Plasma membrane Structure

Read p.115-117

Is there a plasma membrane?

• People were skeptical that the plasma membrane existed (too thin to see)

• The theory was formulated purely by circumstantial evidence by the information of what passes in and out of the cell (lipid soluble material = dissolves in fats)

• A test for lipids concluded that it did exist

Visual Evidence

• 1950’s brought visual evidence with the invention of better microscopes– Observed 2 dark

lines separated by a clear line

– Suggested a 2-layer structure

Plasma membrane

• Very thin…8000 membranes = the thickness of 1 page of paper!!

• Serves as boundaries around organelles and the cell itself

• Made of 2 layers of phospholipids

Phospholipid Bilayer

Heads

Tails

Heads

Structure of phospholipid• Head

– Hydrophilic (“water-loving”)

– Polar (easily attracted to charged particles)

– Water soluble, which allows the membrane to act like a fluid

Hea

d

Structure of phospholipid

• Tails (2 tails)

– Hydrophobic (“water-hating”)

– Flexibility varies

– Non-polar (not attracted to charged particles)

Tai

ls

Phospholipid Bilayer

Structure of the membrane

• Phospholipids lay tail to tail creating a phospholipid bilayer

• The bilayer is arranged so that the heads point outward towards the cytoplasm or the watery environment cells live in (both are polar)

• Membrane proteins are found throughout the plasma membrane to perform different jobs

– enzyme activity

– cell to cell recognition

– cell signaling

– exchanging material

Membrane Proteins

p. 117

Heads

Tails