Cell Biology, membrane transport

freely permeable

• small non-polar molecules

• with a gradient, simple diffusion

• freely permeant

• O2

somewhat permeable

• small uncharged polar molecules

• with TM or osmotic gradient

• H2O

• somewhat permeant

somewhat/freely permeable

• moderately sized non-polar + amphipathic molecules

• with TM gradient

• lipids

• somewhat/ freely permeant

impermeable

• ionic (regardless of size or presence of gradient)

• moderately/large polar molecules (regardless of presence of gradient)

• larger/bulkier molecules/macromolecules (regardless of presence of gradient)

example of non polar bond

• C-C

• C-H

Example of polar bond

• O-H

• N-H

membrane permeability based on FFA

• hydrophilic heads, hydrophobic tails

• sterols create tighter packing

• saturated and long = tight

• unsaturated and short = loose

aquaporin characteristics (passive transporter)

• thin pore (single file H2O)

• constitutively active

• osmotic gradient

• hydrophilic tunnel

porin characteristics (passive)

• large pore (non-gated)

• constitutively active

• various ions and small molecules (size exclusive)

• gradient

ion channel (passive)

• very small pore (selective filter and gating domain)

• cycles between open/close

• electrochemical gradient

uniporter

• never a continuous tunnel (revolving door) inward open → occluded → outward open

• specific small molecules

• concentration gradient

active transport

used for against/absence of gradient movement

• uses an energy source (ATP, redox, photon)