Cell Membrane Overview and Composition

Cell Membrane Overview

• The cell membrane is also known as the plasma membrane.
• It's a gatekeeper, separating the cell's interior from the external environment.
• It controls the movement of materials into and out of the cell.
• The membrane is semi-permeable, allowing only some substances to pass through.

Cell Membrane Composition

• The cell membrane is composed of a phospholipid bilayer.
• Phospholipids have hydrophilic heads and hydrophobic tails.
• Hydrophilic heads are attracted to water, while hydrophobic tails repel water.
• The bilayer structure arranges the tails inwards, away from the water inside and outside the cell.
• Only small, fat-soluble molecules can pass directly through the phospholipid bilayer.

Proteins in the Cell Membrane

• Proteins act like doorways within the membrane.
• They allow larger or polar molecules to pass through, which cannot pass through the phospholipid bilayer independently.
• Membrane proteins can be either integral or peripheral.
• Integral proteins are embedded within the phospholipid bilayer and frequently span the entire membrane. They assist in transporting large and polar molecules.
• Peripheral proteins are located on the surface of the bilayer. They can assist in cell signaling, acting as enzymes, or influencing shape and structure.
• Integral proteins come in two types: Carrier and Channel
  • Channel proteins are essentially open tubes that create pathways allowing molecules to pass through passively.
  • Carrier proteins "pick up" molecules and carry them across the membrane—this process often requires energy (active transport).

Carbohydrates in the Cell Membrane

• Carbohydrate chains adhere to the membrane's outer surface.
• Carbohydrates help cells recognize other cells and aid in cell adherence.
• Glycoproteins are proteins with attached carbohydrates.
• Glycolipids are lipids with attached carbohydrates.

Cholesterol in the Cell Membrane

• Cholesterol is a steroid embedded within the phospholipid bilayer.
• It helps maintain membrane fluidity, balancing it at various temperatures.
• At high temperatures, cholesterol helps decrease fluidity.
• At low temperatures, cholesterol helps increase fluidity.
• Cholesterol acts as a "membrane antifreeze agent".

Fluid Mosaic Model

• The cell membrane is fluid because of its components (like lipids and proteins) that can move laterally within the membrane.
• The membrane's dynamic behavior is likened to a mosaic, composed of various parts.

Explore the fundamental aspects of the cell membrane, also known as the plasma membrane. This quiz covers its role as a gatekeeper, its phospholipid bilayer structure, and the function of proteins within the membrane. Test your understanding of the cell membrane's properties and composition.