Let's understand some basic composition concepts involved in skin care. This article describes the molecular weight from small to large:
1. A peptide bond (amino and carboxyl)
Amino acid: When two amino acids form a dipeptide through a peptide bond, it is a type of condensation reaction. In this kind of condensation, two amino acids approach each other, with the non-side chain (C1) carboxylic acid moiety of one coming near the non-side chain (N2) amino moiety of the other. One loses a hydrogen and oxygen from its carboxyl group (COOH) and the other loses a hydrogen from its amino group (NH2). This reaction produces a molecule of water (H2O) and two amino acids joined by a peptide bond (−CO−NH−). The two joined amino acids are called a dipeptide.
Carboxyl acid: Carboxyl group is a basic functional group in organic chemistry. It is weakly acidic and consists of one carbon atom, two oxygen atoms and one hydrogen atom. The chemical formula is -COOH. The compound with carboxyl group in the molecule is called carboxylic acid.
2. Amino acid
Amino acid is a small organic molecule that can penetrate human skin. It contains two functional groups, amino and carboxyl. It is an organic compound of basic amino and acidic carboxyl. Its chemical formula is RCHNH2COOH. The R group is a group connected to the carbon atom on the amino acid, which is a common name and represents different groups, and the R group distinguishes different amino acids.
There are about 20 kinds of amino acids that make up organisms, and different amino acids are determined by R. Amino acids are the basic substances that constitute protein required for animal nutrition.
3. Protein
Most proteins consist of linear polymers built from series of up to 20 different L-α- amino acids. All proteinogenic amino acids possess common structural features, including an α-carbon to which an amino group, a carboxyl group, and a variable side chain are bonded. Only proline differs from this basic structure as it contains an unusual ring to the N-end amine group, which forces the CO–NH amide moiety into a fixed conformation. The side chains of the standard amino acids, detailed in the list of standard amino acids, have a great variety of chemical structures and properties; it is the combined effect of all of the amino acid side chains in a protein that ultimately determines its three-dimensional structure and its chemical reactivity. The amino acids in a polypeptide chain are linked by peptide bonds. Once linked in the protein chain, an individual amino acid is called a residue, and the linked series of carbon, nitrogen, and oxygen atoms are known as the main chain or protein backbone.
The peptide bond has two resonance forms that contribute some double-bond character and inhibit rotation around its axis, so that the alpha carbons are roughly coplanar. The other two dihedral angles in the peptide bond determine the local shape assumed by the protein backbone. The end with a free amino group is known as the N-terminus or amino terminus, whereas the end of the protein with a free carboxyl group is known as the C-terminus or carboxy terminus (the sequence of the protein is written from N-terminus to C-terminus, from left to right).
The words protein, polypeptide, and peptide are a little ambiguous and can overlap in meaning. Protein is generally used to refer to the complete biological molecule in a stable conformation, whereas peptide is generally reserved for a short amino acid oligomers often lacking a stable 3D structure. But the boundary between the two is not well defined and usually lies near 20–30 residues. Polypeptide can refer to any single linear chain of amino acids, usually regardless of length, but often implies an absence of a defined conformation.
A linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide. Short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called peptides. The individual amino acid residues are bonded together by peptide bonds and adjacent amino acid residues. The sequence of amino acid residues in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In general, the genetic code specifies 20 standard amino acids; but in certain organisms the genetic code can include selenocysteine and—in certain archaea—pyrrolysine. Shortly after or even during synthesis, the residues in a protein are often chemically modified by post-translational modification, which alters the physical and chemical properties, folding, stability, activity, and ultimately, the function of the proteins. Some proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors. Proteins can also work together to achieve a particular function, and they often associate to form stable protein complexes.
Once formed, proteins only exist for a certain period and are then degraded and recycled by the cell's machinery through the process of protein turnover. A protein's lifespan is measured in terms of its half-life and covers a wide range. They can exist for minutes or years with an average lifespan of 1–2 days in mammalian cells. Abnormal or misfolded proteins are degraded more rapidly either due to being targeted for destruction or due to being unstable.
Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms and participate in virtually every process within cells. Many proteins are enzymes that catalyst biochemical reactions and are vital to metabolism. Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, which form a system of scaffolding that maintains cell shape. Other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. In animals, proteins are needed in the diet to provide the essential amino acids that cannot be synthesized. Digestion breaks the proteins down for metabolic use.
Proteins may be purified from other cellular components using a variety of techniques such as ultracentrifugation, precipitation, electrophoresis, and chromatography; the advent of genetic engineering has made possible a number of methods to facilitate purification. Methods commonly used to study protein structure and function include immunohistochemistry, site-directed mutagenesis, X-ray crystallography, nuclear magnetic resonance and mass spectrometry.
4. Collagen fibers
Type I collagen is the most abundant collagen of the human body. It forms large, eosinophilic fibers known as collagen fibers. It is present in scar tissue, the end product when tissue heals by repair, as well as tendons, ligaments, the endomysium of myofibrils, the organic part of bone, the dermis, the dentin, and organ capsules.
Collagen fibrils are formed by the aggregation of collagen molecules in the extracellular matrix. Under the action of endopeptidase, the procollagen cuts off the spherical configuration at both ends of the molecule to form a procollagen molecule, which is about 1.5nm thick and about 300nm long, and the procollagen molecules are arranged in parallel and aggregated into collagen fibrils.
During polymerization, the adjacent molecules parallel to each other are staggered by 1/4 of the molecular length, and the molecules in the same row face each other head to tail and keep a certain distance, polymerize into a bundle, and the basic functional groups in the molecule and between the molecules undergo condensation and crosslinking to increase the stability of the fibrils and form collagen fibrils with 64nm periodic stripes.
Collagen is secreted by fibroblasts and is a family of proteins with a protein structure consisting of three peptide chain helices. This molecular configuration makes collagen fibers have strong toughness and tensile strength.
5. Elastic fibers
The birth process of elastic fibers is like that of collagen fibers. Fibroblasts synthesize elastin, and elastin aggregates into elastic fibers outside the cell membrane. Elastic fibers have no obvious bonding process, so the molecular weight is much smaller than that of collagen fibers.
Elastin acts as a rubber band in the skin, giving the skin the ability to stretch and fold. It functions like a spring in a mattress, responsible for maintaining and supporting the elasticity of the skin. Therefore, elastin plays an important role in maintaining skin elasticity. Coexistence of elastic fibers and collagen fibers gives the dermis elasticity and tensile strength.
6. Fibroblasts
Fibroblasts are the main cells resident in the dermis, with vigorous functional activities, large cells and nuclei, clear outlines, and large and prominent nucleoli. Fibroblasts synthesize proteins and secrete hyaluronic acid, which plays a vital role in the care of the dermis.
Fibroblasts in a mature or quiescent state have smaller cell bodies, long spindle-shaped cells, underdeveloped rough endoplasmic reticulum and Golgi complex, and are called fibrocytes. The functional activities of fibrocytes are not active, the cell outline is not obvious, the nuclei are small and darkly stained, the nucleoli are not obvious, the cytoplasm is less, and they lose the function of synthesizing protein and secreting hyaluronic acid.
Fibroblast growth factor: a polypeptide secreted by the pituitary gland and hypothalamus. When human tissue is injured or damaged by disease, it will stimulate the production of fibroblast growth factor. These fibroblast growth factors rush to fight the fire like a fire brigade.
One of the core mechanisms of dermal care: activation of fibrocytes into fibroblasts. Under the stimulation of trauma and other factors, fibroblast growth factor will repair fibrocytes and re-transform into fibroblasts, and their functional activities will also be restored, participating in the repair of tissue damage.
7. Hyaluronic acid
Hyaluronic acid is secreted by fibroblasts and widely exists between tissue cells and various structural tissues of the human body. Hyaluronic acid under the dermis determines the nutrition and plumpness of the skin. The rich intercellular matrix in young skin is rich in hyaluronic acid. Supplementing hyaluronic acid can greatly enrich the synthesis of subcutaneous mucopolysaccharides and glucose, making the skin plump and textured.