Problem 89 - Objective Biology for NEET

Question

Which of the following membrane proteins are partially or totally buried in cell membrane? (a) Integral proteins (b) Peripheral proteins (c) Both (a) and (b) (d) Glycoproteins

Step-by-Step Solution

Answer

The correct answer is (a) Integral proteins, they are the ones that are partially or completely buried within the cell membrane.

Step 1: Understanding terminology

First, let's understand these terms. Integral proteins are those which are embedded within the membrane, often spanning the whole width. Peripheral proteins are typically attached to the inner or outer surfaces of the cell membrane, while Glycoproteins are proteins that have carbohydrate molecules attached.

Step 2: Identifying proteins

Given the definitions, it can be deduced that integral proteins are the ones that are either partially or completely buried within the cell membrane. Peripheral proteins, are not buried within the membrane, but are loosely bound to the surface. Glycoproteins can be either peripheral or integral.

Step 3: Eliminating options

Considering the above information, both peripheral proteins (option b) and glycoproteins (option d) can be disregarded as they are not always embedded in the membrane.

Key Concepts

Integral Proteins

Integral proteins play crucial roles in the structure and function of cell membranes. These proteins are embedded directly within the lipid bilayer of the cell membrane. Often, they go all the way through the membrane, meaning they span from one side of the cell to the other. This complete integration into the cell membrane makes them vital for various cell processes.

These proteins serve several important functions:

• Transport: They help move substances across the cell membrane. Some act as channels or carriers for molecules too large or polar to cross the lipid bilayer without assistance.
• Signaling: They act as receptors, allowing the cell to communicate with its environment by binding with specific molecules such as hormones.
• Structural roles: They help maintain the cell’s shape and structure.

Integral proteins are essential for maintaining the integrity and functionality of biological membranes. Their ability to span the membrane makes them ideal for roles that require interaction with both the internal and external environments of the cell.

Peripheral Proteins

Unlike integral proteins, peripheral proteins do not embed within the lipid bilayer. Instead, they are more loosely attached to the exterior or the interior surfaces of the membrane. This attachment often occurs through interactions with integral proteins or through associations with the polar heads of the membrane phospholipids.

The main characteristics of peripheral proteins include:

• Attachment: They associate with the membrane's surfaces without penetrating its hydrophobic core.
• Flexibility: Due to their non-covalent attachment, they can be easily detached and reattached according to the cell’s needs.
• Functional roles: They often participate in signaling pathways, provide support and shape to the cell, and aid in cellular movement.

Peripheral proteins are key contributors to the dynamic processes of cell membranes. Their ability to detach and reattach allows them to participate in many cellular activities as needed, offering flexibility to the cell membrane's functionality.

Glycoproteins

Glycoproteins are proteins that have carbohydrate groups attached to their polypeptide chain. These carbohydrate molecules are typically found on the extracellular side of the cell membrane, which means they face outside of the cell. The combination of proteins and carbohydrates forms molecules that play several important roles in the cell.

The primary functions of glycoproteins include:

• Cell recognition: They serve as unique markers that help cells identify each other, which is crucial for immune response and cell communication.
• Protection: The carbohydrate portion can act as a protective barrier against harsh extracellular environments.
• Stability: They contribute to the structural stability of the cell surface.

Glycoproteins can be either integral or peripheral, depending on their association with the membrane. Their carbohydrate portions make them ideally suited for interacting with molecules in the cell's external environment, helping the cell to adhere to its surroundings and facilitating communication between cells.