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Delve into the intricacies of cell membranes, including characteristics, fluidity factors, protein functions, transport mechanisms, and membrane structure studies in this detailed exploration. Uncover the impact of molecules on membrane permeability and how mutations like in Cystic Fibrosis affect cell function. Gain insights into osmosis, tonicity, and facilitated transport mechanisms. Discover the secrets of membrane fluidity and cholesterol's role, alongside the energy sources for active transport.
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Chapter 5: Membrane Structure Topics you are not responsible for: details of Na-K pump (fig 5-15) End of Chapter questions: Understand: all Apply: all Synthesize: 1 & 2 Do all mQuiz questions Membrane Structure
What causes Cystic Fibrosis? Symptoms: -- Lungs: mucous accumulation infections -- affects other organs also Mutation to “CFTR” CF-Transmembrane- Conductance Regulator 1480 amino acids glycoprotein Membrane Cl- channel Mutation alters water transport -- How? -- Why? Membrane Structure
Solutions are isotonic What is Osmosis? How does solute concentration affect osmosis? Tonicity Osmotic pressure How does osmotic pressure affect cells? Turgor pressure Osmosis Question Membrane Structure
How do we know that phospholipids are arranged as a bilayer? Langmuir Trough exp – 1925 -- creates monolayer Used RBCs: (lack internal membranes) Surface area of 1 ml of RBCs = 5x109 cells x 130 um2 / cell = 650 mm2 (~25 cm2) Actually observed ~1300 mm2 Why? Question Membrane Structure
What is the structure of cell membranes? Phospholipids “Amphipathic” Spontaneously form bilayer Question Models Membrane Structure
What are some key characteristics of cell membranes? Selectively permeable Contain other components proteins other lipids cholesterol Fluidity -- a “2 dimensional fluid” Membrane Structure
What factors determine how fluid a membrane is? Properties of P-lipids:Chain length and FA saturation Properties of membranes: Cholesterol content Temperature Models Membrane Fluidity Membrane Structure
Cholesterol How does Alcoholism affect RBC function? Cholesterol content Spur cell formation Function and circulation problems Question Membrane Structure
Why can some molecules diffuse through a membrane, and others cannot? Size Charge Hydrophobicity Membrane Structure
How do molecules pass Through the membrane? Protein transporters high selectivity Vesicular (bulk) transport -- discussed more later Specialized Pores gap-junctions & plasmodesmata nuclear pores Membrane Structure
What are some properties of membrane proteins? Transmembrane (Integral) vs peripheral What are some functions of membrane proteins? Hydrophilic & hydrophobic domains Models Question Membrane Structure
What is facilitated transport? Channel transport proteins a selective pore Carrier transport protein has binding sites Passive Down a concentration gradient Active Against a gradient Requires energy Direction Reversible Membrane transporter Membrane Structure
Where does the energy come from for active transport? ATP e.g. Na/ K pump Sunlight (unusual) e.g. bacteriorhodopsin Gradient via Cotransport Build and use a ion gradient Cotransport Question Membrane Structure
Example: glucose cotransport in intestine Na/glucose symport -- active glucose -- against gradient Na/K pump -- remove Na Glucose uniport -- down gradient Membrane Structure
What types of molecules pass • membranes via “Bulk Transport”? • Particulates/ dissolved molecules • Various forms • Endocytosis vs exocytosis • Phagocytosis • Pinocytosis • Can be “Receptor mediated” • Vesicle “coating” proteins Receptors Vesicle Coating Membrane Structure
How is the structure of membranes studied – I ? • Freeze-fracture electron microscopy • Tissue frozen • Etched • Carbon-coated • TEM Chloroplast thylakoid membranes Membrane Structure
How is the structure of membranes studied – II ? Detergents amphipathtic solubilize lipids/proteins Question Membrane Structure
