Chapter 4: Cells- the working units of life
Chapter 4: Cells- the working units of life 1305
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This 8 page Class Notes was uploaded by Taylor Ann Coit on Wednesday September 28, 2016. The Class Notes belongs to 1305 at University of Texas at El Paso taught by Dr. Schuyler Pike in Fall 2016. Since its upload, it has received 6 views. For similar materials see General Biology in Science at University of Texas at El Paso.
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Date Created: 09/28/16
Chapter 4: Cells: The working Units of Life Cell Theory- was the first unifying theory of biology. -Cells are the fundamental units of life -All organisms are composed of cells -All cells come from preexisting cells. Most cells are tiny, in order to maintain a good surface area- to- volume ratio. Cell Surface=2πr AND Cell Volume=πr 2 The volume of a cell determines its metabolic activity relative to time. The surface area of a cell determines the number of substances that can enter or leave the cell. The Unaided eye can see a little as a butterfly egg. Light microscope can see as little as a virus Electron microscope can see as little as an atom. - Nm= Nanometers= 10 9 meters Light Microscopes- uses 200nm Resolution power; uses light and glass Electron Microscopes- uses 2 nm Resolution power; uses electron and electromagnetic lenses Chemical analysis of cells- involves breaking them open to make a cell-free extract. The composition and chemical reactions of the extract can be examined. The properties of the cell-free extract are the same as those inside the cell. The plasma membrane: -is a selectively permeable barrier that allows cells to maintain a constant internal environment -is important in communication and receiving signals. -Often has proteins for binding and adhering to adjacent cells and surfaces. Prokaryotic cells: - Are enclosed by a plasma membrane - Have DNA located in the nucleoid. The rest of the cytoplasm consists of: Cytosol (water and dissolved material) and suspended particles. Ribosomes-sites of protein synthesis. Flagella- swimming by prokaryotes; made of the protein flagellin A motor protein anchored to the plasma or outer membrane spins each flagellum and drives the cell. Eukaryotic cells are up to 10 times larger than prokaryotes. Eukaryotic cells have membrane-enclosed compartments called organelles. Organelles have specific functions. ORGANELLES: Nucleus- the site of most cellular DNA which, with associated proteins, comprises chromatin. Mitochondria- the cell’s power plants Cytoskeleton- composed of microtubules, intermediate filaments, and microfilaments supports the cell and is involved in cell and organelle movement. A MORE SIMPLIFIED VERSION: -support and maintains cell shape - Holds organelles in position -moves organelles -Is involved in cytoplasmic streaming -interacts with extracellular structures to anchor cell in place COMPONENTS IN THE CYTOSKELETON: Microfilaments: -help a cell or parts of a cell to move -determine cell shape -are made from the protein actin-which attaches to the “plus end” and detaches at the “minus end” of the filament -the filaments can be made shorter or longer Intermediate filaments: -at least 50 different kinds in six molecular classes -have tough, ropelike protein assemblages, more permanent than other filaments and do not show dynamic instability. -anchor cell structures in place -resist tension, maintain rigidity Microtubules: -the largest diameter components -form rigid internal skeleton for some cells or regions -act as a framework for motor proteins to move structures in the cell Dynein- a motor protein that drives that sliding of doublets, by changing its shape Nexin- protein that crosslinks doublets and prevents sliding, so cilia bends Kinesin- motor protein that binds to vesicles in the cell and “walks” them along the microtubule MORE ORGANELLES: Rough Endoplasmic Reticulum (Rough ER)- the site of much protein synthesis. Plasma Membrane- separates the cell from its environment and regulates traffic of materials into and out of the cell. Centrioles- associated with nuclear division. Ribosomes- manufacture proteins. Golgi Apparatus- processes and packages proteins. Plasmodesmata- channels within the cell wall; which allows movement of water, ions, small molecules, hormones, and some RNA and proteins. Chloroplasts- harvest the energy of sunlight to produce sugar. Cell Wall: -provides support for the plant cell and limits volume by remaining rigid - acts as a barrier to infection -contributes to form during growth and development Peroxisomes- collect and break down toxic by-products of metabolism, such as H O2, 2sing specialized enzymes. Smooth Endoplasmic Reticulum (Smooth ER)- proteins and other molecules are chemically modified. Glyoxysomes- found only in plants, are where lipids are converted to carbohydrates for growth. Vacuoles- occur in some eukaryotes, but mainly in plants and fungi, and have several functions: -storage of waste products and toxic compounds; some may deter herbivores -structure for plant cells-water enters the vacuole by osmosis, creating turgor pressure. -Reproduction: vacuoles in flowers and fruits contain pigments whose colors attract pollinators and aid seed dispersal -Catabolism: digestive enzymes in seeds’ vacuoles hydrolyze stored food for early growth. Important Note: Eukaryotic cells have a nucleus and other membrane-bound compartments. Main difference between Animal and Plants cells: Plants cells have a cell wall and an Animal cell does not. Phagocytes- cells that take materials into the cell and break them down. Autophagy- programmed destruction of cell components and lysosomes are where it occurs. Lysosomal storage diseases- occurs when lysosomes fail to digest the components. Contractile vacuoles- found in freshwater protists; get rid of excess water entering the cell due to solute imbalance. The contractile vacuole enlarges as water enters, then quickly contracts to force water out through special pores. Cytoskeletal structure may be observed under the microscope, and function can be observed in a cell with that structure. Observations may suggest that a structure has a function, but correlation does not establish cause and effect. There are two methods that are used to show links between structure (A) and function (B): Inhibition- use a drug to inhibit A—if B still occurs, then A does not cause B Mutation- if genes for A are missing and B does not occur—A probably causes B. Extracellular structures are secreted to the outside of the plasma membrane. In eukaryotes, these structures have two components: A prominent fibrous macromolecule and A gel-like medium with fibers embedded Many animal cells are surrounded by an extracellular matrix. ROLES OF THE EXTRACELLULAR MATRIX: -hold cells together in tissues -contribute to physical properties of cartilage, skin, and other tissues -filter materials -orient cell movement during growth and repair The fibrous component is the protein collagen. The gel-like matric consists of proteoglycans. A third group of proteins links the collagen and the matrix together.
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