Macromolecule

Chemical structure of a polypeptide, an example of macromolecule

A macromolecule is a large molecule commonly created through the polymerization of smaller subunits (monomers). They are usually made up of thousands, or more, atoms. They can be both organic and inorganic, and the most common in biochemistry are biopolymers (nucleic acids, proteins, carbohydrates, and polyphenols) and large non-polymeric molecules (such as lipids and macrocycles). Examples of synthetic macromolecules are common plastics and synthetic fibers, as well as some experimental materials, such as carbon nanotubes.

The term macromolecule originally referred to molecules that weighed more than 11,000 daltons in atomic mass, although they can reach millions of AMUs.

Definition

The term “macromolecule” (macro- + molecule) was coined by the Nobel laureate [[Brother

Staudinger]] in the 1920s, although his first relevant publication in this field only mentioned "high molecular weight compounds" (over 1000 atoms). At that time the term "polymer", as had been introduced by Berzelius in 1833, had a meaning different from that of today: it was only another form of isomery, for example, with benzene and acetylene and had little to do with size.

Use of the term to describe large molecules varies across disciplines. For example, while in biology macromolecules are referred to as the four large molecules that make up living things, in chemistry the term can refer to aggregates of two or more molecules held together by intermolecular forces rather than covalent bonds, but not they dissociate easily.

According to the standard IUPAC definition, the term "macromolecule" as used in polymer science refers only to a single molecule. For example, a simple polymer molecule is appropriately described as a "macromolecule" or "polymer molecule" rather than a "polymer", suggesting a substance composed of macromolecules.

Because of their size, macromolecules cannot be conveniently described in terms of stoichiometry alone. The structure of simple macromolecules, such as homopolymers, can be described in terms of the individual monomer subunit and with the total molecular mass. Complicated biomacromolecules, on the other hand, require a multifaceted structural description, such as the hierarchy of structures used to describe proteins. In British English, the term "macromolecule" tends to be called "high polymer".

Description

They form long chains that are joined together by Van der Waals forces, hydrogen bonds or hydrophobic interactions and by covalent bonds.

In general, molecules are analyzed in which the number of atoms is very small, which also consist of a relatively small molecular mass. For example, the water molecule (H₂O) consists of only three atoms (triatomic molecule) and the relative molecular mass is 18. In contrast, there are many kinds of molecules that have a much more complex composition. more complicated, that is, a large number of atoms and a large value in its molecular mass; This class of compositions is called macromolecules. Specifically, a macromolecule has a minimum quantity of 1,000 and a mass of not less than 10,000. Furthermore, the links that unite the molecule do not lead to variation in physical properties, if they are added in a complementary way. For example, the polyethylene molecule, whose relative molecular mass is 280,000 and consists of 20,000 links of -CH₂- groups. Another example is the ribonucleic acid molecule; consists of repeating ribonucleotide links. Its chemical formula is C₅₇₅H₉₀₁O₁₉₃N₁₇₁S₁₂, and its relative molecular mass is 13,682. Polymers are substances made up of macromolecules.

For some time, a certain group of molecules was called colloids, at a time when the existence of macromolecules was unknown. The colloids have an adhesive gelatinous appearance, with a low diffusion speed without being able to cross the membranes, contrary to what happens, for example, with common salt, which diffuses very well and passes through the membranes. These substances were called crystalloids because of their good structural conformation. Subsequently, it was discovered that, under certain conditions, crystalloids could acquire a «colloidal state», if their molecules could be united in groups and with a low relative mass. The aggregation of crystalloid molecules, leading to the appearance of colloidal properties of their molecules, is usually a manifestation of secondary valence forces, and the bonding of atoms in macromolecules is covalent.

Types of macromolecules

Macromolecules can be classified in different ways.

• According to their origin, they can be:

• Natural:

• Polysaccharides (starch, glucogen, cellulose, thyrin, etc.)
• Proteins
• Nucleic acids (DN and RNA)
• Carbohydrates
• Lipids

• Artificial:

• Polymers (Poliurethane, Polyethylene, Polyviline Cloride (PVC) or Polytetrafluoroethylene)
• Carbon Nanotubo

• According to its molecular structure:

• Linears: monomers are joined by two sites (head and tail).
• Ramified: If any monomer can be joined by three or more sites

• According to its composition:

• Homopolymers: formed by a single repeat monomer.
• Copolymers: formed two or more monomers.