Cells, membranes and environments

4.2 Cell Membranes  Control the movement of substances into and out of cells  Important functions in cell recognition and communication

4.2 Cell Membranes  Plasma and non-plasma membranes  Plasma membranes enclose the cytoplasm  Non-plasma membranes are intracellular and connect the plasma membrane with other internal membranes (golgi bodies, endoplasmic reticulum, vesicles, etc.)

4.2 Cell Membranes  Plasma membranes  Enclose the contents of the cells  Enables cytosol to maintain a different composition from the intracellular fluid  Control movement of substances  7 – 9 nm (nanometres) thick  Carbohydrates attached to plasma membranes are usually found on the outer surface linked to protruding proteins and are involved in recognition and adhesion between cells

4.2 Cell Membranes  Non-plasma membranes  Form boundaries of discrete compartments within the cell  Control movement of substances between the organelles  5 – 7 nm (nanometres) thick  Chemical contents of nucleus, mitochondria, chloroplasts, golgi bodies, vesicles are distinct from each other

4.2 Cell Membranes  Non-plasma membranes  Nucleus – double membrane layer (nuclear envelope) with specialised nuclear pores. Nuclear pores regulate movement of mRNA and large proteins.  Mitochondria – outer membrane and inner folded membrane containing enzymes for aerobic respiration.  Chloroplasts have a double membrane enclosing more membranous structures containing enzymes for photosynthesis.

4.2 Cell Membranes  Functions of Membranes  Regulate movement of molecules in and out of cell and organelles  Active sites for chemical reactions  Create compartments with cells  Restrict movement of substances between different parts of cell and other cells  Contain receptors for intercellular communication (directly between adjacent cells and by hormones and nerves  Recognition of cells by other cells  Produce electrical potential in excitable cells (muscle and nerves)

4.2 Cell Membranes  Membrane composition  Basic structure of all membranes is the same.  Two layers of phospholipids (hydrophilic head and hydrophobic tail) associated with proteins (channels through membranes, binding sites), carbohydrates and cholesterol (provide stability)  Fluid-mosaic model  Most membranes are asymmetrical

4.2 Cell Membranes  Wiki Wiki