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Unformatted text preview: A Preview of the Cell All organisms consist of one or more cells. A. The cell is the basic unit of structure for all organisms. B. All cells arise only from preexisting cells. C. Cell Theory I. Chapter 1 Monday, August 28, 2006 9:30 AM Biology I Page 1 Cells and Organelles Prokaryotic - small, no nucleus, but has nucleoid : the bundled chromosome, binary fission 1. Eukaryotic - large, nucleus with nucleolus, organelles, microtubules, microfilaments, intermediate filaments, exocytosis, endocytosis, mitosis and meiosis 2. Prokaryotics vs. Eukaryotic Cells A. Some eukaryotes have microvilli to increase surface area i. Surface area : Volume Ratio a. Large molecules diffuse slowly, small molecules diffuse quickly i. Membrane-bound organelles increase the rate of diffusion. ii. Cytoplasmic streaming , a process that involves active movement and mixing of cytoplasmic contents, acts as an alternative to diffusion. iii. Rates of Diffusion b. Eukaryotic organelles concentrate reactants and catalysts in order to increase reaction rates through compartmentalization of activities . i. Concentration of Reactants and Catalysts c. Cell-size Limiting Factors 1. Eukaryotes use internal membranes extensively for compartmentalization. 2. Microtubules (cilia and flagella), microfilaments (found in muscle fibrils), and intermediate filaments (stress-resistant) are key components of the cytoskeleton. 3. Endocytosis : portions of the plasma membrane invaginate and are pinched off to form membrane-bound cytoplasmic vesicles containing substances that were previously on the outside of the cell. 4. Exocytosis : membrane-bound vesicles inside the cell fuse with the plasma membrane and release their contents to the outside of the cell. 5. Organelles B. Properties and Strengths of Cells I. Phospholipid bilayer 1. Plasma Membrane A. During mitosis, these are bundled tightly, but are dispersed during interphase as chromatin . a. Genetic material: bundled DNA called chromosomes 1. Two phospholipid bilayers: inner and outer nuclear membranes that together make up the nuclear envelope . 2. The nuclear envelope has pores that allow for the transport of water-soluble molecules into and out of the nucleus. 3. Histones: eukaryotes only 4. Nucleolus : responsible for the synthesis and assembly of ribosomes 5. Nucleus B. The internal volume of the cell exclusive of the nucleus is called the cytoplasm and is occupied by organelles and by the semi-fluid cytosol in which they are suspended. 1. Two phospholipid bilayers: inner and outer membranes a. Oxidizes sugars and stores the energy in adenosine triphosphate (ATP) b. Contain infoldings of the membrane, called cristae , and a semi-fluid matrix where the oxidation steps occur....
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