Biology 103: Chapter 19 Objectives

List components common to all free viral particles.

All free viral particles, also known as virions, share certain components that are essential for their ability to infect host cells. Here are some of the common components found in most virions: 1. Nucleic acid: All virions contain either DNA or RNA as their genetic material. The genetic material can be single-stranded or double-stranded, linear or circular, and can vary in length depending on the virus. 2. Capsid: The nucleic acid in virions is surrounded by a protein shell called the capsid. The capsid provides protection for the genetic material and helps to deliver it into host cells during infection. Capsids can have various shapes, including icosahedral, helical, or complex. 3. Envelope (optional): Some virions have an outer envelope that surrounds the capsid. The envelope is derived from the host cell membrane and contains viral proteins that are involved in attachment and entry into host cells. Not all viruses have an envelope, and those that do can vary in their composition and structure. 4. Spike proteins (optional): Some viruses have spike proteins on their outer surface that are involved in attachment to host cells. These proteins can interact with specific receptors on the surface of host cells and facilitate entry of the virus into the cell. Spike proteins are often found in viruses that have an envelope. Together, these components allow free viral particles to enter and infect host cells, leading to the replication and spread of the virus. However, the exact composition and structure of virions can vary greatly between different types of viruses.

Explain the function of an endospore.

An endospore is a dormant and highly resistant structure that is formed by some species of bacteria, such as Bacillus and Clostridium. Endospores are formed in response to adverse environmental conditions, such as nutrient depletion, high temperature, or exposure to chemicals or radiation. The function of an endospore is to allow the bacterial cell to survive in a dormant state until conditions become favorable again. Endospores are formed through a process called sporulation, in which the bacterial cell undergoes a series of changes to transform into an endospore. During sporulation, the bacterial cell dehydrates and its genetic material is condensed and protected by a specialized protein coat. The endospore is highly resistant to heat, radiation, desiccation, and chemical agents, allowing it to survive in harsh environmental conditions. When conditions become favorable again, the endospore can germinate and develop into a vegetative cell. Germination involves the activation of enzymes that break down the protein coat and rehydrate the endospore. The genetic material is then released, and the endospore begins to grow and divide, resuming its normal metabolic activity. The ability to form endospores is an important survival mechanism for some species of bacteria, allowing them to survive in harsh environmental conditions for long periods of time. Endospores can also be a challenge for the food and healthcare industries, as they can survive on surfaces and in food products, leading to contamination and transmission of bacterial infections.

List some traits of archaea and in what types of environments the major types can be found.

Archaea are a group of single-celled microorganisms that are distinct from bacteria and eukaryotes. Here are some general traits of archaea and some examples of where they can be found: 1. Cell wall: Archaea have a unique cell wall that is different from both bacteria and eukaryotes. The cell wall of archaea is made up of different types of molecules, such as pseudopeptidoglycan, which are distinct from the peptidoglycan found in bacterial cell walls. 2. Membrane lipids: Archaea have unique membrane lipids that are different from those found in bacteria and eukaryotes. Archaeal membrane lipids are made up of isoprene units and can form a range of different structures. 3. Extremophiles: Some types of archaea are extremophiles, meaning that they can survive in extreme environments. For example, methanogens are archaea that produce methane and can be found in anaerobic environments such as swamps, marshes, and the digestive tracts of some animals. Halophiles are archaea that can survive in high-salt environments, such as salt pans, brine pools, and salted foods. Thermophiles are archaea that can survive in high-temperature environments, such as hot springs and deep-sea hydrothermal vents. 4. Methanogenesis: Some archaea are capable of methanogenesis, which is the production of methane as a metabolic byproduct. Methanogens are found in anaerobic environments such as wetlands, rice paddies, and the digestive tracts of some animals. 5. Symbiosis: Some types of archaea are involved in symbiotic relationships with other organisms. For example, some methanogens live in the digestive tracts of ruminant animals and help to break down cellulose in their food. Overall, archaea are a diverse group of microorganisms with unique characteristics and adaptations to different environments. Some types of archaea are important for their roles in biogeochemical cycles, such as methanogenesis, while others are being studied for their potential uses in biotechnology and other applications.

List three human diseases caused by bacteria.

Bacteria can cause a wide range of diseases in humans, from mild infections to life-threatening illnesses. Here are three examples of human diseases caused by bacteria: 1. Tuberculosis (TB): TB is a bacterial infection caused by Mycobacterium tuberculosis. It primarily affects the lungs, but it can also affect other parts of the body, such as the kidneys, bones, and brain. Symptoms of TB include coughing, fever, and weight loss. TB is a serious disease that can be fatal if left untreated. 2. Cholera: Cholera is a bacterial infection caused by the bacterium Vibrio cholerae. It is primarily spread through contaminated water or food, and it can cause severe diarrhea and dehydration. Cholera is a major public health problem in many parts of the world, particularly in areas with poor sanitation and hygiene. 3. Lyme disease: Lyme disease is a bacterial infection caused by the bacterium Borrelia burgdorferi. It is spread through the bite of infected ticks, and it can cause a range of symptoms, including fever, fatigue, and a characteristic rash. If left untreated, Lyme disease can lead to more serious symptoms, such as joint pain and neurological problems. These are just a few examples of the many diseases caused by bacteria. Other bacterial infections include strep throat, urinary tract infections, and meningitis. Antibiotics and other treatments can be effective in treating bacterial infections, but it is important to use antibiotics appropriately to prevent the development of antibiotic-resistant bacteria.

List four ways in which bacteria benefit other organisms.

Bacteria play important roles in many biological processes and can provide a range of benefits to other organisms. Here are four ways in which bacteria can benefit other organisms: 1. Digestion: Bacteria in the gut of many animals, including humans, help to break down food and extract nutrients that the animal cannot digest on its own. For example, bacteria in the human gut produce vitamin K, which is essential for blood clotting. 2. Nitrogen fixation: Some bacteria are able to convert atmospheric nitrogen into a form that plants can use, through a process called nitrogen fixation. This helps to increase soil fertility and can benefit plants by providing them with the nitrogen they need to grow. 3. Disease prevention: Some bacteria can help to prevent the growth of harmful bacteria by competing for resources or producing antimicrobial compounds. For example, some bacteria in the human gut produce compounds that inhibit the growth of pathogenic bacteria. 4. Symbiosis: Bacteria can form symbiotic relationships with other organisms, in which both organisms benefit. For example, some bacteria live in the roots of leguminous plants and help to fix nitrogen, while the plants provide the bacteria with nutrients. These are just a few examples of the many ways in which bacteria can benefit other organisms. Bacteria are incredibly diverse and play important roles in many ecological and biological processes.

Describe the process by which bacteria reproduce.

Bacteria reproduce asexually through a process called binary fission. Here is a step-by-step description of the process: 1. DNA replication: Before cell division can occur, the bacterial cell must replicate its DNA. The two strands of the circular chromosome separate, and each strand serves as a template for the synthesis of a new complementary strand. 2. Elongation: Once DNA replication is complete, the bacterial cell begins to elongate. The cell wall and cell membrane grow, pushing the two ends of the cell apart. 3. Septation: As the cell elongates, a structure called the septum begins to form in the middle of the cell. The septum is made up of cell wall and cell membrane, and it separates the two replicated chromosomes and other cellular components. 4. Division: Once the septum is complete, the bacterial cell divides into two identical daughter cells. Each daughter cell contains a complete copy of the bacterial chromosome and other cellular components, and is ready to begin the process of binary fission again. The process of binary fission is a rapid and efficient method of bacterial reproduction, allowing bacteria to rapidly increase in number under favorable conditions. Some bacteria can divide as quickly as every 20 minutes, leading to exponential growth in a population. However, binary fission can also lead to genetic uniformity and lack of genetic diversity in a bacterial population, which can make them more vulnerable to environmental stressors and antibiotic resistance.

Contrast the structure of a bacterial cell with a eukaryotic cell.

Bacterial cells and eukaryotic cells have distinct differences in their cellular structure. Here are some of the main differences between the two cell types: 1. Cell size: Bacterial cells are typically much smaller than eukaryotic cells. Bacterial cells are typically 1-10 micrometers in diameter, while eukaryotic cells are typically 10-100 micrometers in diameter. 2. Cell wall: Bacterial cells have a rigid cell wall made of peptidoglycan, which provides structural support and protection. Eukaryotic cells may or may not have a cell wall, depending on the cell type. Plant cells have a cell wall made of cellulose, while fungal cells have a cell wall made of chitin. Animal cells do not have a cell wall. 3. Membrane-bound organelles: Eukaryotic cells have membrane-bound organelles, such as the nucleus, mitochondria, and endoplasmic reticulum, which perform specialized functions within the cell. Bacterial cells do not have membrane-bound organelles, but they do have specialized structures, such as ribosomes and flagella. 4. Nucleus: Eukaryotic cells have a distinct nucleus, which contains the genetic material (DNA) of the cell and is surrounded by a nuclear membrane. Bacterial cells do not have a distinct nucleus, and their genetic material is located in a single, circular chromosome located in the cytoplasm. 5. Cytoskeleton: Eukaryotic cells have a cytoskeleton made of protein fibers that provides shape, support, and facilitates movement. Bacterial cells do not have a cytoskeleton, but they do have a cell membrane and cytoplasm that provide some support and structure. Overall, eukaryotic cells are generally larger and more complex than bacterial cells, with a distinct nucleus, membrane-bound organelles, and cytoskeleton. Bacterial cells are smaller and simpler in structure, with a rigid cell wall and a single, circular chromosome located in the cytoplasm.

Discuss how bacterial conjugation differs from reproduction.

Bacterial conjugation is a mechanism of horizontal gene transfer between bacterial cells, in which genetic material is transferred from a donor cell to a recipient cell. Bacterial conjugation differs from reproduction in several ways: 1. Genetic material: In bacterial conjugation, genetic material is transferred between bacterial cells, while in reproduction, genetic material is replicated and divided between daughter cells. 2. Involvement of another cell: In bacterial conjugation, two bacterial cells are involved - a donor cell that transfers genetic material, and a recipient cell that receives the genetic material - while in reproduction, a single bacterial cell divides into two identical daughter cells. 3. Mechanism of transfer: In bacterial conjugation, genetic material is transferred from a donor cell to a recipient cell through a conjugation bridge, which is a specialized appendage called a sex pilus. In reproduction, genetic material is replicated and divided through the process of binary fission. 4. Genetic diversity: Bacterial conjugation can lead to increased genetic diversity within a bacterial population, as genes can be transferred between cells and incorporated into the recipient cell's genome. Reproduction, on the other hand, typically leads to genetic uniformity within a bacterial population. Bacterial conjugation is an important mechanism of genetic exchange in bacteria, allowing for the transfer of genes that confer antibiotic resistance, virulence, and other traits. It is also an important mechanism of evolution, allowing bacterial populations to adapt to changing environmental conditions. However, bacterial conjugation can also contribute to the spread of antibiotic resistance and the emergence of new infectious diseases.

Explain the difference between the two bacteriophage replication pathways.

Bacteriophages are viruses that infect bacteria. They have two different replication pathways, known as the lytic cycle and the lysogenic cycle. Here is an explanation of the difference between these two pathways: 1. Lytic cycle: In the lytic cycle, the bacteriophage infects the host bacterium and immediately begins to replicate its genetic material and produce viral proteins. The new viral particles assemble inside the host cell, and then the cell lyses (breaks open), releasing the viral particles to infect other host cells. The lytic cycle is characterized by rapid replication and lysis of the host cell, leading to the death of the host bacterium. 2. Lysogenic cycle: In the lysogenic cycle, the bacteriophage infects the host bacterium and integrates its genetic material into the host cell's chromosome. The viral genetic material is then replicated along with the host's genetic material during cell division. The integrated viral genetic material is known as a prophage. Under certain conditions, such as exposure to UV radiation or chemicals, the prophage can become activated and enter the lytic cycle, leading to the production of new viral particles and lysis of the host cell. The main difference between the two pathways is that the lytic cycle leads to rapid replication and lysis of the host cell, while the lysogenic cycle involves integration of the viral genetic material into the host's chromosome and replication of the viral genome along with the host's genetic material. The lysogenic cycle can be thought of as a "silent" infection, where the virus is present in the host cell but does not cause immediate harm. In contrast, the lytic cycle is a more "active" infection, where the virus replicates rapidly and causes the host cell to lyse, leading to the release of new viral particles.

Identify two emerging viral diseases.

Emerging viral diseases are those that have recently appeared in a population or are rapidly increasing in incidence or geographic range. Here are two examples of emerging viral diseases: 1. COVID-19: COVID-19 is a respiratory illness caused by the SARS-CoV-2 virus, which was first identified in Wuhan, China in December 2019. Since then, it has rapidly spread around the world, causing a pandemic. COVID-19 can cause a range of symptoms, from mild to severe, including fever, cough, and difficulty breathing. COVID-19 is primarily spread through respiratory droplets when an infected person coughs, sneezes, or talks. 2. Zika virus disease: Zika virus disease is a mosquito-borne illness caused by the Zika virus. It was first identified in the Zika Forest of Uganda in 1947, but it was not until a large outbreak in Brazil in 2015 that it gained widespread attention. Zika virus disease can cause fever, rash, joint pain, and conjunctivitis. It can also cause birth defects if a pregnant woman is infected, including microcephaly and other developmental abnormalities. Zika virus is primarily spread through the bite of infected Aedes mosquitoes, but it can also be sexually transmitted. These are just two examples of emerging viral diseases, but there are many others, including Ebola virus disease, Middle East respiratory syndrome (MERS), and severe acute respiratory syndrome (SARS). Emerging viral diseases can pose significant challenges for public health, as they often have no effective treatments or vaccines and can spread rapidly.

Distinguish between endotoxins and exotoxins.

Endotoxins and exotoxins are two types of toxins produced by bacteria that can cause harm to the host organism. Here are some of the main differences between endotoxins and exotoxins: 1. Source: Endotoxins are part of the outer membrane of certain gram-negative bacteria, while exotoxins are proteins that are secreted by both gram-positive and gram-negative bacteria. 2. Structure: Endotoxins are lipopolysaccharides (LPS) that are part of the outer membrane of gram-negative bacteria. Exotoxins are proteins that can be classified into different types, such as A-B toxins, membrane-damaging toxins, and superantigens. 3. Release: Endotoxins are released when the cell wall of gram-negative bacteria is disrupted, such as during bacterial lysis or when antibiotics are used. Exotoxins are actively secreted by bacteria and can be released into the surrounding environment or directly into host cells. 4. Effects: Endotoxins can cause a range of harmful effects in the host organism, such as fever, inflammation, and septic shock. Exotoxins can also cause a range of harmful effects, depending on the type of toxin. For example, A-B toxins can interfere with host cell function, while membrane-damaging toxins can disrupt cell membranes. Superantigens can cause excessive activation of the immune system. 5. Treatment: Endotoxins are difficult to treat, as they are part of the bacterial cell wall and cannot be neutralized by antibodies or other treatments. Exotoxins can be targeted with specific antibodies or antitoxins, and some types of exotoxins can be blocked with vaccines. Overall, endotoxins and exotoxins are two types of bacterial toxins that can cause harm to the host organism. While there are some similarities between the two types of toxins, they differ in their source, structure, release, effects, and treatment.

Distinguish between gram-positive and gram-negative bacteria.

Gram-positive and gram-negative bacteria are two broad categories of bacteria that are distinguished by their cell wall structure and their response to a staining technique called the Gram stain. Here are some of the main differences between gram-positive and gram-negative bacteria: 1. Cell wall structure: Gram-positive bacteria have a thick layer of peptidoglycan in their cell wall, which makes them appear purple when stained with the Gram stain. Gram-negative bacteria have a thinner layer of peptidoglycan and an outer membrane, which makes them appear pink when stained with the Gram stain. 2. Staining response: Gram-positive bacteria retain the crystal violet stain used in the Gram stain, while gram-negative bacteria do not. This is because the thick peptidoglycan layer in gram-positive bacteria traps the stain, while the outer membrane and thinner peptidoglycan layer in gram-negative bacteria do not. 3. Lipopolysaccharides: Gram-negative bacteria have lipopolysaccharides (LPS) in their outer membrane, which can trigger an immune response in humans and animals. Gram-positive bacteria do not have LPS. 4. Antibiotic susceptibility: Gram-negative bacteria are generally more resistant to antibiotics than gram-positive bacteria, due to the presence of the outer membrane and efflux pumps that can expel antibiotics from the cell. 5. Toxins: Gram-negative bacteria can produce endotoxins, which are released when the cell wall is disrupted. Endotoxins can cause fever, shock, and other symptoms in humans and animals. Gram-positive bacteria can produce exotoxins, which are released into the surrounding environment and can cause a range of symptoms, depending on the toxin. Overall, gram-positive and gram-negative bacteria have distinct differences in their cell wall structure, staining response, and other characteristics. These differences have important implications for their identification, treatment, and pathogenesis.

Explain the beneficial effects of our normal microbiota.

The normal microbiota, also known as the microbiome, refers to the community of microorganisms that live on and inside the human body. These microorganisms include bacteria, viruses, fungi, and other microbes, and they play important roles in maintaining human health. Here are some of the beneficial effects of our normal microbiota: 1. Digestion: The microbiota in the gut helps to break down food and extract nutrients that the human body cannot digest on its own. These microbes produce enzymes that break down complex carbohydrates, and they help to synthesize vitamins, such as vitamin K and B vitamins. 2. Immune system: The microbiota helps to train and regulate the immune system. By interacting with immune cells in the gut and other tissues, the microbiota helps to maintain a balance between protective immune responses and tolerance to harmless antigens. 3. Pathogen defense: The microbiota helps to protect against colonization by pathogenic microorganisms. By occupying niches in the body and producing antimicrobial compounds, the microbiota can prevent the growth of harmful bacteria and other microbes. 4. Metabolism: The microbiota can play a role in regulating metabolism and energy balance. Some studies have suggested that changes in the gut microbiota can contribute to the development of metabolic disorders, such as obesity and type 2 diabetes. 5. Mental health: The microbiota may also play a role in regulating mood and behavior. Some studies have suggested that changes in the gut microbiota can be associated with conditions such as depression and anxiety. Overall, the normal microbiota is an important component of human health, and disruptions to the microbiota can have negative effects on various aspects of health. Maintaining a healthy and diverse microbiota through diet, probiotics, and other interventions may be an important strategy for promoting health and preventing disease.

Describe how viral genomes can be altered.

Viral genomes can be altered in several ways, both naturally and artificially. Here are some examples: 1. Mutation: Viral genomes can undergo spontaneous mutations, which can alter the genetic sequence of the virus. Mutations can occur during viral replication or as a result of exposure to environmental factors such as radiation or chemicals. Mutations can lead to changes in viral virulence, antigenicity, or drug resistance. 2. Recombination: Viral genomes can undergo recombination, where genetic material from two different viruses is exchanged during replication. Recombination can result in the emergence of new viral strains with different characteristics, such as altered virulence or antigenicity. 3. Insertion and deletion: Viral genomes can undergo insertions or deletions of genetic material, which can alter the function of viral genes or regulatory elements. These changes can affect viral replication, virulence, and other characteristics. 4. Gene editing: Viral genomes can be artificially altered using gene editing techniques such as CRISPR/Cas9. Gene editing can be used to insert, delete, or modify specific genes or regulatory elements in the viral genome. This can be used to create attenuated or modified live vaccines, or to study the function of specific viral genes. 5. Synthetic biology: Viral genomes can be artificially synthesized from scratch using synthetic biology techniques. This can be used to create modified versions of existing viruses or to create entirely new viruses with desired characteristics. Overall, viral genomes can be altered through a variety of natural and artificial processes. These alterations can have significant effects on viral virulence, antigenicity, drug resistance, and other characteristics. Understanding the mechanisms underlying viral genome alteration can help in the development of effective antiviral therapies and vaccines.

List some common diseases caused by viruses.

Viruses are responsible for a wide range of diseases in humans, animals, and plants. Here are some common diseases caused by viruses: 1. Influenza: Influenza is a respiratory illness caused by influenza viruses. It can be a mild illness, but it can also cause severe illness and even death, especially in high-risk groups such as young children, older adults, and those with underlying health conditions. 2. Common cold: The common cold is a viral infection of the upper respiratory tract caused by several different viruses, including rhinoviruses and coronaviruses. It is a mild illness that typically resolves on its own within a week or two. 3. Chickenpox: Chickenpox is a highly contagious viral infection caused by the varicella-zoster virus. It causes a rash of itchy blisters all over the body, along with fever and other symptoms. Chickenpox is usually a mild illness, but it can be more severe in adults and those with weakened immune systems. 4. Measles: Measles is a highly contagious viral infection caused by the measles virus. It causes fever, cough, runny nose, and a rash all over the body. Measles can be a severe illness, especially in young children and those with weakened immune systems. 5. Human immunodeficiency virus (HIV): HIV is a viral infection that attacks the immune system, leading to acquired immunodeficiency syndrome (AIDS) if left untreated. HIV is transmitted through contact with infected bodily fluids, such as blood and semen. 6. Hepatitis: Hepatitis is a viral infection that causes inflammation of the liver. There are several types of hepatitis viruses, including hepatitis A, B, C, D, and E. Hepatitis can cause a range of symptoms, from mild to severe, and can lead to long-term liver damage. 7. Ebola virus disease: Ebola virus disease is a severe and often fatal viral illness caused by the Ebola virus. It is transmitted through contact with infected bodily fluids, such as blood and semen, and can cause a range of symptoms, including fever, vomiting, and bleeding. These are just a few examples of the many diseases caused by viruses. Vaccines and antiviral medications are available for some viral illnesses, but many viruses do not have specific treatments. Prevention measures such as hand hygie