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 Transport
Doesn’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 Diffusion
Higher
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
Inner Life of the Cell
• http://youtu.be/yKW4F0Nu-UY