Chapter 5 The Plasma Membrane and Transport

Transcription

1 Chapter 5 The Plasma Membrane and Transport State Standard Standard 1.a. Membrane Function 1, Forms a boundary between living cells and their surroundings. 2. Controls the movement of molecules into and out of the cell - Selective permeability Membranes can contain enzymes that function in various chemical reactions. Membrane Structure The plasma membrane is 8 nm thick. It is mainly made up of

2 Membrane phospholipids Phospholipids have a hydrophilic head and two hydrophilic tails. The phospholipids - The hydrophilic heads face outward and the hydrophobic tails face inward Membrane Proteins

3 Membrane proteins are found within the phospholipid bilayer integral proteins They can be found embedded on either surface peripheral proteins Functions of Membrane Proteins Some proteins transport substances across the membrane by forming channels or by Functions of membrane proteins include: Transport of substances across the membrane Join cells to one another Bind to chemical messengers from other cells Act as identification tags so Attach to cytoskeleton and the extracellular matrix Membrane cholesterol and carbohydrates Cholesterol Cholesterol is found within the phospholipid bilayer It helps Carbohydrates Located on outer layer of membrane only Bound to proteins (glycoproteins) or phopholipids (glycolipids) Act as identification tags for Fluid Mosaic Model The membrane is a fluid mosaic Fluid the phospholipids and the proteins drift within the membrane Mosaic the diversity of proteins found within the membrane and the

4 Transport Across the Membrane Diffusion The tendency of particles of any kind to spread from regions of Requires no energy, results from Passive Transport They spread from areas of high concentration to areas of lower concentration At equilibrium the molecules continue to move but there is no net change in the concentration on either side of the membrane

5 Osmosis Osmosis is Water travels from an area of lower solute concentration to an area of higher solute concentration Hypertonic - the solution with the higher solute concentration Hypotonic - the solution with the lower solute concentration Water moves from the Water continues to cross the membrane until the solute concentrations are equal on both sides of the membrane Isotonic - solutions with equal solute concentrations Water molecules continue to move across the membrane but Osmosis Problems Draw a diagram illustrating the problem, identify the solutions as hyper, hypo or isotonic, and show the direction osmosis will occur 1. A cell containing 2% solute is placed in a solution containing 10% solute. 2. A candy containing 15% solute is placed in a solution containing 12% solute. 3. A cell containing 7% solute is placed in a solution containing 9% solute. 4. A candy containing 10% water is placed in a solution containing 90% water. 5. A fish contains 95% water lives in freshwater that contains 68% water.

6 How Does Osmosis Affect Cells? Distilled Water 3x Saline Induces turgor in plant cell Induces turgor in animal cell Makes plant cell pull away from cell wall Makes plant cell lyse Makes animal cell lyse Makes animal cell shrivel Explain the different outcomes of adding distilled water to the plant and animal cells. Which conditions best model the effects of drought on plant cells? Explain your answer. Hypothesize why plants grow better when the water surrounding their cells is slightly hypotonic to the cell. Water balance between cells and their surroundings is crucial to organisms Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution.

7 Facilitated Diffusion Small non-polar molecules diffuse freely through the phospholipid bilayer This type of transport is called facilitated diffusion Active Transport Transport proteins can move solutes across the membrane - This is called active transport Active transport requires ATP cells use energy to move the molecule across the membrane. The solute is moved from Exocytosis and Endocytosis To move large molecules or particles across the membrane a vesicle may fuse with the membrane and expel its contents Or the membrane may fold inward, trapping material from the outside, and form a vesicle that carries the material into the cell There are 3 kinds of endocytosis: Phagocytosis a cell brings in Pinocytosis the cell takes in Receptor-mediated endocytosis specific molecules bind to receptors on the membrane that signal to the cell to take the molecule in Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors