The Plasma
Membrane
The Plasma
Membrane

Also called cell membrane

Cell’s boundary


Maintains cell’s shape

Protects the cell
Controls what goes in and out of
the cell
Plasma membrane

Termed the phospholipid bilayer

Made of phospholipids

A bilipid layer – 2 layers
Fluid Mosaic Model

Structure

Flexible membrane



Phospholipids can move side to side
or flip-flop
Acts like an oil
Composition

Other molecules in the membrane
are like a mosaic

Different “textures” and “patterns”
(proteins and carbs, etc)
Phospholipids


Polar head (phosphate)

Can form hydrogen bonds

Hydrophilic
Nonpolar tails (fatty acids)

Hydrophobic
Phospholipids

Water inside the cell and
water outside the cell

Orient themselves

Heads face water

Tails face inside
The Plasma
Membrane


Within it there are:

Proteins

Cholesterol

Carb chains
Within the cell there is:

Cytoskeleton – Why?

For structure/support
Protein


Channels – What do they do?

Transports substances in/out of the cell

Normally they can’t get in (ex: glucose
or sodium)
Receptors – What do they do?

detect and respond to a signal

Intracellular


Within the cell

Carries signal to an area of the cell

Ex: steroids  affect DNA/genes
Membrane

Signal molecule binds to a receptor

Receptors starts a chain of events

Causes a response
Cholesterol – What does it do?


Makes membrane more fluid

able to change shape

Less rigid/more flexible
More space = more fluid (liquidlike)
Carb Chains – What do they do?

Carbs attached to:

The membrane (glycolipid)

A protein (glycoprotein)

Tells immune system that these are “self” cells

All cells have them as “identifiers”
Selective
Permeability

What does this mean?

Some substances can get in
and out

Small and/or uncharged =


Large and/or charged =


can get in/out without help
can’t get in without help
How does this relate to
homeostasis?
Plasma Membrane Videos

https://www.youtube.com/watch?v=6fhbbFd4icY
(Amoeba Sisters – Homeostasis)

https://www.youtube.com/watch?v=S7CJ7xZOjm
0 (Bozeman Science)
Building the Membrane!

Build your own plasma membrane!

Use foam shapes, pipe cleaners, markers, and more to make a model
of what the plasma membrane could look like.

This will vary between students, but make sure to include carb chains
(glycoproteins, glycolipids, and carbohydrates), proteins (channels
and receptors), cholesterol, and phospholipids