Lecture 10 Membranes PDF

Associate professor Zanda Daneberga Molecular transport – plasma membrane 1 The endomembrane system ◼ Endomembrane system includes: Nuclear envelope, The endoplasmic reticulum (ER), Golgi apparatus, Lysosomes, Vesicles....

Associate professor Zanda Daneberga Molecular transport – plasma membrane 1 The endomembrane system ◼ Endomembrane system includes: Nuclear envelope, The endoplasmic reticulum (ER), Golgi apparatus, Lysosomes, Vesicles. 2 3 The endoplasmic reticulum (ER) 4 ER continued ◼ Rough ER ◼ Smooth ER Site for membrane bound Lipid synthesis; protein synthesis; Glycogen synthesis; Protein translocation, folding Synthesis of steroid hormons and transport; (e.g. gonads); Glycosylation (addition of Metabolism of carbohydrates; sugar groups); Detoxification function (e.g. Disulfide bond formation (to liver cells); stabilize the tertiary and quaternary structures of Major storage and released site proteins). of calcium ions (e.g. muscle cells). 5 The Golgi apparatus 6 Functions of Golgi apparatus ◼ Protein sorting and export – secretory pathways; ◼ Protein glycosylation; ◼ Lipid and polysaccharide metabolism and transport; ◼ Formation of lysosomes. 7 Transport to/from Golgi apparatus 8  Lysosomes ◼ Organelles of animal cells; ◼ Contain ~ 50 different hydrolytic enzymes; ◼ Function in destruction of cell`s own organelles and their replacement – autophagy. ◼ Take part in phagocytosis. 9 Lysosome 10 The endomembrane system 11 Plasma membrane 12 13 Plasma membrane Source: Encyclopaedia Britannica/UIG/Getty Images 14 Lipids ◼ Amphipathic molecules – consist of polar (hydrophilic) head group and hydrophobic tail. The hydrophobic effect and van der Waals interactions cause the tail groups to self- associate into a bilayer with the polar head groups oriented toward water. 15 Lipids - continued ◼ Phosphoglycerides - the most abundant class of lipids in most membranes. Contain glycerol backbone. The head group is the phosphate and an alcohol (serine, ethanolamine, inositol, or choline) = phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine etc. The hydrophobic portion of the phospholipid is a long fatty acid tail. 16 Lipids - continued ◼ Sphingolipids - derived from sphingosine (amino alcohol). Contain a long-chain fatty acid attached to the sphingosine amino group. Glycosphingolipids - polar head groups are sugars. 2–10 % of the total lipid in plasma membranes (most abundant in nervous tissue). ◼ Sterols - the basic structure is a four-ring hydrocarbon. Cholesterol is especially abundant in the plasma membranes of mammalian cells. 17  Proteins ◼ Integral membrane proteins (transmembrane proteins) - span a phospholipid bilayer. The cytosolic and exoplasmic domains have hydrophilic exterior surfaces (interact with the aqueous solutions on the cytosolic and exoplasmic faces of the membrane). The membrane-spanning domain contains many hydrophobic amino acids. 18 Proteins - continued ◼ Lipid-anchored membrane proteins - bound covalently to one or more lipid molecules. 19 Proteins - continued ◼ Peripheral membrane proteins - do not interact with the hydrophobic core of the phospholipid bilayer, localized to either the cytosolic or the exoplasmic face of the plasma membrane. 20  Carbohydrates ◼ Transmembrane proteins contain carbohydrate chains, they are always located in the exoplasmic face of membrane and are available to interact with components of the extracellular matrix as well as growth factors and antibodies. Source: Encyclopaedia Britannica/UIG/Getty Images 21 Functions of plasma membrane ◼ Compartmentalization – incloses contents of the entire cell. Nuclear and cytoplasmic membranes enclose intracellular spaces. ◼ Scaffold for biochemical activities – in membrane embedded components (e.g. proteins). ◼ Barrier with selective permiability – prevent unrestricted movement of molecules. ◼ Transport of solutes – has mechanism for transport of molecules. ◼ Response to external stimuli - involved in the signal transduction. 22