Membrane Structure & Function

• the fluid mosaic model
• semi-permeable
• fluid portion is a double layer of phospholipids, called the phospholipid bilayer

• Isolate the cytoplasm from the external environment
• Regulate the exchange of substances
• Communicate with other cells
• Identification

• Phospholipids contain a hydrophilic head and a nonpolar hydrophobic tail.
• Hydrogen bonds form between the phospholipid "heads" and the watery environment inside and outside of the cell.
• Hydrophobic interactions force the "tails" to face inward
• Phospholipids are not bonded to each other, which makes the double layer fluid.
• Cholesterol embedded in the membrane makes it stronger and less fluid.

• ^{_{1. Channel Proteins - form small openings for molecules to difuse through}}
• 2. Carrier Proteins- binding site on protein surface "grabs" certain molecules and pulls them into the cell
• 3. Receptor Proteins - molecular triggers that set off cell responses (such as release of hormones or opening of channel proteins)
• 4. Cell Recognition Proteins - ID tags, to idenitfy cells to the body's immune system
• 5. Enzymatic Proteins - carry out metabolic reactions

Simple Diffusion - water, oxygen and other molecules move from areas of high concentration to areas of low concentration, down a concentration gradient.

Facilitation Diffusion - diffusion that is assisted by proteins (channel or carrier proteins)

• diffusion of water. Salt Sucks
• Osmosis affects the turgidity of cells, different solution can affect the cells internal water amounts
• Contractiles Vacuoles are found in freshwater microorganisms - they pump out excess water
• Turgor pressure occurs in plants cells as their central vacuoles fill with water.

- involves moving molecules "uphill" against the concentration gradient, which requires energy

- taking substances into the cell (pinocytosis for water, phagocytosis for solids

- pushing substances out of the cell, such as the removal of waste

- pumps out 3 sodiums for ever 2 potassium's taken in against gradient