Cell Membrane - Lecture Notes PDF

cell membrane By  What is the cell The cell is functional and structural unit of the living system The cell consists of many organelles surrounded by a cell membrane The cell components are including * Cell membrane * Organelles * Cytosk...

cell membrane By  What is the cell The cell is functional and structural unit of the living system The cell consists of many organelles surrounded by a cell membrane The cell components are including * Cell membrane * Organelles * Cytoskeleton * Organelles * Endoplasmic reticulum * Nucleus * Ribosomes * Peroxisome * Mitochondria * Lysosomes * Cytosol * Glogi apparatus Function of different organelles of the cell  1- Nucleus * DNA , and chromosomes replication * Transcription of DNA * Play important role in protein synthesis inside the cell 4 2-mitochondria * It is the power house of the cell * It is site of the oxidation of CHO, lipid , amino acid to CO2 + H2O * Important enzymes are located in inner membrane e.g. * Electron transport. * ATP formation `. * Energy liberation `. 5  3- Golgi apparatus * Packing :It is responsible for packing of protein *Addition: It is responsible for addition of non protein fragment to protein e.g * Glycoprotein * Addition of Zinc to proinsulin to form insulin * Formation :Help the plasma membrane and lysosome membrane * Secretion: of cell products to outside the cell 6  4- Ribosome * Translation :It is the site of protein synthesis 5- Lysosome * Digestion of materials brought into cell ( by endocytosis ) * Digest of cell components after cell death 7  What the type of living cell Eukaryotic cells Prokaryotic cells DNA within Nuclear cell membrane Present Not present Mitochondria Present Not present Cell wall Not present Present Lysosome Large Small Pinocytosis Present Not present Example Human Bacteria, algae 8 9 Cell membrane ( plasma membrane/ plasma lamemma) What is the function of cell membrane? A- structural function *Separate the internal organelles of the cell from external environment *cell membrane also formed around specific intra cellular organelles e.g. ( nucleus , mitochondria) B- Metabolic Function 1- selectively permeability 2- it contains specific receptors 3- it contains specific molecular pumps and gates 4-it is the site of energy production In which ATP production by oxidative phosphorylation occurs in the inner mitochondrial membrane 11 Cell membrane structure 12  Lipid Protein Carbohydrate Phospholipid Glycolipid Cholesterol 13  1-Lipid A- phospholipid 1- glycerophospholipid 2- Sphingophospholipid ( Sphingomyeline) Glycerol Sphingosine Saturated fatty acid ( palmitate C16, stearate C18) Choline Unsaturated fatty acid Bases ( choline , serine , ethanolamine , inositol) Present mainly in myelin sheath Lecithin Phosphatidyl Cephalin Phosphatidyl serine inositol 14 1- glycerophospholipid 2- Sphingophospholipid ( Sphingomyeline) 15  B- Glycolipid Ceramide 1- cerebroside 2- gangilosides Sphingosine Kerasin ( lignoceric ) Sphingosine Fatty acid Nervon ( nervonic C24 ∆15 ) Fatty acid Galactose Galactose oxynervon ( oxynervonic C24 ∆15 OH ) Glucose Cerebron ( cerebronic acid C24 OH ) N-acetyl Galactosamine Sialic 16 17 18  C- Cholesterol * it act as 20-50% of the cell membrane * it present mainly in the plasma membrane * it is present at low amount in mitochondrial and nuclear cell membrane * It is incorporated within the lipid bilayer 19  Lipid bilayer membrane Unsaturated FA saturated FA 20 * Lipid of cell membrane is amphipathic because the head of lipid has polar ( hydrophilic) , tail has nonpolar ( hydrophobic) * In aqueous mediums, membrane lipids spontaneously organize into bilayers with the polar ends oriented towards ( outside), and the non-polar ends oriented away from the solution (inside). * The tail of phospholipid was formed from straight ( saturated FA), and kinked tail ( unsaturated FA) * The more kinked tail is more fluidity 21 The forces that maintain on the stability of cell membrane 1- The hydrophobic interaction is the major force 2- Van Der Waals (VDW) attractive forces between the hydrocarbon tails 3- Electrostatic and hydrogen bonding : between the polar head group and water molecule 22  Function of cholesterol * Stability of the cell membrane * Regulation of the membrane fluidity in body temperature 23  Membrane protein There are two type of membrane protein 1- peripheral protein 2- integral protein 24  1- peripheral protein * Is not embedded into the lipid bilayer , they are loosely attached with membrane. Can be removed by salt solution without disturbance of the membrane * Usually located to the inner membrane ( adjacent to cytoplasm) Function * Form the link between the cell membrane and cytoplasmic component 25  1- integral protein * They are embedded within the lipid bilayer * Most of these protein traverse the whole thickness of the membrane and called transmembrane * some of these protein partially embedded within the membrane * They are strongly attached by Van Der Waals forces * Thus remove it need detergent 26 Main function of integral protein 1- pumps : transport ions ( Na+, K+) actively across membrane 2- channels : transport substance by passively diffusion 3- Receptors : it binding by specific molecules e.g. hormones 4- Enzymes : e.g. ATPase synthase of the inner membrane of mitochondrial membrane , digestive enzyme in the small intestine 5- Linkers : Anchor the intracellular cytoskeleton to the extracellular matrix 6- Structural proteins : forming junctions between neighboring cells 27 Specific function of protein 1- form immunoglobulin : these are integral protein of lymphocyte 2- Erythrocyte membrane proteins have important functions What is erythrocyte membrane proteins have important functions ? A- Ankyrin and spectrin B- Glycophorin C- Anion channel protein 28 A- Ankyrin and spectrin 1-They are peripheral proteins bound together within cell membrane 2- Function :They maintain on biconcave shape of red cells 3- Mutation of the spectrin protein lead to hereditary spherocytosis disease, in which loss of biconcave shape of red cells ‫ ــــــ‬rupture of cells ‫ـــــ‬hemolytic anemia 29 B- Glycophorin * It is integral protein , it is glycoprotein * Its is formed of protein portion ( single poly peptide) + carbohydrate ( 16 sugar unit rich in sialic acid) * Function:- 1- constitute the blood group substance (ABO) 2- give hydrophilic charged coat around red cells which enable it to circulate without adhering to vessel wall and other cells 30 C- Anion channel protein * It is consist of 2 identical subunit * Function: play important role in transport of CO2 via blood 31  Fluid mosaic model * It describes the molecular arrangement of membrane proteins within the fluid nature of the lipid layers * When viewed from above : proteins are scattered via phospholipid bilayer in a mosaic pattern 32 * It describe the membrane lipid as sea, and protein molecules are floating like icebergs * some membrane protein are able to move laterally within the lipid bilayer 33  3- Membrane carbohydrates They are present as glycoprotein and glycolipid They are arranged toward the outside surface of the membrane and forming cell coat or glycocalyx E.M. Cell coat take Fuzzy shape 34 Function of mebrane carbohydrate 1- receptors : in form of glycoprotein 2- cell adhesion 3- glycophorin : constituent of blood group ( ABO) 35 The properties of cell membrane du to membrane lipid 1- Fluidity 2- Selective permeability 3- Asymmetry 1- Fluidity D.F. is ability of cell membrane components for movement * It depends on temperature and lipid content 1- the more temperature , the more fluidity 2- the more unsaturated , the more fluidity 36  2- Selective permeability Allow passage of 1- Fat soluble substances 1- small nonpolar substance * Prevent passage of 1-Ionic an 2-polar substance can not pass through the cell membrane due to the hydrophobic nature of hydrocarbon chain of lipid bilayer * Ionic and polar substance can pass through the cell membrane by specific membrane protein channel 37  3- Asymmetry D.F. Lipid component of each of each half of bilayer is different from each other protein and carbohydrate is irregularly distributed what is the causes of Asymmetry of cell membrane? 1- phosphatidyl choline present in outer membrane While phosphatidyl serine present in inner membrane 2- carbohydrate mainly located in outer surface 3- Protein irregularly distributed. In which many of proteins are located in outer membrane. e.g. hormone receptors 38  3- Transport system D.F it means the system of transport of organic and inorganic substance inside / outside the cell Types of transport system Transport system was classified according to the ingredient concentration Passive transport Active transport 39 Passive transport Transport substance from high concentration to low concentration No energy needed 40 Active transport Transport substance from low concentration to high concentration Energy needed 41  Passive transport Simple diffusion Facilitated diffusion No need carrier need carrier ( Glucose and amino acid) Fat soluble Ions H2O2 molecules ( need channel) ( called osmosis ) 42 Facilitated diffusion Glucose , amino acid There are two type ( Unipart: transport one molecule , Symport ( transport of two molecule) 43  Active transport system Transport the substance from low concentration to high concentration * Need energy There are two types 1- primary 2- secondary Na+/ K+ pump ( Antiport) sodium Glucose transport system ( symport) 44 Unipart : mean transport of one molecule in one direction Symport port : mean transport of two molecules in one direction Antiport : mean transport of two molecules in opposite direction 45  Vascular transport Endocytosis and exocytosis Is transport system for large molecule Endocytosis : is of molecule from out side to inside the cell membrane Exocytosis : is exit of molecule from inside to out side the cell membrane Endocytosis Phagocytosis Pinocytosis Usually solid molecule so called Cell eating Usually fluid so called Cell drinking 46  Pinocytosis Phagocytosis * It occurs in all cells to uptake of fluid * It occurs in special cell as macrophage * In which the cell membrane is surround * Liver uptake chylomicrons, HDL by the bacteria to form pahogosomes which fuse pinocytosis with lysosome forming phagolysosomes inside which particles are digested 47  Exocytosis * Is used for release of macromolecules and/ or cell debris from inside the cell to outside the cell * e.g. release of insulin hormone from β-cells of islets of Langerhans in pancreas 48 Additional information * The chromosomes in human somatic cell is 46 pairs * Ribosome present in human eukaryotic cell is 80S Some MCQ 1- The main lipid present in cell membrane bilayer is a- cholesterol b- Triglycerides c- Phospholipid c- Phospholipid D- Fatty acid 49 2- The following cell organelle is involved in protein biosynthesis a- Nucleus b- Lysosomes D- Ribosomes c- Golgi apparatus D- Ribosomes 3- Nucleus is present in all cells , except a- immature erythrocytes b- white blood cell c- mature erythrocytes c- mature erythrocytes D- Platelets 4- Active transport requires following execpt a- carrier protein b- concentration gradient b- concentration gradient c- energy D- Na+/K+ pump 50 5- Glucose enters RBCs by a- Passive diffusion b- Facilitated transport c- Active transport c- Active transport D- Endocytosis 6- one of the following is Not required for passive diffusion a- concentration gradient b- solubility of solute D- energy c- hydrostatic pressure D- energy 7- Facilitated diffusion depends on a- energy b- solubility of solutes c- carrier c- carrier D- Na+/ K+ ATPase 51 52