Protein is an important macronutrient found throughout the body—in muscles, bones, skin, hair, and virtually every other body part or tissue. They make enzymes that drive many chemical reactions and hemoglobin that carries oxygen in your blood. At least 10,000 proteins make you what you are and keep you going.
What are Proteins?
Proteins are the utmost rich biological macromolecules, existing in all cells. It is also the most versatile organic molecule of living systems and occurs in great diversity; thousands of species, from relatively small peptides to large polymers. They do most of the work in cells and are essential for the structure, function, and regulation of body tissues and organs. A high protein intake can offer a number of benefits, including helping you lose weight, gain muscle, and improve body composition and metabolic health.
Sources of protein– Eggs, almonds, chicken breast, cottage cheese, greek yogurt, lentils, fish, etc.
Proteins can be divided into two types: complete and incomplete proteins. Proteins are composed of smaller units labeled as amino acids. Complete proteins contain all the amino acids your body needs and include meat, fish, poultry, dairy, and soy products. Foods lacking or very low in one or more essential amino acids are considered incomplete proteins. These foods include beans, grains, nuts, and vegetables.
Structure of Proteins
The linear sequence of amino acid residues in a polypeptide chain determines the three-dimensional configuration of a protein, and the structure of a protein determines its function. All proteins contain the elements carbon, hydrogen, oxygen, nitrogen, and sulfur, some of them may also contain phosphorus, iodine, and trace metals such as copper, zinc, and manganese ions. A protein can contain 20 different types of amino acids. Each amino acid has an amine group at one end, an acidic group at the other, and a characteristic side chain.
The structure of proteins can be split into four levels of organization:
- Primary structure- The primary structural protein consists of a linear system of amino acids linked together by polypeptide bonds. Since the primary structure is the basic line of amino acids in a protein, note that each amino acid has its properties. Some amino acids are hydrophobic (otherwise known as hating water), and polar, meaning they contain a hydroxyl group that can react with water and is charged due to the negative or positive charge on them. All these properties can be found due to the composition of their R groups.
- Secondary structure- Secondary structure has continuous regions of polypeptide chains that fold into alpha helixes or beta-folded sheets. The main type of bond observed in an alpha helix is hydrogen bonding, which occurs between peptide bonds. Every hydrogen bond that occurs in an alpha helix is parallel, as can be seen in the figure below, and there are 3.6 residues present on each turn of the alpha helix.
- Tertiary structure- In tertiary structure, amino acids are spatially arranged in a linear system, and residues that are adjacent to the sequence are also spatially arranged. When the stability increases, a hydrophobic effect is present, allowing the interaction of the R group.
- Quaternary structure- Proteins that contain more than one polypeptide chain are described as quaternary structures. There are four main interactions such as hydrogen bond, ionic bond, disulfide bridge, and hydrophobic interaction. Here, more than one polypeptide chain interacts to form a single unit that enhances the function of a protein in the example of hemoglobin in the blood, allowing for maximum oxygen transport in the body in red blood cells.
Properties of Proteins
- Solubility- The solubility of proteins in water is so variable that it has been proposed to classify them according to their solubility. Some proteins are soluble in pure water (albumins), others—especially globulins—dissolve only in the presence of neutral salts or when the medium is slightly acidic or weakly basic, and some others (scleroproteins) are insoluble even under these different conditions.
- Molecular weight- The average molecular weight of an amino acid is considered to be 110. The overall sum of amino acids in a protein multiplied by 110 gives the relative molecular mass of that protein. Different proteins have different amino acid compositions; therefore, their molecular weights also differ. The molecular weight of proteins ranges from 5000 to 109 Daltons.
- Denaturation- Partial or complete unfolding of the native (natural) conformation of a polypeptide chain is known as denaturation. Proteins can be denatured by agents such as thermal acids, bases, alcohol, acetone, urea, and beta-mercaptoethanol, which cause the unfolding of polypeptide chains without causing the hydrolysis of peptide bonds. If the denatured protein returns to its native state after the removal of the denaturing agent, the process is called renaturation.
- Coagulation- When proteins are denatured by heat, they form insoluble aggregates known as coagulums. All proteins are not heat-coagulable, only some like albumins, and globulins are heat coagulable.
- Isoelectric pH- The pH at which a protein has an equal number of positive and negative charges is called isoelectric pH. When exposed to an electric field, proteins do not move toward either the anode or the cathode, so this property is used to isolate proteins. Proteins become least soluble at pHI and precipitate. The pH value of casein is 4.5 and at this pH, the casein in milk coagulates and produces curd.
Functions of Protein
- Protein is crucial for the growth and repair of tissues. Our body’s protein needs rely upon our health and activity level.
- Enzymes are proteins that assist thousands of biochemical reactions that take place inside and outside the body’s cells. Body activities that depend on enzymes comprise- Digestion, Energy production, blood clotting, and muscle contractions.
- Amino acid chains of different lengths make up the proteins and peptides that make up several of the body’s hormones and carry information between cells, tissues, and organs.
- A class of proteins known as fibrous proteins provides structure, strength, and flexibility to various parts of the body. These proteins include keratin, collagen, and elastin, which help form the connective framework of certain structures in the body.
- Proteins act as a buffer system to help the body maintain a proper pH. It plays a vital role in regulating acid and base concentrations in the blood and other body fluids. For example hemoglobin, the protein that makes up red blood cells. Hemoglobin binds small amounts of acid and thus helps to maintain a normal blood pH value.
- Proteins regulate body processes to maintain fluid balance. Albumin and globulin are proteins in the blood that help maintain fluid balance in the body by attracting and retaining water.
- Proteins make antibodies that protect the body from foreign invaders such as disease-causing bacteria and viruses.
- Transport proteins carry substances through the bloodstream – into cells, out of cells, or inside cells. Substances transported by these proteins include nutrients such as vitamins or minerals, blood sugar, cholesterol, and oxygen. For example, hemoglobin is a protein that carries oxygen from the lungs to the body’s tissues. Glucose transporters (GLUTs) transport glucose into your cells, while lipoproteins transport cholesterol and other fats in the blood.
- Protein can serve as a valuable source of energy, but only in situations of starvation, exhausting exercise, or insufficient caloric intake.
Protein is a key part of any diet. The average person needs about 7 grams of protein daily for every 20 pounds. Because protein is found in abundance in foods, many people can quickly meet this goal. Protein helps to build muscle and strengthen bones to lower blood pressure and improve sleep and brain health, protein plays a role in nearly every bodily function. Eating protein first at a meal can help you feel full and keep your blood sugar and insulin from rising too high.