General organic and biological chemistry structures of life CH 19 1 proteins amino acids GOB structures 5th ed

Give the name and abbreviations for an amino acid, and draw its zwitterion... Amino AcidsAmino acids, the molecular building blocks of proteins, have a central carbon atom called the α c

Lecture Presentation

Chapter 19

Amino Acids and Proteins

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

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

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.

Draw the zwitterions for the amino acids serine and aspartate.

ANALYZE Given Need

THE serine draw the zwitterions

PROBLEM 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

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.

Chemistry Link to Health:

Essential Amino Acids