Enzymes and Protozoa Overview

Acetylcholinesterase (AChE)

• A serine hydrolase enzyme rapidly hydrolyzing acetylcholine (ACh).
• Catalytic steps include substrate binding, active site acylation (Ser200), deacylation, and product release.
• Multiple isoforms (AChE-T, AChE-R, AChE-H) with varying tissue distributions and regulation.
• High catalytic efficiency stops cholinergic signaling quickly, preventing prolonged effects.
• Structure and function conserved across species, vital for neuronal communication.
• Tightly regulated transcriptionally and post-translationally.
• Inhibition leads to severe consequences (e.g., organophosphate poisoning paralysis).
• Isoform differences' specific physiological roles remain under research.
• Allosteric modulation impacting drug design is crucial.

Protozoa

• Traditionally classified as a kingdom of unicellular eukaryotes.
• Molecular analysis shows polyphyletic nature (don't share a single common ancestor).
• Formerly protozoan lineages part of distinct eukaryotic supergroups (Excavata, SAR, Archaeplastida).
• "Protozoa" now largely a functional group (unicellularity, heterotrophic nutrition), not a precise phylogenetic classification.
• Show vast diversity of forms, lifestyles, and ecological roles (free-living, symbionts, parasites).

Eukaryote

• Organisms whose cells have a membrane-bound nucleus containing DNA organized into chromosomes.
• Defined by membrane-bound organelles (mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes).
• Plant and algal cells have chloroplasts for photosynthesis.
• Complex cytoskeleton provides structure and intracellular transport.
• Significantly more complex than prokaryotic cells.
• Evolutionary origins of eukaryotic cells, particularly endosymbiotic theory, are debated and researched areas.

Amoeba

• Single-celled eukaryotic organisms using pseudopodia for locomotion and phagocytosis.
• Pseudopodia temporary cytoplasm projections enabling amoeboid movement and prey capture.
• Varied lifestyles (free-living, parasitic, e.g., harmful human diseases).
• Highly dynamic cellular processes with constant shape changes.
• The term "Amoeba" often informally refers to any amoeboid organisms.

Metazoa (Animalia)

• Multicellular animals with cellular differentiation, tissue organization, and development from a blastula.
• Complex organization into tissues, organs, and organ systems with specialized functions.
• Exhibit diverse body plans and environmental adaptations.
• Evolutionary history spans billions of years.
• Phylogenetic relationships refined through molecular and developmental studies.
• Early animal evolution and multicellularity are ongoing areas of research.

Archaea

• Single-celled prokaryotes distinct domain of life from Bacteria and Eukaryotes.
• Unique biochemistry (lack peptidoglycan, unusual membrane lipids, specific RNA polymerases).
• Often thrive in extreme environments (extremophiles).
• Also found in diverse moderate habitats (soil, oceans).
• Remarkable metabolic diversity from energy production and carbon fixation.
• Discovery of Archaea revolutionized understanding of the tree of life.

Eubacteria (Bacteria)

• Single-celled prokaryotes.
• Lack a membrane-bound nucleus and organelles.
• Diverse morphologies (cocci, bacilli, spirilla), metabolism, and ecological roles.
• Cell walls typically contain peptidoglycan.
• Crucial roles in nutrient cycling, decomposition, and symbiotic relationships.
• Many are essential to human health; others are pathogenic.
• Diversity poses challenges for classification and characterization.
• 16S rRNA gene sequencing revolutionized bacterial taxonomy.

Homeostasis

• Ability of an organism or cell to maintain stable internal environments despite external changes.
• Involves intricate regulatory mechanisms sensing deviations and restoring balance.
• Typically uses negative feedback loops.
• Examples: Thermoregulation, osmoregulation, blood glucose control.

Polyphenism

• Phenomenon where a single genotype produces multiple phenotypes depending on environmental signals.
• Phenotypic changes are often irreversible and represent environmentally triggered developmental switches.
• Common in insects in response to environmental factors (food, temp, predators).
• Significant role of environmental factors in shaping phenotypes.
• Understanding genetic and epigenetic mechanisms mediating developmental switches is focus of research.

Organophosphate

• Chemical compounds containing a phosphate group bonded to organic groups.
• Many are potent AChE inhibitors, leading to acetylcholine buildup and toxic effects.
• Applications as insecticides, herbicides, and nerve agents.
• Toxicity from AChE irreversible inhibition.
• Antidotes (e.g. pralidoxime) develop for reactivation.
• Public health concern due to unsafe handling and disposal.

Gene

• Fundamental unit of heredity with a specific sequence of DNA coding for a functional product (protein or functional RNA).
• Organized into chromosomes, transcribed to RNA, and translated to proteins (protein-coding).
• Contains regulatory sequences (promoters, enhancers, silencers) to control expression.
• Variations in sequences (alleles) cause genetic diversity.
• Concept evolved incorporating non-coding RNAs and regulatory elements, genomics.

Negative Feedback Loops vs. Positive Feedback Loops

• Negative feedback loops counteract changes resulting in stable homeostasis.
• Positive feedback loops amplify changes to accomplish a specific goal, often rapidly.

Phenotypic Plasticity

• Ability of a genotype to generate multiple phenotypes in response to environmental variations.
• Allows adaptation without genetic changes, often adaptive and increasing fitness.
• Limited by genetic and developmental factors.
• Degree of plasticity varies among species and traits.

Types/Rules of Chemical Reactions in Biological Processes

• Acid-Base: Essential for pH balance and enzyme function (proton transfer).
• Redox: Central for energy metabolism (electron transfer).
• Hydrolysis: Polymer breakdown using water.
• Dehydration synthesis/Condensation: Polymer formation by removing water.
• Phosphorylation: Adding a phosphate group, often regulating molecule activity/function.
• Isomerization: Rearranging atoms within a molecule.
• Ligase: Joining molecules using ATP energy.
• Transferase: Transferring functional groups.
• Rules: Conservation of mass and energy, reaction equilibrium, reaction rates (temperature/concentration/catalysts), enzyme specificity.