Chapter 5: Structure and Function of Plasma Membranes

active transport

method of transporting material that requires energy

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

aquaporin

channel protein that allows water through the membrane at a very high rate

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 uptake 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

exocytosis

process of passing bulk material out of a cell

facilitated transport

process by which material moves down a concentration gradient (from high to low concentration) using integral membrane proteins

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

glycoprotein

combination of carbohydrates and proteins

hydrophilic

molecule with the ability to bond with water; “water-loving”

hydrophobic

molecule that does not have the ability to bond with water; “water-hating”

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 solutes 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

passive transport

method of transporting material through a membrane that does not require energy

peripheral protein

protein found at the surface of a plasma membrane either on its exterior or interior side

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

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

pump

active transport mechanism that works against electrochemical gradients

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 (also known as semipermeable)

solute

substance dissolved in a liquid to form a solution

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 one specific ion or molecule