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Unformatted text preview: 1 C h a p t e r 1 Microscopy and the Cell In this experiment, you will study various aspects of cell structure. OBJECTIVES 1. To study cell structure and learn the characteristics of different types of cells. a. To identify organelles such as nuclei, chloroplasts and mitochondria. b. To learn which cell organelles cannot be seen using a light microscope. 2. To become familiar with the light microscope. CELL STRUCTURE An understanding of cell structure is fundamental to an understanding of biology. According to cell theory, (1) all organisms are made up of cells and (2) all cells come from other cells. PROKARYOTIC AND EUKARYOTIC CELLS Prokaryotic and eukaryotic cells, the two types of cells, differ with respect to cell organization. Prokaryotic cells lack a true nucleus and membrane-bound organelles. Most lack internal membranes, although internal membranes are present in photo- synthetic bacteria and cyanobacteria. The DNA is located in a region of the cell called the nucleoid. It is packaged in a single, circular chromosome with few accompanying proteins. Prokaryotic cells do not divide by mitosis. In contrast, eukaryotic cells contain a true nucleus surrounded by a double membrane known as the nuclear envelope. They typically have several chromosomes, linear stretches of DNA packaged together with histones and other proteins. Eukaryotic cells also contain much more DNA than do prokaryotic cells. Eukaryotic cells divide by a process called mitosis. They also contain organelles such as mitochondria, chloroplasts, Golgi, endoplasmic reticulum, etc. The differences between prokaryotic and eukaryotic cells are summarized in Table 1-1. Organelles such as chloroplasts and mitochondria also contain DNA. The mitochondrial and chloroplast chromosomes are small, circular and devoid of protein. Thus, they more closely resemble the prokaryotic chromosome than the chromosomes found in 2 BIO 100 Microscopy and the Cell the nucleus of the eukaryotic cells of which they are a part. This has led to the theory of endosymbiosis that states that the ancestors of mitochondria and chloroplasts were once free-living organisms. Eukaryotic cells developed when these free-living organisms were incorporated into other prokaryotic cells and lived in a symbiotic relationship with them. In time, some of the genes of the organelles were transferred to the cell nucleus. Table 1-1. Differences between prokaryotic and eukaryotic cells. Characteristic Prokaryotic Cells Eukaryotic Cells Membrane-bound organelles None Mitochondria, Chloroplasts, Golgi, Endoplasmic Reticulum, etc. Nucleus No true nucleushave a nucle- oid or nuclear region True nucleus surrounded by a nuclear membrane Organization of DNA Few proteins, 1 circular chromosome DNA packaged in > 1 chromosome with histones and other proteins Type of cell division No mitosis Mitosis Size Small Large PROKARYOTIC CELLS Several types of prokaryotic organisms exist including: a. Archaebacteriasome methanogenic; some reduce sulfur...
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This note was uploaded on 10/27/2010 for the course BIO 102 taught by Professor Alaie during the Fall '08 term at CUNY Hunter.
- Fall '08