CELL MEMBRANES and TRANSPORT. Regular Biology Mr. Wilbrandt

Transcription

1 CELL MEMBRANES and TRANSPORT Regular Biology Mr. Wilbrandt 1

2 Targets I will be able to.. Identify the parts of the cell or plasma membrane Compare and contrast how the different parts of the membrane work. 2

3 The Cell 3

4 Cell membrane All living things are surrounded by a membrane. A cell membrane is also known as plasma membrane. Controls exchange of materials such as nutrients and waste between cells and their environment. Has other important functions for example to enable cells to receive hormones. To understand the function of anything in biology, you must study the structure first! 4

5 Cell Membranes from Opposing Neurons (TEM x436,740). Nerve cell Gap between cells Cell membrane { } cell membrane Nerve cell 7nm wide AS Biology. Foundation. Cell membranes and Transport 5

6 Cell membranes are made of PHOSPHOLIPIDs HYDROPHILIC (+) heads (water liking) -Attracted to the water HYDROPHOBIC (-) tails (water fearing) -Not attracted to the water A Phospholipid 6

7 Phospholipids are important structural components of cell membranes. Phospholipids are modified so that a phosphate group (PO 4 -) replaces one of the three fatty acids normally found on a lipid. The addition of this group makes a polar "head" and two nonpolar "tails". 7

8 HYDROPHILIC HEAD At the other end of the phospholipid is a phosphate group and several double bonded oxygens. The atoms at this end of the molecule are not shared equally. This end of the molecule has a charge and is attracted to water. It is POLAR A phospholipid HYDROPHOBIC TAILS The two long chains coming off of the bottom of this molecule are made up of carbon and hydrogen. Because both of these elements share their electrons evenly these chains have no charge. They are NON POLAR. Molecules with no charge are not attracted to water; as a result water molecules tend to push them out of the way as they are attracted to each other. This causes molecules with no charge not to dissolve in water. 3D model of a Phospholipid AS Biology. Foundation. Cell membranes and Transport 8

9 A Phospholipid Bilayer Phospholipids can form: BILAYERS -2 layers of phospholipids with hydrophobic tails protected inside by the hydrophilic heads. The PHOSPHOLIPID BILAYER is the basic structure of membranes. 9

10 10

11 Take Two. Take a minute or two to discuss with the person next to you what is meant by polar head and non-polar tails. What do they look like? 11

12 Diagram representing the cell membrane Remember the membrane is 7nm wide 12

13 Fluid mosaic model Cell membranes also contain proteins within the phospholipid bilayer. FLUID- because individual phospholipids and proteins can move around freely within the layer, like it s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above. 13

14 Diagram of a cell membrane 14

15 Cell Membranes from Opposing Neurons (TEM x436,740). } Phospholipid Bilayer 7nm wide AS Biology. Foundation. Cell membranes and Transport 15

16 Features of the fluid mosaic model Double layer BILAYER of phospholipids which can move about by in their own. Phospholipid tails point inwards forming a.. interior. The phospholipid heads point outwards facing the aqueous (water containing) medium surrounding the membrane. Some phospholipids fatty acid tails are.. straight so fit together tightly. Some are bent so fit together. The more unsaturated tails there are the more the membrane becomes. The lower the temp, the.fluid. Most protein molecules. like icebergs in the layers, some are fixed to. inside the cell and don t float. Some proteins are embedded in the outer layer, some in the inner layer and some the two layers. Hydrophobic and Hyrdophilic parts of the protein molecules sit next to the and.. portions of the of the membrane. This ensures the proteins stay in the membrane. The membrane is nm thick on average. Some phospholipids have carbohydrates attached to them called-.. Some of the proteins have carbohydrates attached to them called The membrane also contains molecules of.. 16

17 Features of the fluid mosaic model Double layer BILAYER of phospholipids which can move about by DIFFUSION in their own MONOLAYER Phospholipid tails point inwards forming a NON-POLAR HYDROPHOBIC interior. The phospholipid heads point outwards facing the aqueous (water containing) medium surrounding the membrane. Some phospholipids fatty acid tails are SATURATED straight so fit together tightly. Some are UNSATURATED bent so fit together loosely. The more unsaturated tails there are the more fluid the membrane becomes. The lower the temp, the less fluid. Most protein molecules float like icebergs in the layers, some are fixed to structures inside the cell and don t float. Some proteins are embedded in the outer layer, some in the inner layer and some span the two layers. Hydrophobic and Hyrdophilic parts of the protein molecules sit next to the Hydrophobic and Hydrophilic portions of the phospholids of the membrane. This ensures the proteins stay in the membrane. The membrane is 7nm thick on average. Some phospholipids have carbohydrates attached to them GLYCOLIPIDS Some of the proteins have carbohydrates attached to them GLYCOPROTEINS The membrane also contains molecules of CHOLESTEROL 17

18 Movement of selected molecules across the cell membrane 18

19 It s Alive!!! Moving amoeba AS Biology. Foundation. Cell membranes and Transport 19

20 And so I now am able to.. Identify the parts of the cell or plasma membrane Compare and contrast how the different parts of the membrane work. 20

21 The End 21