Chapter 5 Structure & Function of Plasma Membranes

Vocabulary flashcards covering the components, structure, and transport mechanisms of plasma membranes including the fluid mosaic model, types of passive and active transport, and bulk transport processes.

Fluid Mosaic Model

States that a membrane is a fluid structure with a "mosaic" of various proteins embedded in a fluid matrix of the lipid bilayer.

Selective Permeability

The property of the plasma membrane that allows some substances to cross it more easily than others.

Amphipathic

A molecule, such as a phospholipid, containing both hydrophobic and hydrophilic regions.

Cholesterol

A sterol found in animal cell membranes that helps regulate fluidity relative to temperature changes.

Phytosterols

The group of sterols found in the membranes of plants.

Fucosterol

The specific sterol found in the membranes of algae.

Ergosterol

The sterol found in the membranes of fungi and yeast.

Hopanoids

Components found in bacteria that are not sterols but serve similar functions in the membrane.

Integral Proteins

Proteins integrated completely into the bilayer that span the membrane and are often amphipathic in nature.

Peripheral Proteins

Proteins that occur only on the exterior or interior surfaces of the membrane, typically serving as enzymes or structural attachments.

Glycoproteins

Carbohydrates bound to membrane proteins that function in cell-cell recognition and attachment.

Glycolipids

Carbohydrates bound to a phospholipid on the exterior surface of the plasma membrane.

gp 120

A glycoprotein used by HIV to adhere to the human immune cell $CD4$ receptor.

Endomembrane System

A group of membranes and organelles including the Endoplasmic Reticulum (ER), Golgi apparatus, Nuclear Envelope, Plasma Membrane, and Lysosomes.

Diffusion

The tendency for molecules of any substance to spread out evenly into the available space, moving down their concentration gradient.

Facilitated Diffusion

The movement of substances down their concentration gradients using transmembrane proteins like channel or carrier proteins.

Aquaporins

Specific water channels that allow for the bulk transport of water across the hydrophobic plasma membrane.

Carrier Proteins

Proteins that bind to a specific substance, change conformation (shape), and carry the substance to the other side of the membrane.

Osmosis

A special type of diffusion involving the movement of water across a semipermeable membrane from areas of low solute concentration to high solute concentration.

Tonicity

The ability of a solution to cause a cell to gain or lose water, affecting its volume through osmosis.

Isotonic

A solution where the concentration of solute is the same as the cell, resulting in no net movement of water.

Hypotonic

A solution describing where the concentration of solute is lower than the cell, causing the cell to gain water.

Hypertonic

A solution describing where the concentration of solute is higher than the cell, causing the cell to lose water.

Osmoregulation

The process by which organisms control water flow and solute concentrations within their cells or bodies.

Active Transport

The movement of molecules against their concentration gradient (low to high) requiring energy input, usually in the form of $ATP$.

Uniporter

A carrier protein that carries one molecule or ion.

Symporter

A carrier protein that carries two different molecules or ions in the same direction.

Antiporter

A carrier protein that carries two different molecules or ions in opposite directions.

Sodium-Potassium Pump

A primary active transport mechanism that moves $3\,Na^+$ out and $2\,K^+$ in using one $ATP$.

Electrochemical Gradient

A gradient of ions across a membrane arising from the combined effects of concentration and electrical gradients.

Electrogenic Pump

A transport protein that generates voltage across a membrane.

Secondary Active Transport

Transport that uses an electrochemical gradient as an energy source to move ions or molecules up their concentration gradient.

Bulk Transport

The import or export of molecules or particles, such as large proteins or macromolecules, that are too large to pass through a transport protein.

Endocytosis

A type of bulk transport where the cell takes in molecules by forming new vesicles from the plasma membrane.

Exocytosis

A type of bulk transport where transport vesicles migrate to the plasma membrane, fuse with it, and release contents to the extracellular environment.

Phagocytosis

A type of endocytosis commonly referred to as "cellular eating."

Pinocytosis

A type of endocytosis commonly referred to as "cellular drinking."