Cell Membranes and Transport

Practice vocabulary flashcards generated from Biol 120.03 Lecture 3 on Cell Membranes and Transport.

Amphipathic

Describing a molecule that contains both hydrophobic (water-fearing) and hydrophilic (water-loving) regions.

Phospholipids

The most abundant lipid type in plasma membranes, consisting of a glycerol linked to a phosphate group and an organic molecule forming a polar head, attached to non-polar fatty acid tails.

Fluid Mosaic Model

A model of membrane structure depicting membranes as a fluid lipid bilayer in which proteins are embedded and float freely, drifting laterally.

Frye–Edidin Experiment

An experiment demonstrating membrane fluidity by fusing a human cell labeled with red fluorescent dye and a mouse cell labeled with green fluorescent dye, resulting in completely intermixed surface proteins after $40$\,minutes.

Desaturases

Enzymes that produce unsaturated fatty acids during fatty acid synthesis to regulate membrane fluidity, which are broken down as temperature increases.

Cholesterol (in plasma membrane)

A steroid in animal cell membranes that regulates fluidity by restraining phospholipid movement at warmer temperatures ($37\,^{\circ}\text{C}$) and preventing tight packing at cooler temperatures.

Integral Protein

A membrane protein that penetrates the hydrophobic core of the phospholipid bilayer. Transmembrane proteins are integral proteins that span the entire membrane.

Peripheral Protein

A membrane protein that is not embedded in the lipid bilayer, but sits bound to the membrane surface.

Simple Diffusion

The passive net movement of a substance down its concentration gradient from a region of higher concentration to lower concentration without needing a transport protein or expending chemical energy.

Facilitated Diffusion

Passive transport of molecules across a membrane down their concentration gradient with the assistance of a specific transporter protein, reaching a maximum rate when all transporters are saturated.

Voltage-Gated Transporters

Transporter proteins involved in facilitated diffusion whose activation gates open or close in response to changes in voltage across the membrane.

Carrier Protein

A transport protein that binds a specific single solute and undergoes conformational changes to move the solute-binding site progressively from one side of the membrane to the other.

Osmosis

The passive diffusion of water molecules across a selectively permeable membrane from a solution of lower solute concentration to a solution of higher solute concentration.

Tonicity

The relative solute concentration of solutions separated by a membrane, categorized into hypotonic (lower solute concentration; cells swell), hypertonic (higher solute concentration; cells shrink), and isotonic (equal solute concentration; no net water movement).

Primary Active Transport

An active transport mechanism where the transport protein directly hydrolyzes ATP to power the movement of positively charged ions across a membrane against their concentration gradient.

Sodium–Potassium Pump

A primary active transport protein that hydrolyzes ATP to move $3\,\text{Na}^+$ out of the cell and $2\,\text{K}^+$ into the cell against their respective concentration gradients.

Secondary Active Transport

Transport driven indirectly by ATP hydrolysis, using a favorable concentration gradient of ions established by primary active transport as its energy source.

Symporter

A cotransport protein channel that moves two different molecules across the membrane in the same direction.

Antiporter

A cotransport protein channel that moves two different molecules across the membrane in opposite directions.

Exocytosis

A bulk transport process (secretion) in which secretory vesicles fuse with the plasma membrane to release their contents to the cell exterior.

Endocytosis

A bulk transport process (uptake) in which a segment of the plasma membrane pockets inward and pinches off into an endocytic vesicle to bring extracellular materials into the cell.

Pinocytosis

Also called bulk-phase endocytosis, a non-specific form of endocytosis where the plasma membrane pockets inward to import extracellular water and dissolved solutes without surface receptor binding.

Receptor-Mediated Endocytosis

A selective form of endocytosis where specific target molecules attach to cell surface receptor proteins lined with clathrin before pinching off into a coated endocytic vesicle.