Membranes are important to cell structure and function. The plasma membrane –surrounds the cells cytoplasm –separates the cell from its environment –regulates what moves in and out of the cell
Internal membranes surround and form part of the structure of many of the organelles of eukaryotic cells Nucleus Endoplasmic reticulum Mitochondria and chloroplasts Golgi bodies Lysosomes
Phospholipids form the framework of a cells membranes. A phospholipid molecule consists of two parts: –a hydrophilic head, which contains phosphorus. –a hydrophobic tail, composed of two fatty acid molecules
H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2OH2OH2O H2OH2O H2OH2O Water makes up a major part of the cells internal and external surroundings. Membrane
The tails project inward--away from the water. The hydrophilic heads are in contact with the water. The framework of the membrane is a phospholipid bilayer.
Phospholipid molecules arrange themselves in two layers facing each other. H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2OH2OH2O H2OH2O H2OH2O
Proteins are also an important part of membrane structure. Some proteins penetrate the entire phospholipid framework; others do not.
Carbohydrate molecules attached to the outer surface help the membrane recognize various substances.
Osmosis is the diffusion of water through a semipermeable membrane.
Solute molecules Solvent Molecules Think of an example of a substance that could be a solvent. Think of an example of a substance that could be a solute.
What would happen to a cell placed in pure water? 90% water 10% solute 100% water What would happen to a cell placed in a 20% salt solution? 90% water 10% solute Cells are about 90% water. 80% water
Transport proteins are embedded in cell membranes Facilitated diffusion is a passive method that uses transport proteins. Molecules move along a concentration gradient. No energy is required.
Active transport uses transport proteins to move some types of molecules against a concentration gradient. Active transport requires the cell to use energy.
Exocytosis and endocytosis also require energy. These processes involve rearrangement of the membrane. ooo oo o oo o o oo o ooo o o oo o o oo
Review: Substances pass through membranes in several different ways: Diffusion Osmosis Facilitated Diffusion Active Transport Exocytosis and Endocytosis } Forms of Passive Transport; do not require energy } Require energy as ATP.