Membrane Biochemistry Lecture 1 (Bio-4117) PDF

Membrane Biochemistry (Bio-4117) lecture-1 level-4 Dr. Mariam Osama [email protected] Office: 236 Biotechnology...

Membrane Biochemistry (Bio-4117) lecture-1 level-4 Dr. Mariam Osama [email protected] Office: 236 Biotechnology Office Hours: Wednesday 2: 4 Textbooks Wardhan, R., & Mudgal, P. (2017). Textbook of membrane biology (Vol. 35, No. 8, pp. 942-946). Singapore:: Springer.  Teaching and Learning Method Power Discussion Lectures Assignment points group E-learning Student Assessment Methods Lecture 2(2), Tutorial 2(1), Total: 3 credit hours Periodical Quizzes 15.00 % Mid-Term Examination 15.00 % Practical Examination 20.00 % Oral Exam 10 % Final-term Examination 40.00 % Total 100 % 2 Introduction to Membrane Biochemistry Plasma Membrane: The Gate Keeper Plasma Membrane Lesson Objectives Students will be able to: Use vocabulary related to transport across the plasma membrane Differentiate between active and passive transport Identify membrane structures that permit transport Understand the function of the plasma membrane as a “gate keeper” What is a Plasma Membrane? All living cells have them Selective permeability Asymmetric Gives cell structure Cell-cell recognition Fluid mosaic model Lipid movement in bilayer Maintains homeostasis Animal and Plant Plasma (cell) Membrane Plasma Membrane Function Separate inside organelles from external environment Regulate entrance and exit of substances Transfer information Establishment of electric potential difference Site of biological activities Attachment between cells Removal of waste Plasma Membrane Photograph: Cell Membrane Plasma Membrane Structure Lipids Phosphlipids, Glycolipids, Steroids Hydrophilic and hydrophobic properties Gives flexibility Proteins Integral - transport channels Peripheral - recognition sites Determines membranes’ specific functions Carbohydrates Lipid Bilayer Model Cross Section Two sheets of lipids 7.5 nm thick Found around the cell Embedded with proteins Strengthened with cholesterol molecules (animal) Lipid Bilayer Model Phospholipid Hydrophilic Water loving Phosphate end Outside and inside Hydrophobic Water fearing Lipid tail region Center Plasma Membrane Hydrophilic and Hydrophobic  Membrane Lipids Membrane Lipids (Lipid Bilayer)  Phospholipids o Most abundant lipids in cell membranes. o Arranged in lipid bilayer form. o Lipid bilayer:  Made up of two layers of lipids opposed to each other like a sandwich.  Phosphate heads of phospholipid molecules are on outer surfaces, in contact with intracellular and extracellular water.  Lipid tails of phospholipid molecules are deeper in the central part of the bilayer, away from water.  The bilayer exists in fluid form (Fluid Mosaic Model of the cell membrane).  Cholesterol o Dissolved in the lipid bilayer. o Determine the fluidity of the membrane.  at modest concentration → decreases fluidity.  at higher concentrations → increases fluidity.  Permeability: o As lipid bilayer is formed with lipids...  other lipids and lipid-soluble substances → can dissolve in it → pass through the lipid bilayer.  water and water-soluble substances → cannot dissolve in the lipid bilayer → cannot cross it. o Large molecules → cannot penetrate the bilayer → cannot cross it.  Membrane Proteins  Mostly in the form of glycoproteins.  Types o Integral Membrane Proteins: Integrated tightly to the lipid bilayer o Peripheral Membrane Proteins: Attached loosely to lipids or integral membrane protein  Functions o Transport Proteins: Allow passage of water and water-soluble substances across the membrane o Receptors: Receive signals for cell-to-cell communication. o Second Messengers: Participate in intracellular signaling. o Enzymes:... serve as enzymes! o Adhesion Molecules: Attach the cell to extracellular matrix or to other cells. o Submembrane Cytoskeleton: Provide strength and resistance to the membrane. o Antigen: Participate in immune reaction. Passive Transport Simple Diffusion No energy needed Diffusion and osmosis High concentration to low concentration: small molecules O2 , CO2, H2O Simple Diffusion Passive Transport Facilitated Diffusion Proteins act as tunnels Carrier proteins help larger polar molecules cross membrane Glucose Moves materials along with concentration gradient  Active Transport Energy is needed Low-concentration to high- concentration Movement of molecules up the concentration gradient Sodium-potassium pump Active Transport Movement of large substances by vesicles Endocytosis – taking into cell Phagocytosis Pinocytosis Receptor mediate Exocytosis – expelling from cell ER or Golgi Apparatus Types of Solutions Isotonic Concentration of dissolved substances is the same inside and outside the cell Hypotonic Concentration of dissolved substances is lower outside than inside Hypertonic Concentration of dissolved substances is higher outside than inside Homeostasis Plasma Membrane Maintains constant internal environment Controls movement of materials in and out of the cell as a “gate keeper” Dynamic equilibrium Separates cellular organelles from external environment Vocabulary Review Plasma Membrane Hydrophobic Homeostasis Endocytosis Passive Transport Exocytosis Simple Diffusion Isotonic Facilitated Diffusion Hypertonic Active Transport Hypotonic Hydrophilic