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The Cell Notes Lecture 2.docx

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Biology 1201A
Jennifer Waugh

Jessica Hogle 9/10/12 4:16 PM Biology 1201A Gardiner Chapter 2 The Cell: An Overview History of the Cell - Robert Hooke, mid-1600’s, discovered the cell - Late 1600’s, Anton van Leeuwenhoek discovered and described diverse protists, sperm cells, and bacteria (1673) - Robert Brown discovered the nucleus - Rudolf Virchow proposed that cells arise only from pre-existing cells by a process of division Cell Theory 1. All organisms are composed of one or more cells 2. The cell is the basic structural and functional unit of all living organisms 3. Cells arise only from the division of pre-existing cells 2.1 Basic Features of Cell structure and Function - Cells carry out the essential processes of life - Contain highly organized systems of molecules such as DN and RNA - Use chemical molecules or light as energy sources for their activities - Respond to changes in their external environment by alternating their internal reactions - Duplicate and pass on hereditary information as part of cellular reproduction - Unicellular: almost all bacteria and archaea, some protists such as amoebas, and some fungi such as yeast - Unicellular is a type of cell that is a functionally independent organism capable of carrying out all activities necessary for life - Plants and animals are multicellular, which means that the activities of life are divided among varying numbers of specialized cells - If cells are broken open then the property of life is lost. The cells are not able to grow, reproduce, or respond to outside stimuli in a coordinated fashion 2.1a Cells Are Small and Are Visualized Using a Microscope - All forms of life are grouped into one of the three domains: the Bacteria, the Archaea, and the Eukarya - Bacteria and Archaea also grouped together in Prokaryota - Microscope used for microscopy - Two common types of microscopes are light microscopes which use light to illuminate the specimen, and electron microscopes which use electrons to illuminate the specimen - The volume of a cell determines the amount of chemical activity that can take place within it - Surface area determines the amount of substances that can be exchanged between the inside of the cell and the outside environment - Nutrients must constantly enter the cell and wastes must constantly leave - Past a certain point, increasing the diameter of a cell gives a SA that is insufficient to maintain an adequate nutrient-waste exchange for its entire volume - Cells can increase ability to exchange by flattening or by developing surface folds/extensions that increase SA. Example: human intestinal cells have closely packed finger-like extensions that greatly help in enhancing their ability to absorb digested food molecules 21b Cells Have a DNA-Containing Central Region that is Surrounded by Cytoplasm - all cells bounded by plasma membrane (bilayer made of lipids with embedded protein molecues) - lipid bilayer is hydrophobic barrier to the passage of water-soluble substances - Central region of cells contain DNA and proteins that help maintain the DNA structure and enzymes that duplicate DNA and transfer it into RNA - Al parts of the cell between plasma membrane and central region make up the cytoplasm - Cytoplasm contains organelles, cytosol, cytoskeleton - Organelles: small, organized structures important for cell function - Cytosol: aqueous solution containing ions and various organic molecules - Cytoskeleton: protein-based framework of filamentous structures thatm among other things, helps maintain proper cell shape and plays key roles in cell division and chromosome segregation from cell generation to cell generation - Synthesis and assembly of most molecules required for growth and reproduction, and conversion of chemical and light energy into forms that can be used by cells occur in the cytoplasm 2.1c Cells occur is Prokaryotic and Eukaryotic Forms, Each with Distinctive Structures and Organization - Prokaryotic refers to a particular call architecture that is lacking a nucleus - Nucleoid has no boundary membrane separating it from the cytoplasm - Many species of archaea and bacteria contain few if any internal membranes, but a number of other species of both groups contain extensive internal membranes - Eukaryotes are defined by having cells where DNA is contained within a membrane-bound compartment called the nucleus - Cytoplasm of these cells contain s extensive membrane systems that form organelles with their own distinct environments and specialized functions 2.2 Prokaryotic Cells - organism in which the DNA is suspended in the cell interior without separation from other cellular components by a discrete membrane - Three shapes that are most common are spherical, rodlike, and spiral - E. Coli is a rodlike prokaryotic cell - Genetic material for archaea and bacteria is held in the nucleoid - Cell wall provides rigidity to the cell and protects it from physical damage - Wall is coated with external layer of polysaccharides called glycocalyx which is a carbohydrate cell coat covering the cells surface - When glycocalyx is diffuse and loosely attached it is a slime layer - When glycocalyx is gelatinous and more firmly attached to cell it is a capsule - Glycocalyx helps protect from physical damage and desiccation, and may enable the cell to attach to a surface such as other prokaryotic cells, eukaryotic cells, and non-living substrate (rock) - Plasma membrane transports materials in and out of cell as well as containing most of the molecular systems that metabolize food molecules into the chemical energy ATP - Prokaryotic cytoskeletons create and maintain the proper shape of cells in cell division and determine the polarity of cells - Can move across liquid surfaces with flagella - Pili, which are hairlike shafts of protein, extend from the cell walls so that they can help attach the cell to other cells 2.3 Eukaryotic Cells - Divided into four major groups: protists, fungi, animals, and plants 2.3a Eukaryotic Cells Have a True Nucleus and Cytoplasmic Organelles Enclosed within a Plasma Membrane - true nucleus enclose by membrane - plasma membrane carries out various functions through several types of embedded proteins - some of these proteins form channels through the plasma membrane that transport substances into and out of the cell - other proteins in plasma act as receptors binding and recognizing specific signal molecules in the cellular environment and trigger internal responses 2.3b The Eukaryotic Nucleus Contains Much More DNA Than the Prokaryottic Nucleoid - nucleus separated form cytoplasm by nuclear envelope - nuclear pore complexes are embedded in the nuclear envelope, which are large, octagonally symmetrical, cylindrical structures formed of many types of proteins called nucleoporins - It exchanged components between the nucleus and cytoplasm and prevents the transport of material not meant to cross the nuclear membrane - Nucleoplasm is a liquid or semi-liquid within the nucleus - Most of the space in the nucleus is filled with chromatin - Eukaryotic nuclei contain much more DNA than prokaryotic nucleoids - Also contains one or more nucleoli 2.3c Eukaryotic Ribosomes Are Either Free in the Cytosol or Attached to Membranes - Eukaryotic ribosome consists of a large and a small subunit - Structures of bacterial, archaeal, and eukaryotic ribosomes are similar no identical - Ribosomes larger than archaeal and bacterial - Ribosomes function identical to those of prokaryote: use info in mRNA to assemble amino acids into proteins - Some are freely suspended in the cytosol, others attached to membranes - Most are attached to ER 2.3d An Endomembrane System Divides the Cytoplasm into Functional and Structural Compartments - ER: collection of interealated internL membranous sacs that divide the cell into functional and structural compartments - Functions: synthesis and modification of proteins and their transport into membranes and organelles or the outside of the cell, synthesis of lipids, and detoxifications of some toxins - Membranes in system are connected directly or indirectly by vesicles (small membrane-bound compartments that transfer substances between parts of the system - Components: nuclear envelope, endoplasmic reticulum, golgi complex, lysosomes, vesicles, and plasma membrane - ER:extensive interconnected network o
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