Major Site Plans and Neighborhood Meetings
Applicants may be required to hold neighborhood meetings for Major site plans that will result in new street connections or stubs in single-family residential subdivisions. Applicants must send neighborhood meeting notification letters to all affected landowners and post neighborhood meeting notice signs in the project area. The City will hold a public hearing on the neighborhood meeting. 메이저사이트
Synthesis of Lipids
The thousands of proteins that make up the membranes of eukaryotic cells require a wide range of different lipid molecules for their proper function. Glycerophospholipids, sphingolipids and sterols are the main constituents of membranes but other lipids also exist, including fats, waxes and water-soluble vitamins. In eukaryotic cells, lipids are synthesised at the endoplasmic reticulum (ER) and delivered to their destination membranes.
Most lipids are synthesised at this organelle, which is organised into a network of branching tubules and flattened sacs that extend throughout the cytosol. The ER is in close contact with other organelles, including mitochondria and the Golgi apparatus, and lipids can easily move between these compartments by passive diffusion.
For example, cholesterol synthesis in the ER can be shut down by a mechanism that involves the lipid transfer protein GRAMD1. This protein has a domain that can transport cholesterol from the lysosomal membrane back to the ER, where it can then be recycled to the plasma membrane.
Synthesis of Hormones
The endocrine system produces hormones to regulate the body’s metabolism of carbohydrates and lipids, growth and development, water balance, blood pressure, heart rate, and other vital functions. Hormones are released from specialized endocrine glands that include the hypothalamus, pituitary gland, adrenal glands, gonads (i.e., the testes and ovaries), thyroid gland, parathyroid glands, and pancreas.
The major classes of hormones are steroids, polypeptides, and amino acid derivatives. Steroid hormones are produced by the adrenal cortex and gonads. They have a molecular structure similar to cholesterol and can enter cells where they interact with receptor proteins that are already associated with specific regions of the cell’s DNA.
Polypeptide and protein hormones are synthesized in the hypothalamus, pituitary, and some adrenal glands. They are cleaved from inactive precursors, called prohormones. The hormones are then stored in the posterior pituitary gland until they are ready to be secreted into the bloodstream. One example is antidiuretic hormone (ADH). This peptide hormone controls the body’s retention of water.
Synthesis of Proteins
Proteins are a major type of macromolecule that is found in all living cells. They play a crucial role in many aspects of cell function, including structural components of the cell membrane, production of hormones and enzymes, and cell repair. Protein synthesis is an intelligent process that involves two steps: transcription and translation.
In the first step, DNA in the nucleus serves as a template for making a messenger RNA (mRNA) copy of a specific sequence of amino acids. The mRNA then exits the nucleus through a nuclear pore and enters the cytoplasm where it attaches to a ribosome. The ribosome then reads the genetic code in the mRNA and creates an amino acid chain, which eventually folds into a protein.
Once a protein is made, it is transported to the rough endoplasmic reticulum (ER). There, it undergoes quality control to ensure that only correctly folded proteins exit the ER for the plasma membrane or Golgi apparatus. The ER is also the site for lipid synthesis and is sensitive to perturbations in homeostasis, such as elevated levels of reactive oxygen species or advanced glycation end products (AGE).
Synthesis of Nucleic Acids
Nucleic acids are biopolymers, macromolecules essential for all living cells. They consist of sugars and phosphate groups linked by nitrogenous bases. The two main types of nucleic acid are DNA and RNA. Each has a unique sugar and phosphate backbone that differs from the other, giving them different structures. Nucleic acid molecules contain a sequence of nucleobases: the nitrogenous bases guanine and cytosine pair together, while adenine pairs with uracil.
In plants, ribosomal RNA (rRNA) directs the synthesis of amino acids. In bacteria, the synthesis of rRNA is controlled by a gene cluster called the rRNA operon. This contains genes for the 30S ribosomal RNA precursor and the genes for several transfer RNAs that carry amino acids to the ribosome, such as tRNA Thr and tRNA Gly.
The synthesis of rRNA is catalyzed by an enzyme called DNA-dependent RNA polymerase. This enzyme recognizes a section of DNA known as a scripton and adds building blocks to the chain called ribonucleoside triphosphates (ATP, GTP, UTP). The addition of these building blocks results in the synthesis of an RNA chain that is extended through a process called elongation.