CH 19: Viruses

Virus Classification

Viruses are classified based on several structural and genetic features. Understanding these features helps in identifying and studying different viruses.

• Shape: Viruses can be helical, icosahedral, complex, or enveloped.

• Genetic Material: Viruses may contain DNA or RNA, which can be single-stranded or double-stranded.

• Genome Size: Viral genomes vary in size, influencing their complexity and replication strategies.

• Capsid: The protein shell that encases the viral genome.

• Viral Envelope: A lipid membrane derived from the host cell, present in some viruses.

• Bacteriophage: Viruses that infect bacteria.

• H1N1 Flu: 'H' stands for hemagglutinin, 'N' for neuraminidase—surface proteins important for viral entry and exit.

• Transmission: Vertical transmission is from parent to offspring; Horizontal is between individuals of the same generation.

Lytic vs. Lysogenic Cycles

Viruses can replicate via two main cycles in host cells.

• Lytic Cycle: Virus replicates rapidly, lyses (breaks open) the host cell, releasing new viruses.

• Lysogenic Cycle: Viral DNA integrates into the host genome and replicates with it, remaining dormant until triggered.

• End Result: Lytic—host cell death; Lysogenic—host survives until induction of lytic cycle.

• Cycle Choice: Environmental conditions and host factors influence which cycle is used.

Restriction Enzymes

Restriction enzymes are bacterial proteins that cut DNA at specific sequences, often palindromic.

• Palindrome: A DNA sequence that reads the same forward and backward (e.g., GAATTC).

• Mechanism: Enzymes recognize specific sites and cleave the DNA, producing fragments.

• Applications: Used in molecular biology for cloning and DNA analysis.

• Visualization: DNA fragments can be separated by agarose gel electrophoresis.

CRISPR-Cas System

The CRISPR-Cas system is an adaptive immune mechanism in bacteria.

• Mechanism: Bacteria capture viral DNA and use it to recognize and cut future invaders.

• Importance: Provides immunity against viruses; basis for genome editing technologies.

Animal Viruses and Disease Transmission

• Examples: Influenza, HIV, Herpes, Rabies, Ebola.

• Transmission Patterns:

  • Pandemic: Worldwide outbreak (e.g., COVID-19).

  • Epidemic: Widespread in a region (e.g., Ebola in West Africa).

  • Sporadic: Occasional cases (e.g., rabies).

  • Endemic: Constantly present in a population (e.g., common cold).

HIV and Vaccines

• HIV: High mutation rate, targets immune cells, difficult to treat.

• Medications: Reverse transcriptase inhibitors, protease inhibitors, entry inhibitors.

• Vaccines: Stimulate immune response; not always 100% effective due to viral mutation.

• Reasons for Not Vaccinating: Medical, religious, or personal beliefs; access issues.

Viral vs. Bacterial Diseases

• Differences: Viruses require host cells; bacteria are independent cells.

• Treatment: Antivirals for viruses, antibiotics for bacteria.

• Plant vs. Animal Viruses: Differ in structure and transmission methods.

Prions

• Definition: Infectious proteins causing neurodegenerative diseases (e.g., mad cow disease).

• Difference from Viruses: No nucleic acids; only protein.

CH 31: Fungi

Fungal Lifestyles: Decomposers, Parasites, Mutualists

Fungi exhibit diverse lifestyles, each with unique ecological roles and adaptations.

• Decomposers: Break down dead organic matter; food source is non-living material.

• Parasites: Extract nutrients from living hosts, often causing disease.

• Mutualists: Form beneficial relationships (e.g., mycorrhizae with plants).

• Structures: Specialized hyphae for nutrient absorption or host penetration.

Fungal Structure and Mycorrhizae

• Structure: Composed of hyphae (filamentous cells) forming a mycelium.

• Difference from Other Multicellular Organisms: Cell walls made of chitin, not cellulose.

• Mycorrhizae: Symbiotic association between fungi and plant roots; enhances nutrient uptake.

Fungal Reproduction: Plasmogamy and Karyogamy

• Plasmogamy: Fusion of cytoplasm from two parent mycelia.

• Karyogamy: Fusion of nuclei, forming a diploid zygote.

• Reproduction: Both sexual and asexual; sexual involves plasmogamy and karyogamy.

Fungal Evolution and Major Groups

• Closest Relatives: Animals; both belong to the Opisthokonta clade.

• Major Groups:

  • Chytrids: Flagellated spores; aquatic.

  • Zygomycetes: Resistant zygosporangium.

  • Glomeromycetes: Form arbuscular mycorrhizae.

  • Ascomycetes: Sac fungi; produce ascospores.

  • Basidiomycetes: Club fungi; mushrooms, puffballs.

Lichens and Fungal Diseases

• Lichen: Symbiotic association between a fungus and a photosynthetic partner (alga or cyanobacterium).

• Types: Crustose, foliose, fruticose.

• Ecological Role: Pioneer species, soil formation.

• Ergotism: Poisoning from Claviceps purpurea (ergot fungus) on grains; causes hallucinations, convulsions.

• Other Diseases: Athlete's foot, ringworm, yeast infections.

• Medical Role: Source of antibiotics (e.g., penicillin).

CH 32: Overview of Animal Diversity

Key Characteristics of Animals

• Multicellularity: Composed of multiple cells with specialized functions.

• Heterotrophy: Obtain energy by consuming other organisms.

• Motility: Most animals can move at some stage of life.

• Development: Embryonic development includes blastula and gastrula stages.

Animal Diversity and Evolution

• Described Species: Over 1.3 million; actual number likely higher.

• Common Ancestor: Lived ~700 million years ago.

• Significant Eras:

  • Neoproterozoic: Early animal fossils.

  • Paleozoic: Cambrian explosion; rapid diversification.

  • Mesozoic: Dinosaurs, first mammals.

  • Cenozoic: Mammal and bird diversification.

Animal Body Plans and Cavities

• Body Plans: Symmetry (radial, bilateral), tissue layers (diploblastic, triploblastic).

• Lines of Symmetry: Radial—multiple; bilateral—one.

• Body Cavities:

  • Acoelomate: No body cavity.

  • Pseudocoelomate: Body cavity not fully lined by mesoderm.

  • Coelomate: True body cavity, fully lined by mesoderm.

• Functions: Cushion organs, allow growth/movement.

Developmental Patterns and Phylogeny

• Protostome vs. Deuterostome:

  • Protostome: Mouth develops first.

  • Deuterostome: Anus develops first.

• Phylogenetic Analysis: Morphology, molecular data, developmental patterns.

• Key Phylogenetic Points: Common ancestry, symmetry, tissue layers, body cavities, developmental modes.

• Major Clades: Deuterostomia, Lophotrochozoa, Ecdysozoa (within Bilateria).

• Diploblastic vs. Triploblastic: Two vs. three germ layers.

• Hox Genes: Regulate body plan development; highly conserved.

CH 33: Invertebrates

Invertebrate Diversity and Classification

Invertebrates are animals without backbones, comprising the majority of animal species.

• Major Groups:

  • Porifera: Sponges; simple, filter feeders.

  • Cnidaria: Jellyfish, corals; radial symmetry, cnidocytes.

  • Lophotrochozoa: Flatworms, molluscs, annelids.

  • Ecdysozoa: Nematodes, arthropods (largest group).

  • Deuterostomia: Echinoderms, chordates.

• Largest Group: Arthropods (insects, crustaceans, etc.).

Key Invertebrate Features and Adaptations

• Surface Area:Volume Ratio: Important for gas exchange and nutrient uptake; smaller organisms have higher ratios.

• Metamorphosis:

  • Complete: Distinct larval, pupal, and adult stages (e.g., butterflies).

  • Incomplete: Juveniles resemble adults (e.g., grasshoppers).

• Hermaphroditism: Individuals have both male and female organs; increases reproductive flexibility.

• Cnidocyte: Specialized stinging cell in cnidarians.

• Polyp vs. Medusa: Sessile vs. free-swimming body forms in cnidarians.

• Medusozoans vs. Anthozoans: Medusozoans (jellyfish) have medusa stage; anthozoans (corals) do not.

• Diseases: Schistosomiasis (trematodes), tapeworm infection.

• Radula: Feeding organ in molluscs for scraping food.

• Cuticle and Molting: Protective exoskeleton in ecdysozoans; shed during growth.

• Circulatory Systems:

  • Open: Hemolymph bathes organs directly (e.g., insects).

  • Closed: Blood circulates in vessels (e.g., annelids).

Table: Major Invertebrate Groups and Examples

Additional info: This table summarizes the main invertebrate groups, their features, and examples for quick reference.