 Transportation of Materials Across the Cell Membrane 1

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 Composed of double layer of phospholipids and proteins  Controls what enters or leaves the cell  Surrounds outside of ALL cells Outside of cell Inside of cell (cytoplasm) Cell membrane Proteins Protein channel Lipid bilayer Carbohydrate chains 3

 The cell membranes of all cells are selectively permeable  This means that some materials can pass easily through the membrane  Examples: H 2 0, CO 2 and O 2  This also means that some materials cannot pass easily through the membrane  Examples: glucose and salts 4

 Proteins help move large molecules or aid in cell recognition  Peripheral proteins are attached on the surface (inner or outer)  Integral proteins are embedded completely through the membrane 5

 Provide a binding site for enzymes  Interlocking surfaces bind cells together (junctions)  Contains the cytoplasm (fluid in cell) 6

 Phospholipid bilayer makes up the cell membrane  Contains a polar head (attracts H 2 O) and 2 non-polar fatty acid tails (repels H 2 O) How is a phospholipid different from a triglyceride? 7

8 Fluid: individual phospholipids and proteins can move side-to- side within the layer, like a liquid. Mosaic: the pattern produced by the scattered proteins on the surface of the cell when the membrane is viewed from above.

 Materials that are soluble in lipids can pass through the cell membrane easily  Ex: Oxygen, carbon dioxide, and water 9

Passive Transport  Does not require cellular energy  Types: 1. Simple Diffusion 2. Osmosis 3. Facilitated Diffusion Active Transport  Does require cellular energy  Types: 1. Membrane Pumps 2. Endocytosis 3. Exocytosis 10

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 Movement of materials from a region of high concentration to a region of low concentration  Materials are moving down/with their concentration gradient  Example: Oxygen diffusing into a cell and carbon dioxide diffusing out using kinetic energy 12

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 Osmosis is the passive transport (diffusion) of water across a membrane  Moves from a region of HIGH water potential (low solute) to a region of LOW water potential (high solute) 14

 The purpose of osmosis is to balance out the concentration of materials between the environment inside of the cell and the environment outside the cell  Water moves because the other materials cannot  This allows the cell to be in equilibrium - balance 15

 Solution - a liquid mixture in which the minor component (the solute) is uniformly distributed within the major component (the solvent).  Examples – salt water or glucose solutions; solutes are salt or glucose, solvent is water  Types of solutions: 1. Isotonic 2. Hypotonic 3. Hypertonic 16

10% NaCL 90% H 2 O ENVIRONMENT CELL 10% NaCL 90% H 2 O Q: What is the direction of water movement in an isotonic solution? 17 A: No net movement (water molecules moving equally back and forth)

ENVIRONMENT 10% NaCL 90% H 2 O 20% NaCL 80% H 2 O CELL Q: What is the direction of water movement in a hypotonic solution? 18 A: Water moves into the cell

ENVIRONMENT CELL 15% NaCL 85% H 2 O 5% NaCL 95% H 2 O Q: What is the direction of water movement in a hypertonic solution? 19 A: Water moves out of the cell.

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 Hypotonic solution will result in cytolysis – cell bursts from build up of water inside cell  Hypertonic solution will result in plasmolysis – cell membrane pulls away from the cell wall in plant, fungal or bacterial cells  Plant cells prefer a hypotonic environment  Animal cells prefer an isotonic environment 22

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 Uses transport proteins to move materials from high to low concentration  Examples: Glucose or amino acids moving from blood stream into a cell. 24

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 Types of Membrane Proteins: 1. Structural 2. Cell recognition 3. Communication 4. Transport: a. Channel proteins are embedded in the cell membrane & have a pore for materials to cross b. Carrier proteins can change shape to move material from one side of the membrane to the other 26

27 Channel proteins act as bridges to allow materials to pass across the membrane

Some Carrier proteins do not extend through the membrane. They bond and drag molecules through the lipid bilayer 28

 Cells need a steady supply of sodium (Na + ), potassium (K + ), calcium (Ca 2+ ) and hydrogen (H + ) in order to function correctly  Protein pumps that span the cell membrane are powered by ATP and supply these materials to the cell on demand  This requires a steady supply of ATP  Materials are moving from and area of low concentration to an area of high concentration  They are moving up/against their concentration gradient 29

3 Na+ pumped out for every 2 K+ pumped in 30

 Q: What is a vesicle?  A: A small bubble within a cell surrounded in its own lipid bilayer.  Q: What is the function of a vesicle?  A: Vesicles are involved in: Metabolism Transport of materials Enzyme storage  Types of active transport using vesicles: Exocytosis Endocytosis 31

32 Exocytosis -using a vesicle to move big stuff out of the cell

 How it works: 1. Vesicle is formed around some sort of material made by the cell (like proteins or hormones) 2. Vesicle is released and travels toward cell membrane 3. Vesicle fuses with cell membrane 4. Vesicle expels materials to the outside of the cell membrane 33

 Large amount of materials move into the cell by one of two forms of endocytosis:  Pinocytosis -  Materials dissolve in water to be brought into cell  Called “Cell Drinking”  Phagocytosis - Used to engulf large particles such as food, bacteria, etc. into vesicles.  Called “Cell Eating”  White blood cells eat foreign substances in your body this way 34

35 Pinocytosis