Cell Biology Overview Cell Membranes Cell Cycle and Specialization Microscopes Introduction / Cell Theory Cellular Respiration Cell Cycle and Specialization Cell Division Protein Synthesis

Cell Membranes Amoeba moving Cells Dividing The cell membrane surrounds the cell and forms a boundary between the cell and its environment. It is fluid, flexible and dynamic. The cell membrane changes shape as a cell moves. It divides in two when the cell divides. So how does the cell membrane do this? Amoeba moving Cells Dividing

The Cell Membrane’s role? Cell Membrane Roles Flexible Boundary Platform for cell recognition communication The cell membrane has three main roles in the life of a cell. It forms a boundary, a fence around the cell It controls what enters and leaves the cell It serves as a platform for molecules used in cell-cell adhesion, recognition and signaling Access Control

What makes these roles possible? Cell Membrane Building Blocks Phospholipids Glycoproteins Cholesterol Glycolipids Proteins These roles are possible because of the molecules that make up the cell membrane. Phospholipids and cholesterol made up most of the membrane, making it semi-permeable. Proteins span the membrane and serve as channels for molecules entering and leaving the cell. Glycoproteins and glycolipids are hybrid biomolecules (they are made of protein and glycogen or glycogen and lipids joined together) that provide glue for cells to attached to one another, serve as signatures identifying self from nonself and signal other cells in the body. Flexible Boundary Platform for cell adhesion cell recognition cell communication Controls access

Chemistry Reboot!!!

Phospholipids Phospholipids are the most common molecules in the cell membrane. Each phospholipid molecule has a polar (hydrophilic) head and two nonpolar (hydrophobic) tails. The phospholipids are aligned tail to tail so a nonpolar area forms a hydrophobic region between the hydrophilic heads on the inner and outer surfaces of the membrane. Cholesterol molecules are embedded among the phospholipids. The cholesterol molecules add rigidity to the layer. The cholesterol molecules keep the phospholipids from flying apart in warmer temperatures and they keep the membranes flexible at colder temperatures.

Cell Membrane Structure the fluid mosaic model This diagram shows the molecules that make up a typical cell membrane. Here are the phospholipids interspersed with cholesterol. Proteins are embedded in the membrane as are glycoproteins Glycolipids are anchored in the outer layer.