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Lecture 5: Membrane structure
Bio 93: DNA to Organisms Lecture 5: Membrane structure Bio 93 (Summer 2017), Copyright © 2017, Dr. Salme Taagepera. All rights reserved.
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Lecture 5: Learning Objectives
5.1 – Describe the structure and function of the plasma membrane and the extracellular matrix 5.2 – Predict the fluidity and permeability of a plasma membrane given several factors 5.3 – Analyze and draw conclusions from scatter plots with multiple sets of data
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Lecture 5: Key terms Plasma membrane Glycolipids Selectively permeable
Glycoproteins Amphipathic Transport proteins Fluid mosaic model Collagen Cholesterol Proteoglycans Integral proteins Fibronectin Peripheral proteins Integrins Transmembrane proteins FRAP Diffusion coefficient New terms from lecture!
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Lecture 5: Membrane Structure
Phospholipid structure Membrane proteins Fluidity of membranes affected by: Measure membrane fluidity with FRAP Temperature Saturation of fatty acid Cholesterol concentration Membrane permeability affected by: Membrane thickness Bio 93 (Summer 2017), Copyright © 2017, Dr. Salme Taagepera. All rights reserved.
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Bio 93 (Summer 2017), Copyright © 2017, Dr. Salme Taagepera
Bio 93 (Summer 2017), Copyright © 2017, Dr. Salme Taagepera. All rights reserved.
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If you zoomed in on this box, what would you see?
5.1
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Membrane phospholipids are amphiphilic
Membrane lipids differ in: head group length of hydrophobic tail degree of saturation of the hydrophobic tail polar nonpolar * Cpoyright 2005 Dr. Salme Taagepera, All rights reserved.
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Which statement about phospholipids is FALSE?
1 Which statement about phospholipids is FALSE? A – Phospholipids are amphipathic B – The fatty acid tails are non-polar C – Phospholipid heads are hydrophobic D – The fatty acid tails would interact well with certain portions of a transmembrane protein 5.1
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2 In a membrane protein, where do you think you would find this stretch of amino acids? A – in the core of a glycoprotein B – in the part of an integral protein that is in the middle of the plasma membrane C – in the core of a peripheral protein D – in the part of an integral protein that is exposed to the cytoplasm 5.1
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What factors affect membrane fluidity and permeability?
2 What factors affect membrane fluidity and permeability? Can you draw how temperature and percent of saturated fatty acids are related to membrane fluidity? Fluidity Fluidity 5.2 Percent of saturated fatty acids Temperature
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How can you visualize and measure membrane fluidity?
Fluorescence recovery after photobleaching (FRAP) Diffusion coefficient (D; mm2 / sec) Fluorescence intensity Higher diffusion coefficient = more fluid membrane
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RATE and EXTENT of recovery
Data for movement of lipids? Fluorescence Recovery After Photobleaching (FRAP) FRAP: Label membrane lipids or proteins (shown here) with fluorescent tag FRAP experiments can quantify lateral movements of lipids and proteins within the plasma membrane Recovery rate and extent NOTE: Measured by RATE and EXTENT of recovery
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FRAP data shows: Typical lipid molecule exchanges places with
its neighbors in its leaflet about 107 times /sec Lipids can diffuse several micrometers/sec (37°C) Membrane lipid could diffuse: length typical bacterial cell = 1 sec length typical animal cell = 20 sec Lipids found in membranes have similar diffusion rates to lipids found in olive oil!
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2 How does cholesterol affect membrane fluidity?
Experiment: Added cyclodextrin to cell membranes, used FRAP to measure diffusion coefficient at 37oC (Cyclodextrin dislodges cholesterol from membranes) 2 * How does cholesterol affect membrane fluidity? A – Cholesterol increases membrane fluidity B – Cholesterol decreases membrane fluidity Diffusion coefficient 5.2 [Cyclodextrin] (mg/ml)
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Experiment: added various levels of cholesterol to membranes and measured permeability at different temperatures 2 How does cholesterol affect membrane permeability? A – Percent cholesterol and permeability are directly proportional B – Percent cholesterol and permeability are inversely proportional C – Percent cholesterol does not affect permeability 0% Cholesterol Permeability 5.2 5.3
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Based on these two figures, how are membrane fluidity and permeability related?
2 * 0% Cholesterol Permeability [Cyclodextrin] (mg/ml) As cholesterol level decreases, membrane fluidity increases. As cholesterol level decreases, membrane permeability increases. Permeability 5.2 Fluidity
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What about plasma membrane thickness?
3 What about plasma membrane thickness? How do you think plasma membrane thickness affects membrane permeability? Why? Can you design an experiment to test how membrane thickness affects membrane permeability? 5.2
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Summary How does… Temperature affect fluidity?
Percent fatty acid saturation affect fluidity? [Cholesterol] affect fluidity? [Cholesterol] affect permeability? Membrane thickness affect permeability?
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Rank these membranes from least fluid to most fluid
2 Rank these membranes from least fluid to most fluid A – A membrane with 10% saturated fatty acids at 37 oC B – A membrane with 50% saturated fatty acids at 25 oC C – A membrane with 10% saturated fatty acids at 25 oC 5.2 Which membrane is most permeable?
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