proteins (nutrition)

Proteins: Structure, Digestion, and Roles in Nutrition

Learning Objectives

• Recognize the chemical structures of amino acids and proteins.

• Summarize protein digestion and absorption.

• Describe how the body makes proteins and uses them in various roles.

• Explain the differences between high-quality and low-quality proteins, including notable food sources of each.

• Identify the health benefits of, and recommendations for, protein consumption.

Proteins and Amino Acids

Definition and Basic Structure

Proteins are large, complex compounds found in all living cells. They are essential for the structure and function of every cell in the body.

• Protein: A macromolecule composed of one or more long chains of amino acids.

• Amino acid: The building block of proteins. Each amino acid contains carbon (C), hydrogen (H), oxygen (O), and nitrogen (N).

• All amino acids share a common structure: a central carbon atom bonded to a hydrogen atom, an amino group (–NH2), a carboxyl (acid) group (–COOH), and a unique side chain (R group) that distinguishes each amino acid.

General structure of an amino acid:

• Central carbon (C)

• Amino group (–NH2)

• Carboxyl group (–COOH)

• Hydrogen atom (H)

• Side chain (R group, varies for each amino acid)

Additional info: The side chain (R group) determines the chemical properties and function of each amino acid.

Functions of Proteins in the Body

Proteins are the predominant structural and functional materials in every cell. The human body contains thousands of different proteins, each with specific roles.

• Muscle tissue: Proteins are abundant in muscle, providing structure and enabling movement.

• Immune function: Some proteins, such as antibodies, are essential for immune system function.

• Structural proteins: Keratin forms fingernails and hair.

• Digestive enzymes: Proteins facilitate digestion by catalyzing biochemical reactions.

Proteins are involved in virtually all life processes, and the body cannot function or survive without them.

Key Terms

• Enzyme: A protein that acts as a biological catalyst, speeding up chemical reactions in the body.

• Antibody: A protein produced by the immune system to identify and neutralize foreign substances.

• Keratin: A fibrous structural protein found in hair, nails, and skin.

Examples and Applications

• Example: Hemoglobin is a protein in red blood cells that transports oxygen throughout the body.

• Application: Enzymes such as pepsin and trypsin are involved in the digestion of dietary proteins.