1. And movement through membranes

2. Phospholipids Phospholipids are made up of a Phosphate head and Two fatty acid tails The head portion “loves water”: It is HYDROPHILIC The tails “hate water”: They are HYDROPHOBIC

3. Phospholipid Bilayer Cytoplasm of cells is water based and most cells live in a watery environment. The phosphate heads are attracted to this water. Watery environment Watery cytoplasm

4. Phospholipid Bilayer The fatty acid tails form a lipid layer in the middle of the membrane. Water and water soluble substances do not move easily through this lipid layer. The membrane can therefore be a barrier or partition between two parts of a cell. Lipid Layer

5. Proteins in Membranes Globular proteins can be a variety of shapes. These can be found attached to (peripheral), or within membranes(integral). Proteins can also have hydrophobic and hydrophilic surfaces, and this affects how they will sit in the phospholipid bilayer.

6. Proteins in Membranes Hydrophobic portions of the proteins are repelled by water. Proteins will lie in the membrane so that the hydrophobic areas are surrounded by fatty acid tails. Hydrophilic areas will be exposed to water.

7. Cell Membrane Structure Glycocalyx Channel protein Intrinsic protein Exterior of Cell Cytoskeleton fibrils Other non-globular proteins and cholesterol also in membrane Transmembrane Protein Interior of Cell

8. Fluid Mosaic Model The membrane is fluid in the sense that the proteins can move within the membrane. It is a mosaic because the distribution of the molecules is not regular.

9. Diffusion through Membranes Movement of dissolved substances between the phospholipid molecules is very limited. (So, it happens, but not much!) The phospholipids are always moving past each other, and this leaves occasional gaps.

10. Channel Proteins Some proteins are shaped like channels. The inner surfaces of the channel are hydrophilic. This allows water and dissolved substances to move through the membrane. The channels are like pores in the membrane.

11. Facilitated Diffusion Some channels are specifically adapted to transport certain molecules across the membrane. Facilitated diffusion is a passive process and uses no energy. membrane molecule Channel protein

12. Facilitated Diffusion The molecule interacts with the channel protein and causes it to change shape. Only certain molecules can cause this to happen

13. Facilitated Diffusion The molecule is released by the channel protein It has been moved across the membrane, down its concentration gradient The channel protein will return to its original shape.

14. Active Transport Active transport occurs in a similar manner to facilitated diffusion EXCEPT that energy is required to make it happen. Like active transport there will be an interaction between the molecule and the channel protein.

15. Active Transport Energy is supplied by ATP The molecule is moved across the membrane AGAINST its concentration gradient.

16. Active Transport Active Transport is used when the cells need to accumulate certain substances at a higher concentration than they are found in the environment. ATP = Adenosine Tri Phosphate ADP = Adenosine Di Phosphate ATP is regenerated in the mitochondria

17. Membrane movements: EXOCTYOSIS: The process of exporting material from the cell. Vesicles are released from the Golgi body and fuse with the cell membrane during this process. ENDOCYTOSIS: The process of taking material into the cell. (Think “entrance”). There are two types: PHAGOCYTOSIS – like “cell eating” PINOCYTOSIS – like “cell drinking”

18. Exocytosis Exocytosis is a process that allows substances to be exported from a cell. The membrane of the secretory vesicle moves towards the cell membrane. Digestive enzymes are exported this way.

19. Exocytosis: A vesicle moves towards the cell membrane. When the vesicle touches the cell membrane the process of exocytosis can start. vesicle Cell membrane Substance for export

20. Exocytosis The cell membrane and the membrane of the vesicle fuse. The contents of the vesicle are expelled from the cell.

21. Exocytosis The membrane that surrounded the vesicle becomes part of the cell membrane. The vesicle membrane is shown here in orange before and after exocytosis. Vesicle membrane

22. Endocytosis: Phagocytosis Large particles that are outside the cell may be taken in by a process called PHAGOCYTOSIS (a type of ENDOCYTOSIS) The cell membrane moves around the particles to form a food cup. Food cup

23. The out-foldings of the cell membrane are called pseudopodia (pronounced sudo-pode-ee-aa). Pseudo = false. Pod = foot. A food vacuole is formed. Endocytosis: Phagocytosis Pseudopodia Food vacuole

24. Endocytosis: Phagocytosis The contents of the food cup will usually be digested by enzymes from a lysosome. The membrane of the lysosome fuses with the membrane of the food vacuole. lysosome enzymes

25. Active and Passive Processes Processes that are PASSIVE require no input of energy. They include: Diffusion Osmosis Facilitated Diffusion Processes that are ACTIVE require energy in the form of ATP to happen. They include: Active Transport Exocytosis Endocytosis