The Plasma Membrane

1
The Plasma Membrane
2
Only 2 molecules thick, this membrane allows the
passage of essential molecules in and out of the
cell.
3
Definition

• A plasma membrane functions as a selective
  barrier that allows sufficient passage of oxygen,
  nutrients, and wastes to service the entire
  volume of the cell.
• The plasma membrane is located at the boundary of
  every cell. It is composed of phospholipids and
  proteins
• The membrane building blocks are phospholipids
  containing hydrophilic and hydrophobic parts.
• Every cell has a plasma membrane.

4
The plasma Membrane

• The fluid mosaic model (S.J Singer)
• it is semi-permeable (some items are allowed in,
  others arent..its picky!)
• fluid portion is a double layer of phospholipids,
  called the phospholipid bilayer

5
Jobs of the Cell Membrane (think of a police
officer!)

• To isolate the cytoplasm from the external
  environment.
• Regulate the exchange of substances into and out
  of the cell.
• To communicate with other cells.
• To identify proteins required by the cell.

6
What the Cell membrane is made up of

• Phospholipids contain a hydrophilic head and a
  non-polar hydrophobic tail.
• Hydrogen bonds form between the phospholipid
  "heads" and the watery environment inside and
  outside of the cell.
• Hydrophobic interactions force the "tails" to
  face inward.
• The heads are hydrophillic (like water)
• The tails are hydrophobic (afraid of water)

7
DRAW AND LABEL!


8
Layer make-up!

• The phospholipids are not bonded to each other,
  instead the heads line up beside each other
  packed together like sardines. Because the heads
  are close together, the membrane is said to be
  fluid...it can bend and twist and break off to
  form vesicles.

9
Layer Make-up!

• The membrane is also super strong thanks to
  cholesterol molecules that are embedded in the
  membrane makes it stronger.

10
So how do Molecules go from the Cytoplasm to the
Extracellular fluid?
11
5 VERY IMPORTANT PROTEINS!

1. Channel Proteins - form small openings for
   molecules to diffuse through. There are two types
   of channel proteins (open channel proteins and
   gated channel proteins). Similar to a tunnel
   water slide...if the slide is open and you can
   fit...you can go through!

12
Proteins Proteins and MORE Proteins! WOW!

• 2. Carrier or Transport Proteins- binding site on
  protein surface "grabs" certain molecules and
  pulls them into the cell.

13
Proteins Proteins and MORE Proteins! WOW!

• 3. Receptor Proteins - molecular triggers that
  set off cell responses (such as release of
  hormones or opening of channel proteins). Must be
  activated on one side of the cell membrane, to
  release something on the other side.

14
Proteins Proteins and MORE Proteins! WOW!

• 4. Cell Recognition Proteins - ID tags, to
  identify cells to the body's immune system. Very
  similar to security at the dance.

15
The last important Protein for now!

• 5. Enzymatic Proteins - carry out metabolic
  reactions. There are different protein enzymes
  for every biochemical function in the body. These
  special proteins need to be activated before they
  are turned on.