Chapter 19 Amino Acids and Proteins Lecture Presentation Chapter 19 Amino Acids and Proteins Karen C. Timberlake

Chapter 19 Amino Acids and Proteins Radiology technicians work with radiologists to produce images that allow for the diagnosis and treatment of certain medical conditions. Technicians operate imaging equipment such as X-ray, computed tomography (CT), and positron emission tomography (PET).

Chapter 19 Readiness Key Math Skill Calculating pH from [H3O+] (11.6) Core Chemistry Skills Writing Equations for Reactions of Acids and Bases (11.7) Naming Carboxylic Acids (16.1) Forming Amides (18.5)

19.1 Proteins and Amino Acids Protein molecules, compared with many of the compounds we have studied, can be gigantic. The horns of animals are made of proteins. Learning Goal Classify proteins by their functions. Give the name and abbreviations for an amino acid, and draw its zwitterion.

Functions of Proteins Proteins in the body are polymers made from 20 different amino acids. differ in characteristics and functions that depend on the order of amino acids that make up the protein. form structural components such as cartilage, muscles, hair, and nails. function as enzymes to regulate biological reactions such as digestion and cellular metabolism. including hemoglobin and myoglobin transport oxygen in the blood.

Structural Classification of Proteins and Functions

Amino Acids Amino acids, the molecular building blocks of proteins, have a central carbon atom called the α carbon, bonded to two functional groups: an ammonium group (— NH3+) and a carboxylate group (— COO−) a hydrogen atom and an R group or side chain in addition to the carboxylate and ammonium groups.

Zwitterions At physiological pH, the ionized ammonium and carboxylate groups give an amino acid a balance of positive and negative charge, which gives an overall zero charge. neutral amino acid, which is called a zwitterion, occurs at a specific pH value known as its isoelectric point (pI). Core Chemistry Skill Drawing the Zwitterion for an Amino Acid

Classification of Amino Acids Amino acids are classified using their specific R groups. The nonpolar (hydrophobic) amino acids have hydrogen, alkyl, or aromatic R groups. polar amino acids have R groups that interact with water, which makes them hydrophilic. polar neutral amino acids contain an hydroxyl (— OH), a thiol (— SH), or an amide (— CONH2) R group polar acidic amino acids contain a carboxylate (— COO−) R group. polar basic amino acids contain an ammonium (— NH3+) R group.

Classification of Amino Acids A summary of amino acid types and their interactions with water

Nonpolar Amino Acids An amino acid is nonpolar when the R group is H, alkyl, or aromatic.

Polar Amino Acids, Neutral R Groups An amino acid is polar when the R group is an alcohol, a thiol, or an amide.

Amino Acids, Charged R Groups An amino acid is charged when the R group is a carboxylate (— COO−) or an ammonium (— NH3+) group.

Study Check Draw the zwitterions for the amino acids serine and aspartate.

Solution Draw the zwitterions for the amino acids serine and aspartate. Serine Aspartate ANALYZE Given Need THE serine draw the zwitterions PROBLEM aspartate

Amino Acid Abbreviations Amino acids have three-letter abbreviations derived from their names, given in Table 19.2. one-letter abbreviations to allow the faster transfer of data. Of the 20 amino acids, 11 have one-letter abbreviations that are the same as the first letter in their names and 9 use different letters. arginine R and tyrosine Y use the second letters in their names; phenylalanine is F; and lysine is K, which is near L in the alphabet.

Amino Acid Stereoisomers Amino acids can exist as D and L stereoisomers called enantiomers. We draw Fischer projections for α-amino acids by placing the carboxylate group at the top. the R group at the bottom. the — NH3+ group of the L isomer on the left. the — NH3+ group of the D isomer on the right.

Study Check Identify the following amino acids as D or L enantiomers: A. B.

Solution Identify the following amino acids as D or L enantiomers: A. B. L-Phenylalanine D-Serine

Chemistry Link to Health: Essential Amino Acids Of the 20 amino acids used to build the proteins in the body, only 11 can be synthesized in the body; the other 9 are essential amino acids that must be obtained from the proteins in the diet.

Chemistry Link to Health: Essential Amino Acids Complete proteins such as eggs, milk, meat, and fish contain all of the essential amino acids. Incomplete proteins from plants such as grains, beans, and nuts are deficient in one or more essential amino acids.