First of all, protein is an important structural component of organisms. From various organs in our body, to connective tissue as scaffold, to layered structure and various organelles in each cell, their composition is inseparable from protein's participation. According to statistics, protein content in human body can account for 16%-20% of body weight. You don't think the proportion is high, but don't forget that the human body is 60%-70% water. That is to say, besides water, protein is the most basic component of our body.
Besides, you shouldn't just understand protein as a brick that constitutes our human body building. It is an important substance in many life activities. The hemoglobin used to transport oxygen in our body is protein, the enzyme used to catalyze various reactions is protein, the carrier responsible for transporting lipids, as well as hormones, antibodies, signal molecules and so on. , is protein. It is no exaggeration to say that there would be no life activities without protein.
Why can protein achieve so many functions? Here, let's talk about the complexity of protein's structure. As mentioned earlier, protein is actually a long chain of amino acids, that is, the structure formed by dehydration and condensation of amino groups in one amino acid molecule and carboxyl groups in another amino acid molecule, which is biochemical called peptide bond. This linear structure is also called the primary structure of protein. But in fact, protein is by no means a simple chain. Instead, it will form a complex regional structure through spatial folding and spiral rising, and these structures can be aggregated by various forces to form a complex three-dimensional spatial structure of level 2, level 3 or even level 4. As there are as many as 20 kinds of amino acids that make up protein, their combination order is ever-changing, so they can form various structures and realize different biological functions. Because of this, protein is also called "molecular tool".
According to the different structure of protein, we can generally divide the protein in the organism into two categories, one is fibrin, which is protein that looks like a fiber or a thin rod. This is the main structural protein in organisms. For example, keratin is the main protein of biological skin and the main protein of all kinds of hair, nails, scales and feathers. Collagen is widely found in our cartilage, tendons, skin and bones, and it is also a very important structural protein. As for actin and myosin in skeletal muscle, they can also be classified as fibrin. Another kind of protein is globulin. It should be noted that globulin is sometimes used to refer to immunoglobulin, that is, antibody. What is said here is that all three-dimensional conformations are spherical protein. Various biological enzymes, hemoglobin that transports oxygen, antibodies and hormones all belong to globulin, so this kind of protein is mainly functional protein.
Back to the topic, I just talked about two functions of protein, one is structural composition, the other is biological function, and the third function of protein is that it is also an energy donor substance, just like sugar and lipid. Every gram of protein contains 4. 1 kcal, which is similar to sugar. Therefore, in some cases, our body will also break down a part of protein to provide energy for the body. Comparing the three energy-supplying substances, it can be said that if the human body is compared to a house, a stove needs to be burned inside to keep warm, then sugar is like coal, which is convenient, cheap and large in dosage; Fat, like gasoline, has a high calorific value and is easy to store. Protein is made of wood. Usually, houses and furniture inside are made of wood. If there is no other energy-supplying material, it can also be cut for firewood.