OCR F211 Cell Membranes

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  • Created on: 29-04-16 17:51
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Module 1: Cells
1.1.2 Cell Membranes
(a) outline the roles of membranes within cells and at the surface of cells
Membranes at the SURFACE of cells (Plasma Membranes WITHIN cells
controls which substances enter and leave the separates organelles from the cytoplasm
cell controls which substances enter and leave the
allow recognition/signalling by other cells organelle
allow cell communication can form vesicles to transport substances
(b) state that plasma (cell surface) membranes are partially permeable barriers
Plasma membranes are partially permeable meaning they let some molecules through but not others.
(c) describe, with the aid of diagrams, the fluid mosaic model of membrane structure
The phospholipid bilayer is the basic structural component of plasma membranes. It consists of 2 layers of
phospholipid molecules. The centre of the bilayer is hydrophobic so the membrane doesn't allow watersoluble
substances (like ions) through it it acts as a barrier to these dissolved substances
In the fluid mosaic model, phopholipid molecules form a continuous double layer (bilayer). The bilayer is 'fluid'
because the phospholipids are constantly moving . The fluid mosaic model also contains cholesterol molecules,
proteins , glycoproteins and glycolipids.

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Module 1: Cells
(d) describe the roles of components of the cell membrane:
Molecule Structure Function
Stability Cholesterol Small, steroid molecules, Binds to the hydrophobic tails,
longer than they are wide causing them to pack more
Hydrophobic fit between closely together makes the
fatty acid tails membrane less fluid and more
Helps make the barrier
complete so substances can't
easily pass
Transport Channel Tubular proteins with a Allows the movement of some
Proteins hydrophilic lining down their substances across a membrane
centre small and…read more

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Module 1: Cells
Increasing the temperature gives the molecules more kinetic energy, so
they move faster, making the membrane 'leaky' and more permeable
Temperature above 45oC The phospholipid bilayer starts to melt (break down) and the membrane
becomes more permeable
Channel proteins and carrier proteins in the membrane denature so they
can't control what enters or leaves the cell this increases the
permeability of the membrane
(f) explain the term cell signalling
(g) explain the role of membranebound receptors as sites where hormones and drugs…read more

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Module 1: Cells
acting as antigens on the surface of cells. Cells of the immune system have receptors that detect the
glycoproteins and can determine whether they are 'self' or 'non self'
Many drugs work by binding to receptors in cell membranes. They either trigger a response in the cell, or block
the receptor and prevent it from working e.g. cell damage causes the release of histamine. Histamine binds to
receptors on the surface of other cells and causes inflammation.…read more

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