Cell Membrane Intro

Cell Membrane

The outer layer of the cell that controls what enters and exits—a characteristic known as semi-permeability.

Intracellular

Inside

Extracellular

Outside

Semi-permeability

A characteristic of the cell membrane that allows certain substances to pass (enter and exit) while keeping others out.

Factors that affect permeability.

• Size ~ small molecules pass through more easily.

• Polarity ~ The inside of the cell is hydrophobic, so nonpolar molecules are preferred.

Phospholipids

The primary building blocks of the cell membrane, consisting of a phosphate head group, glycerol backbone, and two fatty acid tails.

Hydrophilic

Describes a molecule, like the phosphate head of a phospholipid, that interacts favorably with water. (Polar)

Hydrophobic

Describes a molecule, like the fatty acid tails of a phospholipid, that does not interact favorably with water.

Amphipathic

A molecule that has both hydrophobic and hydrophilic sections.

Phospholipid Bilayer

The arrangement of phospholipids in two layers, forming the fundamental structure of the cell membrane. Hydrophilic heads near water and hydrophobic tails away.

Passive Diffusion

The process by which small, nonpolar molecules pass through the cell membrane easily.

Small, Nonpolar Molecules

Gases like O2 and CO2 pass through easily (Passive diffusion) because they are small and nonpolar.

Small, Polar Molecules

Water and ethanol can pass through, but slowly, as the hydrophobic region of the cell membrane resists them.

Large, Nonpolar Molecules

Benzene can pass through, but slowly, because it is hydrophobic and mix well with the hydrophobic region.

Large, Polar Molecules

Sugar (glucose) can not pass through because it is large and polar.

Charged Molecules

Ions (Chloride or Sodium) and amino acids cannot pass through due to their charge.