Plasma Membrane

The Plasma Membrane

  • The plasma membrane acts as a gateway to the cell.

Cell Membrane

  • The cell membrane is flexible, allowing unicellular organisms to move.

Homeostasis

  • Homeostasis is the balanced internal condition of cells, also called equilibrium.

  • It is maintained by the plasma membrane, which controls what enters and leaves the cell.

Functions of Plasma Membrane

  • Protective barrier.

  • Regulates transport in and out of the cell (selectively permeable).

  • Proteins on the cell membrane allow cell recognition.

  • Provides anchoring sites for filaments of the cytoskeleton.

Structure of the Cell Membrane

  • The cell membrane consists of a lipid bilayer with protein molecules and carbohydrate chains.

Membrane Components

  • The main components of the cell membrane are phospholipids, cholesterol, proteins, and glycocalyx.

  • It also interacts with the cytoskeleton.

Phospholipids

  • Form a bilayer.

Cholesterol

  • Present in animal cells.

Proteins

  • Various types and duties; can be peripheral or integral.

Glycocalyx

Phospholipids

  • Make up the cell membrane.

  • Contain two nonpolar fatty acid chains and a polar head with a phosphate group.

Fluid Mosaic Model

  • The membrane is fluid because individual phospholipids and proteins can move freely within the layer, like a liquid.

  • It is mosaic because of the pattern produced by the scattered protein molecules when the membrane is viewed from above.

Polar and Nonpolar Regions

  • Polar heads are hydrophilic ("water-loving").

  • Nonpolar tails are hydrophobic ("water-fearing").

  • This makes the membrane selective in what crosses.

Cell Membrane and Transport

  • Hydrophobic molecules pass easily through the cell membrane; hydrophilic molecules do not.

  • The cell membrane is made of two layers of phospholipids called the lipid bilayer.

Solubility

  • Materials that are soluble in lipids can pass through the cell membrane easily.

Cholesterol

  • Only present in animal cells.

  • Stabilizes the membrane by reducing membrane fluidity and permeability to some smaller solutes.

Semipermeable Membrane

  • Small, non-charged molecules move through easily; examples include O2andandCO2.

  • Ions and large molecules such as glucose and amino acids do not move through the membrane on their own; they must use transport proteins.