Cell Membrane Transport Lecture Notes

Vocabulary terms and definitions related to passive and active transport mechanisms, osmolarity, neuronal ion exchange, and vesicular transport based on the provided lecture transcript.

Semi-permeable

A quality of cellular membranes where only certain materials freely cross, while large and charged substances are typically blocked.

Selective

A quality of cellular membranes where membrane proteins regulate the passage of material that cannot freely cross.

Passive Transport

The movement of material along a concentration gradient (high to low) without the expenditure of energy ($ATP$ hydrolysis).

Simple Diffusion

The passive movement of small or lipophilic molecules (e.g. $O_2$, $CO_2$) along a concentration gradient until equilibrium is reached.

Osmosis

The net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration.

Facilitated Diffusion

The passive movement of large or charged molecules across the cell membrane via the aid of membrane proteins (channel or carrier proteins).

Active Transport

The movement of materials against a concentration gradient (low to high) requiring the expenditure of energy (e.g. $ATP$ hydrolysis).

Primary active transport

Direct use of metabolic energy ($ATP$ hydrolysis) to mediate the movement of materials against a concentration gradient.

Secondary active transport

Indirectly coupling the transport of a molecule with another molecule moving along its electrochemical gradient.

Cotransport

The coupled transport of two distinct molecules across a membrane.

Uniport

The movement of a single molecule across a membrane.

Symport

The coupled transport of two distinct molecules in the same direction.

Antiport

The coupled transport of two distinct molecules in opposite directions.

Sodium-potassium pump

An integral protein and antiporter that uses $ATP$ hydrolysis to exchange $3$ sodium ($Na^+$) ions out of the cell for $2$ potassium ($K^+$) ions into the cell.

Osmolarity

A measure of solute concentration defined by the number of osmoles of a solute per litre of solution ($osmol/L$).

Hypertonic

A solution with a relatively higher osmolarity (high solute concentration) that causes a cell to lose water.

Hypotonic

A solution with a relatively lower osmolarity (low solute concentration) that causes a cell to gain water.

Isotonic

A solution that has the same osmolarity as another solution, resulting in no net water flow.

Crenation

The effect in animal cells where water leaves the cell in a hypertonic solution causing it to shrivel.

Lysis

The effect in animal cells where water enters the cell in a hypotonic solution causing it to swell and potentially burst.

Plasmolysis

In plant tissues, the shrinking of the cytoplasm in a hypertonic solution while the cell wall maintains shape.

Turgor

In plant tissues, the expansion of the cytoplasm in a hypotonic solution that is constrained by the cell wall.

Carrier Proteins

Integral glycoproteins that bind specific solutes and undergo conformational changes, transporting at a rate of approximately $1,000$ molecules per second.

Channel Proteins

Integral lipoproteins containing a pore for ion-selective transport along a concentration gradient; they are often gated and faster than carrier proteins.

Depolarization

An electrical change within a neuron from a negative to positive charge ($-70\text{ mV}$ to $+30\text{ mV}$) caused by $Na^+$ influx via sodium channels.

Repolarization

An electrical change within a neuron from a positive to negative charge ($+30\text{ mV}$ to $-80\text{ mV}$) caused by $K^+$ efflux via potassium channels.

Endoplasmic Reticulum (ER)

A membranous network that synthesizes secretory proteins (Rough ER with ribosomes) or lipids and carbohydrates (Smooth ER).

Golgi Apparatus

An organelle that receives materials at its cis face and sorts/modifies them before release from the trans face for secretion or lysosome transport.

Constitutive secretion

The default pathway for secretion used to replenish material at the plasma membrane and membrane-bound organelles.

Regulatory secretion

A process where secreted material is stored in intracellular vesicles until a signal triggers its release.

Endocytosis

A process by which large substances enter the cell without crossing the membrane via the formation of an invagination and intracellular vesicle.

Phagocytosis

A type of endocytosis by which solid substances are ingested by the cell.

Pinocytosis

A type of endocytosis by which liquids or dissolved substances are ingested by the cell.

Exocytosis

The active process by which vesicles fuse with the plasma membrane to expel large substances into the extracellular environment.