Lecture Notes: Chemistry of Cells - Amino Acids PDF

LECTURE NOTES Coverage: CHEMISTRY OF CELLS A. Topic 1: Introduction to Biochemistry B. Topic 2: The Cell C. Topic 3: Amino Acids D. Topic 4: Polypeptides E. Topic 5: Enzymes TOPIC 3 AMINO ACID...

LECTURE NOTES Coverage: CHEMISTRY OF CELLS A. Topic 1: Introduction to Biochemistry B. Topic 2: The Cell C. Topic 3: Amino Acids D. Topic 4: Polypeptides E. Topic 5: Enzymes TOPIC 3 AMINO ACIDS  TOPIC 3 OBJECTIVES At the end of Topic 3, the students are expected to: 1. Describe the general structure of an amino acid. 2. Write the structures of different amino acids 3. Explain the behavior of amino acids based on their structures.  AMINO ACIDS AS BUILDING BLOCKS PROTEIN OF PROTEIN ❑ Greek word, "proteios," meaning primary. ❑ Make up 3/4th of total dry body weight ❑ Contain the major components of C,H,O, N while S and P minor components ❑ Distinguished by nitrogen ❑ Commonly contain 20 types of amino acids.  Role Examples Functions Digestive Amylase, lipase, Break down nutrients in food into TYPES AND enzyme pepsin small pieces that can be readily FUNCTIONS OF absorbed PROTEINS Transport Hemoglobin Carry substances throughout the body in blood or lymph Structure Actin, tubulin, keratin Build different structures, like the cytoskeleton Hormone Insulin, glucagon Coordinate the activity of signaling different body systems Defense Antibodies Protect the body from foreign pathogens Contraction Myosin Carry out muscle contraction Storage Legume storage Provide food for the early proteins, egg white development of the embryo or (albumin) the seedling AMINO ACIDS ❑ The building blocks of proteins ❑ Also used as single molecules in biochemical pathways ❑ Two functional groups: carboxylic acid group amino group on the alpha () carbon  ❑ Have different side groups (R) AMINO ACIDS Properties dictate behavior of amino acids Structure of R also influence solubility Figure 3.0 Amino acid AMINO ACIDS ❑ Both the –NH2 and the –COOH groups in an amino acid undergo ionization in water. ❑ At physiological pH (7.4), a zwitterion forms Both + and – charges Overall neutral Amphoteric ▪ Amino group is protonated ▪ Carboxyl group is deprotonated ❑ Soluble in polar solvents due to ionic character AMINO ACIDS Figure 3.1 Zwitterion STRUCTURE OF The α carbon is chiral or asymmetric ( 4 different AMINO ACIDS groups are attached to the carbon; exception is glycine.) Amino acids exist as stereoisomers (same molecular formula, but differ in arrangement of groups). Designated D(right) or L(left). Amino acids used in nature are of L configuration. α amino group orientation determines NH3+ on left = L NH3+ on right = D STRUCTURE OF AMINO ACIDS Figure 3.2 Amino acid configuration STRUCTURE OF AMINO ACIDS There are 20 standard amino acids (Figure 3.3) called α -amino acids because they all have an amino (NH3+) group and a carboxyl group (COOH) attached to C-2 carbon (α - carbon).  STANDARD AMINO ACIDS Figure 3.3 Structures of Standard Amino Acids CLASSIFICATION Classify by structure of R OF AMINO ACIDS – Nonpolar – Polar – Aromatic – Acidic – Basic  Hydrophobic, neutral, aliphatic NON POLAR AMINO ACIDS Figure 3.4 Non-polar Amino Acids  Hydrophilic, neutral, typically H-bond POLAR AMINO ACIDS Figure 3.5 Polar Amino Acids  DISULFIDE BONDS Formed from oxidation of cysteine residues POLAR AMINO ACIDS Figure 3.6 Disulfide Bond  Bulky, neutral, polarity depend on R AROMATIC AMINO ACIDS Figure 3.7 Aromatic Amino Acids AROMATIC AMINO ACIDS Figure 3.8 Synthesis of Serotonin from Tryptophan  BASIC AND ACIDIC AMINO ACIDS Figure 3.9 Acidic Amino Acids  Basic BASIC AND – R group = amine ACIDIC AMINO – Accepts H+ ACIDS – Positively charged – His ionizes at pH 6.0 Figure 3.10 Basic Amino Acids  AMINO ACID ORGANIZATION Figure 3.11 Amino Acid Organization  All amino acids (except glycine) STEREOCHEMISTRY are optically active OF AMINO ACIDS Fischer projections: Figure 3.12 Stereochemistry of Amino Acids LECTURE NOTES CHEMISTRY OF CELLS Thank you!!!