Lipids, Membranes, and the First Cells

Facilitated diffusion and Active Trasport

Carbon containing compounds that are largely non-polar and hydrophobic

molecules that contain only hydrogen and carbon

Fatty Acid

Hydrocarbon chain bonded to a carboxyl group.

Fats

Steroids

Phospholipids

three fatty acids linked to a glycerol

family of lipids distinguished by a four-ring structure

Glycerol linked to a phosphate group and either 2 chains of isoprene or fatty acids

Containing both hydrophobic and hydrophillic parts

Two sheets of phospholipid molecules align where the non-polar tails face each other and the polar head are facing the surrounding solution.

They form spontaneously with no outside input of energy

small and nonpolar molecules move across the bilayer quickly

Charged or large polar substances move across slowly, if at all

has a double bond between two carbons in a hydrocarbon chain

hydrocarbons without double bonds

molecules in the bilayer move more slowly

decreases permeability

Small ions and molecules in a solution

Solute concentration higher outside the cell, so water moves out of the cell

Solute concentration higher inside the cell, so water moves into the cell

Solute concentration are equal inside and outside the cell.

Transmembrane proteins

transport of selected ions and molecules across the plasma membrane

Transport proteins

Channels

Carrier Proteins

Pumps

Facilitated diffusion

The passive transport (no energy used) of substances that would not otherwise cross the membrane

Channels

Carrier Proteins

Transport of molecules or ions against a electrochemical gradient - requires ATP.

A chemical and electrical gradient across the membrane

Diffusion

Facilitated diffusion

Active Transport