Cell Membrane

Cell Membrane

• Consists of a phospholipid bilayer with embedded proteins.
• It is selectively permeable, controlling what enters and exits the cell.

Cell Membrane Transport

• The movement of substances across the cell membrane.
• Two main types: diffusion and active transport.

Diffusion

• The movement of molecules from an area of high concentration to an area of low concentration.
• Does not require energy.
• Two types: simple diffusion and facilitated diffusion.

Simple Diffusion

• The movement of molecules across the cell membrane through intermolecular spaces or with the help of carrier proteins.
• Its movement is based on the kinetic motion of molecules.

Facilitated Diffusion

• The movement of molecules across the cell membrane with the help of carrier proteins.
• Carrier proteins bind to the molecules and facilitate their movement across the membrane.
• Does not require energy.

Aquaporins

• Water channel proteins that facilitate the movement of water across the cell membrane.
• They allow for rapid water movement.
• Important for maintaining cell hydration.

Osmosis

• The movement of water across a semipermeable membrane from an area of high water concentration to an area of low water concentration.

Osmolality

• The concentration of dissolved particles in a solution.
• It is expressed in osmoles per kilogram of solvent.

Osmolarity

• The concentration of dissolved particles in a solution.
• It is expressed in osmoles per liter of solution.

Active Transport

• The movement of molecules across the cell membrane against their concentration gradient.
• Requires energy.

Primary Active Transport

• The energy for transport comes directly from the breakdown of ATP.
• Examples include the sodium-potassium pump and the calcium pump.

Sodium-Potassium Pump

• Pumps sodium ions out of the cell and potassium ions into the cell.
• Maintains the electrochemical gradient across the cell membrane.
• Necessary for nerve and muscle fiber function.

Calcium Pump

• Pumps calcium ions out of the cell.
• Important for maintaining low intracellular calcium concentration.
• Plays a crucial role in muscle contraction and other cellular processes.

Secondary Active Transport

• The energy for transport is derived indirectly from the movement of another substance down its concentration gradient.
• Two types: co-transport and counter-transport.

Co-Transport

• Two molecules move in the same direction across the cell membrane.
• One molecule's concentration gradient drives the movement of the other.
• Example: glucose-sodium co-transport in the small intestine.

Counter-Transport

• Two molecules move in opposite directions across the cell membrane.
• One molecule's concentration gradient drives the movement of the other.
• Example: sodium-hydrogen counter-transport in the kidney tubules.

Voltage-Gated Channels

• Channel proteins that open or close in response to changes in the membrane potential.
• Important for generating and transmitting nerve impulses.
• Examples: sodium channels and potassium channels.

Sodium Channels

• Allow sodium ions to flow into the cell.
• Open when the membrane potential depolarizes.

Potassium Channels

• Allow potassium ions to flow out of the cell.
• Open when the membrane potential repolarizes.

Ligand-Gated Channels

• Channel proteins that open or close in response to the binding of a specific ligand.
• Examples: acetylcholine receptor channels.

Membrane Stabilizers

• Substances that decrease membrane excitability by decreasing the permeability of the membrane to sodium ions.
• Examples: calcium ions.

Local Anesthetics

• Substances that block the activation gates of sodium channels, reducing membrane excitability.
• Examples: lidocaine, procaine.

Test your knowledge on cell membrane structure and transport mechanisms. This quiz covers concepts such as diffusion, facilitated diffusion, and the role of aquaporins. Understand how substances move across the cell membrane effectively.