"They do most of the work in cells and are required for the structure, function, and regulation of the body's tissues and organs," (https://ghr.nlm.nih.gov/primer/howgeneswork/protein). Protein is also a source of food we eat to obtain energy. Without it, you will have growth failure, loss of muscle mass, decreased immunity, weakening of the heart and respiratory system, and death.
"Proteins in food are broken down into pieces (called amino acids) that are then used to build new proteins with specific functions, such as catalyzing chemical reactions, facilitating communication between different cells, or transporting biological molecules from here to there. When there is a shortage of fats or carbohydrates, proteins can also yield energy," (http://www.diabetesforecast.org/2011/mar/how-the-body-uses-carbohydrates-proteins-and-fats.html).
Protein comes from foods such as fish and nuts, which is then eaten to be used for energy inside of your body. Inside of your body, your cells needs protein too. They make their protein by using ribosomes, whose job is to create protein for the cells.
Credits:
Created with images by phylofigures - "1471-2148-10-365-4" • zephious - "beef ribeye steak"