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All references made are to the unit 1 Scholar book. Page numbers may vary each year as different versions of the book are released.


• also called the plasma membrane • barrier separating the cell from the external environment • used for making compartments in eukaryotic cells • made of a phospholipid bilayer, with protein molecules interpsersed • called fluid mosaic model •Figure 5.1 p.95


• proteins embedded in the phospholipid bilayer are called integral/intrinsic/transmembrane proteins • proteins on surface are called peripheral/extrinsic • cholesterol is present to give fluidity • glycoproteins and glycolipids are also present


Function of Proteins Read scholar and make your own notes on the function of the membrane proteins. Transport – channel, pore, passive, facilitated diffusion, carrier, integral (Figure 5.3 p.102) Enzymes Receptors Cell adhesion Cell-cell recognition (glycoproteins) Support


Supports cell interior and organelles. 3 components (from smallest to largest in diameter): 1.Actin filaments (microfilaments) 2.Intermediate filaments 3.Microtubules


1.Microfilaments • 2 strands of actin twisted (rope-like) • ~7nm diameter • Polymerise when required • Present throughout cell but highly concentrated just inside membrane • Important in cell movements, cytokinesis, muscle contraction


2. Intermediate Filaments • ~10nm diameter • fibrous keratin family of proteins twisted together • permanent in the cell • mechanical strength in animal cells • anchored to membrane for support of organelles


3. Microtubules • hollow tubes of globular tubulin protein • 1α and 1β sub-unit • set of 13 protofilaments make up one microtubule • important in movement of chromosomes during mitosis and movement within the cell • centrosome is the microtubule organiser


• cytoskeleton also plays a role in cytokinesis • actin/myosin ring constricts around cell • cleavage furrow is formed in animal cells and cytoplasm pinches off • cell wall also forms in plant cells (see cell cycle) • cytoskeleton is not static, it can depolymerise and polymerise as needed

5 Membranes and Cytoskeleton