What exactly is a protein?

Proteins are combined amino acids. All life is chemistry and proteins are the machines that make the cell work her magic. We are nothing more than combined cells that owe their life to proteins. Proteins are the most diverse cl of chemicals there are in their function. They help speed up chemical reactions (enzymes) or the can translate RNA to other proteins (ribosomes) Proteins can help transport chemicals inside or outside cells (transporter proteins). They can relay signals ( receptors Gproteins etc) as diverse as light as matter. All at al it's the proteins that make you alive there not just combined aminoacids but they are little machines capable ofmakingg "dead" cell alive. And those protein markers you mean are proteins itself that help the microbe to survive.