Grade 11A Name:______________________________ Class: _________________ Active reading 11A – Microbiology and Biotechnology Topic 1: Bacteria Prokaryotes are single-celled organisms that do not have nuclei or other membrane-bound organelles. Scientists divide prokaryotes into two major groups: the domain Archaea and the domain Bacteria. Although members of the domain Archaea are prokaryotes, some of their molecules are similar to those of eukaryotes. Many Archaea live in harsh environments, such as hot springs. Most prokaryotes belong to the domain bacteria. Organisms in both prokaryote domains are generally referred to as bacteria. Bacteria have a single chromosome made up of DNA. This chromosome is a large loop gathered into a mass called nucleoid. In addition, bacteria often have small extra loops of DNA called plasmids. The bacteria cell membrane is made up of two lipid layers. A cell wall surrounds the cell membrane. The cell wall is made of a protein-carbohydrate compound called peptidoglycan. In some bacteria such as E. coli shown below, an outer membrane covers the cell wall. Grade 11A Name:______________________________ Class: _________________ Scientists classify bacteria based on their structure using a technique called Gram staining. Gram staining involves colored dyes. As shown below Gram-positive bacteria have a thick layer of peptidoglycan in their cell wall and no outer membrane. They stain darkly with Gram staining dyes because their peptidoglycan layer is very thick. Gram-negative bacteria have a thin layer of peptidoglycan in their cell walls covered by an outer membrane. The thin peptidoglycan layer does not trap the dark dye, but does absorb the pink dye. Their outer membrane makes them more resistant to medicines and the body’s defenses than Gram-positive bacteria. Bacteria can be divided into three groups based on their energy sources. These groups are photoautotrophs, chemoautotrophs, and heterotrophs. Bacteria that use energy from sunlight to make their own food are photoautotrophs. Recall that this process of making food is called photosynthesis. Bacteria that use energy from inorganic molecules, such as sulfur and ammonia, to make their own food are chemoautotrophs. These bacteria are the only organisms that can obtain energy from inorganic sources. Bacteria that use other organisms for food are called heterotrophs. These bacteria cannot make their own food. Most heterotrophic bacteria absorb nutrients from dead organisms. However, some heterotrophic bacteria obtain nutrients from living organisms. Grade 11A Name:______________________________ Class: _________________ Bacteria reproduce by binary fission. They can form new genetic combinations by conjugation, transformation, and transduction. They can also survive harsh conditions by forming endospores. Bacteria reproduce asexually by binary fission. In this process, a single cell divides to produce two genetically identical cells. Mutations often occur during binary fission that can produce new genetic forms of bacteria. Bacteria can transfer genetic material in a process called conjugation. Conjugation occurs when a thin tube, called a pilus, attaches between two bacterial cells. The cells join and exchange genetic information. In conjugation, a pilus extends from one bacterium and attaches to the seconds bacterium. Genetic material is then transferred through the pilus from the first bacterium to the second bacterium. Bacteria can also form new genetic combinations by transformation and transduction. In transformation, bacteria take up small pieces of DNA around them. In transduction, viruses transfer DNA between bacteria. Some bacteria survive harsh conditions by forming thick-walled structures called endospores. Endospores form inside bacteria. They contain a copy of the bacteria’s DNA and a small bit of cytoplasm. Endospores can survive conditions that kill most bacteria, such as heat, radiation, and acids. When conditions improve, endospores form new bacteria. Grade 11A Name:______________________________ Class: _________________ Key words Prokaryotes Plasmid chemoautotrophs Transduction Archaea Peptidoglycan Heterotrophs Endospore Bacteria Gram staining conjugation Nucleoid photoautotrophs Transformation Vocabulary Conjugation in prokaryotes, algae, and fungi, a type of sexual reproduction in which two cells join temporarily to recombine nuclear material Peptidoglycan a protein-carbohydrate compound that makes the cell walls of bacteria rigid Endospore a thick-walled protective spore that forms inside a bacterial cell and resists harsh conditions Plasmid a genetic structure that can replicate independently of the main chromosome(s) of a cell; usually, a circular DNA molecule in bacteria (prokaryotes) Gram-negative describes a type of Transduction the transfer of a bacterial prokaryote that has a small amount of gene from one bacterium to another peptidoglycan in its cell wall, has an through a bacteriophage ( a virus) outer membrane, and is stained pink by a counterstain during gram staining Gram-positive describes a type of prokaryote that has a large amount of peptidoglycan in its cell wall and is stained violet during gram staining Transformation the transfer of genetic material in the form of DNA fragments from one cell to another or from one organism to another Grade 11A Name:______________________________ Class: _________________ A. Write one or more sentences to answer the following questions 1. What are the two major domains of prokaryotes? And which domain do most prokaryotes belong to? _____________________________________________________________ 2. How many chromosomes does a bacterium have? _____________________________________________________________ _____________________________________________________________ 3. Are the ribosomes of E. coli surrounded by a membrane? Explain your answer. _____________________________________________________________ _____________________________________________________________ 4. Why can an infection by Gram-negative bacteria be more dangerous than an infection by Gram-positive bacteria? _____________________________________________________________ _____________________________________________________________ 5. Identify what type of bacteria cannot make their own food _____________________________________________________________ 6. What is a pilus? And what is its function? _____________________________________________________________ _____________________________________________________________ 7. If eight bacterial cells undergo binary fission, how many bacterial cells will result? _____________________________________________________________ Grade 11A Name:______________________________ Class: _________________ B. Describe ways in which the structure of Gram-positive bacteria is different from that of Gram-negative bacteria. Gram-negative bacteria --------------------------------------------------------------------------------------------------------------------------------------------- Gram-positive bacteria --------------------------------------------------------------------------------------------------------------------------------------------- C. Compare between bacteria according to their energy source: D. Explain how do endospores help bacteria survive harsh conditions? ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Grade 11A Name:______________________________ Class: _________________ E. Circle the letter of the phrase that best answers the question. 1. Pili are tubular shafts in bacteria that serve as a means of ... A) genetic exchange B) attachment C) genetic exchange D) protection 2. Bacterial endospores function in A) reproduction B) survival C) protein synthesis D) storage 3. Some bacteria form a thick-walled __________ in response to poor nutrient conditions. A) endospore B) capsule C) sheath D) pilus 4. Bacteria normally contain their genome in A) a nucleoid region B) an endospore C) a plasmid D) a pilus