Glossary Cell Membranes Chp5

Glossary

A Closer Look at Cell Membranes

Chapter 5 ABC transporter

One of a class of ATP-driven membrane pumps, each for a specific substrate (e.g., ions, sugars, amino acids).

active transport

Pumping of a specific solute across a cell membrane against its concentration gradient, through a transport protein's interior. Requires an energy boost, typically from ATP.

adhesion protein Plasma membrane protein that helps cells locate tissue mates and stick together. biofilm

Huge microbial populations anchored to surfaces (e.g., lung epithelia) by their own sticky, stiff polysaccharide secretions.

bulk flow

In response to a pressure gradient, movement of more than one kind of molecule in the same direction in the same medium.

calcium pump

Active transporter protein specific for calcium ions.

communication protein

Part of a protein complex that forms an open channel between cytoplasm of adjoining cells.

concentration gradient

A difference in the number per unit volume of molecules or ions of a substance between two regions. Molecules collide constantly and careen outward to a region where they are less concentrated. All substances tend to diffuse down such gradients.

diffusion

Net movement of like molecules or ions down their concentration gradient.

electric gradient

Difference in electric charge between adjoining regions.

endocytosis

Cell uptake of substances via vesicle formation. Receptor-mediated endocytosis, phagocytosis, and the bulk transport of extracellular fluid are three modes of endocytosis.

exocytosis

Release of a vesicle's contents at cell surface as it fuses with and becomes part of the plasma membrane.

fluid mosaic model

A cell membrane is a mix of lipids (organized as a bilayer) and proteins. Structural lipids make it largely impermeable to water-soluble molecules yet impart fluidity by packing variations and motions. Diverse proteins perform most membrane functions (e.g., transport, signal reception).

hydrostatic pressure

Pressure exerted by a volume of fluid against a wall, membrane, or some other structure that encloses the fluid.

hypertonic solution

A fluid having a greater solute concentration relative to another fluid.

hypotonic solution

A fluid that has a lower solute concentration relative to another fluid.

isotonic solution A fluid having the same solute concentration as a fluid against which it is being compared. lipid bilayer

Phospholipids, mostly, arranged in two layers; the structural basis of all cell membranes. Hydrophobic tails are sandwiched between the hydrophilic heads; the heads are dissolved in intracellular or extracellular fluid.

osmosis

In response to a water concentration gradient, the diffusion of water between two regions that a selectively permeable membrane separates.

osmotic

Pressure that operates after hydrostatic pressure develops in an enclosed region

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pressure

(e.g., a cell); it counters water's inward diffusion (stops further rises in fluid volume).

passive transport

Event in which a transport protein that spans a cell membrane passively permits a solute to diffuse through its interior. Also called facilitated diffusion.

phagocytosis

Of some cells, engulfment of an extracellular target by way of pseudopod formation and endocytosis.

phospholipid

Organic compound that has a glycerol backbone, two fatty acid tails, and a hydrophilic head of two polar groups (one being phosphate). Phospholipids are the main structural component of cell membranes.

pressure gradient

A difference in pressure between two adjoining regions.

receptor protein

Membrane protein (or cytoplasmic protein) that triggers a change in cell activities after it binds signaling molecule.

recognition protein

One of a class of plasma membrane proteins that distinguish nonself (foreign) from self (belonging to a body tissue).

selective permeability

Of a cell membrane, a capacity to let some substances but not others cross at certain sites, at certain times owing to its bilayer structure and its transport proteins.

sodiumType of membrane transport protein that, when activated by ATP, selectively potassium pump transports potassium ions across a membrane against its concentration gradient, and passively allows sodium ions to cross in the opposite direction. transport protein Membrane protein that passively or actively assists specific molecules or ions across a membrane's lipid bilayer. The solutes pass through a channel in its interior

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