Cell Membrane Structure and Signaling

Vocabulary practice flashcards covering membrane structure, fluidity, membrane protein classes and functions, carbohydrates, and selective permeability.

Hydrophobic Interactions in Membranes

The primary weak forces holding biological membranes together, which are much weaker than covalent bonds and allow lipids and some proteins to shift sideways in the plane of the membrane.

Phospholipid Lateral Movement

The rapid shifting of adjacent phospholipids switching positions about $107$ times per second, allowing a phospholipid to travel about $2\,\text{mm}$ (the length of a typical bacterial cell) in $1\,\text{second}$.

Unsaturated Hydrocarbon Tails

Kinked hydrocarbon tails of phospholipids that prevent tight packing together, thereby enhancing membrane fluidity.

Saturated Hydrocarbon Tails

Straight hydrocarbon tails of phospholipids that pack tightly together, thereby increasing membrane viscosity.

Cholesterol in Animal Cell Membranes

A membrane steroid that reduces membrane fluidity at moderate temperatures by restraining phospholipid movement, but hinders solidification at low temperatures by disrupting the regular packing of phospholipids.

Fluid Mosaic Model

A structural depiction of biological membranes as a collage of various proteins, often clustered together in groups, embedded in the fluid matrix of the lipid bilayer.

Integral Proteins

Membrane proteins that penetrate the hydrophobic interior of the lipid bilayer, typically having nonpolar stretches of $20\text{--}30$ amino acids usually coiled into $\alpha$ helices.

Transmembrane Proteins

The majority of integral proteins that span completely across the hydrophobic interior of the membrane.

Peripheral Proteins

Proteins that are not embedded in the lipid bilayer at all, but are loosely bound to the membrane surface, often to exposed parts of integral proteins.

Transport Proteins

Membrane proteins that provide a hydrophilic selective channel for solutes or shuttle substances by changing shape, sometimes hydrolyzing $\text{ATP}$ to actively pump molecules across.

Enzymatic Membrane Proteins

Proteins built into the membrane with active sites exposed to adjacent solutions, sometimes organized in teams to carry out sequential steps of a metabolic pathway.

Signal Transduction Receptors

Membrane proteins with specific binding sites fitting chemical messengers (such as hormones) that change shape to relay external messages to the cell interior.

Cell-Cell Recognition

A cell's ability to distinguish one type of neighboring cell from another by binding to extracellular surface molecules (often carbohydrates), essential for tissue sorting in embryos and immune defense against foreign cells.

Intercellular Joining

A long-lasting membrane protein function in which proteins of adjacent cells hook together in junctions, such as gap junctions or tight junctions.

Attachment to Cytoskeleton and ECM

The noncovalent bonding of membrane proteins to microfilaments or extracellular matrix fibers, helping maintain cell shape, stabilize protein locations, and coordinate extracellular and intracellular changes.

Membrane Carbohydrates

Short, branched chains of fewer than $15$ sugar units on the extracellular side of the plasma membrane that function as distinguishing surface markers.

Glycolipids

Molecules formed when membrane carbohydrates are covalently bonded directly to lipids.

Glycoproteins

Molecules formed when membrane carbohydrates are covalently bonded to proteins, often serving as identification tags recognized by other cells.

ABO Blood Groups

The four human blood types designated A, B, AB, and O that reflect variations in the carbohydrate portion of glycoproteins on red blood cell surfaces.

Selective Permeability

An emergent property of biological membranes that allows some substances to cross more easily than others, enabling the regulation of molecular traffic across cellular boundaries.