5/1/12 Objective: Describe the structure and function of the cell membrane Warm-Up: Cells are surrounded by membranes. Why do cells need membranes?

Cell Membranes

Membrane Structure The cell membrane is a phospholipid bilayer Each phospholipid has a hydrophilic head Each phospholipid also has hydrophobic tails The fluid inside the cell and the fluid outside of the cell are both mostly water

The cell membrane is mostly made of… Nucleic Acids Phospholipids Hydrophobic tails Hydrophilic heads [Default] [MC Any] [MC All]

Membrane Structure Cell membranes also contain cholesterol molecules, which help stabilize the membrane There are proteins that go across the cell membrane, connecting the inside of the cell with the surrounding environment These membrane proteins act like tunnels that allow certain molecules to pass through the membrane There are also membrane proteins that act as receptors—they receive signals

Cholesterol… Is always unhealthy Cannot be used by cells Stabilizes the cell membrane Causes the cell membrane to break apart [Default] [MC Any] [MC All]

In the cell membrane, proteins Can receive signals from other cells Can work like tunnels to get molecules into the cell Connect the inside of the cell with the surrounding environment All of the above [Default] [MC Any] [MC All]

Cell Membrane Function Membranes act as a barrier between the internal and external environments of the cell Membranes control what goes in and out of the cell There are some molecules that can move freely across cell membranes Other molecules cannot move across the membrane

All molecules can easily get through the cell membrane. True False

Selectively Permeable Selectively permeable (sometimes called semi-permeable): describes a membrane that only allows specific kinds of substances to pass through Think of the root word “permeate” to help you remember this one “Large and charged”—molecules that are large and/or charged cannot diffuse freely across the selectively permeable cell membrane

Why did our iodine and starch lab model a semi-permeable membrane? All of the molecules, starch and iodine, passed through the bag Iodine, a small molecule, moved through the bag while starch, a large molecule, did not Starch, a large molecule, moved through the bag while iodine, a small molecule, did not No molecules were able to move through the bag [Default] [MC Any] [MC All]

Which of the following would most likely be able to pass easily through a cell membrane? Oxygen, a small and uncharged molecule Glucose, a very large sugar molecule Sodium ions, which have a full positive charge Chlorine ions, which have a full negative charge [Default] [MC Any] [MC All]