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Chapter 6 - Chapter Six A Tour of the Cell Definitions 1...

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Chapter Six: A Tour of the Cell Definitions 1) Light microscope: visible light is passed through the specimen and then through glass lenses. The lens refracts the light and projects a magnified image into the eye. 2) Magnification: is the ratio of an objects image to its real size. 3) Resolution: is the measure of the clarity of the image 4) Organelles: Membrane-bound structures found within a cell to keep the cell living and to help it to carry out its function 5) Electron microscope: focuses a beam of electrons through the specimen and is reflected back to the eye with a higher magnification and a better resolution 6) Scanning Electron microscope: The electron beam scans the surface of the specimen (usually covered with gold) , the electrons of the surface are then excited and are picked up by some sort of receiver and translated to a visual image giving a specimen topography 7) Transmission Electron microscope: is used to study the ultrastructure of the cell. A beam of electron is shined upon a segment of the specimen that has been stained with atoms of heavy metals, thus enhancing the electron density in certain areas. Then the scope uses special electromagnetic lenses to translate the image onto a photographic film 8) Cytology: the study of cell structures Notes - All organisms are made up of cells (either single cell or multicellular) - Cell walls were first seen by Robert Hook in 1665 of dead tree bark - Antoni van Leeuwenhoek was the first to visualize living cells - A disadvantage of electron microscopy is that it kills the specimen before observation - Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells - The plasma membrane and the organelle membranes also participate directly in the cell’s metabolism b/c of the many enzymes built in them - Biological membranes consist of a double layer of phospholipids and other lipids. Embedded in them are diverse proteins Comparing Prokaryotic and Eukaryotic cells: - All cells have basic features in common, they are: Plasma membrane, cytosol, chromosomes, and ribosome Eukaryotic Cells:
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- Most of the DNA is found in an organelle called the nucleus which is bounded by a double membrane - Within the cytoplasm, suspended in the cytosol are a variety of organelles of specialized form and function. - Eukaryotic cells are about 10 times as big as prokaryotic cells Prokaryotic Cells - DNA is found in a region called nucleoid - Has no membrane bound organelles inside of it - 2 membranes an inner membrane and outer membrane made of peptidoglycan Animal Cells: Nucleus: - Contains most of the genes in the Eukaryotic cell - It is enclosed by the nuclear envelope (is a double membrane, each lipid bi-layer is separated by intermembranal space, connected by nuclear pores) - At the tip of the nuclear pores is a protein structure called “protein complex” that regulates the entry and exit of many proteins and RNA - The nucleus is wrapped by the “nuclear lamina” (a net like array to hold and maintain the shape of the nucleus) - Within the nucleus the DNA is organized into chromosomes. Each chromosome is made up of
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