Microorganisms and Their Characteristics

Microorganisms and Their Characteristics Definition and Characteristics of Microorganisms Microorganisms are the smallest living organisms, requiring a microscope to be seen at some or all of their life stages. They are ubiquitous in nature, found everywhere, including sulfur acid pools, hydrothermal vents, salt flats, and Antarctica. Approximately 90% of microorganisms are harmless, serving as saprophytes, commensals, and mutualists, while around 10% are pathogenic, with about 90% of infectious diseases caused by viruses. Major Groups of Microbes The major groups of microbes include Bacteria, Archaea, Fungi, Protozoa, Algae, Viruses, and Helminths. Bacteria are single-celled prokaryotic microbes that reproduce via binary fission and have cell walls containing peptidoglycan. Archaea are single-celled prokaryotic microbes with cell walls lacking true peptidoglycan, and they include extremophiles such as methanogens, halophiles, and thermophiles. Fungi can be unicellular or multicellular eukaryotic microbes with cell walls containing chitin, and they reproduce sexually and asexually. Protozoa are unicellular eukaryotic microbes that are motile and heterotrophic, reproducing sexually and asexually. Algae are unicellular or multicellular eukaryotic microbes with cell walls made of cellulose, and they are mostly autotrophic, reproducing sexually and asexually. Helminths are multicellular eukaryotic animals lacking cell walls, reproducing sexually and asexually, with some life stages being microscopic. Viruses consist of proteins and nucleic acids, are not true living organisms, and are considered parasites requiring a host for survival. Microbial Systematics and Functions Systematics: Taxonomy and Phylogeny Taxonomy involves creating an orderly arrangement of organisms based on similarities, with taxa reflecting phylogenic relationships and the highest taxa being Domain and Kingdom. Binomial nomenclature assigns a two-part name to each organism, consisting of the genus name (uppercase) and the species name (lowercase), occasionally using subspecies, subtype, strain, or serovar for within species differences. • Phylogeny is the study of the evolutionary history of organisms using taxonomy. Ecological and Industrial Roles of Microbes • Microbes play key ecological roles such as carbon and nitrogen fixation, decomposition of organic matter, serving as the base of the food chain, and symbiotic vitamin production. • They also have various industrial applications in food production, enzyme production, and medical uses. Human-Microbe Interaction • Microbes have been present before and will continue to exist after humans, with a significant impact on their capacity for evolution. • The normal microbiota on the human body, considered commensals or mutualists, play an important role in inhibiting the growth of pathogenic bacteria, producing vitamins, and aiding with digestion. Historical Contributions to Microbiology Major Contributions to Microbiology • 1665 - Robert Hooke observed the first cells in cork, leading to the cell theory. • 1673 - Anton van Leeuwenhoek observed live microorganisms he called 'animalcules'. • 1861 - Louis Pasteur disproved spontaneous generation and proved the role of yeast in fermentation, as well as the effectiveness of pasteurization. • 1867 - Surgeon Joseph Lister began treating wounds with phenol, marking a significant advancement in disease treatment. • 1798 - Edward Jenner gave the first recorded vaccination against smallpox, using cowpox blister scrapings to inoculate an 8-year-old boy. • 1880 - Pasteur showed that avirulent forms of bacteria protected against virulent forms, while Paul Ehrlich proposed the side-chain theory of immunity. • 1900 - Paul Ehrlich theorized about compounds specifically inhibiting pathogens, leading to the discovery of Salvarsan. • 1928 - Alexander Fleming discovered the first known antibiotic, penicillin, with Florey and Chain scaling up its production for usage. Immunity, Infectious Diseases, and Emerging Pathogens Infection, Immunity, and Emerging Infectious Diseases • The body's immune system has the ability to fight infection and 'remember' past experiences. • Emerging Infectious Diseases (EIDs) currently prevalent in human populations include COVID-19, West Nile Encephalitis (WNE), Ebola Hemorrhagic Fever, H5N1 Avian Flu, MRSA/VRSA, Variant CJD/BSE, MERS, and Chagas’ disease in the US. • Key factors contributing to the emergence of EIDs include population density, sanitation, world travel, and deforestation. Protozoa Characteristics of Protozoa • Protozoa are unicellular eukaryotic microbes that are motile and typically inhabit water and soil. • They are chemoheterotrophic and have a feeding/growing stage called trophozoite. • Reproduction occurs both sexually and asexually through processes like fission, budding, and schizogony. Medically Important Protozoa • Some protozoa can be pathogenic, such as Plasmodium spp. which causes malaria, and Nosema locustae which is used to kill grasshoppers. • Flagellated cells like Trypanosoma sp. can cause diseases like African sleeping sickness and Chagas’ disease. • Amoeba like Entamoeba histolytica can cause dysentery in humans. Life Cycle of Protozoa • Protozoa reproduce asexually via fission, budding, or schizogony, and sexually via conjugation. • They can form cysts as a response to poor temperature or nutrition, and most are aerobic chemoheterotrophs. • Ciliates have a mouthlike cytostome for food intake, while others release food through an anal pore or membrane. Slime Molds Cellular Slime Molds • Cellular slime molds ingest fungi and bacteria, and form aggregate structures when distressed. • Plasmodial slime molds move as giant amoebas with muscle-like filaments, and create channels for cytoplasmic streaming. Helminths Characteristics of Helminths • Helminths are multicellular eukaryotic animals with digestive, nervous, and reproductive systems. • They can be classified into Platyhelminthes (flatworms) and Nematoda (roundworms). Helminth Lifecycle • Most helminths produce eggs that develop into larval forms, which further develop into adults. • Some hermaphroditic helminths can self-fertilize, while others copulate with other hermaphrodites. Phylum Platyhelminthes • Class Trematoda includes unsegmented flat worms with complicated life cycles and oral and ventral suckers. • Class Cestoda contains tapeworms with a head segment called a scolex, and body segments called proglottids. Phylum Nematoda • Nematoda are roundworms with most being dioecious, and their eggs or larval forms can infect humans. Fungi Characteristics of Fungi • Fungi have vegetative structures like molds with hyphae, mycelium, and septa, and yeast which are non-filamentous and unicellular. • Dimorphic fungi exhibit two forms of growth, and can reproduce through fragmentation or spore formation. Life Cycles of Fungi • Fungal sexual reproduction involves plasmogamy, karyogamy, and meiosis, resulting in the formation of sexual spores. • Asexual spore forms and sexual spores are dispersed into the environment for reproduction. Microsporidia • Microsporidia are intracellular parasites that lack mitochondria and were thought to be protozoan. General Nutrition and Structure • Fungi have different tolerances than bacteria, preferring a low pH and being resistant to osmotic pressure. • They can grow in both dry and moist environments. Lichens • Lichens are a combination of algae or Cyanobacteria and fungus, forming a mutualistic relationship. • This relationship allows them to exist in places where neither could survive alone, and many are sensitive to pollutants. Discussion questions 1 of 6 Discuss the characteristics of protozoa and their role as medically important microbes. Provide examples of pathogenic protozoa and their impact on human health. Difficulty: Medium Explain the life cycle of protozoa, including their methods of reproduction and encystment. How do these processes contribute to the survival and transmission of protozoa? Difficulty: Hard Compare and contrast the two groups of slime molds, cellular slime molds, and plasmodial slime molds. Discuss their unique characteristics and methods of movement and survival. Difficulty: Medium Describe the life cycle of helminths, including the different stages of development and their methods of reproduction. How do these life cycles contribute to the spread and persistence of helminth infections? Difficulty: Hard Discuss the benefits and detriments of fungi in our world, including their role in decomposition, symbiotic relationships, and infectious diseases. Provide examples of both beneficial and detrimental fungi. Difficulty: Medium Explain the process of fungal sexual reproduction, including the phases of plasmogamy, karyogamy, and meiosis. How does this process contribute to genetic diversit Discuss the ecological roles of microorganisms and their impact on the environment. Provide examples of their contributions to carbon and nitrogen fixation, decomposition, and symbiotic vitamin production. Difficulty: Medium Explain the differences between bacteria, archaea, fungi, protozoa, algae, viruses, and helminths. Discuss their unique characteristics, reproduction methods, and ecological roles. Difficulty: Hard Describe the major contributions of historical figures such as Louis Pasteur, Robert Koch, Edward Jenner, and Alexander Fleming to the field of microbiology. Discuss their discoveries and the impact on human health and medicine. Difficulty: Hard Explain the concept of normal microbiota (flora) and their role in maintaining human health. Discuss the benefits of commensal and mutualistic microbes in inhibiting pathogenic bacteria, producing vitamins, and aiding digestion. Difficulty: Medium Discuss the differences between spontaneous generation and biogenesis, and the impact of Louis Pasteur's experiments on disproving spontaneous generation. Explain the significance of Pasteur's findings on fermentation and spoilage. Difficulty: Medium Explain the concept of emerging infectious diseases (EIDs) and discuss the key factors contributing to their emergence in human populations. Provide examples of prevalent EIDs and their impact on global health. Functional Anatomy of Prokaryotic Cells Size and Shapes of Prokaryotic Cells • Prokaryotic cells have an average size of 2-8 µm in length and 0.2-2.0 µm in diameter. • Basic shapes of prokaryotic cells include cocci and bacilli. • Arrangements of bacteria can be categorized as cocci, bacilli, spiral, or other. Cell Surface Structures • Glycocalyx, located outside the cell wall, is composed of polysaccharides or polypeptides and serves purposes such as attachment, avoiding phagocytosis, and controlling nutrients. • Flagella, composed of flagellin proteins, are located in the cell wall and facilitate cellular movement and identification of bacterial serovars. • Axial filaments, similar to flagella, are wrapped around the cell wall and enable rotational movement in spirochetes. • Fimbriae and pili, composed of pilin, are located at poles or evenly distributed and serve functions such as surface attachment, movement, or DNA transfer. Cell Wall and Membrane Composition • The bacterial cell wall, located in the capsule, cell wall, and plasma membrane, is composed of membrane and peptidoglycan, and its key functions include structural integrity and prevention of dehydration. • Peptidoglycan is a key component of the cell wall and is used to differentiate between Grampositive and Gram-negative bacteria. • Atypical cell walls are found in mycobacteria, mycoplasma, and archaea, each with unique compositions and characteristics. • The cell membrane, located inside the cell wall, is composed of phospholipids, proteins, carbohydrates, and sterols, and it plays a crucial role in selective permeability and unique functions such as ATP production and photosynthesis. Movement Across Membranes • Movement across membranes can occur through simple diffusion, passive transport (facilitated diffusion), or active transport, each driven by different mechanisms and gradients. • Bulk transport processes such as phagocytosis, pinocytosis, and receptor-mediated endocytosis are found in some eukaryotic cell types. • Tonicity affects the movement of water in cells, with different effects on cells with or without cell walls. Internal Structures of Prokaryotic Cells • The interior of prokaryotic cells contains ribosomes, nucleoid, inclusion bodies, enzymes, and structural proteins, but lacks membrane-bound organelles. • The nucleoid region is a condensed area of DNA found within prokaryotic cells, which does not readily stain and appears lighter in color when viewed with a transmission electron microscope. • Endospores, a resting/dormant form found in some genera, are highly resistant to various environmental factors and can germinate into vegetative cells. Comparison of Eukaryotic and Prokaryotic Cells Membrane-bound Organelles • Eukaryotic cells possess membrane-bound organelles such as the nucleus, rough ER, smooth ER, Golgi complex, mitochondrion, chloroplast, and cytoskeleton, each with distinct functions. • The modern endosymbiotic relationship between Paramecium bursaria and Zoochlorella algae exemplifies the integration of eukaryotic cells with other organisms. Discussion questions 1 of 6 Compare and contrast the average size of prokaryotic cells with the average size of eukaryotic cells. Why is it important to understand these size differences? Difficulty: Medium Explain the key functions of glycocalyx in prokaryotic cells and provide examples of how it contributes to bacterial survival. Difficulty: Hard Describe the composition and key functions of flagella in prokaryotic cells. How do different flagellar arrangements contribute to bacterial motility? Difficulty: Medium Discuss the significance of the bacterial cell wall in maintaining structural integrity and controlling materials. How does the composition of the cell wall differ in Gram-positive and Gram-negative bacteria? Difficulty: Hard Explain the movement across membranes in prokaryotic cells, including simple diffusion, passive transport, and active transport. Provide examples of molecules/ions transported through each process. Difficulty: Medium Compare the nucleoid region of prokaryotic cells with the nucleus of eukaryotic cells. What are the key differences in their structure and function? Difficulty: Easy Enzymes Enzyme Function and Terminology • Enzymes catalyze biochemical reactions by lowering the activation energy. • Enzymes are usually proteins and end in -ase. • Enzymes can be affected by temperature, pressure, pH, and ionic concentration. • Enzyme terminology includes catalyst, substrate, active site, enzyme-substrate complex, and product. • Enzymes operate through the induced fit model and have high efficiency rates. • Enzymes have specific active sites with high substrate affinity and have been evolutionarily selected for efficiency. Enzyme Components and Regulation • Most enzymes use cofactors or coenzymes, which can accept or donate atoms or act as electron carriers. • Inhibitors, such as competitive and noncompetitive inhibitors, can control enzyme function. • Feedback inhibition uses allosteric inhibition to control enzyme function by stopping overproduction of a product. • Ribozymes, RNA enzymes, have enzymatic activity and act as catalysts. Microbial Metabolism Basics Metabolism Definitions • Metabolism is the sum of all chemical reactions within a living organism. • Catabolism involves the release of energy and the breakdown of complex molecules, while anabolism uses energy to construct larger organic molecules. • Oxidation and reduction (redox) reactions power metabolism. Molecules Involved in Metabolism • Electron carriers like NAD+, NADP+, and FAD are involved in redox reactions. • ATP, the primary source of metabolic energy, functions via phosphorylation. • Glucose, a simple monosaccharide, is the primary source of metabolic energy. Glycolysis Overview of Glycolysis • Glycolysis is the oxidation of glucose to pyruvic acid, producing 2 ATP and 2 NADH. • It consists of a preparatory stage and an energy-conserving stage. Respiration vs. Fermentation • Respiration uses glycolysis to produce energy and pyruvate as a precursor to the Krebs cycle and the electron transport chain. • Fermentation uses glycolysis to produce energy and pyruvate, which is then further reduced by NADH to other molecular forms. Cellular Respiration Aerobic Respiration • Aerobic respiration uses O2 as the final electron acceptor and includes the Krebs cycle and the electron transport chain. Krebs Cycle • The Krebs cycle releases chemical energy stored in acetyl-CoA molecules and uses redox reactions to transfer potential energy. Electron Transport Chain • The electron transport chain passes electrons through a series of redox reactions to create energy by creating a chemical gradient. Photosynthesis Photosynthesis Process • Photosynthesis involves the conversion of light energy into chemical energy through lightdependent and light-independent reactions. • The Calvin-Benson cycle is part of the light-independent reactions. Discussion questions 1 of 6 Explain the process of glycolysis and its significance in microbial metabolism. How does glycolysis differ in respiration and fermentation? Provide examples of organisms that utilize each pathway. Difficulty: Medium Discuss the role of enzymes in microbial metabolism, focusing on their specificity, efficiency, and the factors that influence their function. Provide examples of how inhibitors and activators can impact enzyme activity. Difficulty: Hard Describe the Krebs cycle and its importance in cellular respiration. How does the Krebs cycle contribute to the generation of ATP? Compare and contrast aerobic and anaerobic respiration in terms of the Krebs cycle. Difficulty: Medium Explain the process of feedback inhibition and its role in regulating metabolic pathways. Provide specific examples of how feedback inhibition controls enzyme function in microbial metabolism. Difficulty: Hard Discuss the significance of the electron transport chain in microbial metabolism. How does chemiosmotic ATP generation contribute to energy production? Compare and contrast the roles of NADH and FADH2 in the electron transport chain. Difficulty: Medium Explain the process of photosynthesis in microbial metabolism, including the light-dependent and light-independent reactions. How does photophosphorylation contribute to ATP generation in p History and Basics Early Discoveries • In 1886, Adolph Mayer demonstrated the transmission of Tobacco Mosaic Disease (TMD) to healthy plants. • In 1892, Dimitri Ivanowski observed that normal bacterial filtering did not prevent TMD infection via filtrates. • In 1935, Wendell Stanley successfully isolated and crystallized the Tobacco Mosaic Virus (TMV). • In 1939, the first electron microscopy of TMV was conducted. Basic Virus Facts • Viruses contain a single type of DNA or RNA (SS or DS) and are covered with a protein coat (capsid), which may be enveloped. • They are obligate intracellular parasites, relying on host machinery for replication, and their single goal is to produce new infectious particles. Comparing Viruses and Bacteria • Viruses fail to satisfy the standard definition of life, as they cannot metabolize, grow, or respond to stimuli. • In comparison to bacteria, viruses lack the capacity for metabolism, growth, and reaction to stimuli. Structure of a Virus Nucleic Acid and Capsid • Viruses contain either DNA or RNA, but not both, and it can be single or double stranded, linear, circular, or segmented. • The capsid is composed of capsomeres and may consist of single or multiple protein types, serving as receptors. Envelope and Spikes • The envelope is derived from the host cell's plasma membrane, while spikes help attach the virus to the membrane when leaving the cell and are used for targeting specific host cell types. Viral Taxonomy • Family names of viruses end in “-viridae” (e.g., Herpesviridae, Retroviridae), while genus names end in “-virus” (e.g., Oncovirus, Enterovirus, Influenzavirus). • Viral species are groups of viruses sharing the same genetic information and ecological niche, such as Human Immunodeficiency Virus (HIV) and Herpes Simplex Virus (HSV). • Viral subspecies (strains) are designated with numbers, like HIV-1, HIV-2, HSV-1, HSV-2, H5N1. Viral Growth Curve and Identification • Virus identification can be achieved through cytopathic effects at the cellular level, serological tests like Western blot and ELISA, and PCR for amplifying the virus's nucleic acid. • The viral growth curve involves stages of attachment, penetration, biosynthesis, maturation, and release. Multiplication of Bacteriophages Lytic and Lysogenic Cycle • Bacteriophages can multiply through the lytic cycle, involving attachment, penetration, biosynthesis, maturation, and lysis (release). • The lysogenic cycle of temperate bacteriophages includes the incorporation of phage DNA into host DNA, potentially causing phage conversion and altering host characteristics. Bacteriophage Lysogeny and Multiplication • During lysogeny, prophage DNA multiplies with host cell DNA, leading to altered host characteristics, immunity to infection by the same phage type, and transduction (transfer of genes from old host). • Lysogeny can also result in phage conversion in bacteria, where characteristics are changed, and latency, similar to lysogeny, can lead to cell transformation causing cancer. Multiplication of Animal Viruses Entry and Replication • The entry of nonenveloped viruses into animal host cells occurs through receptor-mediated endocytosis, while enveloped viruses enter through plasma membrane-mediated fusion. • The replication of RNA viruses and retroviruses involves specific processes, and enveloped viruses are released by budding. Animal Virus vs. Bacteriophage • The multiplication of animal viruses differs from that of bacteriophages, and the terms “prophage” and “provirus” have distinct meanings. Viruses and Cancer, Latent Infections, and Prions Viruses and Cancer • Approximately 10% of cancers are known to be virus-induced, and some viruses can turn on oncogenes and transform host cells. Latent and Persistent Infections • Latent and persistent infections are phenomena associated with viruses, and prions are infectious proteins that cause transmissible neurological diseases. Prions and Viroids • Prions are highly resistant to heat and some chemicals, causing diseases like Creutzfeldt-Jakob disease and mad cow disease. • Viroids are infectious circular RNA strands capable of self-replication, causing plant diseases and having similar sequences to introns. Discussion questions 1 of 6 Compare and contrast the structure and replication strategies of DNA and RNA viruses. How do these differences impact their ability to infect host cells? Provide examples of each virus type. Difficulty: Hard Explain the differences between lytic and lysogenic cycles in bacteriophages. How can lysogeny alter the characteristics of the host cell and what implications does this have for bacterial evolution? Difficulty: Hard Discuss the role of viruses in cancer development. How do oncogenic DNA and RNA viruses contribute to the transformation of host cells? Provide specific examples of each virus type. Difficulty: Medium Explain the concept of latent and persistent infections caused by viruses. How do these types of infections differ and what are the implications for disease transmission and management? Difficulty: Medium Describe the structure and characteristics of prions. How do prions cause transmissible neurological diseases and what makes them highly resistant to heat and chemicals? Difficulty: Medium Discuss the nature and impact of viroids on plant health. How do viroids replicate and spread, and what are the similarities between viroids and introns? Bacterial Classification and Identification Gram Staining and Bacterial Groups • Gram-negative bacteria include Borrelia. • Gram-positive bacteria include Staphylococcus. • Mycoplasmas lack a cell wall. • Spirochetes are not easily observed with brightfield microscopy. • Pseudomonas is a gram-negative bacterium. • Haemophilus is identified based on X and V factors. Bacterial Characteristics and Differentiation • Rickettsias require an arthropod for transmission. • Listeria does not belong with other gram-positive bacteria. • Staphylococcus and Streptococcus can be differentiated by growth in high salt concentrations. • Mycoplasmas lack a cell wall. • Mycoplasmas differ from other bacteria in lacking a cell wall. • Mycoplasmas differ from other bacteria in lacking a cell wall. Bacterial Infections and Diseases • A dimorphic fungus is the likely cause of the infection described. • Ringworm is caused by a fungus. • Helminthic diseases are usually transmitted via the gastrointestinal route. • Insulin-dependent diabetes and prednisone use can complicate wound healing. • Lichens are a symbiotic relationship between a fungus and an alga. Virology and Viral Classification Virus Classification and Characteristics • Reverse transcriptase is utilized by Hepadnaviridae and Retroviridae viruses. • Latent viruses, like human herpesvirus 1, infect cells without causing symptoms. • Lysogeny does not cause lysis of host cells. • Viral ability to infect cells depends on various factors including receptor sites and viral nucleic acid type. • Alcohols do not effectively inactivate nonenveloped viruses by attacking lipids. Antimicrobial Control and Viral Replication • Ethylene oxide is a sterilizing agent. • Chlorhexidine is used for surgical hand scrubs. • Freezing is used to preserve food by slowing microbial metabolic processes. • 70% ethanol concentration is the most effective bactericide. • Microbial death occurs at a constant rate. Viral Replication and Mechanisms • Chloramphenicol prevents translation in prokaryotes by binding the 50S ribosomal subunit. • Glucose inhibits the lac operon through catabolite repression. • Latent viruses infect cells without causing symptoms. • Viral nucleic acid acts directly as mRNA in +ssRNA viruses. • RNA-dependent RNA transcriptase is required for replication of -ssRNA viruses. Molecular Biology and Genetics Genetic Mutations and Transcription • Silent mutations do not change the amino acid coded for. • Missense mutations result in a different amino acid sequence. • AAA to AAG mutation still codes for lysine. • RNA polymerase copies DNA to make RNA. • Translation involves mRNA, rRNA, and tRNA. Enzymes and Cellular Processes • The lac operon is regulated by catabolite repression. • Enzymes like RNA polymerase are involved in DNA to RNA transcription. • DNA and RNA polymerases share the direction of polymerization. • Endospores are used to measure autoclave sterilization effectiveness due to their resistance. • Washing dishes in hot water and detergent is a disinfecting process. Classification and Replication • Bergey's Manual classifies prokaryotes based on rRNA sequences. • Protozoa classification is not based on habitat. • Replication of most dsDNA viruses is similar to cellular processes. • Enveloped viruses contain a lipid membrane. • Translation involves mRNA, rRNA, and tRNA. Microbiology and Microscopy Microbial Mutations and Processes • Missense mutation involves a single nucleotide change resulting in a different amino acid. • Translation involves mRNA, rRNA, and tRNA in protein synthesis. • Disinfecting involves washing with detergent and hot water to kill or remove microorganisms. • Endospores are used to measure autoclave sterilization effectiveness due to their resistance. • Betadine contains halogen as a chemical agent. • Desiccation preserves food by reducing water content to inhibit metabolic functions. Microbial Sterilization and Enzymes • Commercial sterilization targets Clostridium botulinum endospores. • RNA polymerase transcribes RNA from DNA, not DNA synthesis. • DNA polymerase adds nucleotides to the 3' end of a growing DNA strand. • MicroRNAs inhibit protein production in eukaryotic cells. • Photolyases repair thymine dimers caused by UV light. • Lac operon repressor binds to the operator in the absence of lactose. Microbial Diversity and Characteristics • Plasmids are not essential for the survival of the organism in most situations. • Lyme disease is caused by Borrelia burgdorferi transmitted by ticks. • Wolbachia is an infectious genus living inside insect cells. • Green sulfur and nonsulfur bacteria conduct anoxygenic photosynthesis. • Facultatively anaerobic gram-negative rods are primarily found in human intestines. • Heat-sensitive solutions are sterilized using filtration. Microbial Classification and Diseases • Euglena is a photoautotrophic protozoan. • Sexual spore production involves plasmogamy, karyogamy, and meiosis. • Malaria parasite life cycle involves humans as intermediate hosts and mosquitoes as definitive hosts and vectors. • Paralytic shellfish poisoning is caused by saxitoxin-secreting dinoflagellates. • Lyme disease is vectored by ticks, and malaria is caused by Plasmodium vivax. • Prion diseases are not acquired via inhalation. Microbial Processes and Experiments • Reverse transcriptase uses viral RNA to produce complementary double-stranded DNA. • RNA viruses carry RNA-dependent RNA polymerase. • Virus infectivity in animal cells depends on receptor sites on the cell membrane. • Sanitization lowers microbial counts on utensils for public health. • Most disinfectants work better in warm solutions. • Transcription starts with RNA polymerase binding to the promoter region on DNA. Microscopy Techniques and Microbial Studies • Electron microscopes visualize internal cell structures. • Darkfield microscopes produce light cell images against dark backgrounds. • Scanning tunneling microscopes visualize DNA and toxins. • Total magnification is calculated by multiplying ocular and objective lens magnifications. • Transmission electron microscopes are used to observe viruses and cell structures. • Resolution in microscopy refers to the ability to distinguish fine details in a specimen. Microbial Cell Structure and Function Gram-Negative Cell Walls • Sensitivity to penicillin is a characteristic of gram-negative cell walls. • The outer membrane of gram-negative bacteria contains lipopolysaccharides that contribute to their pathogenicity. • Gram-negative cell walls have a thinner layer of peptidoglycan compared to gram-positive cell walls. • Penicillin targets the peptidoglycan layer, disrupting cell wall synthesis and leading to cell lysis. • Examples of gram-negative bacteria include Escherichia coli and Pseudomonas aeruginosa. Prokaryotic Cell Structures • Cilia are not found in prokaryotic cells; they are characteristic of eukaryotic cells. • Prokaryotic cells may have flagella for motility, pili for attachment, and a cell wall for structural support. • Examples of prokaryotic cells include bacteria and archaea. • The absence of a true nucleus is a defining feature of prokaryotic cells. • Prokaryotic cells lack membrane-bound organelles found in eukaryotic cells. Glycocalyx Functions • The glycocalyx is a sticky layer outside the cell wall that can be a capsule or slime layer. • Functions of the glycocalyx include protection against desiccation, phagocytosis evasion, and attachment to surfaces. • It plays a role in biofilm formation, aiding in microbial survival in harsh environments. • The glycocalyx is involved in cell-cell recognition and communication. • Binary fission is a method of bacterial cell division and is not a function of the glycocalyx. Cell Movement and Structures Taxic Movements • Bacterial cells exhibit taxic movements in response to attractants or repellents. • The terms 'run' and 'tumble' are associated with the movement of bacteria such as Escherichia coli. • Chemotaxis is the movement of cells towards or away from a chemical stimulus. • Flagella play a crucial role in bacterial motility and chemotaxis. • Understanding taxic movements helps in studying bacterial behavior and ecology. Phospholipids in Eukaryotic Cells • Phospholipids are a major component of cell membranes in eukaryotic cells. • They form a lipid bilayer that provides structural integrity and regulates molecular transport. • Phospholipids are amphipathic molecules with hydrophilic heads and hydrophobic tails. • They are found in the plasma membrane, organelle membranes, and around cellular structures like flagella. • Phospholipids contribute to cell signaling, membrane fluidity, and compartmentalization in eukaryotic cells. Spirochetes vs. Spirilla • Spirochetes and spirilla are types of bacteria with distinct morphological differences. • Spirochetes have axial filaments for motility, while spirilla have external flagella. • Examples of spirochetes include Treponema pallidum, the causative agent of syphilis. • Spirilla like Spirillum volutans are known for their helical shape and flagellar arrangement. • Understanding these differences aids in bacterial identification and classification. Discussion questions 1 of 7 Explain the significance of the Gram stain in the identification of prokaryotic cells. How does the Gram stain work and what information does it provide? Difficulty: Medium Discuss the role of endospores in bacterial survival. How do endospores form, and why are they difficult to kill? Difficulty: Medium Explain the process of transcription in gene expression. What is the role of RNA polymerase, and how does it differ from DNA replication? Difficulty: Medium Discuss the significance of biofilms in healthcare-associated infections. How do biofilms contribute to the persistence of infections? Difficulty: Medium Explain the concept of competitive inhibition in enzymatic reactions. How does competitive inhibition affect enzyme activity? Difficulty: Easy Describe the process of binary fission in bacterial reproduction. How does binary fission differ from eukaryotic cell division? Difficulty: Easy Discuss the role of the Gram stain in differentiating between Gram-positive and Gram-negative bacteria. How does the cell wall composition influence the sta