I've been taught 2 things that seem to contradict each other:  Cooked meat has plenty of protein Heating proteins denatures them and damages/changes them  If this is the case, then cooked meat must have very little usable protein, which is clearly not the case. How does protein in a fully cooked food, e.g. chicken/pork/eggs survive the cooking process in a usable form? Note I'm not asking about burnt meat, browning or flavour reactions, or rare meat e.g. a medium/rare cooked steak. 
Structural proteins in foods, i.e. albumin in eggs, myosin in muscle meats, gluten in wheat, are formed by amino acids in complex structures. Proteins are folded and clumped chains of peptides, and peptides are chains of amino acids. Your body uses stomach acid and proteases (enzymes) to break down proteins in digestion, but this requires time and energy (stomach churning, body heat). The amino acids are what your body requires. They're used to build more complex proteins. Cooking gives a head start in un-clumping/unfolding proteins, and in some conditions into peptides and amino acids, that are easier for your body to digest making them more 'bioavailable'. Some of these amino acids can be produced by your body using nitrogen compounds from breaking down other amino acids and nutrients. The ones your body can't produce on its own have to be obtained in the proteins you eat. These are called 'essential amino acids'. Different protein sources have different amino acid compositions, giving them different 'protein values' in how complete the range of essential amino acids are available; i.e. collagen/gelatin is a common structural protein that provides great texture for sensory applications, but the protein value is 0 for regulatory labelling requirements in some countries since it is missing an essential amino acid. 