Body and spare parts: Proteins
Proteins are the most diverse of all living organisms molecules, virtually plays a role in every aspect of the amazing phenomenon known as life. In fact, all life processes are conducted, mostly, on the proteins surface.
Some proteins have a globular structure and many of them function as enzymes, immunoglobulins, hormones, transport proteins or fulfill a structural role in tissues and cells.
Life is possible due to enzymatic proteins function, in human body being at least l0.000 different enzymes. Beside globular proteins, there are fibrous proteins that can have solid consistency – nails, hair, hooves or feathers of birds.
The protein name comes from the Greek word protos, which means “the first”.
Proteins are made from amino acids molecules (a total of 20), which engages in various sequences to produce great variety of proteins, which are met in nature. Each being has its own proteins, composed of amino acids produced by the body or taken from food. The human body can not produce all the amino acids and, because is essential that they be obtained from food, they are-known as essential amino acids, which does not mean they are more valuable than the others. Amino acids that can be synthesized by the human body are called nonessential, but they are not less important.
Essential amino acids are: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine and histidine. Actually, histidine is not an essential amino acid for adults, but is included because of children who can not synthesize.
Nonessential amino acids are: glycine, glutamic acid, arginine, aspartic acid, proline, alanine, serine, tyrosine, cysteine, asparagine and glutamine. To these re added the hydroxyproline amino acids and citrulline, which is why in some publications, you will find that there are 22 amino acids.
Human proteins are made up of hundreds of amino acids, some even over a thousand. The human body contains approximately 50,000 of different proteins and in every cell are found 4000-5000 of proteins, with the most varied functions.
The main supplier of proteins are plants, which is why vegetable proteins are called primary, while those of animal origin are called secondary proteins. To may be used, the proteins must be disolved in the digestive tract, in the amino acids that re made of regardless of their origin.
“The grinding” action of proteins is carried out by enzymes and starts in the stomach.
To be attacked by enzymes, proteins of animal origin requires a higher acidity than those of plant origin. So, egg white needs a pH of 1.5, which is much more acidic than the optimum value for the enzyme. Animal proteins requires a longer stay in the stomach, which gives the extended satiety sensation, but without any nutritional advantage. In reality, the delay of gastric emptying, along with an increased acidity, favors the acid aggression on the gastric mucosa with its inevitable consequences. To these is added another unfavorable factor – high levels of fats in animal products. Practically, fat is not digested in the stomach because the gastric lipase plays a minor and limited role, but they cover the food with a layer that harden the pepsin hydrosoluble activity on proteins.