Structure and function of cell components Carbohydrates Lipids Proteins Nucleic Acids Membranes Cytoskeleton

Cell membranes Many organelles contain or are enclosed by membranes, including Plasma membrane Mitochondria Chloroplasts Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Microbodies (aka perioxisomes) Remind selves of what all of these cell parts do. ER = phospholipid synthesis and protein synthesis. Golgi = modify, store and transport proteins and other secretory substances. Lysosomes = digest foreign invaders and unwanted organelles. Microbodies = contain enzymes that need to be kept separate from the rest of the cytosol. The functions of each of these also lead to some of the roles of the membranes in cells

Role of Cell Membranes Based on the functions of the above organelles / membranes write down some of the roles of the membranes in the cells (Leave some space as we will be adding to this list)

Structure of Cell membranes Fluid Mosaic Model Study the diagram – What features do the students already know about. Which are new? What isn’t shown in this diagram? (how saturated the fatty acids in the chains are and the movement of the lipids). Note the phospholipids can move around the circumference of an average cell in a few seconds.

Electron micrograph of cell membrane

Structure of Cell membranes Lipids Remember lipids have hydrophilic head and hydrophobic tails To avoid the hydrophobic tails coming in contact with water a continuous bilayer sphere is formed. Therefore hydrophobic interactions hold membranes together

Structure of Cell Membranes Proteins Integral proteins (intrinsic) Proteins that are embedded in the membrane They are held in place by hydrophobic interactions (integral proteins have hydrophobic groups on their outer surface) Peripheral proteins (extrinsic) Proteins attached to the surface of the membrane (often forming non-covalent bonds with integral proteins)

Proteins cont…

Function of Membrane Proteins Attachment Cytoskeleton Extracellular matrix Intercellular Junctions Plasmodesmata Tight Junctions Gap Junctions Desmosomes Plasmodesmata – between plant cells. Tight junctions = 2 membranes fused together to produce a water tight seal to prevent fluid leaking into or out of extracellular space. Gap junctions – areas where cells have a low blood supply and therefore they rely on links (via channel proteins) to get nutrients they require. Desmosomes ‘tie’ cells together to keep them in place.

Function of Membrane Proteins Transport Carrier Proteins Channel Proteins Receptors Enzymes Cell to Cell recognition Receptors – binding of regulatory protein e.g. a hormone, which can stimulate or inhibit molecular events in the cell. Cell to cell recognition – glycoproteins provide markers for an organism to recognise self and organise tissues. Proteins on non-self cells act as antigens and stimulate the production of antibodies.

Learning Activities Use all resources to find out more about the functions of membrane proteins. Based on the functions of proteins, add to your list on the role of membranes in cells Read DART pgs 54 – 56 Scholar 5.1 (of interest, but you aren’t required to know it, may be the history of understanding the cell membrane structure) The Structure of Membranes worksheet The Role of Membranes worksheet Advanced Higher Questions