21.+Prokaryotes


 * 1) **Prokaryotes**
 * **Characteristics **
 * Structure of prokaryotes includes few membrane bound compartments and reactions tend to take place in the cytoplasm or in the plasma membrane. The cell wall is a semi-rigid, permeable structure that helps maintain the shape and strength when internal pressure rises. Its size pertains to microorganisms which can't be seen without microscope, measured in micrometers (millions of a meter.) There are 3 types of shapes of prokaryotes. The Coccus- spherical (also oval or flattened), Bacillus- Rod-shaped (may be skinny or tapered), or Spirillum- cell body with one or more twists.
 * Metabolic Diversity of prokaryotes are of various types. First, there are the **photoautotrophs**. These are self-feeders. They use sunlight for energy by process of photosynthesis and use carbon dioxide as a carbon source. Some use electrons and hydrogens from water molecules for synthesis reactions and release oxygen. Whereas, some are anaerobic and get electrons and hydrogen from inorganic compounds. A few examples would consist of: Cyanobacteria, green sulfur bacteria, and purple sulfur bacteria. Then there are the **chemoautotrophs**. These are also self-feeders that use carbon dioxide as carbon source. Some of these oxidize organic compounds for energy. While others obtain the required energy by oxidizing inorganic substances. Some examples are: Nitrifying, sulfur-oxidizing, and iron-oxidizing bacteria. Next there are the **photoheterotrophs**. These are not self-feeders. They capture sunlight energy for photosynthesis. They get carbon from organic compounds produced by other organisms. Some examples are: Purple nonsulfure and green nonsulfur bacteria. Finally, there the **chemoheterotrophs**. These are not self-feeders and that usually are parasites or saprobes. Parasites draw glucose and other nutrients from living host. Saprobes get nutrients by digesting organic products, wastes, or remains of other organisms.
 *  **Growth and Reproduction**
 * The size of a prokaryotic cell is measured in terms of increase in numbers in a population. Prokaryotic Fission is the way a prokaryotic cell reproduces. It begins with when a parent cell replicates its DNA - two DNA molecules attach to plasma membrane at adjacent sides. Then there is the synthesis of proteins and lipids, become incorporated into membrane between the two attachment sites. Next, membrane growth moves two DNA molecules apart; new wall material deposited above membrane and then membrane and wall grow through cell midsection and divide cytoplasm. Finally, two genetically equivalent daughter cells, each with a single bacterial chromosome, are formed.
 * 1) [[image:http://trc.ucdavis.edu/biosci10v/bis10v/week7/20f/Slide3.gif width="648" height="486" caption="1. Prokaryotic Fission"]]
 * Conjugation is the transfer of substances between two cells after contact. It begins with the plasmids: a self-replicating circle of DNA with a few genes, transferred from donor cell to recipient. Then, the Sex Pili- hook onto recipient and pulls it next to donor. Soon, certain conjugation tubes forms between donor and recipient cells to allow DNA transfer.
 * Conjugation is the transfer of substances between two cells after contact. It begins with the plasmids: a self-replicating circle of DNA with a few genes, transferred from donor cell to recipient. Then, the Sex Pili- hook onto recipient and pulls it next to donor. Soon, certain conjugation tubes forms between donor and recipient cells to allow DNA transfer.


 * Classification
 * Numerical Taxonomy is the way prokaryotes are classified. It begins when traits of an unidentified cell are compared with those of existing prokaryotic group. They are compared by Shape, Motility, Wall Staining Attributes, Nutritional Requirements, Metabolism, etc. Thus the, greater the number of traits in common, the closer they are related. Some of the key relations and divergences after prokaryotic cells originated are Eubacteria, Archaebacteria, Eukaryotes.


 * Eubacteria (Bacteria) are **photoautotrophs**- these build organic compounds by photosynthesis, photosynthetic machinery is part of their plasma membrane. They are **chemoautotrophs**- these are self-feeders that use carbon dioxide as their carbon course, some oxidize organic compounds for energy, others oxidize inorganic substances. They are also **chemoheterotrophs**- which are parasites or saprobes, parasites draw glucose and other nutriends from a living host, saprobes digest organic products, wastes, or organic remains. Then there are the **Cyanobacteria**. They are an ancient species with aerobic respiration and are photosynthetic. They specialize in nitrogen fixation and live in freshwater habitats. Next there are the **Proteobacteria**. These are important nutrient cyclers. Finally, there are the **endospores**. They contain genetic information, cytoplasm, they are durable, they form the inside of a cell. Also--they are released as spores when plasma membrane ruptures.
 * Bacteria are not simple for the following reasons, despite their small size. First, they are able to respond to stimulus. This means that they movie towards areas where nutrients are plentiful and away from toxins which are harmful. Bacteria also form predatory colonies. These secrete enzymes to digest prey and stick to the colony.


 * Archaebacteria (Archaens) resemble first living cells (//archae// = beginning). What distinguishes them from bacteria? The first is that they have a cell wall. Second, they have a phospholipid bilayer and make histones. Third, they utilize methionine as a start codon. Lastly, there is a difference in their rRNA. One type of Archaebacteria is Euryarchaeota. **Methanogens** produce ATP by anaerobic electron transfer (see section 8.5). They also live in oxygen-free habitats (strict anaerobes) and use carbon dioxide as carbon source. Ultimately, they form methane as a product. E**xtreme Halophile**s are "Salt Lovers" and they produce ATP by anaerobic pathways. They switch to photosynthesis when oxygen levels are low. **Extreme Thermophiles** are anaerobic and are "Heat Lovers" that function best above 80 degrees C. They are found in sulfur rich hot springs, geothermally heated soils, wastes from coal mines


 * An **infection** is when a pathogen invades your body and multiples in cells and tissues. A **pathogen** is an infectious disease-causing agents taht invade target organisms and multiply in or on them. A **disease** results from infection, when defenses cannot be mobilized fast enough to keep the pathogen's activities from interfering with body functions. A **contagious** disease is caused by direct contact or inhalation. **Sporadic** disease occur irregularly and affect few people. An example of this is Whooping cough. An endemic disease occurs continually but do not spread far in large populations. An example would be Tuberculosis. The difference between an **epidemic** and **pandemic** is that an epidemic disease spreads quickly through part of a population for a limited time while a pandemic disease breaks out in different countries at the same time. An example of this is AIDS. Emerging Pathogens are an advancement in travel that has caused emergence of certain pathogens. An example of this is that existing pathogens now taking advantage of human hosts and newly mutated strains of existing pathogens are evolving.


 * **Viruses** are not Prokaryotes. Some characteristics would be that they are noncellular and their structure consists of a protein coat around nucelic acid core (RNA or DNA), helical- rod-shaped coat of protein subunits coiled hilically around nucleic acid, a polyhedral or many-sided coat. Viruses cannot reproduce alone. Each kind can only grow in certain hosts. Genes for viral proteins mutate all the time. **Viroids** are tightly coiled strands or circles of RNA, they are viruses that infect plants, and they do not have a protein coat. **Prions** are abnormal, less soluble forms of proteins necessary for the operation of neurons. They catalyze the conversion of normal proteins into more prions. They also can coagulate in the brain and cause fatal degenerative diseases. **Bacteriophages** is the basis for much of our knowledge or viruses, used in early experiments to determine function of DNA.
 * Multiplication Cycles include many different steps. First there is the **attachment** where the virus attaches to host cell by molecular groups that chemically recognize and lock onto specific molecular groups at the cell surface. Next there is the **penetration** where the whole virus or its genetic material alone penetrate the cell's cytoplasm. Then there is the **Replication** and Synthesis of viral DNA or RNA where the direct host cell produces as many copies of viral nucleic acids and viral proteins, including related enzymes. Finally there is the **assembly** where the viral nucleic acids and viral proteins become organized as new infectious particles and the **Release** where new virus particles released from cell by one mechanism or another. There are two pathways within the multiplication cycles. first is the Lytic pathway. The **Lytic** Pathway (see diagram on page 358 10th edition) is quick and viral particles are released when the cell undergoes lysis. Lysis is when there is damage to a cell's plasma membrane, wall, or both, allowing cytoplasm to dribble out. The second pathway is the **Lysogenic** Pathway (see diagram on page 358 10th edition). Here, there is latent period, there is an integration of DNA into a DNA host, and viral DNA is passed to all descendants of the cell. However, there is also reverse transcription. In **Reverse** Transcription there are only RNA viruses, enzymes transcribe DNA from viral RNA, and RNA serves as a template for synthesizing DNA or mRNA in a host cell's cytoplasm.

Citations: //The Unity and Diversity of Life// - Cecie Starr and Ralph Taggart - Tenth and Eleventh Edition Pictures:
 * 1) Prokaryotic Fission: http://trc.ucdavis.edu/biosci10v/bis10v/week7/20f/Slide3.gif

