5.1-5.4 - Structure, Function, & Transport of Plasma Membranes

active transport

method of transporting material that requires energy: moves substances against their concentration gradient, from areas of lower concentration to areas of higher concentration, utilizing ATP.

amphiphilic

molecule possessing a polar or charged area and a nonpolar or uncharged area capable of interacting with both hydrophilic and hydrophobic environments.

antiporter

transporter that carries two ions or small molecules in different directions. exchanges one substance for another across the membrane.

aquaporin

channel protein that allows water through the membrane at a very high rate: facilitate the passive transport of water molecules, enabling rapid response to osmotic changes in cells.

carrier protein

membrane protein that moves a substance across the plasma membrane by changing its own shape.

caveolin

protein that coats the cytoplasmic side of the plasma membrane and participates in the process of liquid update by potocytosis.

channel protein

membrane protein that allows a substance to pass through its hollow core across the plasma membrane.

clathrin

protein that coats the inward-facing surface of the plasma membrane and assists in the formation of specialized structures, like coated pits, for phagocytosis.

concentration gradient

area of high concentration adjacent to an area of low concentration.

diffusion

passive process of transport of low-molecular weight material according to its concentration gradient.

electrochemical gradient

gradient produced by the combined forces of an electrical gradient and a chemical gradient.

electrogenic pump

pump that creates a charge imbalance.

endocytosis

type of active transport that moves substances, including fluids and particles, into a cell: process involves the engulfing of substances by the plasma membrane, forming a vesicle.

exocytosis

process of passing bulk material out of a cell: process involves the fusion of vesicles with the plasma membrane, allowing the contents to be released into the extracellular space.

facilitated transport

process by which material moves down a concentration gradient (from high to low concentration) using integral membrane proteins: this transport does not require energy input.

fluid mosaic model

describes the structure of the plasma membrane as a mosaic of components including phospholipids, cholesterol, proteins, glycoproteins, and glycolipids (sugar chains attached to proteins or lipids, respectively), resulting in a fluid character (fluidity).

glycolipid

combination of carbohydrates and lipids: vital components of the plasma membrane that play key roles in cell recognition, signaling, and maintaining membrane stability.

glycoprotein

combination of carbohydrates and proteins: important for cell recognition, signaling, and immune response, and contribute to the stability of the plasma membrane.

hydrophilic

molecule with the ability to bond with water, “water-loving” due to polar or charged regions that allow interactions with water molecules.

hydrophobic

molecule that does not have the ability to bond with water, “water-hating” due to nonpolar regions that repel water molecules.

hypertonic

situation in which extracellular fluid has a higher osmolarity than the fluid inside the cell, resulting in water moving out of the cell.

hypotonic

situation in which extracellular fluid has a lower osmolarity than the fluid inside the cell, resulting in water moving into the cell.

integral protein

protein integrated into the membrane structure that interacts extensively with the hydrocarbon chains of membrane lipids and often spans the membrane: these proteins can be removed only by the disruption of the membrane by detergents.

isotonic

situation in which the extracellular fluid has the same osmolarity as the fluid inside the cell, resulting in no net movement of water into or out of the cell.

osmolarity

total amount of substances dissolved in a specific amount of solution.

osmosis

transport of water through a semipermeable membrane according to the concentration gradient of water across the membrane that results from the presence of solute that cannot pass through the membrane: leads to the movement of water from an area of lower solute concentration to an area of higher solute concentration.

passive transport

method of transporting material through a membrane that does not require energy: occurs along the concentration gradient, allowing substances to move from areas of higher concentration to lower concentration without the use of ATP.

peripheral protein

protein found at the surface of a plasma membrane either on its exterior or interior side: these proteins can be removed (washed off of the membrane) by a high-salt wash.

pinocytosis

a variation of endocytosis that imports macromolecules that the cell needs from the extracellular fluid.

plasmolysis

detaching of the cell membrane from the cell wall and constriction of the cell membrane when a plant cell is in a hypertonic solution: results in the cell losing water, causing it to shrink and potentially leading to cell death.

potocytosis

variation of pinocytosis that uses a different coating protein (caveolin) on the cytoplasmic side of the plasma membrane.

primary active transport

active transport that moves ions or small molecules across a membrane and may create a difference in charge across that membrane: requires energy, usually from ATP, to move substances against their concentration gradient.

pump

active transport mechanism that works against electrochemical gradients: uses specific proteins to move ions or molecules across the plasma membrane, typically powered by ATP.

receptor-mediated endocytosis

variation of endocytosis that involves the use of specific binding proteins in the plasma membrane for specific molecules or particles, and clathrin-coated pits that become clathrin-coated vesicles.

secondary active transport

movement of material that is due to the electrochemical gradient established by primary active transport.

selectively permeable

characteristic of a membrane that allows some substances through but not others.

solute

substance dissolved in a liquid to form a solution: can be a solid, liquid, or gas that is present in a lesser amount compared to the solvent.

symporter

transporter that carries two different ions or small molecules, both in the same direction.

tonicity

amount of solute in a solution.

transport protein

membrane protein that facilitates passage of a substance across a membrane by binding it.

transporter

specific carrier proteins or pumps that facilitate movement.

uniporter

transporter that carries on specific ion or molecule: allows the movement of a single type of substance across the membrane.