Transport Mechanisms and Cell Membrane Permeability

The cell membrane is a flexible structure with proteins embedded in a lipid bilayer.

Molecules move from high to low concentration.

The difference in the movement of molecules across a membrane.

The point where net movement of molecules stops.

Movement of molecules across a membrane without energy input by the cell.

Movement of molecules across a membrane requiring energy input.

Difference in concentration of a substance between two areas.

Movement of molecules directly through the phospholipid bilayer.

Ion channels can open or close by three mechanisms: ligand-gated, voltage-gated, and mechanically-gated.

Voltage-gated ion channels open or close in response to changes in membrane potential.

Channel conductance refers to the ease with which ions flow through an open ion channel.

Mediated transport involves the movement of molecules across a membrane using transporter proteins, also known as 'carriers'.

Facilitated diffusion uses transporter proteins to move molecules across a membrane down their concentration gradient, without requiring energy from the cell.

The transport maximum (Tm) is the maximum rate at which a substance can be transported across a membrane.

Factors affecting mediated transport include: solute concentration, transporter affinity, number of transporters, and rate of transporter conformational change.

A small, indented region of the plasma membrane that is coated with clathrin proteins. It plays a crucial role in endocytosis by gathering and enveloping targeted molecules.

The process by which a cell takes in substances from its environment, such as nutrients, by engulfing them in a vesicle.

A small, spherical sac formed by the invagination of a clathrin-coated pit. It carries molecules enclosed within the cell.

A protein embedded in the plasma membrane that binds to low-density lipoproteins (LDL), allowing the cell to take in cholesterol.

The process by which a cell transports a substance from one side of the cell to the other while remaining enclosed in a vesicle.

A clathrin-coated pit forms by gathering around target molecules. The pit invaginates, pinching off as a clathrin-coated vesicle. The vesicle sheds its coat and fuses with cellular organelles like endosomes or lysosomes, delivering its contents.

Clathrin proteins form a cage-like structure around specific molecules on the cell membrane, creating the clathrin-coated pit, which then invaginates to form a vesicle.

The vesicle sheds the clathrin coat and fuses with either intracellular organelles like endosomes and lysosomes, or with the membrane on the other side of the cell, in the process of transcytosis.

The LDL receptor and its bound ligand are recycled back to the cell membrane, allowing for repeated uptake of LDL particles.

The strength of the bond between a transporter protein and a solute. Hormones can influence this by changing the number of transporters or their affinity.

A type of active transport that directly uses ATP to move molecules against their concentration gradient. The ATP hydrolysis changes the transporter's shape and binding affinity.

A primary active transporter that pumps sodium ions (Na+) out of the cell and potassium ions (K+) into the cell. This maintains the electrochemical gradient and is essential for cell function.

A type of active transport that uses the energy stored in the electrochemical gradient of one molecule (usually Na+) to move another molecule against its concentration gradient.

The movement of two different molecules across a membrane using the same transporter protein. One molecule moves down its concentration gradient, providing energy to move the other molecule against its gradient.

The Na+/K+-ATPase establishes and maintains the electrochemical gradient of Na+, which is then used by secondary active transporters to move other molecules against their concentration gradient.

A process where cells engulf specific molecules by enclosing them in vesicle pockets formed by clathrin proteins.

The process where cells engulf large particles like bacteria or cell debris, forming a phagosome.

Proteins that form water-permeable channels across cell membranes, facilitating rapid water movement.

The net movement of water across a semi-permeable membrane from a region of high water concentration to low water concentration.

A membrane that allows some molecules to pass through but blocks others.

The pressure required to prevent the movement of water across a semi-permeable membrane. It's related to the difference in solute concentrations between solutions.

Diffusion is the movement of any molecule from a high concentration region to a low concentration region. Osmosis is the specific movement of water across a selectively permeable membrane due to a difference in solute concentration.

A mathematical equation used to calculate osmotic pressure: P = nRT/V, where P is osmotic pressure, n is the number of moles of solute, R is the ideal gas constant, T is the absolute temperature, and V is the volume of the solution.

The total concentration of solute particles in a solution. It's measured in osmoles per liter (Osm).

A solution with an osmolarity of 300 mOsm, similar to the osmolarity of human body fluids and blood plasma.

A solution having the same osmolarity as another solution.

A solution having a lower osmolarity than another solution.

A solution having a higher osmolarity than another solution.

The effect of a solution on the volume of a cell. Tonicity depends on both the total solute concentration (osmolarity) and the permeability of the membrane to the solutes.