Proteins have many essential functions in living systems including acting as enzymes, transporters, regulators, and providing structure. There are 20 standard amino acids that make up proteins and their side chains determine each protein's unique properties. A protein's amino acid sequence is encoded in DNA and the sequence folds into complex three-dimensional structures that enable proteins to carry out their diverse roles.

1. PROTEIN STRUCTURES & FUNCTIONS

2. FUNCTIONS Proteins function as: 1. Enzymes:biological catalysts 2. Regulators of catalysis-hormones 3. Transport and store i.e. O2, metal ions sugars, lipids, etc.

3. FUNCTIONS 4. Contractile assemblies Muscle fibers 5. Sensory Rhodopsin nerve proteins 6. Cellular defense (antibodies/Ig) 7. Structural (collagen)

4. Proteins play key roles in a living system examples of protein functions Catalysis: Almost all chemical reactions in a living cell are catalyzed by protein enzymes. Transport: Some proteins transports various substances, such as oxygen, ions, and so on. Information transfer: For example, hormones. Alcohol dehydrogenase oxidizes alcohols to aldehydes or ketones Hemoglobin carries oxygen Insulin controls the amount of sugar in the blood

5. Amino acid: Basic unit of protein An amino acid Different side chains, R , determin the properties of 20 amino acids. Amino group Carboxylic acid group COO - NH 3 + C R H

6. 20 Amino acids Glycine (G) Glutamic acid (E) Asparatic acid (D) Methionine (M) Threonine (T) Serine (S) Glutamine (Q) Asparagine (N) Tryptophan (W) Phenylalanine (F) Cysteine (C) Proline (P) Leucine (L) Isoleucine (I) Valine (V) Alanine (A) Histidine (H) Lysine (K) Tyrosine (Y) Arginine (R) White: Hydrophobic, Green: Hydrophilic, Red: Acidic, Blue: Basic

7. Proteins are linear polymers of amino acids R 1 NH 3 ＋ C CO H R 2 NH C CO H R 3 NH C CO H R 2 NH 3 ＋ C COO ー H ＋ R 1 NH 3 ＋ C COO ー H ＋ H 2 O H 2 O Peptide bond Peptide bond The amino acid sequence is called as primary structure A A F N G G S T S D K A carboxylic acid condenses with an amino group with the release of a water

8. Amino acid sequence is encoded by DNA base sequence in a gene DNA molecule ＝ DNA base sequence ・ C G C G A A T T C G C G ・ ・ G C G C T T A A G C G C ・

9. Amino acid sequence is encoded by DNA base sequence in a gene Second letter T C A G First letter T TTT Phe TCT Ser TAT Tyr TGT Cys T Third letter TTC TCC TAC TGC C TTA Leu TCA TAA Stop TGA Stop A TTG TCG TAG TGG Trp G C CTT Leu CCT Pro CAT His CGT Arg T CTC CCC CAC CGC C CTA CCA CAA Gln CGA A CTG CCG CAG CGG G A ATT Ile ACT Thr AAT Asn AGT Ser T ATC ACC AAC AGC C ATA ACA AAA Lys AGA Arg A ATG Met ACG AAG AGG G G GTT Val GCT Ala GAT Asp GGT Gly T GTC GCC GAC GGC C GTA GCA GAA Glu GGA A GTG GCG GAG GGG G

10. Basic structural units of proteins: Secondary structure α -helix β -sheet Secondary structures , α -helix and β -sheet, have regular hydrogen-bonding patterns.

11. Three-dimensional structure of proteins Tertiary structure Quaternary structure

12. Hierarchical nature of protein structure Primary structure (Amino acid sequence) ↓ Secondary structure （ α -helix, β -sheet ） ↓ Tertiary structure （ Three-dimensional structure formed by assembly of secondary structures ） ↓ Quaternary structure （ Structure formed by more than one polypeptide chains ）