Lecture 2: Transport across Cell Membranes

Flashcards on Transport across Cell Membranes

What is Non-mediated transport?

Transport that does not directly use a transport protein.

What is Mediated transport?

Transport that moves materials with the help of a transport protein.

What is Passive transport?

Transport that moves substances down their concentration or electrochemical gradients with only their kinetic energy.

What is Active transport?

Transport that uses energy to drive substances against their concentration or electrochemical gradients.

What molecules can diffuse through the lipid bilayer?

Nonpolar, hydrophobic molecules such as oxygen, carbon dioxide, nitrogen, fatty acids, steroids, small alcohols, ammonia and fat-soluble vitamins (A, E, D and K).

What is the ion selectivity filter?

Specific amino acids lining the pore that determine the channel's selectivity to ions.

What stimuli can control (gate) channel opening and closing?

Voltage, ligand binding, cell volume (stretch), pH, phosphorylation.

What is the mode of action for carrier mediated transport?

The substrate to be transported directly interacts with the transporter protein.

What properties do transport proteins exhibit?

Specificity, Inhibition, Competition, Saturation (transport maximum).

What is transporter saturation?

Glucose transport occurs until all binding sites are saturated.

What happens in facilitated diffusion of glucose?

Glucose binds to transport protein (GLUT), protein changes shape, kinase enzyme reduces glucose concentration.

What is Primary active transport?

Energy is directly derived from the hydrolysis of ATP.

What is Secondary active transport?

Energy stored in an ionic concentration gradient is used to drive the active transport of a molecule against its gradient.

What occurs with the Na/KATPase pump?

3 Na+ ions removed from cell as 2 K+ brought into cell, generates a nett current and is electrogenic.

Why is the Na and K concentration gradient important?

Maintain resting membrane potential, electrical excitability, muscle contraction, steady state cell volume, nutrient uptake, intracellular pH.

What is secondary active transport?

Uses energy stored in ion gradients created by primary active transporters to move other substances against their own concentration gradient.

What is osmosis?

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

What are the properties of Pd (diffusion through lipid bilayer)?

Small, Mercury insensitive, Temp dependent (lipid fluidity).

What are the properties of Pf (diffusion through water channel)?

Large, Mercury sensitive, Temp independent.