH forming new osteoclasts, which ultimately enhances bone resorption.
Kidney -> PTH enhances active reabsorption of calcium and magnesium from distal tubules of kidney. As bone is degraded, both calcium and phosphate are released. It also decreases the reabsorption of phosphate, with a net loss in plasma phosphate concentration. When the calcium:phosphate ratio increases, more calcium is free in the circulation.
Intestine -> PTH enhances the absorption of calcium in the intestine by increasing the production of activated vitamin D. Vitamin D activation occurs in the kidney. PTH converts vitamin D to its active form (1,25-dihydroxy vitamin D). This activated form of vitamin D increases the absorption of calcium (as Ca2+ ions) by the intestine via calbindin.
Fatty Acid Synthesis
BiochemistryThe input to fatty acid synthesis is acetyl-CoA, which is carboxylated to malonyl-CoA.
The ATP-dependent carboxylation provides energy input. The CO2 is lost later during condensation with the growing fatty acid. The spontaneous decarboxylation drives the condensation.
fatty acid synthesis
acetyl-CoA + 7 malonyl-CoA + 14 NADPH → palmitate + 7 CO2 + 14 NADP+ + 8 CoA
ATP-dependent synthesis of malonate:
8 acetyl-CoA + 14 NADPH + 7 ATP → palmitate + 14 NADP+ + 8 CoA + 7 ADP + 7 Pi
Fatty acid synthesis occurs in the cytosol. Acetyl-CoA generated in the mitochondria is transported to the cytosol via a shuttle mechanism involving citrate