Chapter 3 Proteins Outline u Classification of proteins u The basic building blocks of proteins—Amino acids u Structure of proteins u Structure and function relationships of proteins u Properties of proteins u Separation, purification and determination of proteins
What are proteins? Proteins are macromolecules composed of amino acids linked together through peptide bonds, which have a stable conformation and a certain biological function. Proteins are linear polymers聚合物 built of monomer单体 units called amino acids
Section 1 Classification of proteins 1. Chemical Components of Proteins uMajor elements: C, H, O, N, S uTrace elements: P, Fe, Cu, Zn, Mo, I, . u The average nitrogen content in proteins is about 16%, and proteins are the major source of N in biological systems
Section 1 Classification of proteins 1. Chemical Components of Proteins uThe protein quantity can be estimated-Kjeldahl determination（凯氏定氮法） uprotein in 100g sample = N per gram × 6.25 × 100
2. Protein Classification uClassification based on the overall shape Globular protein（球状蛋白质）: globular or ellipsoidal (long/short <10), soluble in water; including enzymes, transportors, receptors, regulators, . Fibrous protein（纤维状蛋白质）: highly elongated; insoluble in water; including collagen（胶原蛋白）, elastin（弹性蛋白）, α- keratin（α-角蛋白）,
uClassification based on chemical compositions Simple protein（简单蛋白质）: made up of amino acids completely, without non- protein components Conjugated protein（缀合蛋白质）: conjugated protein = apoprotein + prosthetic groups Prosthetic group （辅基）is non-protein part, binding to protein by covalent bond. This group can be carbohydrates, lipids, nucleic acids, phosphates, pigments（色素）, or metal ions
Category of conjugated proteins Category（类别）Prosthetic group （辅基） Example（举例） Nucleoprotein （核蛋白） nucleic acids Chromosome, ribosome Glycoprotein （糖蛋白） carbohydrates Immunoglobulin（Ig） Lipoprotein （脂蛋白） lipids High-density lipoprotein Phosphoprotein （磷蛋白） phosphates Casein（酪蛋白） Chromoprotein （色蛋白） pigments Hemoglobin（血红蛋白Hb） Metalloprotein （金属蛋白） metal ions Ferritin（铁蛋白）, calmodulin（钙调蛋白）
uClassification based on biological functions C Enzymes – Ribonuclease（核糖核酸酶） C Regulatory proteins – Insulin and growth hormone C Storage proteins – ovalbumin（卵清蛋白） C Defensive and protective proteins – Antibody, toxin（毒素） C Transport protein – Hemoglobin C Structural proteins – α-keratin, Collagen C Contractile proteins – Actin（肌动蛋白）, Myosin（肌球蛋白）
Section 2 Protein architecture — Amino acids 1. General structure of common amino acid (AA) uThe basic building blocks of proteins uAbout 300 types of AAs in nature, but only 20 types are used for protein synthesis in biological systems. uA typical α-amino acid has an amino group, a carboxyl group, a hydrogen atom and a side-chain (R group) attached to the same carbon atom (Cα )
Different side-chain (R group) Different chemical and physical properties Amino group Carboxyl group