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Bacteria Jessica Harwood Douglas Wilkin, Ph.D. Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) To access a customizable version of this book, as well as other interactive content, visit www.ck12.org AUTHORS Jessica Harwood Douglas Wilkin, Ph.D. EDITOR Douglas Wilkin, Ph.D. CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-source, collaborative, and web-based compilation model, CK-12 pioneers and promotes the creation and distribution of high-quality, adaptive online textbooks that can be mixed, modified and printed (i.e., the FlexBook® textbooks). Copyright © 2015 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution-Non-Commercial 3.0 Unported (CC BY-NC 3.0) License (http://creativecommons.org/ licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated herein by this reference. Complete terms can be found at http://www.ck12.org/about/ terms-of-use. Printed: July 1, 2015 CONTRIBUTORS Doris Kraus, Ph.D. Niamh Gray-Wilson Jean Brainard, Ph.D. Sarah Johnson Jane Willan Corliss Karasov www.ck12.org C HAPTER • • • • Chapter 1. Bacteria 1 Bacteria Describe common bacterial shapes. Summarize the similarities between bacterial cells and eukaryotic cells. Summarize the differences between bacterial cells and eukaryotic cells. Explain the roles of the cell wall and the flagella in bacteria. Are bacteria living things? Bacteria are individual living cells. Bacteria cells are similar to your cells in many ways; yet, they also have distinct differences. Bacteria have many unique adaptations allowing them to live in many different environments. Characteristics of Bacteria Bacteria are the most successful organisms on the planet. They lived on this planet for two billion years before the first eukaryotes and, during that time, evolved into millions of different species. Size and Shape Bacteria are so small that they can only be seen with a microscope. When viewed under the microscope, they have three distinct shapes ( Figure 1.1). Bacteria can be identified and classified by their shape: 1. Bacilli are rod-shaped. 2. Cocci are sphere-shaped. 3. Spirilli are spiral-shaped. 1 www.ck12.org FIGURE 1.1 Bacteria come in many different shapes. Some of the most common shapes are bacilli (rods), cocci (spheres), and spirilli (spirals). Bacteria can be identified and classified by their shape. Similarities to Eukaryotes Like eukaryotic cells, bacterial cells have: 1. 2. 3. 4. Cytoplasm, the fluid inside the cell. A plasma or cell membrane, which acts as a barrier around the cell. Ribosomes, in which proteins are put together. DNA. By contrast though, bacterial DNA is contained in a large, circular strand. This single chromosome is located in a region of the cell called the nucleoid. Many bacteria also have additional small rings of DNA known as plasmids. See bacterial cell pictured below ( Figure 1.2). FIGURE 1.2 The structure of a bacterial cell is distinctive from a eukaryotic cell because of features such as an outer cell wall, the circular DNA of the nucleoid, and the lack of membrane-bound organelles. 2 www.ck12.org Chapter 1. Bacteria Unique Features Bacteria lack many of the structures that eukaryotic cells contain. For example, they don’t have a nucleus. They also lack membrane-bound organelles, such as mitochondria or chloroplasts. The DNA of a bacterial cell is also different from a eukaryotic cell. Bacterial DNA is contained in one circular chromosome, located in the cytoplasm. Eukaryotes have several linear chromosomes. Bacteria also have two additional unique features: a cell wall and flagella. The Cell Wall Bacteria are surrounded by a cell wall consisting of peptidoglycan. This complex molecule consists of sugars and amino acids. The cell wall is important for protecting bacteria. The cell wall is so important that some antibiotics, such as penicillin, kill bacteria by preventing the cell wall from forming. Some bacteria depend on a host organism for energy and nutrients. These bacteria are known as parasites. If the host starts attacking the parasitic bacteria, the bacteria release a layer of slime that surrounds the cell wall. This slime offers an extra layer of protection. Flagella Some bacteria also have tail-like structures called flagella ( Figure 1.3). Flagella help bacteria move. As the flagella rotate, they spin the bacteria and propel them forward. Though some eukaryotic cells do have a flagella, a flagella in eukaryotes is rare. FIGURE 1.3 The flagella facilitate movement in bacteria. Bacteria may have one, two, or many flagella—or none at all. 3 www.ck12.org Vocabulary • bacilli: Rod-shaped. • cell wall: Tough outer layer of bacterial cells that helps support and protect the cell; also found around plant cells. • cocci: Sphere-shaped. • flagella: Tail-like structures that help bacteria move. • nucleoid: DNA, contained in a large circular strand, forming a single chromosome. • parasite: Organism that benefits in a symbiotic (parasitism) relationship in which one organism is harmed. • peptidoglycan: Complex molecule consisting of sugars and amino acids that makes up the bacterial cell wall. • plasmid: Small ring of additional DNA. • spirilli: Spiral-shaped. Summary • Bacteria can be classified by their shape, including bacilli (rods), cocci (spheres), and spirilli (spirals) • Bacteria are like eukaryotic cells in that they have cytoplasm, ribosomes, and a plasma membrane. • Features that distinguish a bacterial cell from a eukaryotic cell include the circular DNA of the nucleoid, the lack of membrane-bound organelles, the cell wall of peptidoglycan, and flagella. Explore More Use the resources below to answer the following questions. Explore More I • Prokaryotic Cells at http://www.youtube.com/watch?v=gGlhCWg5iOM (2:23) 1. 2. 3. 4. What does the word prokaryote mean? How does bacterial DNA differ from the DNA in eukaryotic cells? What is one explanation for this difference? What is the bacterial capsule? Are all bacterial capsules made of the same material? How does the movement of bacterial flagella differ from the movement of eukaryotic flagella? Explore More II • Cells Alive at http://www.cellsalive.com/cells/bactcell.htm 1. Describe three features of a bacterial cell? 2. What is the nucleoid? 3. What is a plasmid? Review 1. 2. 3. 4. 4 How are bacteria classified? How are bacterial cells like your cells? How are bacterial cells different from your cells? Describe the bacterial flagella. www.ck12.org Chapter 1. Bacteria References 1. Mariana Ruiz Villarreal (LadyofHats). Drawing of rod, sphere, and spiral shaped bacteria. Public Domain 2. Mariana Ruiz Villarreal (LadyofHats). Structure of a bacterial cell. Public Domain 3. Zappy’s. Flagella help bacteria move. CC BY-NC 3.0 5