A&P Chapter 3 - Zool 2013 Chapter 3 The Cellular...

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Zool 2013 Chapter 3 The Cellular Level of Organization Lecture Outline Dr. N. Maswood
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INTRODUCTION A cell is the basic, living, structural, and functional unit of the body. Cytology is the study of cell structure, and cell physiology is the study of cell function.
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Major Components of a Cell The cell can be divided into three principal parts for ease of study. Plasma (cell) membrane - lipids, proteins Cytoplasm Cytosol (fluid portion) Organelles (solid structures) cytoskeleton, ribosomes, endoplasmic reticulum, golgi complex, ribosomes, lysosomes, peroxisomes and mitochondria Nucleus - Large organelle houses the DNA (chromosomes & genes)
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Plasma Membrane (Figure 3.2) Flexible but sturdy barrier that surround cytoplasm of cell Fluid mosaic model describes its structure “sea of lipids in which proteins float like icebergs” membrane is 50 % lipid & 50 % protein held together by hydrogen bonds lipid is barrier to entry or exit of polar substances proteins are “gatekeepers” -- regulate traffic 50 lipid molecules for each protein molecule
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The Lipid Bilayer The lipid bilayer is the basic framework of the plasma membrane and is made up of three types of lipid molecules: phospholipids, cholesterol, and glycolipids (Figure 3.2).
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Lipid Bilayer of the Cell Membrane Two back-to-back layers of 3 types of lipid molecules: Phospholipids (about 75% contain phosphate group), Cholesterol ( about 20%) and glycolipids ( about 5% lipids with attached carbohydrate groups).
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The Lipid Bilayer The bilayer arrangement occurs because the lipids are amphipathic molecules. They have both polar (charged) and nonpolar (uncharged) parts with the polar “head” of the phospholipid pointing out and the nonpolar “tail” pointing toward the center of the membrane. Membranes are fluid structures, rather like cooking oil, because most of the membrane lipids and many of the membrane proteins easily move in the bilayer. Membrane lipids and proteins are mobile in their own half of the bilayer. Cholesterol serves to stabilize the membrane and reduce membrane fluidity.
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Arrangement of Membrane Proteins The membrane proteins are divided into integral and peripheral proteins. Integral proteins extend into or across the entire lipid bilayer among the fatty acid tails of the phospholipid molecules. Are transmembrane proteins, they span the entire lipid bilayer. Peripheral proteins are found at the inner or outer surface of the membrane and can be stripped away from the membrane without disturbing membrane integrity.
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Membrane Proteins Integral versus Peripheral Proteins
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Functions of Membrane Proteins Membrane proteins vary in different cells and functions as ion channels (pores), transporters, receptors, enzymes, cell-identity markers, and linkers (Figure 3.3).
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