1. The Cell Membrane

2. Overview
Cell membrane separates living cell from nonliving surroundings
thin barrier = 8nm thick
Controls traffic in & out of the cell
selectively permeable
allows some substances to cross more easily than others
hydrophobic vs hydrophilic
Made of phospholipids, proteins & other macromolecules

3. Phospholipids Fatty acid tails Phosphate group head
hydrophobic
Phosphate group head
hydrophilic
Arranged as a bilayer
Fatty acid
2 layers of
phospholipids….
It must be a
phospholipid bilayer!!

4. Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic
tails
polar
hydrophilic
heads

5. It’s like a fluid… It’s like a mosaic… It’s the Fluid Mosaic Model!
More than lipids…
Membrane proteins
It’s like a fluid… It’s like a mosaic…
It’s the Fluid Mosaic Model!

6. Question:
Describe the modern fluid mosaic model of membrane structure to your neighbor.
Let your neighbor tell you about selective permeability….

7. Filaments of cytoskeleton
A collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer
Glycoprotein
Extracellular fluid
Glycolipid
Transmembrane
proteins
The carbohydrates are not inserted into the membrane -- they are too hydrophilic for that. They are attached to embedded proteins -- glycoproteins.
Phospholipids
Filaments of cytoskeleton
Cholesterol
Peripheral
protein
Cytoplasm

8. Membrane Proteins Proteins determine membrane’s specific functions
cell membrane & organelle membranes each have unique collections of proteins
Membrane proteins:
peripheral proteins
bound to surface of membrane
cell surface identity marker (antigens)
Glycoproteins
integral proteins
penetrate lipid bilayer
transmembrane protein
transport proteins

9. Question:
Can you think of 3 things that all animal cells would need to take in?
List two substances that need to be transported out of animal cells.

10. Why are proteins the perfect molecule to build structures in the cell membrane?

11. nonpolar & hydrophobic
Classes of amino acids
What do these amino acids have in common?
nonpolar & hydrophobic

12. I like the polar ones the best!
Classes of amino acids
What do these amino acids have in common?
I like the polar ones the best!
polar & hydrophilic

13. Proteins domains anchor molecule
Within membrane
nonpolar amino acids
hydrophobic
anchors protein into membrane
On outer surfaces of membrane
polar amino acids
hydrophilic
extend into extracellular fluid & into cytosol
Polar areas
of protein
Nonpolar areas of protein

14. Many Functions of Membrane Proteins
Outside
Plasma
membrane
Inside
Transporter
Enzyme activity
Cell surface receptor
Signal transduction - transmitting a signal from outside the cell to the cell nucleus, like receiving a hormone which triggers a receptor on the inside of the cell that then signals to the nucleus that a protein must be made.
Cell surface identity marker
Cell adhesion
Attachment to the cytoskeleton

15. Membrane carbohydrates
Play a key role in cell-cell recognition
ability of a cell to distinguish one cell from another
antigens
important in organ & tissue development
basis for rejection of foreign cells by immune system
The four human blood groups (A, B, AB, and O) differ in the external carbohydrates on red blood cells.

16. There are lots of membranes in eukaryotic cells!

17. Membrane-Bound Organelles

18. Any Questions??