CHAPTER 5 The Working Cell Modules 5.10 – 5.21

CELL MEMBRANE STRUCTURE AND FUNCTION Cell membranes controls entry and exit of materials into the cell Membranes are selectively permeable or semipermeable (some substances can pass throught it, while others cannot).   Cytoplasm Figure 5.10

Your teacher will draw this on the board for you to copy. The cell membrane has 2 major components: 1. A double layer of phospholipids (lipid bilayer) 2. Protein molecules that serve as channels, pumps or receptors for communication. Your teacher will draw this on the board for you to copy.

Draw this diagram of the cell membrane: Hydrophobic ↵tails fatty acid ↵Phosphate Head phospholipid

5.11 Membrane phospholipids form a bilayer Phospholipids are the main structural components of membranes They each have a hydrophilic head and two hydrophobic tails Head Symbol Tails Figure 5.11A

In water, phospholipids form a stable bilayer The heads face outward and the tails face inward Water Hydrophilic heads Hydrophobic tails Water Figure 5.11B

The plasma membrane of an animal cell Glycoprotein Carbohydrate (of glycoprotein) Fibers of the extracellular matrix Glycolipid Phospholipid Cholesterol Microfilaments of the cytoskeleton Proteins CYTOPLASM Figure 5.12

5.13 Proteins make the membrane a mosaic of function Proteins that serve as channels Others transport substances across the membrane Figure 5.13 Transport

Cell membrane structure http://www.wisc-online.com/objects/index_tj.asp?objid=AP1101

STOP for demonstration

Your cells can move some substances across their membranes using NO ENERGY!

Background Information on Diffusion - Diffusion is a process where molecules move from a region of higher concentration to a region of lower concentration. - The difference in concentration on either side of a membrane is known as a concentration gradient.

Background Information on Diffusion - Diffusion of water molecules across a membrane is known as osmosis. - Diffusion will occur until an equilibrium is reached. (some will move each direction in equal amounts)

5.14 Passive transport is diffusion across a membrane In passive transport, substances diffuse through membranes without work by the cell They spread from areas of high concentration to areas of lower concentration Molecule of dye Membrane EQUILIBRIUM EQUILIBRIUM Figure 5.14A & B

Many membrane proteins are enzymes Some proteins function as receptors for chemical messages from other cells The binding of a messenger to a receptor may trigger signal transduction Messenger molecule Receptor Activated molecule Figure 5.13 Enzyme activity Signal transduction

Transport Across the Cell Membrane The cell uses 2 types of transport: 1. Passive transport - Passive transport requires NO ENERGY use by the cell. Substances move along a concentration gradient.

1. Passive transport continued… a. Molecules may be moved through a process called simple diffusion. - Examples: Water, oxygen, carbon dioxide, lipid soluble molecules

1. Passive transport continued… b. Facilitated diffusion - Uses carrier proteins to transport molecules that are not lipid soluble - Examples: glucose, some ions – sodium, potassium

Link to illustrate passive transport http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html Link to illustrate passive transport

2. Active Transport - This transport requires the cell to USE ENERGY - Examples: large compounds OR when molecules are moved against the concentration gradient.

2. Active Transport 2 types of Active Transport Protein Pumps – carry molecules across the membrane against the concentration gradient (moleculer transport) neuron animation

2. Active Transport b. Bulk Transport - This is where large amounts of molecules are carried across. There are 3 types of this.

2. Active Transport b. Bulk Transport 1. Endocytosis – cell membrane brings materials into the cell by infoldings of the membrane which can form vacuoles. 2 Forms: Phagocytosis – ameba undissolved materials Ex: Ameba eating food Pinocytosis – dissolved materials

or the membrane may fold inward, trapping material from the outside (endocytosis) Figure 5.19B

Material bound to receptor proteins Three kinds of endocytosis Pseudopod of amoeba Food being ingested Plasma membrane Material bound to receptor proteins PIT Cytoplasm Figure 5.19C

2. Active Transport b. Large quantity Transport 2. Exocytosis – removes material from the cell through outpinchings of the cell membrane. Ex: wastes 3. Contractile Vacuole - Used for removing excess water from a cell. Ex: a freshwater paramecium contractile vacuole video

5.19 Exocytosis and endocytosis transport large molecules To move large molecules or particles through a membrane a vesicle may fuse with the membrane and expel its contents (exocytosis) FLUID OUTSIDE CELL CYTOPLASM Figure 5.19A

Link to illustrate active transport http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html Link to illustrate active transport

What will happen to a plant or animal cell when placed in fresh or salt water?

Background Information Hypertonic – Solution that has a higher concentration of Solute than a surrounding solution Hypotonic – Solution that has a lower concentration of solute than a surrounding Solution Isotonic – Two solutions have the same solute concentrations

- water is more highly concentrated outside the cell FRESH WATER Animal Cell Plant Cell - water is more highly concentrated outside the cell - water will enter the cell 100% H20 SAME, but plant w/cell wall Cell85%H20

Red blood cell will explode. (called CYTOLYSIS) Plant Cell will NOT explode because the cell wall prohibits it. (becomes TURGID)

- water is more highly concentrated inside the cell SALT WATER Animal cell Plant Cell - water is more highly concentrated inside the cell - water will exit the cell 80% H20 20% salt SAME, but plant w/cell wall Cell85%H20

- Plant cell will lose water. Animal Cell will lose water and shrink (becomes CRENATE) - The cell membrane will pull away from the cell wall – (this is called PLASMOLYSIS.)

osmosis Red blood cell in isotonic environment Red blood cell in hypertonic solution cytolysis and crenation in red blood cells osmosis http://www.wisc-online.com/objects/index_tj.asp?objid=AP11003

5.15 Osmosis is the passive transport of water Hypotonic solution Hypertonic solution In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration Selectively permeable membrane Solute molecule HYPOTONIC SOLUTION HYPERTONIC SOLUTION Water molecule Selectively permeable membrane Solute molecule with cluster of water molecules NET FLOW OF WATER Figure 5.15

5.16 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 The control of water balance (osmoregulation) is essential for organisms ISOTONIC SOLUTION HYPOTONIC SOLUTION HYPERTONIC SOLUTION ANIMAL CELL (1) Normal (2) Lysing (3) Shriveled Plasma membrane PLANT CELL Figure 5.16 (4) Flaccid (5) Turgid (6) Shriveled

5.17 Transport proteins facilitate diffusion across membranes Small nonpolar molecules diffuse freely through the phospholipid bilayer Many other kinds of molecules pass through selective protein pores by facilitated diffusion Solute molecule Transport protein Figure 5.17