Major Site

Major site is a place where lipids like hormones and steroids are synthesized. These lipids are insoluble in water but soluble in organic solvents. They are synthesized in smooth endoplasmic reticulum.

The major site resides within the CDP-alcohol binding domain of human CEPT1 which extends from residues 88-213 and contains a diacylglycerol binding motif, DGGG(x)xG(y)xD(x)xG(y), in which two aspartates are required for catalysis (Hjelmstad et al., 1995). 메이저사이트

Synthesis of Lipids

Lipids are a group of naturally occurring molecules comprising fats, waxes, cholesterol and other sterols, as well as the structural components of cell membranes and important signalling molecules. They are soluble in non-polar organic solvents, but not in water.

Lipid biosynthesis involves both synthesis of lipids and degradation of existing lipids. The synthesis of lipids is catalysed by a variety of enzymes. The most prominent lipids are phosphatidylcholine (PC) and phosphatidylethanolamine (PE), which form the bilayer of the plasma membrane along with other phospholipids including glycosyl phosphatidyl-inositols and sphingolipids.

Proteins are anchored to the cell membrane by covalently linking a phosphatidylinositol (PI) moiety via a phospholipid transfer protein to the C-terminus of a protein destined for the membrane. This modification, known as a glycosyl phosphatidylinositol anchor, is carried out by enzymes in the ER. Lipids can also serve as energy stores and act as second messengers in cellular signalling. Deregulation of lipid metabolism is associated with cancer, and inhibition of fatty acid synthesis via FASN inhibitors has been shown to reduce tumour growth in preclinical models.

Synthesis of Hormones

The endocrine glands (hypothalamus, pituitary gland, adrenal glands, and gonads) produce hormones that control many functions in the body, including growth and development, metabolism of carbohydrates and lipids, blood pressure and heart rate, sleep-wake cycle, and reproductive function. Many hormones are secreted into the blood stream and carried to target cells in the body.

Hormones come in several classes, differing mainly in their molecular structure and ability to enter target cells. Steroid hormones, produced in the gonads and part of the adrenal gland, for example, have a molecular structure similar to cholesterol and can therefore enter target cells.

Polypeptide and protein hormones, on the other hand, have a much longer chain of amino acids and cannot enter cells. They act by binding to receptor proteins that are already associated with specific regions of a cell’s DNA, thereby modulating the activity of these genes. Some hormone systems operate by positive feedback. In this case, an increase in the levels of a target hormone in the blood causes the hypothalamus and/or pituitary gland to secrete more of this hormone.

Synthesis of Proteins

Proteins are a major type of biomolecule that all living things require to thrive. They are involved in almost all cell functions. Both prokaryotes and eukaryotes produce proteins through a complex series of events that involve transcription and translation.

The first step of protein synthesis – transcription – takes place in the nucleus. Once mRNA (a copy of a section of DNA) has been transcribed it moves into the cytoplasm where ribosomes are located. Ribosomes’read’ the mRNA and translate it into a polypeptide chain of amino acids.

Once the chain of amino acids is made it may undergo additional modifications such as lipid binding to form lipoproteins or carbohydrate binding to form glycoproteins. It then travels to the Golgi apparatus where it is modified for its specific role in the cell.

A protein’s ability to bind and modify other molecules is critical for its function. Consequently, maintaining rates of protein turnover is a key proteostatic mechanism against the accumulation of damaged proteins.

Synthesis of DNA

The accuracy of DNA replication depends on the ability of a DNA polymerase to distinguish its own deoxyribonucleoside triphosphates from those of the template strand. Moreover, because the two strands of a DNA molecule are tightly wound around each other in a double helix, they must be easily separated and exposed so that the incoming deoxyribonucleoside triphosphates can form base pairs with the correct template strand.

In addition, since the DNA code is written in a sequence of three-base triplets that specify amino acids, the polymerase must recognize these triplets accurately. This process is known as transcription.

It is also essential for a DNA polymerase to be able to dissociate rapidly from the DNA template at sites of a mismatch. This is necessary because the lagging strand must be re-oriented to match the DNA template before the polymerase can start a new Okazaki fragment on it.

Unlike DNA, RNA is single-stranded and contains no complementary strand. RNA also has a different sugar, ribose, which has one additional oxygen atom compared with DNA’s deoxyribose sugar. Furthermore, RNA does not contain the base thymine but instead has the base uracil.