Function of the Plasma Membrane• A “selectively” or “semi” permeable
membrane that restricts the movement of various molecules into and out of the cell.
• Allows for communication between cells.
• Provides the cell with a specific “marker” that tells all of the other cells who it is.
Membrane Composition1. Phospholipid molecules:
* make up most of the cell membrane* provides a barrier between cytoplasm & outside the cell
2. Carrier proteins:* used to move molecules across the membrane* some require energy others do not
3. Glycoproteins/ Glycolipids: * used as cell markers
Phospholipids • Hydrophilic (loves H2O )
head represents the PHOSPHO part of the molecule.
• Hydrophobic (hates H2O ) tail represents the LIPID part of the molecule.
• Outside & inside the cell there’s a lot of H2O , therefore the hydrophilic part is in contact with H2O but the hydrophobic part is as far away as possible from H2O.
Carrier Protein• Passive Channel:
*Leakage channel*Requires no cellular energy
• Active Channel:* Open and close to let larger molecules through* Uses Cellular energy (ATP)
• Channel Protein
Plasma (Cell) Membrane
• Animation # 1• Animation # 2• Animation # 3
Moving Materials Across The Cell Membrane
Two ways :1. Passive Transport (PT)
Requires no cellular energy
2. Active Transport (AT)Requires cellular energy (ATP)
Particle Theory
• 1. All matter is made of particles
• 2. The particles are in constant motion (Kinetic motion of particles)
• 3. The closer the particles are together, the greater the attractiveness between them.
Particle Theory
• Solids: definite shape and volume
• Liquids: definite volume but indefinite shape
• Gases: indefinite shape and volume• Matter
Diffusion
• Molecules move from an area of high concentration [ ] to an area of low [ ] until Equilibrium is reached where [ ] levels are equal.
Diffusion
• Small molecules like O2 and CO2 can diffuse across the plasma membrane. Large molecules (ex. Glucose) or ions (an ion is a charged particle) can’t pass through by diffusion.
Osmosis
• Special type of diffusion involving water passing through a selectively permeable membrane.
• Water always move from an area of high [ ] to an area of low [ ].
How Osmosis Works
Movement of water
Dilute sugar solution (Water more concentrated)
Concentrated sugar solution (Water less concentrated)
Sugar molecules
Selectively permeable membrane
Osmosis & Cellular Environments
Hypotonic :water [ ] outside cell is greater than water [ ] inside cell.
Hypertonic: water [ ] outside is less than water [ ] inside.
Isotonic: water [ ] outside equals water [ ] inside.
Animal Cell
Hypotonic Solution
high H2O [ ] outside , H2O flows into cell , pressure builds up , cell bursts which is called cytolysis.
Animal Cell
Hypertonic Solution
low H2O [ ] outside , H2O flows out of cell pressure drops , cell becomes dehydrated and shrivels up.
Animal Cell
Isotonic Solution
The H2O [ ] outside the cell equals the H2O [ ] inside the cell. NO change in cell. H2O moves in and out at the same rate.
Plant Cell
Hypotonic Solution
high H2O [ ] outside the cell , H2O flows in , pressure builds up , cytoplasm pushes against cell membrane & wall. This pressure is Turgor Pressure. The cell looks stiff or Turgid.
Plant Cell
Hypertonic Solution
low H2O [ ] outside cell , H2O flows out , pressure drops, plasma membrane may collapse which is called plasmolysis. The cell is referred to as being wilted or flaccid.
Plant Cell
Isotonic Solution
The H2O [ ] outside the cell equals the H2O [ ] inside the cell. NO change in the cell. H2O moves inside & outside at the same rate.
Facilitated Diffusion
• Form of PT (no ATP)• Uses Passive Channel Proteins in cell
membrane to transport large molecules or ions across cell membrane.
• These channel proteins act as ports , shielding these molecules from the cell membrane.
• Still moving from an area of high [ ] to an area of low [ ].
Active Transport (AT)• AT requires ATP to move materials across the
cell membrane against the [ ] gradient.
• 3 Types of AT :1. Endocytosis2. Exocytosis3. Active Channel Proteins
Endocytosis• A cell extends its plasma
membrane around very large items and engulfs them , moving from an area of decreased [ ] to an area of increased [ ].
• 2 Types :1.
Pinocytosis (small particles & liquid)
2. Phagocytosis (large particles)
Active Channel Proteins• Proteins or “pumps” in the cell membrane bind to
small molecules or ions and by changing shape move molecules from an area of low [ ] to high [ ] .
• Movement against the Concentration Gradient • Particles are drawn against the concentration
gradient using active channels that open and close using cellular energy ATP
• L to H • L-H
Homeostasis
• All these examples of cellular traffic are designed to help the cell maintain a state of balance between the inside and the outside of the cell.