cell membrane

• the cell membrane consist of a phospholipid bilayer
• each phospholipid has a hydrophilic head and a hydrophobic tail
• phosphate heads face the outside and lipid tails face the inside
• cholesterol and protein molecules are embedded in the bilayer
• cholesterol molecules provide structure and support
• the cell membrane has carrier proteins, channel proteins and receptor proteins
• the cell membrane acts as a physical barrier, regulates the passage of materials, is sensitive to change, and provides cell support
• passive processes don't use energy to move along the concentration gradient, and occur in the phospholipid bilayer
• active processes require energy to move against the concentration gradient, and occur in carrier proteins
• materials stop moving by passive transport when equilibrium has been reached
• diffusion is the passive movement of molecules from an area of high concentration to low concentration
• oxygen and carbon dioxide diffuse through the bilayer
• alcohol, steroids and fat diffuse through the lipid portions of the membrane
• larger or charged molecules require active transport
• osmosis is the movement of water across a membrane from a high concentration to a low concentration
• in a hypotonic solution, the cell can swell and pop
• in a hypertonic solution, the cell can shrivel up
• protein channel provide a pathway for molecules to travel without contact with the lipid tails
• substance bonds to binding site of carrier proteins and are released on the other side
• carrier proteins are specific, can become saturated, and are regulated by hormones
• active transport happens via carrier proteins only
• vesicular transport is the movement of substances across the membrane in vesicular sacs
• phagocytosis is the transport of solids, pinocytosis is the transport of liquids
• exocytosis consists of membrane fusion
• examples of simple diffusion is water, carbon dioxide, alcohol and steroids
• example of osmosis is water
• example of facilitated transport is glucose and amino acids
• examples of active transport are ions, glucose and amino acids
• examples of endocytosis is cholesterol, cell debris, microorganisms
• examples of exocytosis is secretions like mucus and digestive juices
• receptor proteins receive signals
• carrier proteins bind specific molecules to be transported on one side