Question

inpasive transport across a membrane, when two protein roleculs move in opposite direction it is called as (a) inport (b) antiport (d) grport (d) Co-port.

Short answer

The correct answer is (b) antiport.

Step-by-step solution

Understanding Passive Transport

Passive transport refers to the movement of substances across a cell membrane without the need for energy input from the cell. It relies on the inherent kinetic energy of particles, allowing them to move down their concentration gradient.

Identifying the Type of Transport

The question specifies that two protein molecules move in the opposite direction across a membrane. The term for this type of transport needs to be identified from the given options.

Matching Descriptions with Terminology

The movement of substances in opposite directions through a transport protein is termed 'antiport'. An 'antiporter' facilitates the transport of two types of molecules in opposite directions.

Key concepts

Antiport

Antiport systems are integral to the functioning of cells, performing a crucial role in maintaining homeostasis. These systems involve a specific type of passive transport mechanism, wherein two different molecules or ions are moved across a cell membrane in opposite directions. Each movement happens down its own concentration gradient, meaning that no external energy source, such as ATP, is required for the process to occur.

Antiporters, the proteins that facilitate this transport, are embedded within the cell membrane and operate on the principle of a reciprocal exchange. For instance, as one ion moves into the cell, another ion of typically different kind, moves out. A well-known example of an antiporter is the sodium-potassium pump, which plays a critical role in nerve function. Although this pump operates using ATP, its name illustrates the idea of two substances being transported in reverse directions - which is characteristic of antiport systems.

Cell Membrane

The cell membrane, also known as the plasma membrane, is a vital component of all cells. It's a semi-permeable barrier that encases the cell, providing structural support and determining what enters and exits the cell. Structurally, it is mostly made up of lipids and proteins, which form a bilayer that is both flexible and sturdy.

The fluid mosaic model describes the dynamic nature of the cell membrane, where various proteins float in or on the lipid bilayer, much like boats on a sea. These proteins serve many functions, including acting as enzymes, signal receptors, and transport mechanisms for substances across the membrane. Understanding the cell membrane is key to grasping how passive transport, such as antiport or other mechanisms like diffusion and osmosis, operate to regulate the cell's internal environment.

Concentration Gradient

A concentration gradient represents the difference in the concentration of a substance between two regions. Inside cellular contexts, gradients are often measured across the cell membrane, with the substance being more concentrated on one side than the other. This gradient is the driving force behind passive transport, where substances move from areas of higher concentration to areas of lower concentration in an attempt to reach equilibrium.

Molecules will naturally follow their concentration gradient in a spontaneous process that doesn't require energy. This is why substances, including ions, water, and small metabolites, move passively across membranes until their concentrations are equal on both sides, or as close to equal as the system allows. It is crucial for students to understand that the existence of a concentration gradient allows passive transport mechanisms, like simple diffusion, facilitated diffusion, and antiport, to function effectively.