Proteins - how are they made, what are their properties?

Proteins are organic compounds with a complex chemical structure and great variety. These are polymers made of amino acids, while amino acids are connected with each other by peptide bonds. The number of amino acids in a protein varies, sometimes it even reaches 1000. In the human body, about 65% is water, and 20% is protein, therefore, one of the main components of the human body. What are they characterized by? How can we divide them? Check it out!

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1. What are proteins?

Proteins (proteins) are multi-molecular biopolymers made of amino acids linked together by peptide bonds -CONH-. They are found in every living organism and virus. Their synthesis takes place with the participation of ribosomes - special cell organelles.

2. Structure of proteins

A protein chain synthesized in a single cell resembles a thread floating freely in solution, which can take any shape (it is technically referred to as a random ball). However, it undergoes the process of folding, as a result of which it creates a more or less rigid spatial structure, which is called the structure or conformation of the native protein.

Usually, only those molecules that have folded into such a structure can play a proper biochemical role for a given protein. However, there are proteins without a tertiary structure that are the exception to the rule.

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Given the spatial scale, the complete structure of the protein can be described at four levels:

  • primary protein structure (primary protein structure, amino acid sequence) - the order of amino acids in the polypeptide chain;
  • protein secondary structure - spatial arrangement of fragments of polypeptide chains. These structures include:
    • alpha helix;
    • beta harmonica;
    • beta bend.
  • protein tertiary structure - the mutual position of the elements of the secondary structure;
  • protein quaternary structure - the mutual position of polypeptide chains and possibly non-protein structures (prosthetic group): sugars in glycoproteins, lipids in lipoproteins, nucleic acids in nucleoproteins, dyes in chromoproteins and the rest of phosphoric acid in phosphoproteins.

What elements does protein consist of? These are:

  • carbon (50-55%);
  • oxygen (19-24%);
  • nitrogen (15-18%);
  • hydrogen (6-8%);
  • sulfur (0.3-3%);
  • phosphorus (0-0.5%).

Their composition sometimes also includes metal cations Zn2 +, Fe2 +, Mg2 +, Cu2 +, Co2 +, Mn2 + and many others. The above-mentioned composition does not coincide with the composition of the amino acids. This is because most proteins have other molecules attached to their amino acid residues.

Additionally, sugars are attached, and many different organic compounds that act as coenzymes, as well as metal ions, can be joined by hydrogen bonds or covalently.

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3. Properties of the protein

When proteins are heated in a solution or in a solid state, above a certain temperature, they undergo a process of denaturation (the cutting of protein fibers). This is a change in structure as a result of which the protein ceases to be biologically active. A good example of this is boiling or frying an egg - in this case this is the process that is going on.

This is due to the irreversible loss of the tertiary or quaternary structure of the protein. Denaturation can also occur under the influence of strong acids and bases, heavy metal salts, aldehydes, low-molecular alcohols and radiation. The exceptions are simple proteins that can undergo the process of renaturation (the reverse of denaturation) after removing the factor that leads to denaturation.

A small fraction of proteins is permanently denatured by a higher concentration of salt in the solution, but the process is usually reversible, allowing the proteins to be separated and isolated.

Regarding melting, proteins do not have a specific temperature at which this reaction would take place. This compound is generally well soluble in water. Proteins that do not have this property include, among others fibrillar proteins in the skin, hair (e.g. collagen, elastin) or muscles (myosin).

Some proteins may be soluble in dilute bases or acids, or in organic solvents. Whether a protein is soluble is greatly influenced by the concentration of inorganic salts in the solution, where a low salt concentration positively affects the solubility of proteins.

However, if the concentration is higher, the solvate shell is damaged, causing the proteins to fall out of solution. In this process, there is no damage to the protein structure, so it is reversible. Its name is the process of salting out proteins.

Hydration is the ability of proteins to bind water particles. Even if we get a sample of dry protein, it will contain water molecules.

Proteins play a very important role in all biological processes. They take, among others participate in catalyzing many changes in biological systems, serve as protective antibodies, participate in the transport of molecules and ions, and also take part in the transmission of nerve impulses as receptor proteins.

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4. Division of proteins

Proteins are divided into simple and complex due to their structure and composition. It is worth noting that this is not the only division of proteins.

Simple proteins (proteins) consist of only amino acids. We divide them into:

  • filamentous proteins (collagens, keratins, fibrinogen, fibroin, elastin);
  • albumin;
  • myosin and actin;
  • globulins.

Complex proteins (formerly proteids):

  • chromoproteins;
  • nucleoproteins;
  • lipoproteins;
  • glycoproteins;
  • metalloproteins.

5. Functions of proteins

Proteins perform a number of vital functions, including:

  • growth and differentiation control;
  • immunological - immunoglobulins;
  • enzymatic catalysis;
  • transport - transferrin, hemoglobin;
  • membrane permeability control;
  • orderly movement - muscle spasms;
  • storage - ferritin;
  • production and transmission of nerve impulses;
  • structural, building structure;
  • cell adherence;
  • regulatory;
  • course of biochemical processes.
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