Presentation on theme: "Cells, membranes and environments. 4.2 Cell Membranes Control the movement of substances into and out of cells Important functions in cell recognition."— Presentation transcript:
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