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Cellular Transport
Movement of Materials
In and Out of a Cell
Plasma Membrane
• Maintains homeostasis (stable environment)
• Membrane is “selectively permeable”
• Only certain things can pass in and out
Structure of the Plasma Membrane
Fluid Mosaic Model
Membrane is not rigid
Molecules can move back and forth (fluid)
• Phospholipid Bi-layer– 2 layers of Phospholipids – Hydrophobic tails and hydrophilic heads
Cholesterol molecules:
sometimes found embedded in membrane to give it more strength and rigidity.
Carbohydrate Chains: help cells identify each other
Membrane Proteins
• Protein Channels – Provide pathway for movement of certain
materials
• Anchor Proteins– Anchor molecules in membrane so they don’t
move around
• Enzyme Proteins– Take part in chemical reactions
• Receptor Proteins – Act as binding sites for specific molecules
• Cellular communication• Recognize foreign cells• Tell cell to begin or stop activity
Movement in a Liquid Medium
• Cytoplasm has many different things dissolved in it.
– Solvent = water– Solute = stuff dissolved (ex: sugar, salt)– Solution = the mixture of solvent and solute– Concentration = how much is dissolved
• All molecules are in constant random motion, so over time they will move from one location to another.
Types of Transport
Passive TransportDoesn’t require energy
• Diffusion:– Movement of materials through the cell
membrane.– Higher concentration to lower concentration– Does not require energy (ATP)
– Ex: oxygen, carbon dioxide, water
– Dynamic Equilibrium: a point of balance that is reached when concentrations stop changing (but particles still moving!)
Example of DiffusionHigher Concentration Outside
Particles Diffuse Into Cell
Equilibrium Reached
(Diffuse In & Out Equally)
• Facilitated Diffusion:– Protein channels facilitate (help) movement
of charged ions and large molecules like glucose to cross cell membrane
– Energy (ATP) not needed
• Osmosis:– Movement (diffusion) of WATER
through the cell membrane– From high concentration to low
(of water)– No energy needed
• Aquaporins: – Water channel proteins– Involved in osmosis– Allow water to move
easily through membrane by diffusion
– Type of facilitated diffusion
Oil (fat) and water don’t mix
Channel helps water get through fatty membrane!!!
• Water moves into an area that is more concentrated with solute particles!!!!
• Equilibrium is reached and concentrations are equal on both sides of membrane
Osmosis
Water moves to area where water is less concentrated
• Osmotic Pressure: force caused by net movement of water into or out of cell
• Isotonic Solution: of the same “strength” – Same concentration as cell
• Hypertonic Solution: “above strength”– More concentrated than cell
• Hypotonic Solution: “below strength”– Less concentrated than cell
What will Happen?
• To a cell in a:– Isotonic Solution?– Hypertonic Solution?– Hypotonic Solution?
– Which way will water move?– Will it fill up and burst, shrink, or stay the same?– Types of Solutions: http://youtu.be/7-QJ-UUX0iY– Egg Experiment: http://youtu.be/SSS3EtKAzYc
• Plasmolysis: when a plant cell loses water
• Normal plant cell – large vacuole stores water
• In salt water, or in times of drought – water leaves cell to go into surroundings (wilts)
• Active Transport:– Requires energy (ATP)– Materials are moved from low to high
concentration
• Protein Pumps:– Membrane proteins– Move small molecules and ions across
membrane– Against concentration gradient (low to high)– Requires energy (ATP)
Endocytosis
• Folding in the membrane to form a vacuole
• Take in large molecules, clumps of food or whole cells
• Requires energy
Types of Endocytosis
• Phagocytosis– Cell “eating”– Cell engulf large particles by sending out
extensions of cytoplasm
– Ex: • Amoeba sends out pseudopods, • White blood cells eat bacteria and damaged cells
• Pinocytosis– Cell “drinking”– Cell takes in liquid– “Pinching in” of cell
membrane to create a storage vacuole
Exocytosis
• Cells releasing (excreting) materials
• Membrane of vacuole fuses with cell membrane
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