Download The Cell Membrane - Solon City Schools

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.
Cell membranes help maintain
homeostasis, what is that?
1.
2.
3.
4.
Cells breathing
Cells getting blood
to them
Cells maintaining
internal conditions
Cells reproducing
How do cell membranes help to
maintain homeostasis?

The cell membrane allows nutrients to
come into the cell


Glucose, amino acids, lipids
The cell membrane removes waste
Selective Permeability

The cell membrane lets some molecules in and
keeps others out

EX. A cell is low on glucose so the membrane lets in
some glucose, but does not overfill the cell with the
macromolecule.
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 cell membrane

Phospholipids
Phosphate head
 Glycerol
 2 Fatty acid tails

(lipids=fats, oils, etc)
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

Structure of Phospholipid
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)

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
Arrangement of phospholipids “tail to
tail”
Arrangement of phospholipids “tail to
tail” due to water inside & outside the
cell
When something is hydrophilic, it…
1.
2.
Has a chemical
makeup that likes to
be around water
Has a chemical
makeup that does
not like to be around
water
Where would you expect to find water in
this cell membrane?
1.
2.
Here
Here
Other components of the cell
membrane

Cholesterol

Helps to stabilize
the
phospholipids
and keep them
from sticking
together
Other components of the cell
membrane

Proteins

Regulate which molecules enter and which
molecules leave a cell.
Types of proteins in the cell
membrane

Carrier Protein

Allow needed substances or waste materials to
move through the cell membrane
Types of proteins in the cell
membrane

Channel or Pore protein

Hydrophilic channel – allows lipid insoluble
substances to pass in and out of cell.
Types of proteins in the cell
membrane

Glycoproteins

Protein with what macromolecule attached to
it?


Carbohydrate
Functions for cell to cell recognition
Types of proteins in the cell
membrane

Receptor Protein

These have binding sites for molecules such as
hormones or substrates to bind to
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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http://www.wisconline.com/objects/index_tj.asp?objid=AP1101