Chapter 8 Membrane Structure and Function

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Chapter 8 Membrane Structure and Function
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Plasma Membrane
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Membrane Composition

• Question How are the
  materials arranged?

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Lipid Bilayer

• Phospholipids
• Hydrophilic heads
• Hydrophobic tails

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Membrane Models
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Davson-Danielli Model 1935

• Lipid bilayer.
• Proteins coat the surfaces.
• Sometimes called the sandwich model.

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Evidence

• Biochemical work.
• TEM pictures show the membrane as a double line.

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Problems

• Not all membranes in a cell were the same.
• How could the proteins stay in place?
• Result - the model was questioned and tested by
  scientific process.

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Fluid Mosaic Model 1972

• New model to fit the new evidence with membranes.
• Example of Science as a
  Process.

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Fluid Mosaic Model
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Fluid
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Ways to keep the membrane fluid
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Mosaic
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Evidence

• TEM pictures of fractured membranes.
• Cell fusion studies.
• Tagging of membrane proteins by antibodies.

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Protein Function in Membranes
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Types of Membrane Proteins

• Integral
• Peripheral -

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Question?

• How do the integral proteins stick to the
  membrane?

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Hydrophilic Amino Acids
Hydrophobic Amino Acids
Hydrophilic Amino Acids
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Membranes are Bifacial
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Carbohydrates
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Membrane Carbohydrates
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Question

• How do materials get across a cell's membrane?

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Problems

• Lipid bilayer is hydrophobic. Hydrophilic
  materials don't cross easily.
• Large molecules don't cross easily. Too big to
  get through the membrane.

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Mechanisms

• 1.
• 2.

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Passive Transport
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Types of Passive Transport

• 1.
• 2.
• 3.

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Diffusion
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Equilibrium
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Factors that Effect Diffusion

• 1.

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Osmosis
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Tonicity
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Isotonic
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Hypotonic
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Hypertonic

• .

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Facilitated Diffusion
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Aquaporins

• Newly found channels for osmosis.

GFP labeled Aquaporins
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Active Transport
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Types of Active Transport

• 1.

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Carrier-Mediated Transport
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Examples

• 1.

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Na- K pump
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Electrogenic or H pumps

• .

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Cotransport
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Exocytosis
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Endocytosis

• .

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Types

• 1.

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Carbohydrates
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Forming vesicles
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Summary

• Know membrane structure.
• Be able to discuss the various methods by which
  cells move materials through membranes.
• Be able to solve problems in osmosis.