1. Proteins and Enzymes Nestor T. Hilvano, M.D., M.P.H. (Images Copyright Discover Biology, 5 th ed., Singh-Cundy and Cain, Textbook, 2012.)

2. Learning Objectives 1.Define key terminologies such as amino acids, peptide, enzymes, polypeptide, protein, and peptide bonds. 2. Describe the basic structure of amino acid. 3. Discuss the functions of proteins, noting examples of each. 4. Describe briefly the 4 levels of protein’s structure. 5.Discuss how denaturation of protein occurs. 6.Describe enzymes and it’s functions. 7.Discuss the types of enzyme’s inhibition.

3. Functions of Proteins Enzymatic – i.e. chemical reactions in GIT Signaling/regulation – i.e. hormones, chemical messengers Transport – i.e. hemoglobin Structural – ie. hair Contractile – i.e. muscle Protective/ defense – i.e. antibodies Storage – i.e. egg white

4. Amino Acids Building blocks of proteins 20 amino acids Basic structure: a carboxyl group (COOH), amino group (NH2), and R group (variable part), bonded to a central carbon (C) Amino acids are grouped into categories based on characteristics of the R group: a) hydrophilic (polar and charged) b) hydrophobic (nonpolar)

5. Fig. 5-17 Nonpolar Glycine (Gly or G) Alanine (Ala or A) Valine (Val or V) Leucine (Leu or L) Isoleucine (Ile or I) Methionine (Met or M) Phenylalanine (Phe or F) Trypotphan (Trp or W) Proline (Pro or P) Polar Serine (Ser or S) Threonine (Thr or T) Cysteine (Cys or C) Tyrosine (Tyr or Y) Asparagine (Asn or N) Glutamine (Gln or Q) Electrically charged AcidicBasic Aspartic acid (Asp or D) Glutamic acid (Glu or E) Lysine (Lys or K) Arginine (Arg or R) Histidine (His or H) * The 20 amino acids of proteins *8 essential a.a., Must be taken in diet

6. Proteins Amino acids are joined together by ____ bond through dehydration reaction (synthesis). ____ - 2 amino acids linked together. ____ – a chain of many amino acids. ____ – can be composed of one or more polypeptides. a. polypeptide c. dipeptide b. protein d. peptide bond

8. Proteins Specific shape determine its function - functional proteins consist of polypeptides folded, twisted, coiled in unique shape The lost of normal structure of protein is called Denaturation. Factors: temp, pH, salt i.e. acid causes milk to curdle; heat causes egg white to coagulate

9. 4 Levels of Protein Structure 1.Primary structure – sequence of amino acids (like order of letters in a long words/sentence; maintain by covalent peptide bonds) 2. Secondary structure – helices and pleated sheets ; maintain by H bonds between amino group and carboxyl group ex. hair (α helix), silk (β sheet)

10. 3. Tertiary structure – 3D structure, globular or fibrous - maintain by R group interactions (H bonds + covalent bonds) ex. hair, hemoglobin 4. Quarternary structure – associations of two or more polypeptide chains in final protein product ex. collagen (fibrous w/ triple helix); hemoglobin (4 globular polypeptide chains) 4 levels of Protein Structure

11. Enzymes Enzymes= Proteins that cause specific chemical change in the body Substrate= substance upon which an enzyme acts Exergonic reaction- releases energy Endergonic reaction- store energy Act as biological catalysts- speed up a chemical reaction Factors that influence the rate of reaction- pH, temp., cofactors, inhibitors

14. Enzymes Inhibition 1.Irreversible- covalent bond which destroys the active site 2.Reversible- non-covalent bond; a) competitive- binds into active site, block substrate b) non-competitive- binds to enzyme, changes shape of enzyme, active site non-functional

15. Figure 5.15A Substrate Enzyme Allosteric site Active site Normal binding of substrate Competitive inhibitor Noncompetitive inhibitor Enzyme inhibition

16. Homework 1.Define – amino acids, denaturation, enzyme, polypeptides, catalyst, substrate, and protein. 2.List 5 functions of proteins. 3.Name 3 factors that cause denaturation of proteins. 4.Compare primary, secondary, tertiary, and quarternary structures of protein. 5.List the factors that affect enzymes reaction. 6.Compare competitive inhibition from non- competitive inhibition of enzymatic reaction.