What are Proteins:
Proteins are macromolecules present in cells that coordinate multiple vital functions. They are also known as polypeptides.
These macromolecules are found in all living matter. In fact, we can nourish ourselves with them through the consumption of animal products such as meat, eggs and dairy products. Grains, nuts and cereals also contain protein, although their nutritional value is lower.
Proteins are made up of chains of organic compounds called amino acids. Therefore, they mainly contain carbon, oxygen, hydrogen and nitrogen. Sometimes they may contain elements such as sulfur, magnesium, phosphorus, iron or copper.
The process of forming proteins is called protein synthesis, and is carried out in the ribosomes of the cell cytoplasm. It is there where the amino acid chains are formed.
Instead, it is called denaturation of a protein to the process in which the structure of the protein undergoes a modification that disables its functions. For example, the albumen in egg white, which turns white when cooked.
Protein characteristics
Proteins characterized by the following attributes:
Function: They are multifunctional, as they control various vital activities, such as creating, regenerating and repairing tissues (organs, muscles, skin, nails); oxygenate the body; protect the body from infections; etc
Size: They can contain from seven amino acids to more than one hundred. For example, insulin has 51 amino acids, and albumin has 585.
Shape: Its forms are varied. For example, while fibrinogen and collagen are linear, immunoglobulins are Y-shaped.
Extremes: Proteins have two ends, one basic end or N-terminal end, and the other acidic or C-terminal end.
Limited life: The cell has to replace its proteins as they stop working.
Protein functions
As there is a great diversity of proteins, each of them deals with specific aspects of the organism. Some specific functions of proteins are listed below.
Structural function. Proteins give structure to cells, transport substances and give elasticity and resistance to tissues. For example, collagen.
Regulatory hormonal function. Hormones are proteins and, as such, they regulate various activities in the body. For example, insulin regulates blood sugar levels.
defensive function. Certain proteins defend the body from infections, bacteria and other pathogens. For example, antibodies.
enzymatic function. It consists of catalyzing the chemical reactions that occur in the body. For example, proteins break down nutrients during digestion.
Conveyor function. Some proteins transport oxygen, lipids and electrons around the body. For example, hemoglobin carries oxygen from the lungs to the tissues.
homeostatic function. They help maintain the body’s pH.
Muscle contraction function. Proteins help contract muscles. This is the case of myosin and actin.
Protein classification
Proteins are classified according to their chemical composition as simple or holoprotein, and conjugated or heteroprotein.
Simple or holoproteic. They are proteins that are only formed with chains of amino acids. These are divided into:
Globular proteins. Those that are present in hormones and antibodies. For example: albumins, enzymes, glutenins, prolamins and the hormone thyritropin.
Fibrous proteins. Those that help give resistance and elasticity to tissues. For example: keratin, elastin, collagen and fibroin.
Conjugated or heteroprotein. They are those that are formed by a protein part and a non-protein part. This part is called the prosthetic group, and it may contain lipids, sugars, nucleic acid, or an inorganic ion. For example, glycoproteins are heteroproteins because they have a sugar attached, that is, there is a bond that unites the protein with the sugar.
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Chemical structure of proteins
Proteins are made up of linear chains of amino acids. Amino acids are joined together by so-called peptide bond. These are formed by joining an amino group (NH2) from one amino acid and a carboxyl group (COOH) from the next amino acid.
A chain made up of peptide bonds is called a polypeptide chain, and one or more polypeptide chains form a protein. For this reason, proteins are also known as polypeptide chains.
Four structural levels of proteins can be distinguished. Namely:
Primary structure. It is established by the number and order of the amino acids present.
Secondary structure. It refers to the folding that the polypeptide chain acquires, due to intramolecular forces such as hydrogen bonds. For example, helix or folded leaf shape.
Tertiary structure. It refers to the three-dimensionality that the polypeptide chain acquires. The function and interaction of proteins with the organism depend on this three-dimensionality.
Quaternary structure. It occurs when several polypeptide chains join together, that is, they contain at least two polypeptide chains. They are characteristics of more complex proteins.
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Examples of proteins
Some examples of proteins and their functions in the human body are:
Insulin: Allows glucose to enter cells.
Glucagon: raises the level of glucose in the blood.
Collagen: forms fibers that strengthen tissues.
Keratin: It helps form the tissues of the skin, hair and nails.
Elastin: provides elasticity to tissues such as veins, among others.
Prolactin: makes breasts grow during pregnancy for breastfeeding.
Fibrin: It collaborates in blood clotting and the formation of scabs.
Myosin: responsible for muscle contraction, vesicle transport and cell division.
Albumin: It transports different substances and prevents fluid from the bloodstream from leaking into other tissues.
Immunoglobulins: They generate antibodies to immunize the body against pathogenic agents.
Foods that contain protein
Proteins are of great benefit to humans and can be obtained through diet. Animal products are the source of protein. We can also find proteins in certain plant products. On the list we can mention the following foods:
animal proteins. Animal proteins are those with the greatest nutritional value, since they provide essential amino acids. They play a very important role in human nutrition.
Meats: beef, pork, poultry, fish, mollusks and shellfish. Dairy: milk (cow, sheep and goat), yogurt, cheese of any variety, curd, cottage cheese. Eggs.
Vegetable proteins. Vegetable proteins have much lower nutritional value than animal proteins. Among all the foods that contain them, legumes are the ones that contain proteins in the highest concentration.
Legumes: beans, chickpeas, lentils, beans, soybeans, peas, peas. Nuts: walnuts, almonds, peanuts, merey. Cereals: quinoa, oats, flax seeds, bran, spelt, wheat, amaranth, buckwheat, rye, millet , barley and corn.