Movement Through the Cell Membrane

Fluid Mosaic Model of the Cell Membrane

Between the inner cell and the conditions of the outer cell stands the cells plasma membrane. It is flexible and not incredibly strong. The lipid molecules of the cell membrane naturally assemble in a double membrane because their tails repel water and their heads attract it. Proteins occur within the lipid molecules. The proteins receive signals from the outside world and they transport nutrients and waste. The molecules located within the cells are constantly moving and changing positions. A semi-permeable barrier around the cell protects the cell because it allows what comes in and what leaves. The barrier acts similar to a border patrol. 

Three things that make up the cell membrane-

1. Lipids

2. Proteins

3. Carbohydrates

Parts to the Cell Membrane

·      Phospholipid Bilayer: Two phospholipid layers

o   Phospholipid bilayer (structure)

o   Carbohydrates (cell identification)

o   Proteins (transport channel)

·      Hydrophilic “Head”: Water liking, attracted to water.

o   Made up of phosphate

·      Hydrophobic “Tail”: Repels water

o   Made up of lipids

·      Passive Transport- is the movement of substances across the cell membrane.

o   What the cell loves

o   Moves back and forth

o   Substances can cross the cell membrane without any input of energy by the cell.

·      Diffusion- is the movement of molecules from an area of higher concentration to area of lower concentration.

o   Moves until it gets to the equilibrium

·      Concentration Gradient- Is the difference in the concentration of molecules across a space.

o   Also moves until it gets to the equilibrium

·      Equilibrium- Is when the concentration of the molecules of a substance is the same Osmosis- is the process by which water molecules diffuse across a cell membrane from high concentration to low concentration.

o   Diffusion stops at the equilibrium

How does diffusion work throughout our cell membrane?

When there is high concentration on the outside of our cell over time it will start to diffuse across Highà Low concentration in the inside of our cell. It will continue to do this until it is balanced. If it becomes too concentrated in the inside of our cell it will diffuse towards the outside of our cell.

·      Three types of Passive Transport

o   Diffusion- high concentrated area à low concentrated area

o   Osmosis- diffusion, but only deals with water

§  It’s the high concentration of water, not sugar, etc.

§  Occurs within our own blood cells

·      Isotonic mediums- perfect balanced (healthy blood cell)

·      Hypertonic mediums- more pure on the inside (unhealthy; causes cell to be damaged)

·      Hypotonic mediums- more pure water on the outside (unhealthy)

o   Facilitative Diffusion- larger molecules use carrier proteins to help them pass through the cell membrane

·      Active Transport

o   Requires Energy

o   Types of active transport

§  Endocytosis- entering the cell

·      Phagocytosis- when cells take in large particles (cell eating)

·      Pinocytosis- when cells take in fluid (cell drinking)

§  Exocytosis- exiting the cell

§  Sodium/potassium pump- pump used to move sodium and potassium ions from low areas of concentration to high concentration

·      Want to actively pump the concentration from the inside to the outside for the sodium ions

·      For the potassium ions we want to have a high concentration on the inside

·      It takes the sodium ions from the inside and loads three of them up into the enzyme. There will be a designated spot for the ions.

·      It takes ATP and drops off one of its phosphates which will allows the enzyme to close.

·      Then the enzyme opens up to the outside and allows the ions to move freely. Which creates a high concentration of sodium on the outside.

·      Then a similar routine occurs with the potassium however only two load up at a time.  

Basic Structure of a Cell Membrane

For more information regarding movement through the cell membrane go to http://www.sophia.org/tutorials/unit-5-movement-throught-the-cell-membrane