All carbs, whatever the source, gets broken down into glucose which your body uses for energy and stores in your muscles as glycogen. Sort of like how all protein gets broken down into amino acids. So sugar in a sense is predigested carbs. Sugar is to carbs as amino acids is to protein.
Yes, and the primary difference when talking about just carbs (not counting any fat or protein that may be contained in the food) is it's glycemic index (the rate at which is converts to glucose and the effect on insulin response). So one of the primary difference between say a bowl of oatmeal and a bowl of jelly beans, both which will be converted into glucose (blood sugar) and used as energy, is the rate of conversion. What determines that rate is the fiber content. Oat meal is high in fiber which requires your body to break it down resulting in a much more sustained release of energy (sugar).
Protein is similar. Whey isolate is faster absorbing than say casien and of course amino acids is the fastest of all. It's a bit more complicated with protein as difference forms has a different amino acid profile. The protein in steak, fish and chicken all get broken down into amino acids but the ratio and types of aminos acids, it's profile, varies according to the source.
