The Plasma (Cell) Membrane The Fluid Mosaic Model

TEM view of the Plasma Membrane

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 Composition 1.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 H 2 O ) head represents the PHOSPHO part of the molecule. Hydrophobic (hates H 2 O ) tail represents the LIPID part of the molecule. Outside & inside the cell there’s a lot of H 2 O, therefore the hydrophilic part is in contact with H 2 O but the hydrophobic part is as far away as possible from H 2 O.

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

Cell Membrane Inside of cell (cytoplasm) Protein channel Phospholipid Bilayer Glycoproteins

Plasma (Cell) Membrane Animation # 1 Animation # 2 Animation # 3

Cellular Traffic Worksheet #1-4

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

Three Types of Passive Transport 1.Diffusion 2.Osmosis 3. Facilitated Diffusion

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 O 2 and CO 2 can diffuse across the plasma membrane. Large molecules (ex. Glucose) or ions (an ion is a charged particle) can’t pass through by diffusion.

Cellular Traffic Worksheet #5-7

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 H 2 O [ ] outside, H 2 O flows into cell, pressure builds up, cell bursts which is called cytolysis.

Animal Cell Hypertonic Solution low H 2 O [ ] outside, H 2 O flows out of cell pressure drops, cell becomes dehydrated and shrivels up.

Animal Cell Isotonic Solution The H 2 O [ ] outside the cell equals the H 2 O [ ] inside the cell. NO change in cell. H 2 O moves in and out at the same rate.

Another look:

Plant Cell Hypotonic Solution high H 2 O [ ] outside the cell, H 2 O 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 H 2 O [ ] outside cell, H 2 O 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 H 2 O [ ] outside the cell equals the H 2 O [ ] inside the cell. NO change in the cell. H 2 O moves inside & outside at the same rate.

Another look:

Cellular Traffic Worksheet #8-11

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 [ ].

Protein channel Glucose molecules

Cellular Traffic Worksheet #12-13

Active Transport (AT) AT requires ATP to move materials across the cell membrane against the [ ] gradient. 3 Types of AT : 1. Endocytosis 2. Exocytosis 3. 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)

Pinocytosis

Exocytosis Excreting materials from a cell packaged in vesicles. The cell uses ATP energy.

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.

Cellular Traffic Worksheet #14-18

Test Yourself #19-22