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Lesson 2: Prokaryotic and Eukaryotic Cells (1.1.2) PROKARYOTIC CELLS There are two basic types of cells: prokaryotic and eukaryotic. A prokaryotic (pro-before; karyotic-nucleus) cell does not have a true nucleus. Prokaryotes’ genetic material is in the shape of a loop and is usually contained in a central location within the cell. A prokaryotic cell has naked DNA because a membrane does not surround it. Bacterial cells are examples of prokaryotes. These cells have an extra piece of DNA in the shape of a ring that carry antibiotic resistant gene. Further-more, prokaryotic cells have no membrane-bound organelles. See Figure 2.1 a drawing of a prokaryotic cell. Prokaryotic cells are the most simplistic and primitive cells. For this reasons, these cells are thought to be the first cells to appear on earth. EUKARYOTIC CELLS A eukaryotic (eu-true; karyotic-nucleus) cell’s DNA is contained in the nucleus surround by a nuclear membrane. It also has several membrane-bound organelles. Eukaryotic cells tend to be larger and more complex than prokaryotic cells. For example, the complex DNA in a human has more than 3 billion kilobase (one thousand) pairs of nitrogen bases. Prokaryotes have small genomes (all the DNA in an organism). For example, cyanobacteria have slightly more than 1 billion kilobase pairs. Prokaryotes have about 1/1000 as much genetic material as eukaryotes. Plant and animal cells are both eukaryotic and, although similar in structure, contain unique cell parts. For instance, plant cells have a cell wall, central vacuole and chloroplasts. Animal cells have centrioles and some even have cilia (found in intestinal cells) and flagella (found in sperm cells). See figure 2.2 for schematic drawings of eukaryotic cells. PLANT VS ANIMAL CELLS Plant and animal cells have many similarities and differences. Plant cells are autotrophs because they make their food through photosynthesis. Animal cells are heterotrophic because they get their food from other sources. The illustration in Figure 2.3 compares and contrasts plant and animal cells. Two visible differences between plant cells and animal cells are chloroplast and the size of vacuoles. Study Figure 2.4 for other similarities and differences. Another comparison of these cells is addressed in 1.2.2 for their reproductive similarities and differences. Activity Read the paragraph below and place the following features of prokaryotes and eukaryotes in a Venn diagram. Eukaryotic cells have internal membranes that compartmentalize their functions where as prokaryotic cells are usually smaller and microscopic in size. Eukaryotic cells are larger; however, both have cytoplasm. A prokaryotic lacks a nucleus; while a eukaryotic cell has a membrane-bound nucleus and some membrane-bound organelles. Prokaryotes have no membrane-bound organelles and are therefore less complex. The DNA of prokaryotes is naked while eukaryotes have DNA with proteins attached to help organize the helical shape. Eukaryotes have two or more chromosomes whereas prokaryote has one chromosome in a loop shaped structure. Lesson 2 Review: Prokaryotic and Eukaryotic Cells A. Define the following terms. prokaryotic heterotroph eukaryotic autotrophy B. Choose the best answer 1. Which cell would provide the best opportunity to study a small ring of DNA that contains antibiotic genes? A. plant cell C. animal cell B. bacterial cell D. viruses 2. How can a prokaryote be distinguished from a eukaryote? A. nucleus C. chloroplasts B. cell wall D. central vacuole 3. Which organelle can be found in both plant and animal cells? A. nucleus C. chloroplasts B. cell wall D. central vacuole 4. Which organelle is found in a prokaryotic cell? A. nucleus C. chloroplasts B. ribosomes D. central vacuole 5. Which of the following would most likely contribute to disease? A. nucleus B. bacteria B. chloroplast D. ribosomes C. Complete the following exercises 1. Explain why prokaryotic cells are thought to be more primitive than eukaryotic cells. 2. Research prokaryotes to determine how they are used to save crops from freezing.