The Cell Membrane and Transport CO 5 The Cell Membrane and Transport

The membrane is a fluid (able to move freely) mosaic (made of many different parts) with a double layer of phospholipids and embedded proteins throughout. Figure 5.2 Jobs: Regulates exchange Creates a barrier Communication Identification

Phospholipids have both hydrophilic and hydrophobic regions Pg 85

The proteins form a mosaic pattern on the membrane The proteins form a mosaic pattern on the membrane.  - Special Membrane Molecules - Cholesterol - reinforces membrane by connecting phospholipids Glycolipids and Glycoproteins – used for cell to cell attachment and cell communication

Special Membrane Proteins 1. Channel Proteins - form small openings for molecules to diffuse through 2. Carrier Proteins- binding site on protein surface that "grabs" certain molecules and pulls them into the cell (uses energy, but not always the cell’s energy) Gated Channels - carrier proteins that are not always "open"

3. Receptor Proteins – communication molecule that triggers a cell response when the correct signal molecule attaches 4. Recognition Proteins - ID tags, identify cells to the immune system 5. Enzymatic Proteins – perform specific reactions

Transport Across Membrane Aquaporin *Selectively permeable – only some things can cross What things can pass? What cannot pass? Figure 5.5

Passive Transport (no energy) Simple Diffusion - water, oxygen and other molecules move themselves from areas of high concentration to areas of low concentration (down a concentration gradient) Figure 5.6

Facilitated Diffusion - diffusion through protein openings (channel or carrier proteins) Figure 5.6c

Salt Sucks! OSMOSIS Osmosis - diffusion of water specifically Water is always welcome to come into the cell. This also means that water is always able to go out. Balancing the amount of water in the cell is crucial to homeostasis. Osmosis affects the amount of water inside cells, and different solutions can draw water out of the cell (dehydrating it) or cause cell to absorb excess water (overhydrating) Simple rule of osmosis  Salt Sucks!

Isotonic solutions– same conc of water and solute, no net movement of water Hypotonic solutions– less solute (and therefore more water) outside cell, water moves into the cell, cell could burst Hypertonic solutions – more solute (and therefore less water) outside cell, water moves out of the cell, cell shrinks

Contractile Vacuoles are found in freshwater microorganisms to pump out excess water in aquatic areas to counterbalance the hypotonic environment (freshwater only) Turgor pressure occurs in plants cells as their central vacuoles fill with water. The cell wall plus pressure helps prevent too much water from coming in.

Osmosis in U Tubes

Active Transport - moving molecules "uphill" against the concentration gradient (from low to high), which requires cell energy (ATP) Endocytosis - taking substances into the cell in vessicles                       (pinocytosis for water, phagocytosis for solids)   

Figure 5.12 Exocytosis – reverse of endocytosis to move stuff out of the cell, such as the removal of waste

Protein Pump – Any protein that uses ATP to actively transport a molecule against a concentration gradient - Ex: Sodium-Potassium Pump – protein that maintains a balance of Na+ and K+ for nervous system function. A huge amount of energy in our bodies is used to power this pump and prevent sodium from building up within our cells. Drives the communication of our nerves

SODIUM POTASSIUM PUMP Figure 5.11