2 Cell Mmebrane.Physiology.pdf

Dynamics of the Cell Membrane Fac. of Health Sciences Istanbul Atlas University Istanbul Sept. 2024 Learning Outcomes Membrane structure and function  Cont. Act as a barrier Receive information Move and expand  Membr...

Dynamics of the Cell Membrane Fac. of Health Sciences Istanbul Atlas University Istanbul Sept. 2024 Learning Outcomes Membrane structure and function  Cont. Act as a barrier Receive information Move and expand  Membranes are active dynamic Plasma Membrane Elastic structure 7.5 to 10 nanometers thick Membranes surrounding the cell Separates cell’s internal structures from extracellular environment It is selectively permeable and controls passage of materials into and out of cell Participates in intracellular communication.  Structure of the cell membrane Composed of : Double layer of phospholipids (hydrophobic/ hydrophilic parts) Proteins span, or partially span the membrane. Negatively charged carbohydrates attach to the outer surface.  Fluid Mosaic Model  Composition of cell membrane Proteins 55% Lipids | 42% Phospholipids … 25% Cholesterol ……. 13% Glycolipids …….. 4% Carbohydrates 3%  Cell membrane lipids A lipid bilayer is a stable, low energy structure Amphipathic (hydrophobic and hydrophilic part) Hydrophobic compounds can reach equilibrium quickly Lipids are effective barriers to some compounds Cell membrane Phospholipids  Consists of: a. Glycerol head that contains phosphate group (polar and hydrophilic) b. 2 fatty acid ‘tails’ (nonpolar and hydrophobic)  Cholesterol The steroid nucleus in the cholesterol molecules is highly fat soluble. They mainly help determine the degree of permeability (or impermeability) of the bilayer to water-soluble constituents of body fluids.  Cholesterol controls much of the fluidity of the membrane as well. Cont. The lipid layer in the middle of the membrane is impermeable to the usual water-soluble substances, such as ions, glucose.  Conversely, fat-soluble substances, such as oxygen, carbon dioxide, and alcohol, can penetrate this portion of the membrane with ease.  Cell membrane Proteins Integral proteins: Internal or intrinsic proteins span the membrane provide structural channels or pores * Some act as enzyme and some as receptor (such as peptide hormones) Peripheral proteins: external or extrinsic proteins embedded in one side (face) of the membrane associated by weak electrostatic bonds to membrane proteins or lipids.  Functions of Plasma membrane Proteins  Membrane proteins have various functions:  transporters  enzymes  cell surface receptors  cell surface identity markers  cell-to-cell adhesion proteins  attachments to the cytoskeleton  Functions of integral protein Channel Protein: Allow a substance to move across the membrane Carrier Protein: Selectively interacts with specific molecules or ions so it can cross membrane Cell Recognition Protein: Called glycoproteins, allow cell to be recognized by body’s immune system Receptor Protein: Specifically shaped to a specific molecule Enzymatic Protein: Catalyze specific reactions  Cell membrane Carbohydrates  Primarily attached to the outer surface of the membrane as:  Glycoproteins (most of it)  Glycolipids (1/10) General functions : Attach cells to each other Act as receptor substances Basis for rejection of foreign cells by immune system Give most of cells overall negative surface charge, which affects the interaction of regulatory molecules with the membrane. THANK YOU  why is fluidity important? Membrane must be fluid to work properly. Solidification may result in permeability changes and enzyme deactivation. Unsaturated hydrocarbon tails enhance membrane fluidity because kinks at the carbon-to-carbon double bonds hinder close packing of phospholipids.  How does the membrane move? A membrane is held in together by weak hydrophobic interactions. Most membrane lipids and some proteins can drift laterally within the membrane Molecules rarely flip transversely (flip-flop) across the membrane, because hydrophilic parts would have to cross the membrane’s hydrophobic core.