CHAPTER 2 CHEMISTRY OF PROTEIN Section 1 IMPORTANT PROPERTIES OF PROTEIN FOR LIFE Section 2 MOLECULAR COMPOSITION OF PROTEINS Section 3 MOLECULAR STRUCTURE OF PROTEINS Section 4 RELATIONSHIP BETWEEN FUNCTION AND STRUCTURE Section 5 PHYSICO-CHEMICAL PROPERTIES OF PROTEINS

Section 1 IMPORTANT PROPERTIES OF PROTEIN FOR LIFE ● PROTEIN CONTENS OF HUMAN BODY Carbohydrates, Lipids, Proteins, Nucleic Acids, Water, Middle/Small Molecules, and inorganic Molecules 15~20% expressed in whole body ~45% expressed in dry weight

● PROTEIN MULTIFUNCTIONS Essential Composition of Tissues or Cells Maintaining Growth, Renew and Repair Oxidative Degradation for Providing Energy Specific Roles in Catalysis enzymes Regulation hormones Transport Hb lipoprotein Albumin Mobile/Physical Exercise actin Signaling Storage Defence ……

Section 2 MOLECULAR COMPOSITION OF PROTEINS —— Chemical Elements C（50~55%）,H（6~8%）,O（19~24%）, N（13~19%, average 16%）,S（0.~4%）、 Metal-Zn, Fe, Mg, Cu…, P, I ● STRUCTURAL UNIT——AMINO ACIDS A. Amino Acids L-α-amino acid CHO C — H CH2OH HO— COOH C — H CH3 NH2— (R)

B. 20 Amino Acids and Its’ Structure

● PHYSICO-CHEMICAL PROPERTIES OF AMINO ACIDS Dipolar State of Amino Acids: zwitterion isoelectric point (pI) B. UV Absorption: aromatic amino acids W,Y,F at 280nm C. Colour Reaction: D.Ninhydrin Reaction: blue-violet, 570nm; yellow P 440nm; brown N E. Peptide Formation: residues H3N+— H C — COO- R + —→ H O C — C — N— | – H2O ‖

Section 3 MOLECULAR STRUCTURE OF PROTEINS ● PEPTIDE BOND、PEPTIDE PLANE AND POLYPEPTIDE φ ψ φ ● PRIMARY STRUCTURE Amino Acid Sequences in Peptides (N to C) ● SECONDARY STRUCTURE α-helix, ß-pleated sheet, ß-turn, random coil

Domain: A distinct structural unit of a polypeptide; domains may have separate functions and may fold as independent, compact units or Some peptide chains fold into two or more compact region that may be connected by a flexible segment of peptide chain, rather like pearls on a string. These compact globular units, called domain, range in size from about 30 to 400 amino acid residues. For example, cell-surface protein CD4 consists of four similar domain.

Motif (Supersecondary Structure): A distinct folding pattern for elements of secondary structure, observed in one or more proteins; also called a fold or supersecondary structure or Certain combinations of secondary structure are present in many proteins and frequently exhibit similar functions. These combinations are called motif or supersecondary structure. For example, HTH

Meek DW, DNA Repair 3 (2004) 1049–1056; Chuikov S et al., Nature 432(2004) 353-360

● TERTIARY STRUCTURY Hydrogen Bonding, Salting Bond, Hydrophobic Interaction, Disulfide bond Van der Waal’s Force ● QUATERNARY STRUCTURE Subunits Prosthetic Group/Co-factor

Section 4 PROTEIN FUNCTION IS RELATED WITH ITS STRUCTURE ● PRIMARY STRUCTURE DECIDES FUNCTION A. Proteins with Similar Structure have Similar Functions B. Proteins with Different Structure have Different Functions C. Primary Structure Decides 2nd/3rd/4th Structure D. Primary Structure Decides Functions C-Y-I-Q-N-C-P-L-G-NH2 S S C-Y-F-Q-N-C-P-R-G-NH2 ADH Oxytocin

● PROTEIN FUNCTION RELATES TO ITS CONFORMATION A. Allosteric Effect & Allosteric Regulation B. Denaturation/Renaturation & Function C. Activation of Zymogen D. Primary Structure & Molecular Diseases active inactive O2

Section 5 PHYSICO-CHEMICAL PROPERTIES OF PROTEINS ● DIPOLAR STATE & ELECTRIC POINT A. Electrophoresis B. Ion –exchange Chromatography ● FEATURES OF MACROMOLECULES A. Colloid B. Sedimentation C. Dialysis & Ultra-filtration D. Gel Filtration ● PRECIPITATION A. Salting-out B. High-metal C. Alkaline D. Organic Reagents

● DENATURATION AND RENATURATION A. Denaturation B. Renaturation C. Flocculation D. Coagulation Aromatic Amino Acids 280nm ● UV ABSORPTION ● COLOUR REACTION A. Biuret Reaction B. Follin’s Reaction