Cell Structure and Function Cell Boundaries

What Are We Learning? Benchmark: SC.912.L.14.2 –...Relate structure to function for the components of plant and animal cells. Explain the role of cell membranes as a highly selective barrier (passive and active transport). Objectives: Describe the arrangement of phospholipids and proteins in the membrane lipid bilayer Explain the processes of diffusion, osmosis, facilitated diffusion, and active transport.

What is the cell membrane?  All cells are surrounded by a thin, flexible barrier made of phospholipids known as the cell membrane.  Regulates what enters and leaves the cell.  Provides protection and support.  Fluid Mosaic Model

Why cells look like they do?  What happens when oil is poured in water?  Water and oil will separate because water is a polar molecule and oil is nonpolar  The cell membrane is shaped by the interaction of water found inside and outside of the cell and the phospholipids that form the cell membrane.

How are cell membranes constructed?  Basic building block of the cell membrane is a kind of lipid molecule called a phospholipid.  Short “head” is joined to two long “tails.”  The head contains phosphorous, which make it polar.  Hydrophilic head  The long tails of fatty acids are nonpolar.  Hydrophobic tails

How are cell membranes constructed?  Water can interact with the polar heads and repel the nonpolar lipids tails.  The polar heads of the phospholipids point toward the water inside and outside the cell.  The tails are buried in the interior of the membrane, directing themselves away from the water.  This double layer of phospholipids forms a flexible lipid bilayer.

What else is There?  In addition to lipids, most cell membranes contain proteins molecules that are embedded in the lipid bilayer.  Proteins form channels and pumps that help to move material across the cell membrane.  Carbohydrates molecules are attached to many of these proteins.  Act like chemical identification cards, allowing cells to identify one another.

What are protein channels and Carriers?  Proteins channels are formed by doughnut- shaped proteins.  Act as passageways through which only certain molecules can pass.  Each channel will admit only certain molecules  Protein carriers are proteins that carry molecules from one side of the membrane to another  Both channels and carriers use no energy Channel Carrier

How does the membrane regulates movement of substances?  Large molecules will not pass due to their size  Polar molecules will not pass because they will not interact with the hydrophobic (nonpolar) tails of the lipids.  Water can pass even though it is polar (very small)  oxygen and carbon dioxide are small, nonpolar molecules and pass with ease

Why is that Smell?  What happens when a bottle of perfume is opened at the front of a room?  Within minutes people further and further from the source can smell the perfume.  Why?  Perfume molecules are more concentrated in the bottle, molecules inside the bottle move to a less concentrated space outside the bottle.

What is diffusion? (passive)  Particles in a solution tend to move from an area where they are more concentrated to an area where they are less concentrated by a process called diffusion.  When the concentration of the solute is the same throughout a system, the system has reached equilibrium.  Because diffusion depends upon particle movements, substances diffuse across membranes without requiring the cell to use energy. High concentration Low concentration Movement of solute (no energy required)

What is osmosis?(passive)  Osmosis is the diffusion of water through a selectively permeable membrane.  If the concentration of H 2 O is lower inside the cell than outside, there will be a net movement of H 2 O to the inside until equilibrium is reached.

 In isotonic solutions the concentration of the solution and cell is the same.  hypertonic solution: A solution that has a solute concentration greater than a cell placed in the solution  Hypotonic solution: A solution that has a solute concentration less than a cell placed in the solution  Water flows from a hypotonic area to a hypertonic area (as long as there is a membrane present and solutes cannot pass thorough it). Less water in cell More water in solution Higher solutes in the cell Water flows into the cell More water in cell Less water in solution Higher solutes in the solution Water flow out of the cell Water is equal inside and outside the cell Solutes equal on both sides Water flows in and out of cell. No net movement

What is facilitated diffusion? (passive)  Cell membranes have protein channels or carriers that make it easy for certain molecules to cross the membrane in a process known as facilitated diffusion.  Facilitated diffusion does not require the use of cell’s energy.  It uses the movement of the solutes from where they are higher in concentration to lower concentration.

What is Active Transport?  During active transport cells move materials against their concentration gradient.  Requires energy (ATP).  Carried out by transport proteins or pumps found in the cell membrane.  Moves molecules in only one direction.  Many cells use such proteins to move Ca 2+, K +, and Na +.  Enables cells to concentrate substances in a particular location, even against the forces of diffusion.  Remember, H + in cellular respiration Squares have a lower concentration Squares have a higher concentration

What is Active Transport? Why do you think is called active? How do substances move during passive transport? Why do you think this process is necessary?

Bulk Transport Endocytosis and Exocytosis Animation

DO now Cut a sheet of paper in half. Keep one and give the other one to a classmate Answer the five following questions. True False

Cell Membrane Model Project On a half sheet of paper, list and explain the components and functions of the parts of the cell membrane. Components to mention: Glycoproteins, Channel Proteins, Carrier Proteins, and Phospholipids.