Chapter 14

1. Chapter 14 Section 14.1-14.4 By: Kellen Kane & Ian Snyder

2. 14.1 What Are the Many Functions of Proteins? • The most important of all biological compounds are proteins • Structure: Proteins are the chief constituents of skin, bones, hair, and nails for animals. Collagen and keratin are two important structural proteins. • Catalysis: All reactions that take place in living organisms are catalyzed by proteins called enzymes. Without enzymes, the reaction would be so slow, that it would be useless.

3. Functions of Proteins Continued • Catalysis: All reactions that take place in living organisms are catalyzed by proteins called enzymes. Without enzymes, the reaction would be so slow, that it would be useless. • Movement: Muscles are made up of protein molecules called myosin and actin which allows you to move.

4. Functions of Proteins Continued • Transport: Many proteins perform transportation duties. Molecules are also transported across the cell membrane by proteins. • Example of transport: Hemoglobin which is a protein in the blood, carries oxygen from the lungs to the cells where it is used, and then takes the carbon dioxide from the cells to the lungs.

5. Functions of Proteins Continued • Hormones: A lot of hormones are proteins, including erythropoietin, insulin, and human growth hormone (HGH). • Protection: Your body makes its own proteins called antibodies to counteract foreign protein and fight diseases. Another protective function is called fibrinogen which is blood clotting. Without blood clotting, we would bleed to death from any small cut.

6. Functions of Proteins Continued • Storage: Proteins store material similar to the way that starch and glycogen store energy. • Casein and milk ovalbumin in eggs and Ferritin stores iron • Regulation: They control what kind of proteins are synthesized in cells.

7. Classification of Proteins • They are categorized into two major types: • Fibrous proteins: insoluble in water and are used for structural purposes. • Globular proteins: less soluble in water and used for nonstructural purposes.

8. 14.2 What are Amino Acids? • Proteins are chains of amino acids and an amino acid is an organic group. • contains an amino group and a carboxyl group. • Many amino acids are synthesized by chemists but there are about 20 that are common in nature. • The 20 acids that are found in nature are called the alpha amino acids.

9. Structures of Amino acids • Has an amino group and a carboxyl group • Amino acids are classified into four groups depending on what R groups are found in it. • Nonpolar • Polar but neutral • Acidic • Basic

10. Structures of Amino Acids continued • Amino acids are chiral since they have four different groups • The carbon acts as the stereocenter • L-isomers are the most common • D-amino acids are very rare

11. 14.3 What are Zwitterions? • Zwitterions are compounds that have a positive charge on one atom and a negative charge on another • Amino acids are zwitterions in both water solution and in solid state • The addition of a strong acid changes amino acids into a positive ion • The addition of a strong base makes the amino acid a negative ion

12. What are Zwitterions continued • The isoelectric point (pI) is when an amino acid has an equal amount of positive and negative charges • 15 out of the 20 amino acids found in nature have an isoelectirc point near 6 • Aqueous solutions of amino acids are buffer solutions

13. 14.4 What Determines the Characteristics of Amino Acids? • The side chain of an amino acid is what determines characteristics • The function of amino acids in proteins are determined by side chains

14. Examples of side chain function determination • Cystine • Dimer of cysteine • Disulfide bond • Presence of Carboxyl group • Forms Carboxylate ion • Aromatic • Allow us to locate and measure proteins

15. Summary of Key Points • Proteins are molecules made of amino acids bonded together by peptide bonds • Proteins have many functions • Structural • Enzymatic • Carrier • Storage • Protective • Hormonal

16. Cont…. • Amino acids are organic compounds containing an amino and carboxylic acid group • The 20 amino acids found in nature are classified by their side chains • Nonpolar • Polar but neutral • Acidic • Basic • Amino acids in both aqueous and solid state carry both positive and negative charges, called zwitterions

17. Cont… • The pH at which the number of positive charges equals the number of negative charges is the isoelectric point • Amino acids are nearly identical in most ways, aside from their side chains • Side chains give the amino acids its properties • Some amino acids have charged side chains