Cell Membrane Biology - PDF

Cell Biology Plasma Membrane Dr. Abdelmonim Hussein Mohamed MBBS  Membrane Function 03 Membrane Function Lecture Outline This part you will get basic knowledge of membrane function and how membrane works...

Cell Biology Plasma Membrane Dr. Abdelmonim Hussein Mohamed MBBS  Membrane Function 03 Membrane Function Lecture Outline This part you will get basic knowledge of membrane function and how membrane works Membrane Structure 02 Membrane Structure This section you will learn about basic components of cell membrane including Lipds, Proteins & etc About Cell Membrane 01 Introduction In this section you will learn some introduction about the plasma membrane & it’s contents.  Introduction Introduction The plasma membrane separates the living cell from its nonliving surroundings. Structure This thin barrier, 8 nm thick, controls traffic into and out of the cell. Like other membranes, the plasma membrane is selectively permeable, allowing some Function substances to cross more easily than others.  Introduction About Cell Membranes 1. All cells have a cell membrane 2. Functions: Structure a.Controls what enters and exits the cell to maintain Pan internal balance called homeostasis b.provides protection and support for the cell Function TEM (Transmission electron microscopy) picture of a real cell membrane.  Introduction About Cell Membranes 3.Structure of cell membrane Lipid Bilayer -2 layers of Structure phospholipids a.Phosphate head is polar (water loving-hydrophillic) Phospholipid b.Fatty acid tails non-polar (water fearing-hydrophobic) Function c.Proteins embedded in membrane Lipid Bilayer  Introduction Structure Function Phosopholipid Bi-Layer -polar heads are hydrophilic “water loving” -tails (fatty acids) are hydrophobic “water fearing” and face inward 6 Function Structure Introduction  Introduction Membrane Structure Lipids and proteins are the main components of the membranes, although carbohydrates are Structure also important. The most abundant lipids in most membranes are phospholipids. Phospholipids and most of proteins of membrane Function are amphipathic molecules.  Introduction Amphipathic molecules A molecule that has both hydrophilic region and a hydrophobic regions. Structure Membrane structure A membrane is a fluid mosaic of lipids, proteins and carbohydrate. The membrane is a mosaic of protein molecules Function bobbing in a fluid bilayer of phospholipids.  Introduction Selectively Permeable The cell membrane only lets certain substances in and out of the cell Structure Function 10 Function Structure Introduction  Introduction Cholesterol Cholesterol found in plasma membranes of eukaryotes, modulates membrane fluidity by making the membrane: Structure Less fluid at warm temperatures (e.g. 37 C body temperature) by restraining the phospholipid movement. More fluid at lower (cool) temperatures by preventing close packing of phospholipids Cells may alter membrane lipid concentration in response to changes in temperature Function  Introduction Cholesterol Type of steroid (lipid) Changes fluidity of cell membrane Higher temps – stiffens membrane Structure Lower temps – prevents membrane from freezing Function Function Structure Introduction  Introduction Membranes are mosaics of structure & function A membrane is a mosaic of different proteins embedded and dispersed in the phospholipid bilayer. Structure These proteins vary in both structure and function, and they occur in two special arrangements: 1- Integral proteins 2- Peripheral proteins Function  Introduction Proteins Integral Proteins that cross both layers of the phosphoplipid bilayer Peripheral Structure proteins that are only on the top half or bottom half of the phospholipid bilayer Function 16 Function Structure Introduction  Introduction 1 Integral proteins 1- Integral proteins, which are inserted into the membrane: Structure Their hydrophobic regions are surrounded by hydrophobic portions of phospholipids. Their hydrophilic ends are exposed on both sides of the membrane. Penetrate the hydrophobic core of the lipid bilayer, Function often completely spanning the membrane (a transmembrane protein).  Introduction 2 Pripheral proteins 2- Peripheral proteins, which are not embedded in the lipid bilayer but attached to the membrane surface: Structure Proteins determine most of the membrane’s specific functions. There are two populations of membrane proteins. – Peripheral proteins are not embedded in the lipid bilayer at all. – Instead, they are loosely bounded to the surface of the Function protein, often connected to the other population of membrane proteins. Function Structure Introduction  Introduction The proteins in the plasma membrane may provide a variety of major cell functions Structure Function  Introduction Membrane carbohydrates are important for cell-cell recognition  Cell-cell recognition: The ability of a cell to Structure distinguish one type of neighboring cell from another.  Cell-cell recognition is crucial in the functioning of an organism. It is the basis for: Function  Introduction Sorting of cells into tissues and organs in an animal embryo’s cell. Rejection of foreign cells by the immune system. Usually branched oligosaccharides (