The chain idea is not an ideal description because it is the molecule's shape that enables the protein to do its task, such as weaken links between sugar monomers. You have to look at the big picture. There are all kinds of chemical bonds, such as disulfide bridges and ionic bonds, that connect amino acids to other ones that are not directly attached to each other via the ribosome to give the protein its shape. The idea of it being a chain is simplistic and does not convey how a protein works very well. For someone who wanted to know about proteins, it would be more useful for them to imagine it as a 3 dimensional molecule, rather than a simplistic 'chain'. As for the differing linkages in starches and any other kind of carbohydrate polymer, a new protein is often needed to break the bond, but the mechanism is the same. The protein will weaken the chemical bonds and allow it to break more easily. Though the carbon atom where the sugar monomers are linked is different for different carbohydrates, it is still a chain nonetheless. As for simple carbohydrates, while they can have different formations such as linear or ring shapes, the shape itself is not so important in terms of understanding its use in beer brewing. Additionally, simple carbohydrates can switch back and forth between linear and ring formations, whereas proteins never exist as a linear 'chain'. As soon as the ribosome begins to build the protein it begins folding and conforming into it's 3 dimensional shape. It never exists in any relative 2 dimensional 'chain' form.
