The Plasma (Cell) Membrane

The Fluid Mosaic Model

TEM view of thePlasma 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 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

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. Diffusion2. Osmosis3. 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 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.

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 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.

Another look:

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.

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. 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)

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