advanced higher biology

• The proteome is the entire set of proteins expressed by a genome.
• The proteome is larger than the number of genes, particularly in eukaryotes, because more than one protein can be produced from a single gene as a result of alternative RNA splicing.
• The set of proteins expressed by a given cell type can vary over time and under different conditions
• Eukaryotic cells have a system of internal membranes, which increases the total area of membrane.
• The endoplasmic reticulum (ER) forms a network of membrane tubules continuous with the nuclear membrane.
• The Golgi apparatus is a series of flattened membrane discs.
• Lysosomes are membrane-bound organelles containing a variety of hydrolases that digest proteins, lipids, nucleic acids and carbohydrates.
• Vesicles transport materials between membrane compartments.
• Lipids and proteins are synthesised in the ER
• Lipids are synthesised in the smooth endoplasmic reticulum (SER) and inserted into its membrane.
• The synthesis of all proteins begins in cytosolic ribosomes.
• The synthesis of cytosolic proteins is completed there, and these proteins remain in the cytosol.
• Transmembrane proteins carry a signal sequence, which halts translation and directs the ribosome synthesising the protein to dock with the ER, forming RER.
• Translation continues after docking, and the protein is inserted into the membrane of the ER
• Once the proteins are in the ER, they are transported by vesicles that bud off from the ER and fuse with the Golgi apparatus.
• As proteins move through the Golgi apparatus they undergo post-translational modification.
• The addition of carbohydrate groups is the major modification.
• Vesicles that leave the Golgi apparatus take proteins to the plasma membrane and lysosomes.
• Vesicles move along microtubules to other membranes and fuse with them within the cell.
• Secreted proteins are translated in ribosomes on the RER and enter its lumen.
• The proteins move through the Golgi apparatus and are then packaged into secretory vesicles.
• These vesicles move to and fuse with the plasma membrane, releasing the proteins out of the cell.
• Many secreted proteins are synthesised as inactive precursors and require proteolytic cleavage to produce active proteins.