The Cell Membrane

1. The Cell Membrane

2. 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.

3. Cell membranes help maintain homeostasis, what is that? • Cells breathing • Cells getting blood to them • Cells maintaining internal conditions • Cells reproducing

4. 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

5. 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.

6. Structure of the cell membrane • What does the cell membrane look like up close? Lets look at one of these structures up close

7. Structure of cell membrane • Phospholipids • Phosphate head • Glycerol • 2 Fatty acid tails (lipids=fats, oils, etc)

8. 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

9. Structure of Phospholipid

10. 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)

11. 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

12. Structure of cell membrane • Phospholipid bilayer • 2 layers of phospholipids make up a cell membrane

13. Phospholipid Bilayer • Remember polar heads and nonpolar tails

14. Arrangement of phospholipids “tail to tail”

15. Arrangement of phospholipids “tail to tail” due to water inside & outside the cell

16. When something is hydrophilic, it… • Has a chemical makeup that likes to be around water • Has a chemical makeup that does not like to be around water

17. Where would you expect to find water in this cell membrane? • Here • Here

18. Other components of the cell membrane • Cholesterol • Helps to stabilize the phospholipids and keep them from sticking together

19. Other components of the cell membrane • Proteins • Regulate which molecules enter and which molecules leave a cell.

20. Types of proteins in the cell membrane • Carrier Protein • Allow needed substances or waste materials to move through the cell membrane

21. Types of proteins in the cell membrane • Channel or Pore protein • Hydrophilic channel – allows lipid insoluble substances to pass in and out of cell.

22. Types of proteins in the cell membrane • Glycoproteins • Protein with what macromolecule attached to it? • Carbohydrate • Functions for cell to cell recognition

23. Types of proteins in the cell membrane • Receptor Protein • These have binding sites for molecules such as hormones or substrates to bind to

24. 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)

25. 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

26. Arrangement of cell surface proteins

27. Cell Membrane Structure

28. Lets build a cell membrane together • http://www.wisc-online.com/objects/index_tj.asp?objid=AP1101