The Cell Membrane

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Cell Membrane

• The membrane of the cell has many different names. You may hear it called:• The phospholipid bilayer• The semi-permeable membrane• Fluid Mosaic Model• Plasma membrane

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Cell Membrane Properties

• Semi-permeable • Some things can move in and out of the cell membrane

freely, while others cannot.

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Phospholipid Bilayers• The major component of Cell membranes are

phospholipids that combine to make a phospholipid bilayer.

• Phospholipid – a type of lipid• Bi – two• Layer – a sheet of material

• Two layers of phospholipids

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Phospholipid Bilayer

• This is a phospholipid • It has a phosphate head and two tails (fatty acid chains)

Head = Hydrophilic(Loves water)

Tails = Hydrophobic(Fears Water)

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Phospholipid Bilayer

• This is a phospholipid Bilayer• There are two layers of phospholipids

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Phospholipid Bilayer Formation• When put into water, phospholipids will arrange

themselves so that their heads are in the water. This allows the tails to group together and stay away from the water.

• https://www.youtube.com/watch?v=lm-dAvbl330• https://www.youtube.com/watch?v=04SP8Tw3htE

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Phospholipid Bilayer

• The Bilayer creates a sphere that is known as a liposome. Our cell membranes are a large liposome.

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Things in the Phospholipid Bilayer

• Phospholipids• Cholesterol• Open Channel Proteins• Gated Channel Proteins• Protein/Sugar Markers

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Phospholipids

• Structure: Lipids

• Function: Makes up majority of the Cell membrane

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Cholesterol

• Structure: Lipids

• Function: Stabilizes the cell membrane

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Open Channel Proteins

• Structure: Proteins

• Function: Allow molecules that cannot pass through the phospholipid bilayer into the cell

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Open Channel Protein Example• Example: Aquaporins• Water is a polar molecule and cannot pass through the

phospholipid bilayer due to the hydrophobic tails. Instead it moves in and out of the cells through a type of open channel protein called an aquaporin.

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Gated Channel Proteins• Structure: Proteins

• Function: Allow molecules that cannot pass through the phospholipid bilayer to pass only if certain conditions are met

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Gated Channel Protein Example• Example: Insulin and Glucose• Before Glucose can go through a gated protein channel,

insulin must first signal the gated protein channel to open.

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Markers• Structure: Proteins + Carbohydrate Chains

• Function: Tag and identify the cell. Important for immune system function.

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Gated Channel Protein Example• Example: Blood Types• Blood Types are determined by the type of carbohydrate chains

you have on your red blood cells.• If you are Type O you have do not have A or B carbohydrate chains

• Your body will attack any cell that has A or B carbohydrate Chains• If you are Type A you have A carbohydrate Chains

• Your body will attack any cells that have B carbohydrate chains• If you are type B you have B carbohydrate chains

• Your body will attack any cells that have A carbohydrate chains• If you are Type AB you have both A and B carbohydrate chains

• Your body will not attack A or B chains

O A B AB

=A

=B

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Solutions

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Solutions

• A solution is made of at least two parts. The solvent and one or more solutes.

• Solvent: A liquid, usually water, that dissolves a solute• Solute: Something that is dissolved by a liquid

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Solution

Water

SolventSolute

Solution

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Concentrations

• Concentration: how much solute is in the solution.

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Different Concentrations

Low Concentration High Concentration

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• Concentration Gradient: A change in concentration between two solutions.

• Equilibrium: the concentration of particles is equal on both sides of the semi-permeable membrane.

Properties of Two Interacting Solutions

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Concentration Gradients

• When two solutions with different concentrations are placed together a concentration gradient appears

Solution with a low

concentration

Solution with a high

concentration

Concentration Gradient

Equilibrium

•When two solutions with different concentrations mix until their concentrations are the same then equilibrium has been met.

Equal Concentrations

Equal Concentrations

Equilibrium

Comparing Solutions• When we compare two solutions together we use three terms to

describe the solutions.

• Hypertonic – a solution that has a higher concentration (amount of solute)

• Isotonic – a solution that has the same concentration (amount of solute)

• Hypotonic – a solution that has a lower concentration (amount of solute)

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Isotonic

• A solution that has the same amount of solutes (concentration) when compared to another solution.

50% H2O50% Solute

50% H2O50% Solute

Have the same concentration

Isotonic

Isotonic

Hypotonic

• A solution that has a lower amount of solutes (concentration) when compared to another solution.

63% H2O37% Solute

90% H2O10% Solute

Hypotonic

Hypertonic

Hypertonic

• A solution that has a higher amount of solutes (concentration) when compared to another solution.

90% H2O10% Solute

40% H2O60% Solute

Hypertonic

Hypotonic