Membrane Structure, Transport, Cell Surface Modifications, and Water Potential

Vocabulary flashcards covering plasma membrane structure and function, passive and active transport mechanisms, cell surface modifications, and water potential calculations.

Plasma Membrane

Structure that separates internal cytoplasm from external, incompatible chemical reactions.

Fluid Mosaic Model

Model describing the plasma membrane structure consisting of a phospholipid bilayer with embedded peripheral and integral proteins, lipids, and cholesterol regulating fluidity.

Phospholipid Bilayer

Membrane structure with hydrophilic polar heads facing the exterior and cytoplasm, and nonpolar hydrophobic fatty acid tails situated between them.

Glycoproteins

Proteins with attached carbohydrate chains located on the outside of the membrane, used in cell identification and blood/tissue recognition.

Glycolipids

Lipids with attached carbohydrate chains on the outside of the membrane that contribute to membrane asymmetry.

Channel Proteins

Proteins that allow the passage of specific molecules directly through the plasma membrane.

Carrier Proteins

Proteins that combine with specific transported substances to assist their passage across the membrane.

Cell Recognition Proteins

Glycoproteins in the plasma membrane that identify foreign substances.

Receptor Proteins

Proteins that bind with specific molecules to respond to cellular signals from other cells.

Enzymatic Proteins

Membrane proteins that directly carry out metabolic reactions.

Junction Proteins

Proteins involved in attaching adjacent cells to one another.

Aquaporins

Specialized protein channels that speed up water transport across the plasma membrane.

Diffusion

The net movement of molecules down a concentration gradient from high to low concentration until solute concentration is uniform.

Equilibrium

The state reached when net movement of molecules stops and solute concentration is uniform throughout a solution.

Osmosis

The diffusion of solvent (water) across a membrane toward a lower water (higher solute) concentration when solute cannot pass.

Isotonic Solution

A solution with the same solute concentration as the cell, resulting in no net gain or loss of water.

Hypotonic Solution

A solution with a lower solute concentration than the cell, causing water to enter the cell, leading to swelling or lysing in animal cells and turgor pressure in plant cells.

Hypertonic Solution

A solution with a higher solute concentration than the cell, causing water to leave the cell, leading to crenation in animal red blood cells and plasmolysis in plant cells.

Facilitated Transport

Movement of molecules (such as glucose and amino acids) down their concentration gradient through carrier proteins without energy expenditure.

Active Transport

Movement of molecules against their concentration gradient (low to high concentration) facilitated by specific carrier proteins and requiring energy expenditure ($ATP$).

Sodium-Potassium Pump

An active transport mechanism that uses $ATP$ to move sodium ions out of the cell and potassium ions into the cell against their concentration gradients through carrier protein shape changes.

Exocytosis

A form of bulk transport where vesicles fuse with the plasma membrane to secrete contents outside the cell.

Endocytosis

A form of bulk transport where the cell membrane engulfs substances into a pouch or vesicle to move particles inside the cell.

Phagocytosis

A form of endocytosis where large solid materials (such as debris or viruses engulfed by human white blood cells) are taken into the cell.

Pinocytosis

A form of endocytosis where vesicles form around liquids or very small particles, also known as cell drinking.

Receptor-Mediated Endocytosis

A specific form of pinocytosis utilizing receptor proteins and a coated pit to take in targeted substances.

Extracellular Matrix (ECM)

A meshwork of proteins and polysaccharides produced by cells and maintained in close connection with them to support structure and assist cell signaling.

Collagen

A protein component of the ECM that resists stretching.

Elastin

A protein component of the ECM that provides resilience.

Fibronectin

An adhesive protein in the ECM that binds antigens.

Integrin

A membrane-associated protein that plays a key role in cell signaling within the ECM.

Proteoglycans

ECM components attached to long centrally placed polysaccharides that resist compression and regulate material passage.

Adhesion Junctions

Connections composed of intercellular filaments between cells, including internal cytoplasmic plaques known as desmosomes.

Tight Junctions

Cellular junctions where plasma membranes form impermeable barriers between cells.

Gap Junctions

Joined plasma membrane channels that allow communication between cells, as seen in heart and smooth muscle.

Plasmodesmata

Channels penetrating plant cell walls that contain strands of cytoplasm to allow passage of materials between adjacent plant cells.

Water Potential ($\Psi$)

Measure of potential energy in water that predicts the direction water will move, defined by the equation $\Psi = \Psi_p + \Psi_s$.

Pressure Potential ($\Psi_p$)

The physical hydrostatic pressure exerted by water inside a plant cell or tissue.

Solute Potential ($\Psi_s$)

The measure of change in water potential due to solute molecules lowering free energy, calculated as $\Psi_s = -iCRT$.

Solute Potential Equation Variables

In $\Psi_s = -iCRT$, $i$ represents the ionization constant ($1.0$ for sucrose), $C$ is the molar concentration, $R$ is the pressure constant ($0.0831\,\text{liter bars mol}^{-1}\text{K}^{-1}$), and $T$ is the temperature in Kelvin ($\text{K} = {^\circ}\text{C} + 273$).