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Prokaryote Metabolism Douglas Wilkin, Ph.D. Jean Brainard, 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 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-content, web-based collaborative model termed the FlexBook®, CK-12 intends to pioneer the generation and distribution of high-quality educational content that will serve both as core text as well as provide an adaptive environment for learning, powered through the FlexBook Platform®. Copyright © 2012 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/NonCommercial/Share Alike 3.0 Unported (CC BY-NC-SA) License (http://creativecommons.org/licenses/by-nc-sa/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/terms. Printed: October 23, 2012 AUTHORS Douglas Wilkin, Ph.D. Jean Brainard, Ph.D. www.ck12.org C ONCEPT Concept 1. Prokaryote Metabolism 1 Prokaryote Metabolism • Identify different types of metabolism found in prokaryotes. What do bacteria need to grow? Like most everything else, they need food. Given the right conditions, bacteria can grow from just a few cells to millions or billions overnight. Prokaryote Metabolism Like all living things, prokaryotes need energy and carbon. They meet these needs in a variety of ways. In fact, prokaryotes have just about every possible type of metabolism. They may get energy from light (photo) or chemical compounds (chemo). They may get carbon from carbon dioxide (autotroph) or other living things (heterotroph). Most prokaryotes are chemoheterotrophs. They depend on other organisms for both energy and carbon. Many break down organic wastes and the remains of dead organisms. They play vital roles as decomposers and help recycle carbon and nitrogen. Photoautotrophs are important producers. They are especially important in aquatic ecosystems. Classification of Prokaryotes Based on Metabolism Two major nutritional needs can be used to group prokaryotes. These are (1) carbon metabolism, their source of carbon for building organic molecules within the cells, and (2) energy metabolism, their source of energy used for growth. In terms of carbon metabolism, prokaryotes are classified as either heterotrophic or autotrophic: • Heterotrophic organisms use organic compounds, usually from other organisms, as carbon sources. • Autotrophic organisms use carbon dioxide (CO2 ) as their only source or their main source of carbon. Many autotrophic bacteria are photosynthetic, and get their carbon from the carbon dioxide in the atmosphere. Energy metabolism in prokaryotes is classified as one of the following: • Phototrophic organisms capture light energy from the sun and convert it into chemical energy inside their cells. • Chemotrophic organisms break down either organic or inorganic molecules to supply energy for the cell. Some chemotrophic organisms can also use their organic energy-supplying molecules as a carbon supply, which would make them chemoheterotrophs. • Photoheterotrophs are organisms that capture light energy to convert to chemical energy in the cells, but they get carbon from organic sources (other organisms). Examples are purple non-sulfur bacteria, green non-sulfur bacteria and heliobacteria. • Chemoheterotrophs are organisms that get their energy source and carbon source from organic sources. Chemoheterotrophs must consume organic building blocks that they are unable to make themselves. Most get their energy from organic molecules such as sugars. This nutritional mode is very common among eukaryotes, including humans. • Photoautotrophs are cells that capture light energy, and use carbon dioxide as their carbon source. There are many photoautotrophic prokaryotes, which include cyanobacteria. Photoautotrophic prokaryotes use similar compounds to those of plants to trap light energy. 1 www.ck12.org • Chemoautotrophs are cells that break down inorganic molecules to supply energy for the cell, and use carbon dioxide as a carbon source. Chemoautotrophs include prokaryotes that break down hydrogen sulfide (H2 S the “rotten egg” smelling gas), and ammonia (NH4 ). Nitrosomonas, a species of soil bacterium, oxidizes NH4 + to nitrite (NO2 − ). This reaction releases energy that the bacteria use. Many chemoautotrophs also live in extreme environments such as deep sea vents. FIGURE 1.1 This flowchart helps to determine if a species is an autotroph or a heterotroph, a phototroph or a chemotroph. For example, “Obtain carbon elsewhere?” asks if the source of carbon is another organism. If the answer is “yes”, the organism is heterotrophic. If the answer is “no,” the organisms is autotrophic. Vocabulary • • • • • • • autotroph: Organism that makes its own food. chemoautotroph: Producer that uses energy from chemical compounds to make food by chemosynthesis. chemoheterotroph: Organism that depends on other organisms for both energy and carbon. heterotroph: Organism that obtains food by consuming other organisms. metabolism: Sum of all the biochemical reactions in an organism. photoautotroph: Producer that uses energy from sunlight to make food by photosynthesis. photoheterotroph: Organisms that capture light energy to convert to chemical energy in the cells, but get carbon from organic sources (other organisms). Summary • Prokaryotes fulfill their carbon and energy needs in various ways. They may be photoautotrophs, chemoautotrophs, photoheterotrophs, or chemoheterotrophs. Practice Use this resource to answer the questions that follow. • http://www.hippocampus.org/Biology → Biology for AP* → Search: Prokaryotic Lifestyles 1. What is nutrition? 2 www.ck12.org 2. 3. 4. 5. Concept 1. Prokaryote Metabolism Distinguish between autotrophs and heterotrophs. Distinguish between phototrophs and chemotrophs. What is a photoautotroph? Describe chemoheterotrophs. Review 1. Compare and contrast prokaryotic metabolism. 2. Which type of prokaryotes are producers, and which are consumers? 3