Amino acids and Proteins (Lecture Notes), Lecture notes of Biochemistry

Download Amino acids and Proteins (Lecture Notes) and more Lecture notes Biochemistry in PDF only on Docsity! CHEM 142_N (LECTURE) : PROTEINS CHARACTERISTICS OF PROTEINS  Account for 15% of a cell’s overall mass  Contain CHON/S(carbon, hydrogen, oxygen, nitrogen, sulfur)  Nitrogen is always present in protein, unlike in carbohydrates and lipids  Nitrogen content: 15.4 %  Specialized proteins like casein and hemoglobin contain phosphorus and iron, respectively  Naturally occurring, unbranched polymer  Monomer units: amino acids I. AMINO ACIDS: THE BUILDING BLOCKS FOR PROTEINS  An organic compound  Contains an amino group(-NH2) and carboxyl group(-COOH)  amino acids found in proteins are always a-amino acids a-amino acids - (-NH2) & (-COOH) are always attached to a-carbon atom General formula: R-GROUP - Aka amino acid side chain - Distinguishes a-amino acids from each other - Vary in size, charge, acidity, functional groups present, h- bonding ability, chemical reactivity STANDARD AMINO ACID - 20 a-amino acids found in proteins 4 Classification Based On The Side- Chain Polarity 1) NONPOLAR 2) POLAR NEUTRAL 3) POLAR ACIDIC 4) POLAR BASIC ESSENTIAL AMINO ACID - 9 amino acids - Must be obtained from dietary sources COMPLETE DIETARY PROTEIN - Protein that contains all essential amino acids - E.g. milk, meat, fish, eggs, soy protein CHIRALITY AND AMINO ACIDS CHIRAL CENTER - Four different groups are attached to the a-carbon atom  19 of the 20 standard amino acids possess a chiral center  except GLYCINE: r-group is hydrogen FISCHER PROJECTION FORMULA ACID-BASE PROPERTIES OF AMINO ACIDS  Amino acids are charged species in both solid state and in a solution → both (-COOH) & (-NH2) are present on the same carbon in a-amino acid In neutral solution… CARBOX YL GROUP Lose protons (H+ donator) AMINO GROUPS Accept protons (H+ acceptor) ZWITTER ION: - Molecule that has a positive charge on one atom, and a negative charge on another, but has no net charge = 0 o ISOELECTRIC POINT AND ELECTROPHORESIS ISOELECTRIC POINT - “no net charge” pH value for an amino acid solution AMINO ACIDS ISOELECTRIC POINT POLAR & NONPOLAR 4.8 - 6.3 BASIC Higher than 6.3 ACIDIC Lower than 4.8 ELECTROPHORESIS - Process of separating charged molecules based on their