Question

Which of the following proteins is most likely to be found extracellularly? (A) Tubulin (B) Myosin (C) Collagen (D) Actin

Short answer

Collagen (C)

Step-by-step solution

Identify the functions of given proteins

Understand the primary functions and locations of each given protein: - Tubulin: Found in the cytoskeleton, it helps in maintaining cell shape and intracellular transport.- Myosin: Found in muscle cells and other cell types, it aids in motor functions, especially in muscle contractions.- Collagen: A structural protein that is a major component in extracellular matrices, providing support and structure to tissues.- Actin: Also part of the cytoskeleton, it works with myosin for muscle contractions and maintaining cell shape.

Determine which protein functions extracellularly

From Step 1, identify which protein is not primarily involved in intracellular processes but rather in providing support to tissues from outside of the cell. Collagen functions in the extracellular matrix, helping to provide structural support and strength to tissues.

Conclude the most likely extracellular protein

Based on the analysis, collagen is the only protein among the options that primarily functions extracellularly.

Key concepts

cytoskeleton

The cytoskeleton of a cell is like its skeleton. It is a network of fibers that crisscrosses the cytoplasm. The cytoskeleton has several important functions: it helps the cell maintain its shape, offers support, and facilitates movement. Here are the primary components:

• Tubulin: This protein forms microtubules, which are large fibers that help maintain cell shape and aid in intracellular transport. Tubulin is not found outside cells but is a crucial part of the cytoskeleton inside cells.
• Actin: Actin proteins polymerize to form actin filaments, which are essential in muscle contractions and other cell movements. Actin works with myosin to enable these movements.

These proteins (tubulin and actin) are key to the functioning of the cytoskeleton but are not found extracellularly. Understanding the cytoskeleton helps us appreciate how cells move and maintain their integrity.

extracellular matrix

The extracellular matrix (ECM) is a complex network of proteins and other molecules outside cells. It is crucial for providing structural support, biochemical signals, and mechanical properties to tissues. The ECM's primary functions include:

• Support: The ECM acts as a scaffold that holds cells together, maintaining tissue structure.
• Signaling: It helps in transmitting biochemical signals regulating cell behavior, like growth and differentiation.
• Barrier function: The ECM can act as a barrier to movement of molecules and cells from one tissue to another.

A key protein in the ECM is Collagen. It provides tensile strength, helping tissues withstand stretching and pulling. Collagen forms a significant part of the ECM and supports tissues from outside the cells, distinguishing it from intracellular proteins like actin and tubulin.

structural proteins

Structural proteins are important for giving cells and tissues their shape and form. These proteins are often involved in providing support and rigidity. Examples include:

• Actin: As we saw earlier, actin is integral to the cytoskeleton and aids in cell movement and stability.
• Collagen: This is the major structural protein in the ECM, making up about 30% of the body's protein. It provides strength and structure outside the cells, playing a critical role in skin, bones, and connective tissues.

Collagen is unique among many structural proteins because it is found extracellularly, reinforcing tissues and organs, whereas others like actin and tubulin work within cells. Understanding these structural proteins helps us appreciate how they contribute to the complex architecture of living organisms.