2010 CELL 1 - Cell Structure I Diane L.M. Hickson-Bick,...

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Cell Structure I Diane L.M. Hickson-Bick, Ph.D. Recommended Reading: Gartner & Hiatt “Color Atlas of Histology”; Chapter 1. Junqueira & Carneiro Basic Histology; Chapter 2; Klein and McKenzie pp 19-25 Goals and Objectives: Describe the structure and function of the major components of the cell. Understand the molecular arrangement of cell organelles and associated structures. Key Words: Cytoplasm, plasma membrane, mitochondria, organelle, peroxisome, lysosome. Cells Structural units of living organisms. A mass of protoplasm containing a nucleus partitioned from the environment by a selectively permeable phospholipid/protein membrane. > 200 different cell types in humans. All share common features: usually a nucleus containing nucleoplasm surrounded by cytoplasm. CYTOPLASM A matrix (cytosol) containing organelles, the cytoskeleton and deposits of carbohydrates, lipids and proteins. It is separated from the extracellular environment by the plasma membrane (plasmalemma). Plasma Membrane (PM) A limiting membrane composed of phospholipids, cholesterol, proteins and oligosaccharide chains. It has several roles, essentially: Acts as a selective barrier allowing material into and out of the cell thereby regulating the intracellular environment distinct from the extracellular environment. Functions in recognition, regulation and controls interactions with the extracellular environment. Structure of the PM 1) 7.5-10nm thick so only visible by EM 2) Electron lucent layer sandwiched between inner and outer electron-dense lines = unit membrane 3) Roughly 45% lipid, 50% protein and 5% carbohydrate. 4) Cholesterol is present and can increase the fluidity of the membrane by breaking up the orderly packing of the long fatty acid chains of phospholipids. 5) Phospholipids are categorized according to the base that forms the hydrophilic head group, e.g. phosphatidyl choline , phosphatidyl serine , phosphatidyl ethanolamine. 6) Phospholipids are most stable when the hydrophobic fatty acid side chains are directed towards the center of the membrane whilst their hydrophilic head groups are directed outward towards the aqueous environment. 7) The lipid composition of each half of the bilayer is different. 8) Glycolipids possess oligosaccharide side chains that extend outward from the surface towards the extracellular milieu. 9) Protein components are either integra l i.e. immersed in the lipid bilayer, or periphera l i.e. lie adjacent to the PM surface.
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Intregral Proteins : Usually transport proteins (e.g. Na + K + ATPase), ion selective channels, receptors or anchoring structural proteins.Some proteins can span the bilayer whilst others are only partially embedded. Polysaccharide may project from the external surface of integral proteins and form a cell surface coat, the glycocalyx . The presence of carboxyl groups and sulphate ions means the glycocalyx bears an overall negative charge. Activities of the PM
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This note was uploaded on 12/25/2010 for the course MSI 1 taught by Professor Rogerj.bick during the Spring '10 term at University of Texas Health Science Center at San Antonio.

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2010 CELL 1 - Cell Structure I Diane L.M. Hickson-Bick,...

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