Which of the following correctly lists functions of proteins?

December 29, 2025 •

4 min read

According to the Cleveland Clinic, proteins are often described as the body's workhorses, participating in nearly every cellular activity. Which of the following correctly lists functions of proteins is a common question that highlights the diverse and essential roles these macromolecules play, from catalyzing metabolic reactions to forming structural components of cells and tissues.

Quick Summary

This article details the vast functions of proteins, including their roles in providing structural support, catalyzing biochemical reactions, acting as chemical messengers, and protecting the body through immune responses. It covers major classes such as structural, enzymatic, hormonal, and transport proteins.

Key Points

Structural Role: Proteins like collagen and keratin provide the framework for cells, tissues, hair, and nails.
Enzymatic Catalysis: Enzymes, which are proteins, accelerate thousands of biochemical reactions in the body, such as digestion and metabolism.
Hormonal Communication: Protein hormones like insulin and glucagon act as messengers, coordinating functions across different organs and systems.
Transport and Storage: Proteins facilitate the movement of molecules, such as hemoglobin carrying oxygen, and store essential nutrients like iron.
Immune Defense: Antibodies are protein-based and are crucial for the immune system, identifying and neutralizing foreign pathogens.
Motor and Contractile Function: Motor proteins like actin and myosin generate movement in muscles and transport cargo within cells.
Fluid Balance: Proteins in the blood, such as albumin, help regulate the balance of fluids within the body.
Energy Source: While not the primary source, protein can be broken down for energy if carbohydrate and fat intake is insufficient.

What Are Proteins and Why Are Their Functions Diverse?

Proteins are large, complex molecules essential for all life, consisting of long chains of amino acids. The sequence and arrangement of these amino acids dictate a protein's unique three-dimensional structure, which in turn determines its specific function. This structural diversity allows proteins to fulfill a vast array of roles within organisms. When considering which of the following correctly lists functions of proteins, it's important to recognize that a single protein can contribute to multiple processes, and a complex process can involve many different types of proteins.

Structural Support

Many proteins serve as the building blocks for the body, providing strength and support to cells, tissues, and organs. Without these structural proteins, the body's framework would not exist.

Collagen: The most abundant protein in mammals, collagen provides the structural framework for bones, tendons, ligaments, and skin.
Keratin: This protein is a major component of hair, nails, and the outer layer of skin, giving them their protective and durable properties.
Actin and Tubulin: These proteins form the cytoskeleton, an internal scaffold that maintains cell shape and is involved in cell movement and division.

Catalyzing Biochemical Reactions

As enzymes, proteins act as biological catalysts, accelerating chemical reactions without being consumed in the process. Most of the body's metabolic reactions are regulated by enzymes, enabling digestion, energy production, and DNA replication to occur at a rate necessary for life.

Lipases: This group of enzymes helps digest fats.
Amylase: Found in saliva, amylase helps break down starches into sugars.
DNA Polymerase: Essential for DNA synthesis and replication, this enzyme helps to build new DNA molecules.

Acting as Chemical Messengers (Hormonal Function)

Some proteins and polypeptides function as hormones, which are chemical messengers that help coordinate specific bodily functions. They are produced by endocrine glands and travel through the bloodstream to bind with specific receptors on target cells, triggering a response.

Insulin: A well-known protein hormone, insulin regulates blood sugar levels by signaling cells to take up glucose.
Glucagon: This hormone signals the liver to break down stored glucose.
Oxytocin: This neuropeptide hormone plays a role in social bonding and triggers uterine contractions during childbirth.

Transporting Materials

Transport proteins carry molecules and ions throughout the body and across cell membranes. This function is critical for delivering essential substances to cells and removing waste products.

Hemoglobin: Found in red blood cells, hemoglobin is a transport protein responsible for carrying oxygen from the lungs to tissues.
Membrane Transport Proteins: These proteins are embedded in cell membranes and act as channels or carriers, mediating the selective passage of molecules like glucose and ions into and out of the cell.

Immune Defense

Defensive proteins protect the body against pathogens such as bacteria and viruses. Antibodies are a key example, acting as part of the immune system's response.

Antibodies: Also known as immunoglobulins, these proteins bind to foreign invaders, neutralizing them and marking them for destruction by other immune cells.
Complement proteins: These proteins are involved in the inflammatory response and help fight infections.

Movement (Contractile and Motor Functions)

Proteins are the driving force behind muscle contraction and other cellular movements.

Actin and Myosin: These two proteins work together in muscle cells to cause contraction, enabling movement.
Kinesin and Dynein: These motor proteins move along microtubules within cells, transporting vesicles, organelles, and other cellular cargo.

Comparison of Protein Function Categories

To better understand the distinct yet interconnected roles of proteins, here is a comparison of some major functional categories:


Function Category	Primary Role	Key Examples	Location	Energy Requirement
Structural	Provide support, shape, and stiffness	Collagen, Keratin, Actin	Cells, tissues, skin, bones	No (for a static structure)
Enzymatic	Catalyze and speed up biochemical reactions	Lipase, Amylase, DNA Polymerase	Within and outside cells	Yes (indirectly, for the reaction)
Hormonal	Act as chemical messengers	Insulin, Glucagon, Oxytocin	Endocrine glands, travel in blood	No (for the protein itself)
Transport	Move substances into, out of, or within cells	Hemoglobin, Glucose Transporters	Blood, cell membranes	Passive or Active (via ATP)
Defense	Protect against pathogens and foreign invaders	Antibodies, Complement Proteins	Immune cells, blood	Yes (for immune cell processes)
Motor	Generate force for movement	Actin, Myosin, Kinesin	Muscle cells, cytoskeleton	Yes (via ATP hydrolysis)

Conclusion

In conclusion, asking which of the following correctly lists functions of proteins reveals the vast and indispensable nature of these macromolecules. From building the body's physical structures with collagen and keratin to initiating and controlling cellular processes with enzymes and hormones, proteins are the central architects of biological function. They operate tirelessly to transport essential materials, defend against disease, and power all forms of movement, both macroscopic and microscopic. The proper functioning of these diverse proteins, dictated by their specific amino acid sequences and complex structures, is fundamental to the health and survival of all living organisms.

Frequently Asked Questions

The primary role of dietary protein is to supply the amino acids needed to build and repair the body's own proteins for both bodily function and structure.

Protein hormones, like insulin and glucagon, are chemical messengers secreted by glands. They travel through the bloodstream and bind to receptors on target cells, coordinating various bodily functions.

A classic example is hemoglobin, a protein found in red blood cells that transports oxygen from the lungs to the body's tissues.

Yes, proteins can provide energy, but the body primarily uses carbohydrates and fats for this purpose. Proteins are typically broken down for energy only when those other sources are insufficient, such as during fasting.

Structural proteins provide support, shape, and rigidity to cells and tissues. Key examples include collagen in bones and ligaments, and keratin in hair and skin.

The immune system relies on defensive proteins called antibodies, which are produced to recognize and neutralize harmful foreign invaders like bacteria and viruses.

Motor proteins, such as myosin and kinesin, are responsible for movement. Myosin enables muscle contraction, while kinesin transports organelles and vesicles within the cell along microtubule tracks.