The Cell Membrane

What is the cell membrane?

• AKA: Plasma membrane• The boundary between the cell and the

environment• Does every cell have a cell membrane?– Yes, Each and every cell has a cell membrane.

How do cell membranes help to maintain homeostasis?

• The cell membrane allows nutrients to come into the cell

• Glucose, amino acids, lipids

• The cell membrane removes waste

Selective Permeability

• The cell membrane lets some molecules in and keeps others out

• EX. A cell is low on glucose so the membrane lets in some glucose, but does not overfill the cell with the monomer.

Structure of the cell membrane

• What does the cell membrane look like up close?

Lets look at one of these

structures up close

Structure of cell membrane

• Phospholipids– Phosphate head– Glycerol– 2 Fatty acid tails

Phospholipids

• 1.) Phosphate Head• Polar• Hydrophilic• Make up the outer borders of the

membrane

• 2.) Fatty Acid Tails• Nonpolar• Hydrophobic• Make up the inner part of the

membrane

Structure of cell membrane

• Phospholipid bilayer– 2 layers of phospholipids make up a cell

membrane

Phospholipid Bilayer

• Remember polar heads and nonpolar tails

The fluid Mosaic Model of the cell membrane

• Lipid bilayer is not strong & firm like a hard shell, but it is fluid like a soap bubble consistency

• So, it is called the Fluid Mosaic Model (fluid like, with many proteins stuck in it)

The fluid Mosaic Model of the cell membrane

• It is a flexible membrane, made fluid because of cholesterol molecules located in the phospholipid bilayer.

• Proteins in the membrane move around.

Other components of the cell membrane

• Cholesterol– Helps to stabilize

the phospholipids and keep them from sticking together

Other components of the cell membrane

• Carbohydrates- linked to lipids or proteins– Recognition of Cells – “Name tag of cell”– Ex. Is the cell a heart cell, liver cell, or brain cell?– Ex. Glycolipids & Glycoproteins (marker protein)

Other components of the cell membrane

• Proteins- make up 50 %- 70% of membrane– Regulate which molecules enter and which

molecules leave a cell.– Receive info & ID the cell

Types of proteins in the cell membrane

• Carrier Protein– Allow needed substances or waste materials

to move through the cell membrane

Types of proteins in the cell membrane

• Receptor Protein– These have binding sites for molecules such as

hormones or substrates to bind to

Types of proteins in the cell membrane

• Channel or Pore protein– Hydrophilic channel – allows lipid insoluble

substances to pass in and out of cell.

Types of proteins in the cell membrane

• Glycoproteins– Protein with what macromolecule attached

to it?• Carbohydrate

– Functions for cell to cell recognition

Where are proteins located in the cell membrane?

• Integral Proteins– Proteins inside the cell membrane

• Peripheral Proteins– Proteins outside the cell membrane