1 Amino Acids Proteins, and Enzymes Types of Proteins Amino Acids The Peptide Bond

2 Types of Proteins TypeExamples Structuraltendons, cartilage, hair, nails Contractilemuscles Transporthemoglobin Storagemilk Hormonalinsulin, growth hormone Enzymecatalyzes reactions in cells Protectionimmune response

3 Amino Acids Building blocks of proteins Carboxylic acid group Amino group Side group R gives unique characteristics Rside chain I H 2 N—C —COOH I H

4 Examples of Amino Acids H I H 2 N—C —COOH I Hglycine CH 3 I H 2 N—C —COOH I Halanine

5 Types of Amino Acids Nonpolar R = H, CH 3, alkyl groups, aromatic O Polar ll R = –CH 2 OH, –CH 2 SH, –CH 2 C–NH 2, (polar groups with –O-, -SH, -N-) Polar/Acidic R = –CH 2 COOH, or -COOH Polar/ Basic R = –CH 2 CH 2 NH 2

6 Essential Amino Acids 10 amino acids not synthesized by the body arg, his, ile, leu, lys, met, phe, thr, trp, val Must obtain from the diet All in diary products 1 or more missing in grains and vegetables

7 Amino Acids as Acids and Bases Ionization of the –NH 2 and the –COOH group Zwitterion has both a + and – charge Zwitterion is neutral overall + NH 2 –CH 2 –COOH H 3 N–CH 2 –COO – glycine Zwitterion of glycine

8 pH and ionization H + OH – + H 3 N–CH 2 –COOH H 3 N–CH 2 –COO – H 2 N–CH 2 –COO – Positive ion zwitterion Negative ion Low pH neutral pH High pH

9 The Peptide Bond Amide bond formed by the –COOH of an amino acid and the –NH 2 of the next amino acid O CH 3 + | | + | NH 3 –CH 2 –COH + H 3 N–CH–COO – O CH 3 + | | | NH 3 –CH 2 –C – N–CH–COO – | peptide bond H

10 Peptides Amino acids linked by amide (peptide) bonds Gly Lys Phe Arg Ser H 2 N- -COOH endPeptide bonds end Glycyllysylphenylalanylarginylserine

11 Amino Acids, Proteins, and Enzymes Primary and Secondary Structure Tertiary and Quaternary Structure Protein Hydrolysis and Denaturation

12 Primary Structure of Proteins The particular sequence of amino acids that is the backbone of a peptide chain or protein Ala-Leu-Cys-Met

13 Secondary Structure – Alpha Helix Three-dimensional arrangement of amino acids with the polypeptide chain in a corkscrew shape Held by H bonds between the H of –N-H group and the –O of C=O of the fourth amino acid along the chain Looks like a coiled “telephone cord”

14 Secondary Structure – Beta Pleated Sheet Polypeptide chains are arranged side by side Hydrogen bonds form between chains R groups of extend above and below the sheet Typical of fibrous proteins such as silk

15 Secondary Structure – Triple Helix Three polypeptide chains woven together Glycine, proline, hydroxy proline and hydroxylysine H bonding between –OH groups gives a strong structure Typical of collagen, connective tissue, skin, tendons, and cartilage

16 Tertiary Structure Specific overall shape of a protein Cross links between R groups of amino acids in chain disulfide –S–S– + ionic –COO – H 3 N– H bonds C=O HO– hydrophobic –CH 3 H 3 C–

17 Globular and Fibrous Proteins Globular proteins Fibrous proteins “spherical” shapelong, thin fibers InsulinHair HemoglobinWool Enzymes Skin AntibodiesNails

18 Quaternary Structure Proteins with two or more chains Example is hemoglobin Carries oxygen in blood Four polypeptide chains Each chain has a heme group to bind oxygen

19 Protein Hydrolysis Break down of peptide bonds Requires acid or base, water and heat Gives smaller peptides and amino acids Similar to digestion of proteins using enzymes Occurs in cells to provide amino acids to synthesize other proteins and tissues

20 Hydrolysis of a Dipeptide

21 Denaturation Disruption of secondary, tertiary and quaternary protein structure by heat/organics Break apart H bonds and disrupt hydrophobic attractions acids/ bases Break H bonds between polar R groups and ionic bonds heavy metal ions React with S-S bonds to form solids agitation Stretches chains until bonds break

22 Secondary Structure – Triple Helix Three polypeptide chains woven together Glycine, proline, hydroxy proline and hydroxylysine H bonding between –OH groups gives a strong structure Typical of collagen, connective tissue, skin, tendons, and cartilage

23 Applications of Denaturation Hard boiling an egg Wiping the skin with alcohol swab for injection Cooking food to destroy E. coli. Heat used to cauterize blood vessels Autoclave sterilizes instruments Milk is heated to make yogurt

Functions of Proteins Structure – collagen, keratin,elastin Enzyme – lysozyme, amylase, Transport – hemoglobin, lipoproteins Contractile – actin, myosin, tubulin Hormone – insulin, growth hormone Antibody – IgG, Pigment – melanin, rhodopsin Recognition – CD4, MHC proteins 24