Lecture 2: Transport across cell membranes

Flashcards for Lecture 2: Transport across cell membranes

Passive Transport

Moves substances down their concentration or electrochemical gradients using only their kinetic energy.

Active Transport

Uses energy to drive substances against their concentration or electrochemical gradients.

Non-mediated Transport

Does not directly use a transport protein for substance movement across membranes.

Mediated Transport

Moves materials with the help of a transport protein.

Diffusion through Lipid Bilayer

A type of non-mediated transport important for nutrient absorption and waste excretion, involving nonpolar, hydrophobic molecules.

Ion Channels

Water-filled pores lined by hydrophilic amino acids that shield ions from the hydrophobic core of the lipid bilayer, allowing rapid ion transport.

Ionic Selectivity

The property of ion channels where specific amino acids lining the pore determine the channel's selectivity to ions.

Channel Gating

The control of channel opening and closing by gates, which can be influenced by stimuli like voltage, ligand binding, cell volume, pH, or phosphorylation.

Patch Clamp Technique

A method used to measure ion channel function by recording the electrical current flowing through an individual channel.

Carrier Mediated Transport

Transport where the substrate directly interacts with a transporter protein, leading to slower transport rates due to conformational changes.

Specificity (Transporter)

Transport proteins exhibit specificity, similar to enzymes, in that they only bind and transport certain molecules.

Saturation (Transporter)

Transport proteins display enzyme kinetics and can become saturated when all binding sites are occupied.

Facilitated Diffusion

Passive transport mediated by a transport protein, such as GLUT, that changes shape to move glucose across the cell membrane down its concentration gradient.

Primary Active Transport

Active transport where energy is directly derived from the hydrolysis of ATP.

Secondary Active Transport

Active transport where energy stored in an ionic concentration gradient is used to drive the transport of a molecule against its gradient.

Na+/K+ ATPase

A primary active transporter that removes 3 Na+ ions from the cell and brings 2 K+ ions into the cell, generating a net current and maintaining ion concentrations.

Na+ Pump Function

Maintains low Na+ and high K+ concentrations in the cytosol, crucial for resting membrane potential, electrical excitability, muscle contraction, cell volume, nutrient uptake and intracellular pH.

Na+ Antiporter (Exchanger)

A secondary active transporter where Na+ ions rush inward and Ca2+ or H+ ions are pushed out.

Na+ Symporter (Cotransporter)

A secondary active transporter where glucose or amino acids rush inward together with Na+ ions.

Osmosis

Net movement of water through a selectively permeable membrane from an area of high water concentration to an area of lower water concentration.

Aquaporins

Water channels (9 isoforms) that mediate water transport across cell membranes (Pf) and are mercury sensitive and temp independent.

Explain the Non- mediated transport: diffusion through the lipid bilayer

It is important for nutrient absorption and excretion of wastes
- Is nonpolar, hydrophobic molecules - (O2, CO2, Nitrogen, fatty acids, steroids, small alcohols, ammonia and fat soluble vitamins (A, E, D, K)