Cell membranes

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Slide 15

Diagram of a cell membrane

Slide 16

TEM of freeze-fractured cell membrane.

The fracture occurs between the two phospholipid layers.

You can clearly see the exposed proteins sticking out of the two layers.

Individual phospholipids are too small to see.

Slide 17

Cell Membranes from Opposing Neurons (TEM x436,740).

} Phospholipid Bilayer

7nm wide

Slide 18

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 ………………………………

Slide 19

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.