Transport of Small Molecules Across Plasma Membrane

What are the ways that small molecules can move across a membrane?

Active and Passive Transport

What is able to passively diffuse across a phospholipid bilayer at significant rates?

Gases (O2 and CO2), hydrophobic molecules (steroid hormones) and small polar molecules (water and ethanol)

What are ions?

H+, Na+, HCO3-, K+, CA^2+, Cl- and Mg^2+

What are small hydrophobic molecules?

O2, N2, CO2 and benzene

What is diffusion?

a particle (solute) is dissolved in a gas or liquid (solvent) and moves from an area of high concentration to an area of lower concentration

What are larger uncharged polar molecules?

amino acids, glucose and nucleosides

What is active transport?

cells use energy to move small molecules, (primary and secondary)

What do transport proteins allow the cell to do?

control the composition of cytoplasm

What does the rate at which a molecule crosses a protein-free lipid bilayer by simple diffusion depend on?

depends on its size and solubility

What is facilitated diffusion?

molecules move across the plasma membrane with the help of a carrier molecule

What is simple diffusion?

molecules pass directly through the plasma membrane without the assistance of another molecule

Can ions diffuse across the membrane in simple transport?

no

Can larger uncharged polar molecules diffuse across the membrane in simple transport?

no

What are transport proteins?

provide a passageway for molecules to travel into and out of the cell

What mediates passage of small molecules?

specific transport proteins

What is the direction of transport determined by?

the concentrations of the molecule inside and outside of the cell

What is osmosis?

the passive diffusion of water (biological systems) across a membrane down its concentration gradient

What is Passive Transport?

the spontaneous diffusion of molecules across a membrane without energy input, (diffusion or osmosis)

What are small uncharged polar molecules?

water, glycerol, ethanol and steroid hormones

Can small hydrophobic molecules diffuse across the membrane in simple transport?

yes

Can small uncharged polar molecules diffuse across the membrane in simple transport?

yes