2. —N——N— —C— | C —N——N— H H H | —C— | C—OH || O R (variable group) amino acid Function: many, many functions hormones movement immune system enzymes Examples muscle skin, hair, fingernails, claws pepsin insulin Building block = amino acids  Proteins fold & twist into 3-D shapes  Different shapes = different jobs  Proteins do their jobs, because of their shape Unfolding a protein destroys its shape wrong shape = can’t do its job unfolding proteins = “denature” Temperature and pH (acidity) can cause Indicator Test Biuret Starts = Blue If Positive = Purple (violet)

3. Proteins