THE PLASMA MEMBRANE

ONLY 2 MOLECULES THICK, THIS MEMBRANE ALLOWS THE PASSAGE OF ESSENTIAL MOLECULES IN AND OUT OF THE CELL.

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.

THE PLASMA MEMBRANE

The fluid mosaic model (S.J Singer) it is semi-permeable (some items are allowed in,

others aren’t..it’s picky!) fluid portion is a double layer of phospholipids,

called the phospholipid bilayer

JOBS OF THE CELL MEMBRANE (THINK OF A POLICE OFFICER!)

1. To isolate the cytoplasm from the external environment.

2. Regulate the exchange of substances into and out of the cell.

3. To communicate with other cells.

4. To identify proteins required by the cell.

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)

DRAW AND LABEL!

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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.

LAYER MAKE-UP!

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

SO HOW DO MOLECULES GO FROM THE CYTOPLASM TO THE EXTRACELLULAR FLUID?

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!

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.

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.

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.

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.