cell membrane selectively permeable. basic structure double layer of phospholipids referred to a...
TRANSCRIPT
Cell Membrane
Selectively Permeable
Basic Structure
• Double layer of phospholipids
• Referred to a bilayer• A phospholipid has a
head and two tails• The phospholipids
face away from each other in the bilayer
Phospholipids
• Phosphate “heads” are water-soluble
• They like water and are attracted to water
• Fatty acid “tails” are not soluble in water
• They repel water and want to stay away from it
Permeability
• Small molecules that dissolve in lipids can pass right through the phospholipid bilayer
• Oxygen, carbon dioxide and some water can also pass through
Permeability
• Glucose, amino acids, and other large molecules that do not dissolve in lipids cannot pass through
• Most water molecules, and ions such as H+, NA+, K+, and Ca+ cannot pass through
Some molecules need help
• We use proteins embedded in the membrane to help get these molecules across the cell membrane
Phospholipid bilayer plus
Notice that there are many structures stuck in the phospholipid bilayer
Proteins scattered throughout
A Gallery of Membrane Proteins
• Adhesion proteins: Help cells of the same type stick together in tissues
• Cell to cell communication proteins: match up with another cell to pass on a signal
A Gallery of Membrane Proteins
• Receptor proteins: stick out of the membrane to bind hormones.
• Recognition proteins: Identify each
person’s cells as their own
• Must be matched in transplants, blood transfusions, etc.
A Gallery of Membrane Proteins
• Passive Transporter proteins: allow molecules to move through them without requiring energy
• Active transporters: use energy to pump molecules “uphill” across the membrane
Transport Across Cell Membranes
Passive or Active
Movement
• Is either passive or active• Passive does not require cell energy• Active uses cell energy
Passive Mechanisms of Transport
• Diffusion: molecules spread or scatter from regions of higher concentration toward regions of lower concentration
• Molecules will travel down the concentration gradient
Passive Mechanisms of Transport
• Facilitated Diffusion: molecules cannot
pass through the lipid bilayer without the help of a membrane protein. The molecule being transported combines with a carrier molecule which moves it to other side
Passive Mechanisms of Transport
• Osmosis: the diffusion of water. Water moves from a region of higher concentration to a region of lower concentration
• In this example, the membrane is NOT permeable to the solute
Passive Mechanisms of Transport
• Filtration: forces molecules through membranes
• Often used to separate solids from liquids
• Kidneys filter blood, the force coming from blood pressure
Active Mechanisms of Transport
• Active transport: uses energy and carrier proteins to move molecules from areas of LOW concentration to areas of HIGH concentration
• Against the concentration gradient; a pump
Active Mechanisms of Transport
• Endocytosis: uses cellular energy to form a vesicle from a section of cell membrane to bring IN substances
• Exocytosis: uses energy to secrete a substance stored in a vesicle