Membrane Transport Lecture Notes Review

Flashcards covering membrane transport mechanisms, Fick's Law, osmosis, concentration units, active transport, and vesicular transport based on lecture notes.

What are the two main categories of transport based on energy requirements?

Passive Transport (downhill movement along a gradient without energy) and Active Transport (uphill movement against a gradient requiring ATP).

What are the two types of Passive Transport?

Simple diffusion and facilitated diffusion.

What characterizes the movement of atoms or molecules in Simple Diffusion?

Net movement from a region of high concentration to a region of low concentration due to random Brownian movement.

Which substances can pass directly through the lipid bilayer during Simple Diffusion?

Fat-soluble (lipid-soluble) substances such as Oxygen ($O_2$), Carbon Dioxide ($CO_2$), alcohol, fatty acids, and steroid hormones.

How are protein channels classified by their gating mechanisms?

Non-gated always open (leak channels), Ligand-gated (response to chemical messengers like $ATP$ or $cAMP$), Voltage-gated (response to membrane potential changes), and Mechanically-gated (response to physical stretch).

What is the Transport Maximum ($V_{max}$) in facilitated diffusion?

The point at which the process becomes saturable because all carrier proteins (transporters) are busy, preventing the rate of transport from increasing further.

What is Fick's First Law of diffusion?

The magnitude of the net flux ($J$) is calculated as $J = D \times A \times \frac{(C_o - C_i)}{X}$, where $D$ is the diffusion coefficient, $A$ is surface area, and $X$ is the membrane thickness.

Define Osmosis.

The net diffusion of water across a semipermeable membrane toward the side with a higher concentration of non-penetrating solutes.

What are aquaporins?

Specialized integral membrane proteins that act as channels specifically for water.

What is the difference between Isotonic and Isoosmotic solutions?

Isotonic solutions have the same concentration of non-penetrating solutes as ECF (cell size remains unchanged), while Isoosmotic solutions have the same concentration of all solutes as ECF.

What are the typical plasma values for Osmolarity and Osmolality?

Osmolarity is $300\,mosmol/L$ and Osmolality is $285 \pm 10\,mosmol/kg$.

How does the $Na^+/K^+\text{-ATPase}$ pump operate as a Primary Active Transport mechanism?

It acts as an ATPase enzyme to split $ATP$ for energy, pumping $3\,Na^+$ out of the cell and $2\,K^+$ into the cell.

Differentiate between Cotransport (Symport) and Countertransport (Antiport) in Secondary Active Transport.

In Cotransport (Symport), both substances move in the same direction; in Countertransport (Antiport), substances move in opposite directions (e.g., $Na^+/Ca^{2+}$ exchange).

What are the energy and ion requirements for Exocytosis and Endocytosis?

Both require energy ($ATP$) and are $Ca^{2+}$ dependent.

What proteins facilitate the fusion of secretory vesicles with the membrane during Exocytosis?

SNARE proteins.

What are the three types of Endocytosis?

1. Phagocytosis ("cell eating"), 2. Pinocytosis ("cell drinking"), and 3. Receptor-mediated endocytosis (using clathrin-coated pits).

How do cholesterol levels affect membrane permeability?

High cholesterol levels typically decrease membrane fluidity and permeability.

How does glucose transport differ between most cells and the kidneys/gut?

In most cells, glucose is transported by facilitated diffusion (passive), but in the kidneys and gut, it is transported by secondary active transport.

Molarity

Amount of substance per unit volume of solvent

Mol/L

Osmolarity

Concentration of all osmotically active particles per volume

Osmol/L

Molality

Amount of substances per unit mass of solvent

Mol/kg

Osmolality

Particles per mass of solvent

Osmol/kg