Membranes and Cell Signaling in Physiology

Flashcards covering cell membrane structure, transport mechanisms (passive, active, and vesicular), osmotic conditions, and cell-to-cell signaling principles from Physiology Lecture 2.

Plasma Membrane

The selectively permeable bilayer of amphipathic phospholipids that separates the cell’s interior from the external environment and facilitates necessary chemical reactions.

Amphipathic

A molecule that contains both a polar, hydrophilic region and a nonpolar, hydrophobic region.

Phospholipid Head

The polar, hydrophilic region of a phospholipid consisting of a glycerol, a phosphate, and a charged group containing highly polar covalent bonds.

Phospholipid Tail

The nonpolar, hydrophobic region of a phospholipid comprised of two fatty acid or isoprene chains.

Fluid-Mosaic Model

The model describing the membrane as a dynamic mosaic where lipids and proteins can move laterally throughout the lipid bilayer.

Selective Permeability

The tendency of a membrane to allow small or nonpolar molecules to move across quickly while charged or large polar substances cross slowly, if at all.

Cholesterol

Molecules in the membrane that decrease the permeability of the phospholipid bilayer.

Passive Transport

Transport that does not require energy from the cell, where materials move "down" from an area of higher concentration to an area of lower concentration.

Active Transport

Transport that requires energy ($ATP$ or an electrochemical gradient) to move materials "up" or against their concentration gradient.

Simple Diffusion

The spontaneous movement of small and/or nonpolar (uncharged) molecules, such as $O_2$ or $CO_2$, from high-concentration regions to low-concentration regions.

Osmosis

The special case of diffusion specifically referring to the movement of water from regions of low solute concentration to regions of high solute concentration.

Facilitated Diffusion

The movement of large and/or polar (charged) molecules across the membrane from high to low concentration using specific integral transport proteins.

Bulk Filtration

The simultaneous diffusion of both liquids (solvents) and dissolved molecules (solutes).

Concentration Gradient

A difference in solute concentrations between two regions that creates a spontaneous net movement of molecules to increase entropy.

Integral Proteins

Amphipathic proteins that span the membrane, with segments facing both the interior and exterior surfaces.

Peripheral Proteins

Proteins found only on one side of the membrane, often attached to integral proteins.

Channels

Transmembrane proteins that form a water-filled pore for the passage of specific ions.

Carrier Proteins (Transporters)

Transport proteins that change shape during the transport process to move molecules down their concentration gradient.

Pumps

Membrane proteins that provide active transport of molecules or ions against an electrochemical gradient using energy from $ATP$.

Uniport

A type of carrier protein that moves a single type of solute across the membrane, such as plasma membrane glucose transporters.

Symport

A type of cotransport where two substances are moved in the same direction, such as intestinal glucose transporters.

Electrochemical Gradient

The collective gradient established when ions build up on one side of a membrane, creating both a concentration gradient and a charge gradient.

Ligand-gated Channels

Ion channels that are regulated and opened by the binding of a specific molecule.

$$GLUT-1$$

A specific glucose transporter protein that increases membrane permeability to glucose.

Primary Active Transport

A process where $ATP$ is directly consumed to move a substance against its concentration gradient, such as the $Na^+/K^+\text{-ATPase}$ pump.

$$Na^+/K^+\text{-ATPase}$$

An active transport pump that uses $ATP$ to move $Na^+$ and $K^+$ against their respective concentration gradients.

Secondary Active Transport

Also called cotransport, it uses the energy of an existing ion gradient (usually $Na^+$) to move a second solute against its own gradient.

Vesicular Transport

The energy-dependent transport of materials facilitated by the reorganization of the cytoskeleton and the formation of vesicles.

Exocytosis

The process where materials to be secreted are packaged into vesicles that fuse with the plasma membrane to release contents outside the cell.

Endocytosis

The process where the membrane surface indents to take materials into the cell and package them into vesicles.

Phagocytosis

A type of endocytosis where the cell engulfs a bacterium or other large particle.

Pinocytosis

A non-specific type of endocytosis where the cell takes in extracellular fluid and dissolved solutes.

Receptor-mediated Endocytosis

A specific type of endocytosis triggered by the binding of ligands to membrane receptors.

Hypertonic

A solution with a higher concentration of non-penetrating solutes compared to the inside of the cell, causing the cell to shrink.

Hypotonic

A solution with a lower concentration of non-penetrating solutes compared to the inside of the cell, causing the cell to swell.

Isotonic

A solution where solute concentrations are equal on the outside and inside of the cell, resulting in no net water movement.

Electrical Signals

Physiological signals involving changes in the membrane potential of a cell.

Chemical Signals

Signals secreted by cells into the extracellular fluid (ECF) that are responsible for most communication within the body.

Target Cells

Cells that possess specific receptors to respond to physiological signals.

Lipid-Soluble Messengers

Messengers that diffuse through the plasma membrane to bind with intracellular receptors, altering gene transcription via signal-receptor complexes.

Cross-talk

Complex interactions where active molecules generated in one signal transduction pathway alter the receptors or molecules of another pathway.