Welcome to an Amoeba Sisters Short: this one about the many roles of proteins. So, we mention food sources of proteins: beans, meat, nuts, eggs – just a few examples. These can supply us with amino acids – building blocks of proteins - that can be used in protein synthesis. While protein is often something people think of with muscles – and it is correct that the proteins actin, myosin, and many others are involved in muscle contraction and the general structure of muscles – it should be noted that proteins have many more roles. Some critical hormones such as insulin are proteins. Most enzymes are made of proteins. Enzymes can build up or break down substances in all kinds of metabolic processes. Proteins can serve as channels or pumps in cell membranes, helping move substances around. Proteins can also be receptors which are critical in cell signaling so cells can coordinate actions together. Antibodies – which are made by B cells – are proteins and they are involved in defense as part of the immune system. Proteins can make up all kinds of structures – hair or collagen - for example.