Biology: Three Domains of Life

Characteristics of Bacteria, Eukarya, and Archaea

• Bacteria have no membrane-bound nucleus or mitochondria, possess a cell wall, and reproduce via binary fission.
• Eukarya consist of organisms with internal membranes, a membrane-bound nucleus, and mitochondria; their DNA is organized into true chromosomes, and they divide through mitosis.
• Archaea produce methane and thrive in extreme environments (e.g., hot springs, high salinity), lack internal membranes, and share DNA replication machinery similarities with eukaryotes but have bacterial-like metabolism.

Molecular Organization and Chemical Foundations

• Cells are organized hierarchically, starting from organelles to supramolecular complexes and macromolecules.
• Biochemistry explains biological form and function in terms of chemical principles, with about 30 naturally occurring elements essential for life.
• The four most abundant elements in organisms are Hydrogen (H), Oxygen (O), Nitrogen (N), and Carbon (C), together making up over 99% of cellular mass.
• Bulk elements are required in grams daily, while trace elements (e.g., Fe, Cu, Zn) are needed in small milligram quantities.

Classification of Organisms by Energy Sources

• Organisms can be classified based on energy sources: phototrophs use sunlight, while chemotrophs derive energy from chemical fuel oxidation.
• Phototrophs can be autotrophs (synthesizing biomolecules from CO2) or heterotrophs (requiring preformed organic nutrients).
• Examples: cyanobacteria are photoautotrophs; humans are chemoheterotrophs.

Roles of ATP and NAD(P)H in Metabolism

• ATP serves as the energy currency, linking energy-releasing and consuming processes, produced in exergonic reactions and utilized in endergonic ones.
• NAD(P)H acts as a cofactor that collects electrons, vital for anabolic reactions, and needs constant regeneration through catabolic reactions.

Enzymes as Biocatalysts

• Enzymes are proteins that facilitate biochemical reactions at body temperature quickly.
• Each enzyme has specificity for its substrate; the combination of the enzyme and substrate produces products.
• Enzymes may contain an apoenzyme (inactive part) and a cofactor; together, they form an active holoenzyme.

Cofactors and Coenzymes

• Cofactors can be divided into those involved in electron transfer (e.g., NAD+) and those transferring other groups.
• NAD+ assists in the conversion of lactate to pyruvate using lactate dehydrogenase, accepting hydrogen atoms to form NADH.
• ATP is created during the oxidation of food and serves as chemical energy storage.

Factors Influencing Enzyme Activity

• Temperature: Optimal range (10-40°C) increases reaction rates; denaturation occurs above 40-60°C, reducing enzyme activity.
• pH Levels: Different enzymes have specific optimal pH; e.g., pepsin functions well in acidic stomach conditions, while pancreatic enzymes thrive in alkaline duodenal conditions.
• Substrate/Product Concentrations: Increased substrate concentration raises reaction speed until enzyme saturation; high product levels can slow down reactions.
• Cofactors: The presence of cofactors is crucial for enzyme activity.
• Effectors: Chemicals that modify enzyme activity can act as activators (increasing activity) or inhibitors (decreasing activity), with reversible or irreversible effects.

Clinical Significance of Enzymes

• Lactate Dehydrogenase (LDH): A tetramer that varies between heart and muscle; elevated levels indicate myocardial infarction, peaking around the 5th day post-attack.
• Creatine Kinase (CK): A dimer with isoforms representing brain and muscle; rising levels help detect myocardial infarction early.
• Alanine Amino Transferase (ALT): Normal levels are 10-30 U/L; extreme rises (>100 U/L) indicate acute hepatitis; moderate increases (25-100 U/L) suggest chronic liver diseases.
• Alkaline Phosphatase (ALP): A nonspecific enzyme with an optimum pH of 9-10; increases are noted in hepatic and bone diseases.

Explore the fundamental characteristics of the three domains of life: Bacteria, Eukarya, and Archaea. This quiz will test your understanding of cellular structure, division, and unique traits that differentiate these domains. Perfect for biology students looking to strengthen their knowledge in microbiology.