Cell Membrane Structure and Function

1. Cell Membrane Structure and Function

2. Cystic Fibrosis •most common autosomal recessive disease affecting Caucasian populations • •incidence of 1 in 2000 births •Clinical features • •pulmonary obstruction and infection • •recurrent and persistent infections • •exocrine pancreatic dysfunction • •infertility, especially in males

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4. Diagnosis • failure to thrive -child fails to gain weight despite a good appetite • sweat test -chloride concentration greater than 60 meq/liter • life expectancy now often >30 years • this was the disease most people thought would be a good candidate for gene therapy

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6. Metabolic Basis of Disease • defect in a single gene on chromosome 7 that encodes a cAMP-regulated chloride channel • called Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) • resides on the apical surface of epithelial cells lining the airways, intestines, vas deferens, sweat ducts, and pancreatic ducts

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8. Genetics and Epidemiology • autosomal recessive • 4-5% of Americans have at least one CF allele • >900 different mutations (.F508, ~70% of CF alleles) • ~50% of the patients are homozygous for the .F508 mutation

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10. Consequences of Disease • Loss of CFTR function • fluid secretion is insufficient • protein portions of the secretions become viscous • results in obstruction in the ducts and eventual organ dysfunction

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12. Lung Disease • accounts for much of the morbidity and nearly all the mortality from the disease • bacterial infections become soon after birth, and remain difficult to stop • Pseudomonas aeruginosais the main agent in patients 18 or older • bacterial resistance to antibiotics results in mucoid coating of lungs, and subsequent decline in lung

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14. Cystic Fibrosis

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16. Membrane Functions • Isolate the cell’s contents from the external environment • Regulate traffic in and out of the cell • Communicate with other cells

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18. Plasma membrane structure and functions The phospholipid bilayer and isolation • Impermeable to water-soluble and polar molecules, ions • Permeable to small and nonpolar molecules • Lipids oriented with polar heads facing out

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20. tails (hydrophobic) head (hydrophilic)

21. extracellular fluid (watery environment) phospholipid hydrophilic heads hydrophobic tails bilayer hydrophilic heads cytoplasm (watery environment)

22. Membrane Structure and Function • Membranes are “fluid mosaics” with proteins embedded in or attached to the membrane • Proteins can move within the fluid lipid bilayer

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24. extracellular fluid (outside) recognition protein receptor protein transport protein binding site phospholipid bilayer carbohydrate cholesterol phospholipid protein filaments cytoplasm (inside)

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28. Types of Membrane Proteins • Transport proteins • regulate the movement of water-soluble molecules across the membrane • Channel proteins • Carrier proteins

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30. Types of Membrane Proteins 2. Receptor Proteins • trigger cellular response when specific molecules bind to them Nervous system Endocrine system

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32. Types of Membrane Proteins 3. Recognition proteins • act as ID tags and cell surface attachment sites • the immune system

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35. Key Classes of Membrane Proteins • A.Transport channels-Intergral • 1. Membrane selects what substances will enter • 2. Take up molecules present in high concentration • 3 Part of protein extends through bilayer • 4. May be non polar helix beta-pleated sheets of non polar amino acids • 5. Non polar portion held within interior of bilayer • 6. Polar ends protrude from both sides of membrane • B. Enzymes • 1. Chemical reactions carried out on interior surface of membrane • 2. Enzymes attached directly to membrane-carry out actions within the cell • 3. Cell surfacereceptors-glycoproteins, glycolipids, oligosaccharides • a. Membranes sensitive to chemical messages • b. Receptor proteins on surface act as antennae-interpresurroundings • c. Receptors for extra cellular signals are also single-pass anchors • d. Portion of receptor that sticks outward binds with molecules • e. Binding induces changes in part of protein on the inside

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37. C. Glycoproteins-MH-ID tags -recognition • a.self recognition-cells to other cells • b. Creates proteins/carb chains shaped for specific person • c. self recognition • 2. Glycolipid- • a. Tissue recognition • b. Lipid/carb chain • c. Specific for each tissue • d. Blood types • D. Cell adhesion proteins • a. Cells use certain proteins to glue themselves to one another • b. Some are detachable, others are permanent • 4. Attachments to the cytoplasm-peripheral • a. Surface proteins may interact with other cells • b. Often linked to cytoskeleton by proteins

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39. The Extracellular Matrix • Structure: • Glycoproteins • Collagen • Glycolipids • Functions: • Support, adhesion, movement • In Embryonic development - guides movement of cells

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41. Intracellular Junctions Tight junctions • Epithelial cells (surface): Seal cells together • Prevent molecules from ‘leaking’ through between cells --> Keep integral proteins in place • Adherins junctions: • Transmembrane proteins that span 2 cells • Hold cardiac cells together • May be responsible for contact inhibition

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43. More junctions • Gap Junctions: permit flow of substances b/w cells flow of ions • allow all cells of heart to contract @ same time • allow muscles in uterus to contract simultaneously during childbirth • Desmosomes: patches that hold cells together • Breakdown of desmosomes may contribute to metastasis of cancer • Plasmodesmata: • Allow for continuous stream of cytoplasm b/w plant cells

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45. Transport across membranes • Passive transport is a function of molecular size, lipid solubility, and size of the concentration gradient 1. Simple diffusion

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47. 2 Dye molecules diffuse into the water; water molecules diffuse into the dye. 3 Both dye molecules and water molecules are evenly dispersed. 1 A drop of dye is placed in water. drop of dye pure water

48. (a) simple diffusion (extracellular fluid) (cytoplasm)

49. Transport across membranes Passive transport…(cont.) • 2. Osmosis • a. Isotonic • b. Hypertonic • c. Hypotonic

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