Do Now
• Handout 7.2 The Plasma Membrane
Before you read handout
• Homework
– Eukaryotic Cell Structure handout
– Organelle quiz on Friday
• Know the structures and functions
• Be able to label a diagram
– Test next Tuesday on Chapter 7
Lipids and Cell Membrane
Structure
Lipids (a.k.a. Fats)
• Lipids are NOT soluble in water.
– Lipids are non-polar.
• Lipids store large amounts of energy.
• The monomers are called fatty acids.
• Lipids make up most of the cell membrane.
Phospholipids
The cell membrane is made of special lipids called
phospholipids.
Polar heads are hydrophilic – “water loving”
Non-polar tails are hydrophobic – “water
fearing”
The polarity determines the arrangement of the
phospholipids.
Phospholipids form two layers – called lipid
bilayer
Polar heads face outward (water outside and
inside the cell)
Non-polar tails face inward (creates barrier to
protect the cell)
Cell Membrane Structure
• The cell membrane also contains other fats,
proteins, and carbohydrates.
Cell Membrane Proteins
1. Integral Proteins

Proteins that penetrate completely through
the membrane (inside)
2. Peripheral Proteins


Embedded but not all the way
Located on the outside surface and function to
help transport different substances into and out
of the cell.
fluid mosaic model
Cell Membrane Functions
• Controls what enters and exits the cell.
– Selectively Permeable - only lets certain molecules into
and out of the cell
• Maintains cell’s shape.
• Connects each cell to other cells near it.
• Can allow movement of the cell
– parts can move around each other, called the fluid
mosaic model.
fluid mosaic model
Cell Membrane Model Answers
• 1. Phospholipid molecules move freely
throughout the membrane in a fluid
motion, while the overall structure of the
membrane remains unchanged.
• 2. Phospholipid has two distinct parts
– Polar, hydrophilic head form the inside and
outside surfaces of the membrane
– 2 Nonpolar, hydrophobic tails form the interior
core of the membrane
Membrane Model Answers
• 3. Selective permeability refers to the fact
that the membrane functions as a
gatekeeper, monitoring and facilitating the
entry and exit of molecules into and out of
the cell.
• 4. Channels or pumps that actively move
waste out of cell and move nutrients into
the cell.
Closure
• Complete The Plasma Membrane handout
pg 72-73
• Turn in as you walk out