Biological Membranes and Transport Mechanisms

Flashcards covering key vocabulary related to biological membranes, transport mechanisms, concentration gradients, osmosis, and different types of membrane proteins.

Biological Membranes

Thin, fluid structures surrounding cells, containing floating proteins, and constantly moving.

Selective Permeability Barrier

The primary function of a biological membrane, controlling what enters and exits a cell to maintain distinct internal and external chemical compositions.

Membrane Transport Proteins

Proteins embedded in biological membranes responsible for recognizing and moving specific molecules or ions across the membrane.

Concentration Gradient

A difference in the concentration of molecules or ions across a barrier, leading to a natural tendency for movement from high to low concentration.

Movement Down a Concentration Gradient

The natural, spontaneous movement of molecules or ions from an area of higher concentration to an area of lower concentration, which releases energy.

Movement Against a Concentration Gradient

The non-spontaneous movement of molecules or ions from an area of lower concentration to an area of higher concentration, which requires an input of energy.

Sodium-Potassium Gradients

Electrochemical gradients across cell membranes characterized by high potassium inside and low sodium inside, sustained by active transport.

Osmolarity

A measure of the total concentration of all solutes in a solution.

Osmosis

The process by which water moves naturally to regions of higher solute concentration (higher osmolarity).

Hypertonic Solution

A solution with a higher solute concentration than inside a cell, causing water to move out and the cell to shrink (crenate).

Hypotonic Solution

A solution with a lower solute concentration than inside a cell, causing water to move in and the cell to swell and potentially burst.

Crenation

The process of a cell shriveling or shrinking due to water loss in a hypertonic solution.

Cell Wall

A rigid outer layer in plant cells (made of cellulose) that provides structural strength and prevents excessive swelling under hypotonic conditions.

Simple Diffusion

The passive movement of hydrophobic (oil-soluble) molecules across a membrane by dissolving directly in the lipid bilayer and moving down their concentration gradient.

Hydrophilic Molecules

Water-loving, often charged or polar molecules (e.g., ions, sugars, amino acids) that cannot cross membranes by simple diffusion and require transport proteins.

Integral Membrane Proteins

Proteins that are permanently embedded in the lipid bilayer, often spanning it, and are crucial for membrane functions like transport.

Channels

Integral membrane proteins that form a hydrophilic pore across the membrane, allowing specific ions to rapidly diffuse through when open, typically in response to signals.

Pore

An aqueous pathway or opening within a channel protein that permits the rapid diffusion of specific ions across a biological membrane.

Carriers

Integral membrane proteins that bind to specific solutes and transport them across the membrane by undergoing a conformational (shape) change, a slower and more selective process than channels.

Conformational Change

A change in the three-dimensional shape of a carrier protein, necessary for binding a solute on one side and releasing it on the other side of the membrane.

Uniporter

A type of carrier protein that transports a single specific solute across a membrane (e.g., glucose transporter in red blood cells).

Symporter

A type of carrier protein that transports two or more different solutes in the same direction across a membrane simultaneously.

Antiporter

A type of carrier protein that transports two or more different solutes in opposite directions across a membrane.

Passive Transport

The movement of molecules or ions across a membrane down their concentration gradient, which does not require direct cellular energy input.

Facilitated Diffusion

A type of passive transport where specific transport proteins (channels or carriers like uniporters) assist the movement of solutes across a membrane down their concentration gradient.

Active Transport

The movement of molecules or ions across a membrane against their concentration gradient, which requires the cell to expend energy.

Primary Active Transport

Active transport that directly uses energy released from the hydrolysis of ATP to pump solutes against their concentration gradient.

Sodium-Potassium Pump

A primary active transporter (carrier protein) that uses ATP to pump three sodium ions out of the cell and two potassium ions into the cell, maintaining crucial electrochemical gradients.

Secondary Active Transport

Active transport that uses the energy released from the movement of one solute down its electrochemical gradient (often established by primary active transport) to simultaneously move another solute against its concentration gradient.

Sodium-Glucose Symporter

A secondary active transporter found in the intestine and kidney that co-transports sodium (down its gradient) and glucose (against its gradient) into cells.