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

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

Section 2 MOLECULAR COMPOSITION OF PROTEINS

● 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 ACIDSA. Dipolar State of Amino Acids: zwitterion isoelectric point (pI)B. UV Absorption: aromatic amino acids W,Y,F at 280nmC. Colour Reaction:D.Ninhydrin Reaction: blue-violet, 570nm; yellow P 440nm; brown NE. Peptide Formation: residues

‖H3N+—

H

C — COO-

R

H3N+—

H

C — COO-

R

+ —→ H3N+—

H O

C — C

R

— N—

H

C — COO-

R |H

– H2O

Section 3 MOLECULAR STRUCTURE OF PROTEINS

Amino Acid Sequences in Peptides (N to C)

● PEPTIDE BOND、 PEPTIDE PLANE AND POLYPEPTIDE

● PRIMARY STRUCTURE

● SECONDARY STRUCTURE

α-helix, ß-pleated sheet, ß-turn, random coil

ψ φφ

Domain:

A distinct structural unit of a polypeptide; domains may have separate functions and may fold as independent, compact unitsorSome peptide chains fold into two or more compactregion that may be connected by a flexible segmentof 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; alsocalled a fold or supersecondary structureorCertain combinations of secondary structure arepresent in many proteins and frequently exhibit similarfunctions. These combinations are called motif orsupersecondary 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 FunctionsC. Primary Structure Decides 2nd/3rd/4th StructureD. 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

S SADH

Oxytocin

● PROTEIN FUNCTION RELATES TO ITS CONFORMATION

A. Allosteric Effect & Allosteric Regulation B. Denaturation/Renaturation & FunctionC. Activation of ZymogenD. Primary Structure & Molecular Diseases

active

inactive

active

O2O2

O2 O2

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. RenaturationC. FlocculationD. Coagulation

Aromatic Amino Acids 280nm

● UV ABSORPTION

● COLOUR REACTION

A. Biuret Reaction B. Follin’s Reaction