The Major Site in Cells
Major site is a large protein that has an essential role in the synthesis of hormones, lipids, and nucleic acids. It is found in the smooth endoplasmic reticulum. The CDP-alcohol phosphotransferase motif, DG(x)2AR(x)8G, is located within this protein. The phosphotransferase activity is induced by diacylglycerol. The function of this protein is also dependent on other proteins. 메이저사이트
Synthesis of Lipids
Lipids are the building blocks of membranes that enclose all cellular compartments and provide an essential platform for protein recruitment. Cells uphold a differential composition of lipids in the different organelle membranes, and transport mechanisms move lipids together with proteins into these compartments.
Glycerophospholipids, sphingolipids and sterols are the major components of cellular membranes. They are synthesised by a complex set of enzymes in the endoplasmic reticulum (ER) and other organelles such as mitochondria, Golgi apparatus and lysosomes.
The starting molecule for lipid biosynthesis is the fatty acid (FA) phosphatidylethanolamine or phosphatidylserine, which is converted to PI in two steps. PI is characterised by having C18:0 in the sn-1 position and the unusual chemical property that its head group can be flipped between the two leaflets of the bilayer, depending on which side it is facing (Figure 3). The flipping step determines whether the PI molecule will have its head group oriented toward the cytosol or towards the extracellular milieu. The decision is influenced by the shape of the lipid which is determined by its metabolism by elongase and desaturase enzymes.
Synthesis of Hormones
Several classes of hormones exist, which differ in their molecular structure. Steroid hormones (produced in the gonads and by a region of the adrenal cortex) have a structure similar to cholesterol and can diffuse into cells. They interact with receptor proteins that are already associated with specific regions of the cell’s DNA and modify the activity of those genes.
Amino acid derivatives, like the peptide hormone vasopressin (ADH), can also enter cells and affect their function. Protein hormones, like insulin and glucagon, are secreted from the pancreas into the bloodstream.
Many endocrine hormones are part of regulatory hormonal cascades, such as the hypothalamic-pituitary-adrenal axis, which controls body temperature, blood pressure, the sleep-wake cycle, ovulation and menstrual cycles, sexual functions and behaviors, and metabolic pathways, including carbohydrate metabolism, fat synthesis, and glycerol production. Other endocrine hormones affect various organ systems, including the thyroid and gastrointestinal tract. Some, such as sex hormones, act locally in a single tissue.
Synthesis of Proteins
The code of letters in DNA contains a recipe to make proteins, which are the building blocks of cells and help maintain homeostasis. When a cell needs a new protein, the DNA molecule is transcribed into mRNA and then translated into a protein product. This process is called protein synthesis.
The first step of protein synthesis is transcription, which is when the RNA polymerase enzyme creates mRNA from a piece of DNA. mRNA is a single-stranded nucleic acid that has the same structure as DNA but differs in several ways. For one, mRNA has no complementary strand and instead of the base thymine it has uracil. Also, the end of mRNA has about 30 extra adenines called a poly A tail that helps the mRNA leave the nucleus.
Once the mRNA is in the cytoplasm it can enter a ribosome, where the next step of protein synthesis takes place. During translation, the ribosome reads the genetic code in mRNA and makes amino acids. These amino acids are linked together by peptide bonds to form a protein.
Synthesis of Nucleic Acids
Nucleic acids are the information-carrying molecules that determine inherited characteristics in all living organisms. They contain the genetic instructions that make proteins that are responsible for most of the processes in cells. The major varieties are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). They consist of long, spiral-spiraling sugar and phosphate backbones connected by nitrogen-containing bases. The bases are arranged in pairs of the five primary ones: adenine (A), guanine (G), cytosine (C), thymine (T) and uracil (U). A, G, C and T are categorized as purines while U is a pyrimidine.
A specialized enzyme adds a phosphate group to the five carbon sugar of the DNA building block called deoxyribose to produce ribonucleoside triphosphate. This is then used by a polymerase to add nitrogen-containing pyrimidines to form ribonucleotides. The nucleotide chains are added to the DNA template in the 5′- 3′ direction. The RNA polymerase then adds the corresponding phosphates to the terminal mono- or oligonucleotide end of each new nucleotide. This process is known as transcription.