Structural and mechanical support function
Proteins are the plastic elements from which most cellular and organic structures are built. For instance:
The glycoproteins form the cell membranes where they perform functions such as transport of substances between exterior and interior, neurotransmitter receptors or hormones, etc.
Another group of proteins is the cytoskeleton of the cell, the fibers of the spindle, the cilia and the flagella, the ribosomes, etc.
The histones form part of the structure of chromosomes in eukaryotes, performing functions of regulating the activity of genes .
The collagen, which is found in connective tissue, tendons form, bone , etc.
The elastin, the elastic connective tissue (ligaments, walls of blood vessels, etc.).
The keratin in the epidermal cells, forming flakes of reptiles, the stratum corneum of the epidermis, the grip, nails, hairs and barbs of mammals, the feathers of birds, etc.
The fibroin protein secreted by spiders and silkworms to build the web or silk cocoon.