Lecture 6 - The Cell Membrane and Membrane Transport

Lecture 6 - The Cell Membrane and Membrane Transport -...

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1 The Cell Membrane and Membrane Transport Biology 1F25 for Biology Non-Majors Lecture 6 Background Reading Textbook, Chapters 2 and 21 The People Who Prepared This Lecture Harry Peery Jeff Stuart (1) The cell is a factory Builds itself, and bits for other cells Nucleus – manager’s office Ribosomes – assembly lines mRNA - foreman Endoplasmic reticulum - finishing touches Golgi apparatus – packaging Membrane – a wall with lots of doors and antennae Mitochondria – furnace Food – fuel for furnace
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2 The Cell Membrane in Eukaryotes • Surrounds all cells Cell Membrane For more information about the cell membrane, see pages 46-48 of your textbook and the following slides. It is a double layer of lipids… From Life: An Introduction to Biology, 3 rd ed. By Beck, Liem and Simpson, 1991. Harper Collins, New York, p. 129 Layer 1 Layer 2 It has proteins inserted… From Life: An Introduction to Biology, 3rd ed. By Beck, Liem and Simpson, 1991. p. 131 The cell membrane
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3 Lipid Rafts and Cholesterol • Lipid rafts are areas of the cell membrane where there is a lot more cholesterol. • Although the previous illustrations have indicated cholesterol is distributed evenly throughout the cell membrane, please be aware that this is not the case. A lipid raft on the cell membrane Lipid rafts are areas in the cell membrane characterized by the presence of cholesterol . Illustration and caption are from Wikipedia Outside of cell membrane Inside of cell membrane Lipid Raft Lipid Rafts are Elevated The top picture shows a higher concentration of cholesterol and GPI protein. The bottom picture is a colourized atomic force micrograph showing the raised lipid rafts (green) above the regular cell membrane (black). The spikes are GPI protein, which are found almost exclusively in the lipid rafts. Caveolae are places in the lipid rafts where receptors are located Caveolae (Latin for little caves) are infoldings of the cell membrane at points where there are lipid rafts. These infoldings serve as receptors. Insulin and cholesterol receptors are found only in caveolae. At the top (a) is an electron micrograph of caveolae.
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4 So What? • Lipid rafts are also places where a lot of pathogen exotoxins gain entrance to the cell: – Cholera – Salmonella • Lipid rafts are also where normal prions (PrP C ) are converted to mad-cow disease-causing prions (PrP Sc ) Downer cow (a cow that is lying down because it is sick) with bovine spongiform encephalopathy (BSE) and (bottom) spongiform changes in a cow brain from BSE Prion Interlude • Prions are a normal part of all cells. They are called PrP C (for pr ion p rotein normal c ellular). • Some prions are infectious. These are called PrP Sc (for pr ion p rotein, sc rapie, the disease in sheep, the first recorded prion disease). • Prions cause disease by converting
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Lecture 6 - The Cell Membrane and Membrane Transport -...

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