Section 7.2

The Plasma Membrane

Ticket in the Door• What are the 3 principles of cell

theory?

• What is one main difference between prokaryotes and eukaryotes.

• What is the function of the plasma membrane?

The Plasma Membrane• What is its purpose? • Helps maintain homeostasis by its

structure and selective permeability.

• It allows some substances through and keeps other substances out.

Form Fits Function• The structure of the plasma

membrane controls how, when, and how much of these substances leave the cell.

Structure • Phospholipid bilayer makes up the

membrane• Arranged tail-to-tail

• Phospholipids have a phosphate head (polar) and two fatty acid tails (non-polar)

• The arrangements of the phospholipids creates a barrier that is polar at its surface and non-polar in the middle.

• The polar and non-polar properties of the phospholipid bilayer allows the membrane to separate the inside of the cell from the outside of the cell.

Cholesterol, Proteins, and Carbs

• Proteins: give structure to the cell–On the outer surface they act

as receptors–Help transport needed

substances or waste material through the plasma membrane (transport protein)

Cholesterol, Proteins, and Carbs

• Cholesterol – Prevents the fatty acid tails of the

phospholipids from sticking together.

• Carbohydrates help define the cell’s characteristic and identify chemical signals

Fluid Mosaic Model• The plasma

membrane is in constant motion– The

phospholipids move sideways

– Other components move among the phospholipids