Cells- Part 2:

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• Cells- Part 2
• The Cells Plasma Membrane

All images in this presentation are public domain
unless otherwise indicated. Photo credit is
given where required.
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What is the Plasma Membrane?
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The Plasma Membrane
The Cell

• Forms the outer structure of the cell (like your
  skin in a way)
• Acts as a barrier between the inside and the
  outside of the cell.
• The structure (lipid bilayer) allows the membrane
  to be fluid.

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Well look at each component of the plasma
membrane. As we discuss it label it on your
diagram and add any notes you will find useful
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The Phospholipid Molecule

• One single component of the plasma membrane is
  this molecule The phospholipid. You noted how
  the phospholipids orientated themselves in the
  video.

Wikipedia
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Whats a Phospholipid?

• Its a pair of fatty acid chains and a phosphate
  group attached to a glycerol backbone.
• Polar (water-soluble) heads face out and the
  nonpolar fatty acids hang inside.

Inside the cell
Outside the cell
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Fatty Acid Tails

• Flexibility
• The fatty acid tails are flexible, causing the
  lipid bilayer to be fluid. This makes the cells
  flexible. At body temperature, membranes are a
  liquid with a consistency that is similar to
  cooking oil.

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Membrane Structure

• Plasma Membranes consist of a phospholipid
  bilayer (and proteins) in a specific arrangement.
• The surfaces of cell membranes are hydrophilic
  (water-loving) the interiors are hydrophobic
  (water fearing). Hydrophilic molecules tend to
  interact with water and with each other.
  Hydrophobic molecules avoid interaction with
  water and tend to interact with other hydrophobic
  molecules.

WATERY
Outside the Cell
All cells live in a watery environment
Inside the Cell
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Other components of the plasma membrane
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Proteins

• Proteins are also embedded in the Membrane
• Proteins are scattered throughout the membrane.
• They may be attached to inner surface, embedded
  in the bilayer, or attached to the outer surface.
• Hydrophilic (polar) regions of the protein
  project from the inner or outer surface.  
  Hydrophobic (nonpolar) regions are embedded
  within the membrane.

Proteins
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Transport Proteins
A few substances move freely across the cell
membrane by passive diffusion. Most small
molecules or ions require the assistance of
specific protein carriers to transport them
across the membrane. Note that we will discuss
Transport to a greater extent in section 4 of
this Cell unit
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Cholesterol

• In animals, cholesterol is a major membrane
  lipid. It may be equal in amount to
  phospholipids.
• It is similar to phospholipids in that it one end
  is hydrophilic (water loving -polar), the other
  end is hydrophobic (water hating non-polar). Note
  that the polar head of the cholesterol is
  orientated the same way as the polar head of the
  phospholipids.
• Cholesterol makes the membrane less permeable to
  most biological molecules.

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Cholesterol
Cholesterol helps maintain the fluidity of cell
membranes and by adding firmness to the plasma
membrane also prevents it from becoming overly
fluid so Cholesterol generally helps the plasma
membrane maintain its structure
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Carbohydrate Chains

• Lipids and proteins within the membrane may have
  a carbohydrate chain attached. These
  carbohydrates often function as cell
  identification markers, allowing cells to
  identify other cells.  This is particularly
  important in the immune system where cells
  patrolling the body's tissues identify and
  destroy foreign invaders such as bacteria or
  viruses.

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Cytoskeleton

• The cytoskeleton is a network of protein elements
  that extend through the cytoplasm in eukaryotic
  cells.
• It provides for the distinctive shape of cells
  such as red blood cells, muscle cells, and nerve
  cells (neurons). It produces movement of cells
  and is associated with movement of materials
  within cells.

The Green structure is the cytoskeleton of the
cell
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The Fluid Mosaic Model

• The phospholipids create what is called the Fluid
  Mosaic.
• A fluid can be described as a substance that can
  change positions without separating.
• A mosaic in art is a picture made up of many
  small pieces like little tiles or glass.

Watch this short video for a good explanation of
why the phospholipid bilayer is called a fluid
mosaic
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For further study

• Heres a good link to help you further understand
  the cellular membrane
• The Next lesson in this unit on the cell is
• The Cell Part 3 Organelles