Chem 452 - Lecture 8 Lipids and Cell Membranes Part 3 · Chem 452 - Lecture 8 Lipids and Cell Membranes Part 3 Question of the Day: What role do proteins play in biological membranes?

Chem 452 - Lecture 8Lipids and Cell Membranes

Part 3Question of the Day: What role do proteins play in biological membranes?

Chem 452, Lecture 8 - Lipids and Cell Membranes

Cell Membrane Proteins✦ Form vs. Function

• The membrane lipids give form to the cell membranes

• The membrane proteins provide the function

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Cell Membrane Proteins✦ Membrane proteins function as

• Pumps (Chapter 13)

• Channels (Chapter 13)

• Signal transducers (Chapter 14)

• Energy transducers (Chapter 18 & 19)

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Cell Membrane Proteins✦ Different membranes contain different proteins.

• They can visualized using SDS-Polyacrylamide electrophoresis.

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(Chapter 3, pp.71-75)


Cell Membrane Proteins✦ Different membranes contain different proteins

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Cell Membrane Proteins✦ Different membranes contain different proteins

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RBC plasma membrane muscle cell sarcoplasmic membraneretinal rod cell

photoreceptor membrane


Cell Membrane Proteins✦ Proteins can associate with membranes in

different ways.

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Cell Membrane Proteins✦ Proteins can associate with membranes in

different ways.

✦ We will look a three different examples

• Bacteriorhodopsin (pump)

• Porin (channel)

• Prostaglandin H2 synthase-1 (enzyme)

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Cell Membrane Proteins✦ Three examples of integral membrane proteins

• Archaeal Bacteriorhodopsin (Pump)• Uses light energy to transport ions across the

membrane.

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• Bacteriorhodopsin (7 α-helical bundle)‣ There are 7 non-polar stretches of amino-acids.

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Cell Membrane Proteins✦ Hydropathy plots are used to look for

membrane spanning α-helicies

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Glycophorin




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Glycophorin

DeterminingTransfer Energies




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Glycophorin




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Glycophorin



• Porin (Channel)

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• Porin (Channel)

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• Porin (Channel)

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• Porin (Channel)

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• Porin (Channel)

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• Porin (Channel)‣ Sequence alternates between polar and non-polar

amino acid residues

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amino acid residues

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amino acid residues

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amino acid residues

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• Prostaglandin H2 synthase-1 catalase (Enzyme)

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Promotes inflammation and modulates gastric acid secretion



• Prostaglandin H2 synthase-1 (Enzyme)

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• Prostaglandin H2 synthase-1 (Enzyme)‣ Inhibited by COX inhibitors (NSAID)

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Cell Membrane Proteins✦ Peripheral proteins are often have hydrophobic

lipids attached to them.

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Cell Membrane Proteins✦ Lateral Diffusion in membranes can have a wide

range of values.

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range of values.

21S = (4Dt)1/2



range of values.

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Cell Membrane Proteins✦ Transverse diffusion is very slow.

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Cell Membrane Proteins✦ Fluid Mosaic Model of Singer and Nicolson

(1972).

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Cell Membrane Proteins✦ Membrane fluidity is modulated by

• Fatty acid composition• Cholesterol (animals)

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Cell Membrane Proteins• Membranes are asymmetric

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Cell Membrane Proteins✦ Bacterial cells

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Cell Membrane Proteins✦ Eukaryotic cells

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Next up✦ Unit V, Lecture 9 - Membrane Channels and

Pumps. (Chapter 13)

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Chem 452 - Lecture 8 Lipids and Cell Membranes Part 3 · Chem 452 - Lecture 8 Lipids and Cell Membranes Part 3 Question of the Day: What role do proteins play in biological membranes?

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