(c) The protein keratin(角蛋白) is the chief structural components of hair, scales, horn, wool, nails and feathers
The protein keratin （角蛋白） is the chief structural components of hair, scales, horn, wool, nails and feathers
1. All natural proteins were found to be built from a repertoire of 20 standard a-amino acids The earliest studies of proteins focused on the free amino acids derived from these proteins. The lst amino acid(asparagine) was discovered in 1806 from asparagus(a green vegetable). The last(threonine)was not identified until 1938 All the amino acids were given a trivial(common) name. Glutamate from wheat gluten(sticky). Tyrosine from cheese(“ tyros” in greek
1. All natural proteins were found to be built from a repertoire of 20 standard -amino acids The earliest studies of proteins focused on the free amino acids derived from these proteins. •The 1st amino acid (asparagine) was discovered in 1806 from asparagus (a green vegetable). •The last (threonine) was not identified until 1938! •All the amino acids were given a trivial (common) name. Glutamate from wheat gluten (sticky). Tyrosine from cheese (“tyros” in Greek)
1.1 The 20 a-amino acids share common structural features Each has a carboxyl group and an amino group (but one has an imino group in proline) bonded to the same carbon atom designated as the a carbon ∈ 6 5 2 CH2—CH2—CH2—cH2—cH—COO +NH 13 +NH3 Lysine In protein chemistry, we use Greek letter nomenclature. To find all greek letters, go to http://www.astro.uiuc.edu/kaler/sow/greek.html
1.1 The 20 -amino acids share common structural features. •Each has a carboxyl group and an amino group (but one has an imino group in proline) bonded to the same carbon atom, designated as the - carbon. In protein chemistry, we use Greek letter nomenclature. To find all Greek letters，go to： http://www.astro.uiuc.edu/~kaler/sow/greek.html
.Each has a different side chain(or r group R=“ Remainder of the molecule”) COo 3
•Each has a different side chain (or R group, R=“Remainder of the molecule”)
The a-carbons for 19 of them are asymmetric (or chiral), thus being able to have two enantiomers. Glycine has no chirality RS system re-viSited( Chapter 3, p60) The priorities of some common substituents are OCH2>-OH>-NH2>-C00H>-CHO>-CH2OH>-CH3>-H The chiral atom is viewed with the group of lowest priority pointing away from the viewer. If the priority of the other three groups decreases in clockwise order. the configuration isR(right); if in counterclockwise order, the configuration isL(eft”) CoO COO HRN O 0 NH3 13 CH3 L-Alanine D-Alanine (a
The -carbons for 19 of them are asymmetric (or chiral), thus being able to have two enantiomers. Glycine has no chirality. RS system re-visited (Chapter 3, p60): The priorities of some common substituents are -OCH2 > -OH > -NH2 > -COOH > -CHO > -CH2OH > -CH3 > -H The chiral atom is viewed with the group of lowest priority pointing away from the viewer. If the priority of the other three groups decreases in clockwise order, the configuration is R (“right”); if in counterclockwise order, the configuration is L (“left”)