Bacteria vs Viruses: Structure & Classification

• Bacteria and viruses differ significantly in structure, reproduction, and susceptibility to treatments.
• Bacteria are single-celled prokaryotes with a cell wall, DNA, ribosomes, and often flagella.
• Viruses are acellular, consisting of genetic material (DNA or RNA) enclosed in a protein coat, requiring a host cell to replicate.

Bacterial Cell Structure and Prokaryotic Domains

• Bacterial cells have structural features including a cell wall, plasma membrane, cytoplasm, ribosomes, and a nucleoid containing DNA.
• Archaea and Eubacteria are the main prokaryote domains, differing in cell wall composition, membrane lipids, and ribosomal RNA.
• Archaea often thrive in extreme environments unlike Eubacteria.

Gram-Positive vs. Gram-Negative Bacteria

• Gram-positive bacteria have a thick peptidoglycan layer in their cell wall, retaining crystal violet stain.
• Gram-negative bacteria possess a thin peptidoglycan layer and an outer membrane containing lipopolysaccharides, not retaining crystal violet stain.

Roles of Bacteria

• Bacteria play roles in human health, ecosystems, and food production, both positive and negative.
• Negative impacts include causing diseases like pneumonia and foodborne illnesses.
• Positive impacts include aiding digestion, synthesizing vitamins, nutrient cycling and fermentation in food production (e.g., yogurt).

Antibiotics and Their Targets

• Antibiotics target prokaryotic processes: cell wall synthesis, protein synthesis, and nucleic acid replication.
• Some antibiotics inhibit bacterial cell wall formation.
• Some antibiotics disrupt bacterial protein synthesis by binding to ribosomes.
• Some antibiotics interfere with DNA replication or transcription.

Antibiotics vs. Viruses

• Antibiotics are ineffective against viruses because viruses lack the cellular structures and metabolic pathways that antibiotics target.
• Viruses replicate inside host cells, using host machinery, making it difficult for antibiotics to target the virus without harming the host.

Viruses as Non-Living Acellular Parasites

• Viruses aren't classified as living due to their inability to reproduce independently.
• They are acellular because they lack the structure of cells.
• Viruses are obligate parasites, requiring a host cell to replicate.

Virus Structure

• Viruses consist of genetic material (DNA or RNA) enclosed in a protein coat called a capsid.
• Some viruses have an envelope derived from the host cell membrane.
• Viral structure can vary widely, with shapes including helical, icosahedral, and complex.

Virus Specificity

• Viruses exhibit specificity for the host cell they infect, based on interactions between viral surface proteins and host cell receptors.
• This specificity determines the range of cells a virus can infect.

Viral Diseases

• Viruses cause diseases in plants and animals by disrupting normal cell function and causing cell damage or death.
• Viral infections can range from mild (e.g., common cold) to severe (e.g., HIV).

Lytic vs. Lysogenic Stages

• In the lytic cycle, a virus replicates within the host cell, leading to lysis (bursting) of the cell and release of new virions.
• In the lysogenic cycle, viral DNA integrates into the host chromosome, remaining dormant and replicating along with the host DNA until triggered to enter the lytic cycle.

Viral DNA Integration

• Viral DNA integrates into the host chromosome via enzymes.
• Viral integration can lead to genetic changes in the host cell, potentially causing mutations or altered gene expression.

RNA Viruses vs. Retroviruses

• RNA viruses (e.g., influenza, coronavirus) use RNA as their genetic material and replicate in the host cell cytoplasm.
• Retroviruses (e.g., HIV) use reverse transcriptase to convert their RNA into DNA, which then integrates into the host chromosome.
• Retroviruses become a permanent part of the host cell's genome.

Immune System Functions

• The immune system defends the body against pathogens and abnormal cells.
• Immune defenses include innate (nonspecific) and adaptive (specific) mechanisms.

Innate Immune Response

• Innate immunity provides immediate, nonspecific defense against pathogens.
• Inflammation mobilizes the innate immune response, characterized by redness, swelling, heat, and pain.
• Inflammation involves the release of chemical signals that promote increased blood flow and recruitment of immune cells to the site of infection.

Macrophages, T Cells, and B Cells

• Macrophages are phagocytic cells that engulf and digest pathogens and cellular debris.
• T cells are lymphocytes that mediate cellular immunity, including cytotoxic T cells (killer cells) and helper T cells.
• B cells are lymphocytes that produce antibodies, providing humoral immunity.

Antibodies

• Antibodies are proteins that recognize and bind to specific antigens (foreign molecules) on pathogens.
• Antibody diversity is achieved through genetic mechanisms, including gene rearrangement and somatic hypermutation.

Clonal Selection

• Clonal selection is the process by which immune cells with receptors specific to an antigen proliferate and differentiate into effector cells and memory cells.
• The development of immunity involves the generation of memory cells that provide long-lasting protection against subsequent infection.

Humoral vs. Cell-Mediated Immunity

• Humoral immunity involves the production of antibodies by B cells, targeting pathogens in body fluids.
• Cell-mediated immunity involves T cells directly attacking infected cells, targeting intracellular pathogens.

Cytotoxic vs. Helper T Cells

• Cytotoxic T cells directly kill infected cells by releasing toxic substances.
• Helper T cells secrete cytokines that activate other immune cells, including B cells and cytotoxic T cells.

HIV Infection

• HIV destroys helper T cells, weakening the immune system.
• Loss of helper T cells leads to immunodeficiency and increased susceptibility to opportunistic infections.

Vaccination

• Vaccination introduces weakened or inactive pathogens (or their components) into the body, stimulating an immune response.
• Vaccination results in the development of immunological memory, providing protection against future infection by the same pathogen.

Coronavirus Vaccines

• Pfizer and Moderna coronavirus vaccines are mRNA vaccines.
• mRNA vaccines contain genetic material that codes for a viral protein, stimulating the production of antibodies and T cells against the virus.
• mRNA vaccines do NOT cause the disease, COVID-19
• mRNA vaccines do NOT effect the DNA of the recipent

Explore the structural differences between bacteria and viruses, including cell walls, genetic material, and replication methods. Understand prokaryotic domains, focusing on cell wall composition and environmental adaptations. Learn about Gram-positive and Gram-negative bacteria, emphasizing cell wall structure.