Cell Membrane Functions and Characteristics

Cell Membrane

• The cell membrane is an organelle found in all cells
• It selectively controls the entrance and exit of substances
• Functions of the cell membrane include protection, support, and transport.

Cell Membrane: Characteristics

• Also known as the plasma membrane
• A biological membrane separating the cell's interior from its environment
• A semi-permeable membrane, filtering substances into and out of the cell
• Contains bead-like structures embedded within it
• Coined by C. Nageli and C. Cramer in 1855

Cell Membrane: Functions

1. Protection and Support

• Keeps the cell intact
• Maintains the cell's shape and form
• Acts as a barrier that protects the cell from foreign substances

2. Acts as a Receptor

• A binding mechanism for the cell
• Receives chemical signals from the environment

3. Transportation of Materials

• Regulates the entrance and exit of substances (gases, sugar, amino acids, ions)
• Acts as a medium for nutrients entering and waste exiting the cell

Cell Membrane: Structure

• Composed of a phospholipid bilayer, proteins, and carbohydrates
• Phospholipids have a hydrophilic head and hydrophobic tail. This structure is important to membrane permeability.
• Cholesterol is a lipid that helps maintain membrane fluidity.
• Proteins are embedded within the phospholipid bilayer and perform various functions (structural, transport, receptor).
• Glycoproteins are carbohydrates attached to proteins on the external surface and play a part in receiving/transmitting signals.

Cell Membrane: Chemical Composition

1. Lipids

• Main components of the membrane
• Include phospholipids, glycolipids, sphingolipids, and sterols.

2. Proteins

• 50% of the membrane
• Include structural, transport, receptor, and enzyme proteins.

3. Carbohydrates

• Sugars attached to proteins (glycoproteins) or lipids (glycolipids)
• Primarily located on the outer surface of the membrane and help in cell signaling.

Cell Membrane: Models

1. Davson-Danielli Model (1935)

• Also known as the sandwich model
• Proposes a membrane structure with a lipid bilayer sandwiched between protein layers.
• The polar heads of phospholipids face outwards.

2. Fluid-Mosaic Model (1972)

• The most widely accepted model
• Proposes a fluid, dynamic membrane where lipids and proteins move laterally.
• Lipids and proteins are embedded in the phospholipid bilayer, and the polar heads of the phospholipids face outwards.

This quiz explores the essential functions and characteristics of the cell membrane, also referred to as the plasma membrane. It highlights its role in protection, support, and selective transport of substances. Test your understanding of its structure and significance in cellular biology.