What are Proteins:

Proteins are essential nutrients for the human body, consisting of biological macromolecules formed by one or more amino acid chains.

More than half the dry weight of the cells of all living things is made up of proteins, the most important biological macromolecules.

These macromolecules are abundantly found in animal foods.

Protein Composition

The composition and other characteristics of proteins are the subject of study of biochemistry, which is a subdiscipline of biology.

The protein composition has carbon , hydrogen , nitrogen and oxygen and in almost all of them there is also the presence of sulfur . Elements such as iron , zinc and copper may also be present.

Proteins are basically composed of a set of amino acids that are covalently linked together.

A long chain of amino acids is a polypeptide .

These bonds between amino acids are called peptide bonds .

Peptide bonds occur as a reaction between the amino group (ammonia-derived organic compound) of one amino acid and the carboxyl group ( carboxylic acid component) of another.

peptide bonds
peptide bonds

C = carbon; H = hydrogen; O = oxygen; N = Nitrogen; R = Group R or Side Chain (amino acid identity).

There are 20 amino acids that can combine in various ways to form different types of proteins.

Learn more about amino acids .

Protein Types

Proteins can be classified into two groups according to their function in the body: dynamic proteins and structural proteins.

Dynamic proteins

Dynamic proteins have the function of defending the body, transporting substances, catalyzing reactions and controlling metabolism.

Structural proteins

Structural proteins have the main function of forming the structure of cells and tissues in the body.

Protein Classification

Protein classification varies according to the main factor taken into account.

Composition classification

When the object of study is the composition of proteins, they can be classified into two groups:

  • Simple proteins : are those that during hydrolysis release only amino acids.
  • Conjugated proteins : Proteins that during hydrolysis release amino acids and a non-peptide radical.

Classification by number of polypeptide chains

Regarding the number of polypeptide chains, proteins can be classified as:

  • Monomeric proteins : are proteins that have only one polypeptide chain.
  • Oligomeric proteins : are proteins formed by more than one polypeptide chain.

Form classification

With regard to form, proteins can be classified into two types:

  • Fibrous proteins: In fibrous proteins, polypeptide chains coil like a rope. One of the characteristics of fibrous proteins is that they are not soluble in aqueous solutions. In addition, they are responsible for the strength and flexibility of the structures in which they are present. Examples of fibrous proteins : keratin, collagen
  • Globular proteins: The polypeptide chains of globular proteins fold into approximately spherical shape or as its name implies, globular, making them resemble a globe. Globular proteins are usually soluble in aqueous solutions. Examples of globular proteins : hemoglobin, enzymes.
globular proteins

Images of a fibrous protein and a globular protein

Learn more about hemoglobin and enzyme.

Protein Structure

Regarding the structure of the protein molecule, here’s how it can be classified:

Protein Structure
Protein Structure

Primary structure

The primary structure is genetically determined. It is the simplest structure of all, where amino acids are arranged linearly.

Secondary structure

For a protein structure to be secondary, the primary structure must have covalently linked amino acids. Thus, molecules can rotate and ultimately self-interact in three ways:

  • Alpha-helix : Assumes helical shape when hydrogen bonds occur between amino acids.
  • Beta-leaves : when hydrogen bonds occur between amino acids and the consequent generation of a rigid leaf structure.
  • Loops : They are non-regular structures in the nucleus and their formation occurs outside the folding of the protein.

Tertiary Structure

It occurs when the unfolding of the secondary structure is arranged in space in three-dimensional form.

Quaternary Structure

This structure takes place through an interaction between identical or non-identical polypeptide chains, which group together and form a unique three-dimensional structure.

Protein Functions

Proteins play a key role in the body. They are the basis of the material that forms organs and tissues, as well as the basis of the formation of bones, hair, teeth, etc.

The function of protein varies according to its shape and structure. Virtually all cell functions need to be mediated by proteins.

Check out some of the main functions of proteins.

  • Structure the cells.
  • Act as enzymes and thereby accelerate chemical reactions.
  • Carry molecules and ions.
  • Store substances.
  • Assist the movement of cells and tissues.
  • Build and repair tissues and muscles.
  • Participate in gene regulation.
  • Cause muscle contraction through the action of two types of protein: myosin and actin .
  • Defend the body (antibodies are types of proteins).
  • Carry oxygen (hemoglobin is the protein that carries oxygen throughout the body).
  • Provide power.
  • Act on the regulation of metabolism in the form of hormones.

Protein Characteristics

One of the main characteristics of proteins is a designated denaturing capacity. Denaturation is the irreversible change in the properties of proteins when they are heated or stirred.

As far as the human body is concerned, it is the second largest component of the body, second only to water.

The characteristics of proteins differ according to their origin: those of animal origin have a higher biological value; are considered complete proteins, with all essential amino acids in optimal amounts and proportions.

Protein and food

When we eat a food, our bodies take advantage of protein through digestion.

In digestion, proteins are exposed to acid and hydrolysis and thus denaturation occurs.

When subjected to excessive heat and agitation, for example, secondary and tertiary structures undergo irreversible changes and thus lose their properties. For this reason certain foods lose their nutritional power when they are cooked.

The proteins may be of animal and plant origin.

Know the main characteristics of these proteins.

Animal proteins Vegetable proteins
They have a high biological value. They are complete proteins, with all essential amino acids in optimal amounts and proportions. They have a low biological value, ie the amount of essential amino acids is smaller.
They have a higher amount of nitrogen compared to vegetable proteins. Compared to animal proteins, they present a higher amount of the amino acid arginine, which causes a greater efficiency of the immune system.
They are rich in calcium, iron, vitamin B12 and zinc. They are rich in carbohydrates and vitamins.
Have large amount of harmful fat. They have no harmful fat.
They have few fibers. They are rich in fiber.

Examples of proteins

Animal protein rich foods

Check below for a list of examples of animal protein foods.

  • Tuna fish
  • Shrimp
  • Red meat
  • Chicken (31/100 g of protein in chicken breast)
  • eggs ( 6 g of protein in one egg )
  • Peru
  • Pig
  • Yogurt

Vegetable protein rich foods

Check below for a list of examples of protein foods of plant origin (plant based protein)

  • Almond
  • Peanut
  • Brown Rice
  • Oatmeal
  • Broccoli
  • Pea
  • Spinach
  • Baked Beans (21/100 g of beans protein)
  • Lentils ( 9/100 g of lentils protein)

Among plant foods, there are also some protein-rich fruits :

  • Avocado: 2/100 g of Avocado protein
  • Prune
  • Banana: 1.1/100 g of protein in banana
  • Dried apricot
  • Fig
  • Raspberry
  • Guava
  • Jabuticaba
  • Jackfruit
  • Orange
  • Melon
  • Pass grape
protein-rich fruits
Protein-rich fruits

Best protein bars

The 5 Healthiest Protein Bars

  • EPIC Chicken Sesame BBQ. Traditional beef jerky is all cheap meat, sugar, and nitrates from the curing process.
  • Oatmega Chocolate Coconut Crisp. Oatmega’s bars have a lot going for them.
  • Strong & KIND Honey Mustard. KIND bars are a little bit of a mixed bag.
  • Primal Kitchen Dark Chocolate Almond.
  • GoMacro Protein Purity

Protein digestion

The process of protein digestion begins in the stomach. The hydrochloric acid present in it starts the process by denaturing the proteins, that is, destroying the hydrogen bonds of its structure.

After that, the proteolytic chains lose their shape and are subjected to the action of enzymes. At this point, the pepsin enzyme causes proteins to turn into smaller molecules, ie pepsin causes partial protein degradation and hydrolyzes the peptide bonds.

The second stage of protein digestion occurs in the small intestine. In it, proteins are subjected to the actions of pancreatic enzymes. After that, the peptides and amino acids are absorbed and taken to the liver.

Protein digestion
Protein digestion and absorption

The percentage of protein released by the body in the form of feces is about 1% of the amount ingested.

Protein Synthesis

Protein synthesis is a process determined by DNA, in which biological cells generate new proteins. This occurs in every cell of the body.

During the process, a DNA transcription by the messenger RNA occurs and then a translation of this information by the ribosomes and the carrier RNA, which carries the amino acids.

The amino acid sequence determines protein formation.

Protein synthesis is divided into three phases: transcription , translation and activation of amino acids .

Learn more about RNA .


In the transcription phase, messenger RNA (mRNA) transcribes the message of the citrus (part of the DNA).

The RNA polymerase enzyme binds to an enzyme complex. The double helix is ​​disrupted and as a result the hydrogen bonds that bind the bases of the chains are destroyed.

After that, the process of synthesis of an mRNA molecule begins. During this process, the links between the bases occur:

  • DNA adenine with mRNA uracil.
  • DNA thymine with mRNA adenine.
  • DNA cytosine with mRNA guanine and so on.

In the end, the mRNA molecule separates from the DNA strand (which in turn has hydrogen bonds again) and the double helix is ​​reestablished.

Before leaving the nucleus, RNA is matured or processed. Some of its parts are removed and those that remain bond to each other and form a mature RNA.

This RNA has the coding of amino acids and can pass to the cytoplasm, which is the part of the cell where the translation phase will occur.


It is at this stage that proteins are formed.

The translation phase takes place in the cell cytoplasm and consists of a process where the message present in the mRNA is decoded in the ribosome.

Amino Acid Activation

During the translation process, carrier RNA (tRNA) comes into play. It is so named because it has the function of transporting the amino acids from the cytoplasm to the ribosomes.

Amino acids are then activated by certain enzymes that bind to tRNA, giving rise to the aa-tRNA complex.

Protein electrophoresis

Protein electrophoresis is an examination consisting of the separation of proteins found in urine (urinary proteins) or blood serum (serum proteins).

It is an exam used to detect absence, reduction or increase of proteins, as well as to detect the presence of abnormal proteins. This test assists in the diagnosis of diseases that affect protein absorption, loss and production.

An irregular amount of protein may indicate, for example, kidney problems, diabetes, autoimmune diseases and cancer.

Measuring the amount of total protein can also indicate an individual’s nutritional status.

Excess protein in the body

Protein intake should be moderate as too much protein can result in poor health. An organism that has an excess amount of protein can suffer kidney damage (such as stones) and develop diseases such as arteriosclerosis and osteoporosis, weight gain and liver problems.

For this reason, caution should be exercised when following the so-called “protein diet” (diet based on foods that are good sources of protein) as consumption cannot be overstated.

Little protein in the body

If, on the one hand, too much protein in the body is harmful to the body, too little is also harmful.

One of the effects caused by the low amount of protein in the body is, for example, atrophy of a part of the central nervous system.

In addition, the individual may also experience weight reduction, constant feeling of tiredness, muscle aches, healing problems, hair loss, etc.


Muscle proteins

Consumption of protein rich foods is of fundamental importance for those who exercise with the intention of gaining muscle mass.

muscle mass

During weight training, protein breaks down in muscle tissue. For the repair of these tissues to occur, the body will look for existing proteins in the diet.

For this reason, it is essential that an individual who exercises and wants to achieve certain muscle growth eats protein-rich foods regularly throughout the day.

Some people resort to using protein supplements to supplement their recommended daily intake.

Protein powder

Protein powder is a very popular food supplement. The use of protein powder may help people tone their muscles and can aid weight loss as well.

However, this use should be accompanied by a nutrition expert, who will take into account the eating habits of the person, their lifestyle and the sport practiced, among others.

protein powder

Protein powder

Cow Milk Protein Allergy

Cow’s milk protein allergy, also known as APLV , is considered the most common food allergy. It is estimated that 2.2% of children have APLV in the first years of life.

It is an allergic reaction that the body has not only when in contact with cow’s milk, but also when in contact with its derivatives.


This reaction can manifest in three different ways: IgE-mediated , non-mediated or mixed IgE .

Check out some characteristics of each form of manifestation:

IgE mediated Non-IgE mediated Mixed
The body produces specific IgE antibodies (Immunoglubulins E) to fight milk proteins. The allergic reaction is not triggered by the production of specific IgE antibodies, but by the production of inflammatory cells . The allergic reaction is triggered by the production of IgE-like antibodies and other cells in the body.
Reactions occur immediately , even appearing within seconds of contact with milk or milk products. Reactions may appear hours or days after contact with cow’s milk or dairy products. Reactions may arise immediately after contact with cow’s milk or dairy products, or long after .
Main symptoms: vomiting, red itchy plaques, breathing difficulties, swollen eyes and lips, diarrhea and anaphylactic shock. Main symptoms: vomiting, intestines stuck, diarrhea (sometimes with mucus or blood), cramps and inflamed bowel. Main symptoms: dry, peeling skin (possibly with sores), diarrhea, vomiting, inflamed stomach and / or esophagus, abdominal pain and reflux.


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