YR1 Lecture 1H - Cell Membranes

Cell membranes Dr Morven Cameron [email protected] Learning outcomes Outline the structure and function of cell membranes. Explain that compounds have to cross membranes for communication between compartments and cells. Describe the role of membrane proteins in the function of the plasm...

Cell membranes Dr Morven Cameron [email protected] Learning outcomes Outline the structure and function of cell membranes. Explain that compounds have to cross membranes for communication between compartments and cells. Describe the role of membrane proteins in the function of the plasma membrane. Compartmentalisation To separate ‘self’ from the environment. To separate and optimise vital functions. Communication/exchange must occur across membrane(s). All eukaryotic cells have the same basic set of membrane-enclosed organelles. – – – – – Plasma membrane surrounds entire cell Nucleus Endoplasmic reticulum Golgi apparatus Mitochondria Functions of cell membranes Barrier between the cytoplasm and external environment. Selective permeability. Recognition of antigens and foreign/altered cells. Transport systems for specific molecules. Transduction of extracellular physical or chemical signals into intracellular events. Regulation of cell-cell interactions. Fluid mosaic Fluid mosaic Cell membranes Lipids in cell membranes – – – – Phospholipids Cholesterol Glycolipids Microdomains Membrane proteins – – – – – Adhesion proteins Communication proteins Receptor proteins Recognition proteins Transport proteins – Passive – Active Cell membranes Lipids in cell membranes – – – – Phospholipids Cholesterol Glycolipids Microdomains Membrane proteins – – – – – Adhesion proteins Communication proteins Receptor proteins Recognition proteins Transport proteins – Passive – Active Phospholipids Phospholipid membranes asymmetry Phosphoglyceride - lecithin Found in egg yolks, soybeans. Major component of cell membranes. Can be used to synthesize acetylcholine. Types of phospholipids Molecular Biology of the Cell Glycolipids Extracellular Intracellular Glycolipids – blood types Cholesterol Alters molecular packing of membrane phospholipids. Creates functional sites with sphingomyelin to create “microdomains”. Decreases the permeability of the membrane Types of phospholipids Molecular Biology of the Cell Microdomains - rafts ~ 70nm in diameter. Rich in sphingolipids and cholesterol. Microdomains - rafts Inner Life of the Cell - Biovisions Cell membranes Lipids in cell membranes – – – – Phospholipids Cholesterol Glycolipids Microdomains Membrane proteins – – – – – Adhesion proteins Communication proteins Recognition proteins Receptor proteins Transport proteins – Passive – Active Membrane proteins Membrane protein shapes covalently attached fatty acid alpha-helix single multiple integral proteins peripheral proteins Adhesion proteins Communication proteins Gap junctions – molecules up to 500 Da in size. Recognition proteins Receptor proteins ionotropic metabotropic e.g. glutamate channels Transport proteins Passive Active Diffusion of molecules Movement of ions Ion: An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge. Important ions in biological systems: Na+, K+, Ca2+, Mg2+, Cl- Selectively permeable membrane osmosis Movement of molecules across the membrane Transport across membrane Movement of substances across the membrane can be either "passive", occurring without the input of cellular energy, or "active", requiring the cell to spend energy in transporting it. Ungated ion channels - passive Generally open all the time: – K+ “leak” channels. – Aquaporins. – Hemichannels. Anti/sym/uniporters antiport: cotransports two molecules in opposite directions symport: cotransport two molecules in the same direction. uniport: transports a single type of molecule in either direction. Gated ion-channels Active transport Primary active transport – uses ATP Secondary active transport – uses electrochemical gradient Ion asymmetry Na+/K+-ATPase ATP-driven pumps Cell membranes Lipids in cell membranes – – – – Phospholipids Cholesterol Glycolipids Microdomains Membrane proteins – – – – – Adhesion proteins Communication proteins Receptor proteins Recognition proteins Transport proteins – Passive – Active Questions? Please visit the “Introduction to the human body” discussion board to ask questions.