Transcript 3 Cell membrane Notes

The Cell
Membrane
What is the cell membrane?



AKA: Plasma membrane
The boundary between the cell and the
environment
Does every cell have a cell membrane?

Yes, Each and every cell has a cell membrane.
Structure of the cell membrane

What does the cell membrane look like up close?
Lets look at one
of these
structures up
close
Structure of Phospholipid
Structure of cell membrane

Phospholipids
Phosphate head
 Glycerol
 2 Fatty acid tails

(lipids=fats, oils, etc)
Polar vs. Nonpolar
Polar- positive and negative ends (b/c
electrons are not shared equally)
Ex. Water
 Nonpolar- does not have oppositely
charged ends (atoms share electrons
equally)
 Which of the above is hydrophilic?
Hydrophobic?

Phospholipids

1.) Phosphate Head
Polar
 Hydrophilic
 Make up the outer borders of the
membrane


2.) Fatty Acid Tails
Nonpolar
 Hydrophobic
 Make up the inner part of the
membrane

Why are the phospholipids arranged tail
to tail?

-b/c water is inside and outside the cell
phosphate group is hydrophilic (polar) end
-attracts water
 fatty acid tail end is hydrophobic
(nonpolar)
-repels water

Structure of cell membrane

Phospholipid bilayer

2 layers of phospholipids make up a cell membrane
Phospholipid Bilayer

Remember polar heads and nonpolar tails
Let’s Begin to Build Our Membrane!
1.
2.
Take 1 bag with materials for you & your partner
You are going to build your phospholipids first
a. Marshmallows represent your phosphate head
b. Toothpicks represent your fatty acid tails
1. Break these in half. Please include
unsaturated fatty acid tails.
c.
Make sure to line up the phospholipid
bilayer correctly! Think polar & nonpolar!
Arrangement of phospholipids “tail to
tail”
Arrangement of phospholipids “tail to
tail” due to water inside & outside the
cell
When something is hydrophilic, it…
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2.
Has a chemical
makeup that likes to
be around water
Has a chemical
makeup that does
not like to be around
water
H
1.
Where would you expect to find water in
this cell membrane?
100%
H
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0%
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2.
Here
Here
H
1.
Other components of the cell
membrane

Cholesterol

Helps to stabilize
the
phospholipids
and keep them
from sticking
together
Building Time!
1.
2.
Now let’s add your cholesterol
into the membrane
Use the gummy bears that are in your bags to
represent the cholesterol
a.
b.
Be sure to place them correctly
Check with your teacher once your group has
completed this
Cell membranes help maintain
homeostasis, what is that?
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el
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4.
C
3.
el
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2.
Cells breathing
Cells getting blood
to them
Cells maintaining
internal conditions
Cells reproducing
C
1.
100%
Other components of the cell
membrane

Proteins

Regulate which molecules enter and which
molecules leave a cell.
Selective Permeability

The cell membrane lets some molecules in
and keeps others out
Types of proteins in the cell
membrane

Channel or Pore protein

Hydrophilic channel – allows lipid insoluble
substances to pass in and out of cell.
Let’s Build It!
1.
2.
3.
Take the Twizzler out of your bag.
This represents the channel protein.
You will need to split this in half in order
to represent both sides of the channel.
Types of proteins in the cell
membrane

Carrier Protein

Allow needed substances or waste materials to
move through the cell membrane
Let’s Build It!


Take your Candy Peanut out of the bag.
This will represent the carrier protein.

Keeping in mind what we just talked about in class,
think of a way you can turn this into what a carrier
protein is.
Types of proteins in the cell
membrane

Glycoproteins

Protein with what macromolecule attached to
it?


Carbohydrate
Functions for cell to cell recognition
Let’s Build It!
1.
2.
3.
4.
Take the Pretzel Stick out.
This will represent the “glyco” part of the
glycoprotein.
Also take out the large Gum Drop.
This will represent the protein part of the
glycoprotein
Types of proteins in the cell
membrane

Receptor Protein

These have binding sites for molecules such as
hormones or substrates to bind to
Let’s Build It!
Take your Fruit Gum Drop out of the bag.
 This will represent your receptor protein.
 You will need to use your fingers to “carve
out” the active site for this receptor protein

Types of proteins in the cell
membrane

Enzymatic Protein

Catalyze specific reactions along the inside of the cell
membrane
Let’s Build It!


Take a scrap sheet of paper and cut out a PacMan Shape
Put this cut-out into your membrane
Which way would the protein fit into the membrane?
 What would fit into Pac-Man’s mouth?

Fluid Mosaic Model of Cell Membrane
lipid bilayer is not strong & firm like a hard
shell, but it is fluid like a soap bubble
(often called a fluid mosaic model)
 individual phospholipids, arranged side by
side, float within the bilayer (cholesterol
prevents phospholipids from sticking
together)

Structure of Cell Membrane
nonpolar interior zone- true barrier that
separates the cell from its surroundings
 many polar particles like sugars, proteins,
ions, & most cell wastes cannot cross this
zone b/c they are repelled by the nonpolar
region

Arrangement of cell surface proteins
Cell Membrane Structure
Lets build a cell membrane together

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