What is proteins/protein synthesis?

This subpage about proteins belongs to Biotech Academy’s primary school project
The Body and the Diet

 

Proteins are used to provide energy to the body and are an important building block for our entire organism. Among other things, they transport fatty acids, iron and oxygen around the body and regulate many of the body’s processes.

Proteins are made up of long chains of amino acids (see Figure 2), the basic structure of which consists of the elements carbon (C), oxygen (O), hydrogen (H) and nitrogen (N) as Figure 1 shows. There are 20 different amino acids, eight of which are essential, and these cover the number of amino acids that we cannot form ourselves. This means that they must be supplied through the diet.

If the diet does not contain all the essential amino acids, protein synthesis may be impaired. Lack of essential amino acids is a major problem in developing countries and can lead to diseases such as kwashiorkor, where a child lacks proteins but gets enough energy. If the child does not get enough energy or protein, it is called marasmus.

In Denmark and in the western part of the world, there is no protein deficiency, but rather an overuse of proteins. However, vegetarians must be careful to get enough protein as they do not eat meat.

 


Figure

1
. An amino acid is the building block of proteins. The amino acid consists of a central carbon atom (C), which is attached to a hydrogen atom and to various other groups: an amino group (NH2), an acid group (COOH) and a side chain called R. The side chain “R” varies in the 20 different amino acids, and it is therefore this that gives the amino acid its specific characteristics. The simplest amino acid is called glycine. For glycine, R = H.

Figure 2. Proteins are formed by linking different amino acids together. Each pearl on the chain symbolizes an amino acid.

How are proteins digested?

When food contains proteins, they are cleaved into amino acids during digestion. Figure 3 provides an overview of protein digestion. The breakdown starts in the stomach, where hydrochloric acid and a protein-degrading enzyme, pepsin, convert the proteins into peptides. The peptides are broken down into amino acids by the enzyme peptidase, which the pancreas releases. In the small intestine, the amino acids are absorbed, and via the blood they are transported to the liver.

The liver sends amino acids out to the body’s cells, where they are used to form new proteins. The digestion of protein activates various enzymes that help in its breakdown. Figure 4 gives an overview of the enzymes.

 

Figure 3 . Protein must be broken down into amino acids before the bloodstream can absorb them. The first breakdown occurs in the stomach when the enzyme pepsin is activated. It cleaves the protein into peptides. Then the pancreas secretes the enzyme peptidase, which breaks down the peptides into amino acids.


Figure
4. Overview of enzymes involved in protein breakdown.

What is protein synthesis?

There is a constant breakdown of proteins in the body. The amount of protein your body gets from food is much less than the amount your body metabolizes. This means that the body can recycle the broken down proteins. To understand protein synthesis, please refer to BioStriben’s video on The Central Dogma.

 

How much protein you need to eat:

In a day, 10-20% of your total energy should come from proteins.

When your body breaks down 1 gram of protein, energy is generated that is equivalent to 17 kJ (4.06 kcal).

High protein foods:

Foods that contain all essential amino acids are called complete proteins. These foods include milk, eggs, meat and soy products. Many plant foods lack one or more of the essential amino acids, and they are called incomplete proteins. However, two incomplete proteins can complement each other, as the amino acid in one protein can compensate for the missing amino acid in the other protein. Bread and beans are a great combination that together will provide a complete protein.

It is therefore important that vegetarians make sure to eat a diet where cereals (e.g. rice, wheat, corn) are eaten with legumes (e.g. beans and peas). In this way, the need for essential amino acids is covered.

Does the body absorb the most proteins from animal or plant-based foods?

You can find the answer by clicking here!

This subpage belongs to Biotech Academy’s primary school project Body and Diet