Chapter 1-5: Introduction to Biological Membranes

Vocabulary flashcards covering the structure, composition, properties, and functions of biological membranes, including lipids, proteins, and sugars.

Biological membranes

Structures that separate the inside of a cell from its surroundings and form internal compartments (organelles) within eukaryotic cells.

Plasma membrane

The outer membrane of any cell, serving as a boundary between the cell's interior and its non-living surroundings.

Selective permeability

The property of a cell's plasma membrane that allows some substances to cross it more easily than others, tightly controlling movement.

Organelles

Membrane-bound compartments found inside eukaryotic cells, each with interiors that can differ biochemically from the cytoplasm.

Fluid mosaic model

The fundamental structural model describing biological membranes as a fluid bilayer of lipids with embedded and associated proteins and surface sugars.

Lipids

Relatively small molecules, more complex than simple molecules, that form the primary structural component (bilayer) of biological membranes.

Glycerol

A small three-carbon molecule with three hydroxyl groups, serving as the starting point for building many lipids.

Fatty acid

A long chain of carbons with hydrogens, ending with an organic acid group, that forms the hydrophobic tails of many lipids.

Hydrocarbon tail

The non-polar region of a fatty acid or lipid, composed primarily of carbon and hydrogen atoms, which interacts poorly with water.

Non-polar

Describes molecules or regions where electrons are shared equally between atoms, resulting in no significant partial charges; equivalent to hydrophobic.

Polar

Describes molecules or regions where electrons are unevenly shared, creating partial positive and negative charges; equivalent to hydrophilic.

Phospholipids

The most abundant type of lipid in biological membranes, characterized by a polar phosphate-containing head group and two non-polar fatty acid tails.

Amphipathic molecules

Molecules that possess both non-polar (hydrophobic) and polar (hydrophilic) regions.

Hydrophobic

'Water-fearing'; describes non-polar groups or molecules that do not interact favorably with water.

Hydrophilic

'Water-loving'; describes polar groups or molecules that readily interact with water through hydrogen bonds or charge attractions.

Phosphatidylcholine

The most abundant phospholipid, a primary building block for biological membranes, featuring a choline group in its polar head.

Phospholipid bilayer

A double layer of phospholipids that spontaneously forms the basic structure of biological membranes, with hydrophobic tails oriented inwards and hydrophilic heads oriented outwards towards water.

Hydrophobic interactions

The driving force for the spontaneous formation of phospholipid bilayers, where non-polar tails aggregate to minimize contact with water.

Membrane fluidity

The dynamic characteristic of biological membranes where phospholipids and proteins move constantly within the bilayer.

Lateral movement

The rapid diffusion and swapping of places by phospholipids within the plane of the lipid bilayer.

Unsaturated fatty acids

Fatty acids containing one or more carbon-carbon double bonds, which introduce kinks in the hydrocarbon tails, increasing membrane fluidity.

Saturated fatty acids

Fatty acids containing only single carbon-carbon bonds, resulting in straight hydrocarbon tails that can pack tightly together, decreasing membrane fluidity.

Cholesterol

A rigid, mostly non-polar molecule found in animal membranes (not plant membranes) that moderates membrane fluidity.

Peripheral membrane proteins

Proteins that sit at the surface of the lipid bilayer and primarily interact with the polar head groups of phospholipids or other proteins, not deeply embedded.

Integral membrane proteins

Proteins that are at least partially embedded within the lipid bilayer, either dipping into it or spanning completely across it.

Transmembrane proteins

A type of integral membrane protein that spans entirely across the lipid bilayer, typically containing stretches of non-polar amino acids in alpha helices within the membrane.

Non-polar amino acids

Amino acids whose side chains consist primarily of carbon and hydrogen, making them suitable for forming the segments of integral membrane proteins embedded within the hydrophobic membrane interior.

Alpha helices

A common secondary structure in proteins, often used by transmembrane proteins to span the lipid bilayer with about 19-20 non-polar amino acids per helix.

Fluorescence Recovery After Photobleaching (FRAP)

A technique used to measure the diffusion rates and movement of proteins within a cell membrane by photobleaching a fluorescent region and observing its recovery.

Signal transduction

The process by which cells receive and respond to external stimuli, often involving integral membrane proteins acting as receptors.

Glycocalyx

A 'forest' of sugar chains (oligosaccharides) found on the external surface of cells, attached to either lipids (glycolipids) or proteins (glycoproteins), playing a protective role.

Glycolipid

A lipid molecule with a sugar chain (oligosaccharide) attached, found on the external surface of cell membranes.

Glycoprotein

A protein molecule with a sugar chain (oligosaccharide) attached, found on the external surface of cell membranes.

Oligosaccharides

Medium to long chains of sugar molecules that are abundant on the outer surface of cell membranes, forming part of the glycocalyx.