TRANSPORTE ACTIVO Y TRANSPORTE PASIVO (fácil y sencillito)

Transport Mechanisms in Cells

Overview of Cellular Transport

• Cellular transport refers to the movement of substances across the plasma membrane, categorized into passive transport (no metabolic energy required) and active transport (requires energy, e.g., ATP).

• The plasma membrane's lipid bilayer selectively allows substances to pass, maintaining different solute concentrations inside the cell compared to the extracellular environment.

Passive Transport Mechanisms

• Passive transport enables ions and molecules to move through the plasma membrane without metabolic energy, driven by kinetic energy and natural entropy.

• Key types of passive transport include osmosis, simple diffusion, and facilitated diffusion:

• Osmosis: Movement of water molecules through aquaporins from high to low concentration.

• Simple Diffusion: Nonpolar molecules like oxygen and carbon dioxide diffuse directly through the lipid bilayer.

• Facilitated Diffusion: Larger or hydrophilic molecules require channel proteins or carrier proteins for passage.

Detailed Mechanisms of Passive Transport

• Aquaporins are specialized proteins that form pores in the membrane for water movement along its concentration gradient.

• Channel proteins create hydrophilic tunnels allowing polar or charged compounds to bypass the hydrophobic core of the membrane; they are selective for specific molecules.

• Carrier proteins bind solutes and undergo conformational changes to transfer them across membranes while remaining selective.

Active Transport Processes

• Active transport moves ions/molecules against their concentration gradients using energy. This process is essential for maintaining cellular homeostasis.

• ATP serves as a primary energy source for active transport mechanisms; at least three types of transmembrane proteins facilitate this process.

Notable Examples of Active Transport

• The sodium-potassium pump is a key enzyme that expels three sodium ions out while bringing two potassium ions into cells, crucial for maintaining electrochemical gradients.

• The hydrolysis of ATP provides energy necessary for this pump's function, transforming ATP into ADP while releasing a phosphate group.

Coupled Transport Systems

• Increased extracellular sodium due to pumps creates an electrochemical gradient that can drive other substances' transport against their gradients via co-transporters.

Transport Mechanisms in Cells

Active Transport and Antiporters

• Transporters can move substances in opposite directions; these are known as antiporters or counter transporters. An example is the sodium-calcium exchanger, crucial for cellular processes that remove calcium from cells.

• The sodium-calcium exchanger utilizes the energy from the electrochemical gradient of sodium to transport calcium out of the cell.

Types of Active Transport

• When a process consumes metabolic energy derived from ATP, it is classified as primary active transport. Conversely, secondary active transport occurs when a process does not use ATP but relies on an electrochemical gradient.

Light-Activated Pumps

• Light-activated pumps are predominantly found in bacteria and archaea. They facilitate solute transport from lower to higher concentrations by harnessing light energy.