Membrane Structure and Function

Flashcards covering the structure, composition, and function of cellular membranes.

Plasma Membrane

Defines the exterior of the cell and controls the movement of molecules between the cytosol and the extracellular medium.

Membrane Proteins

Enable each cellular membrane to carry out distinctive activities, such as anchors for cytoskeleton fibers, channels, receptors, and enzymes.

Amphipathic Molecules

Molecules with hydrophilic heads that form hydrogen bonds with water and hydrophobic tails that are excluded by water molecules.

Flippases

Lipids in the outer leaflets are transported by these, contributing to membrane asymmetry.

Fluidity

Important for normal cell growth and reproduction; affected by the composition of fatty acyl chains.

Saturated Fatty Acyl Chains

Pack tightly in the membrane and make it less fluid; contain no double bonds.

Unsaturated Lipids

Pack loosely in the membrane and make it more fluid; contain one, two, or three double bonds.

Short Chains

Melt early, contributing to more fluidity in the membrane.

Long Chains

Have a higher melting point, contributing to low fluidity in the membrane.

Membrane Lipid Composition

The types of phospholipids found in biomembranes, including phosphoglycerides, sphingolipids, and sterols.

Phosphoglycerides

Derivatives of glycerol 3-phosphate; a principal type of biomembrane phospholipid.

Sphingolipids

Derivatives of sphingosine; a principal type of biomembrane phospholipid.

Sterols

Four-ring hydrocarbons; a principal type of biomembrane lipid.

Cholesterol

Determines bilayer fluidity by interacting with fatty acyl chains and tending to immobilize them.

Phosphatidylcholine

Derivatives of glycerol 3-phosphate, most abundant class of membrane lipids

Sphingomyelin

Derivatives of sphingosine; important as a shield in the outer leaflet and in signal transduction.

Cholesterol

Major steroidal constituent of animal cells; a four-ring hydrocarbon.

Membrane Proteins

Can be peripheral, lipid-anchored, or integral, and perform many functions in the membrane.

Peripheral Membrane Proteins

Bound on the surface of the membrane, interacting with polar heads or integral proteins; do not interact with the hydrophobic core.

Lipid-Anchored Proteins

Bound covalently to one or more lipid molecules, anchoring the protein to the membrane.

Integral Membrane Proteins

Have one or more protein segments embedded in the phospholipid layer.

Transmembrane Integral Proteins

Have one or more membrane spanning domains with hydrophobic amino acid residues embedded in the bilayer.

Beta-Barrel

Proteins that use beta-sheets arranged in a cylindrical conformation to cross the bilayer.

Multipass Membrane Proteins

Transmembrane proteins containing two or more membrane spanning alpha helical domains.

Bacteriorhodopsin

A protein found in photosynthetic bacteria with seven transmembrane alpha-helices; uses a retinal pigment to absorb light and pump protons.

FRAP (Fluorescence Recovery After Photobleaching)

A technique used to demonstrate membrane fluidity by labeling membrane proteins and observing their movement after photobleaching.