Classification

Introductory Biology BIO-3002A: Life & Cells week 3 - Classifying Life

Classifying Life & Exploring the Three Domains

  • Focus on the classification of life and exploring prokaryotic diversity.

Outline of Life & Cells, Week 3

  • Classification of life

  • Three Domains

  • Prokaryotic Diversity

Taxonomy

  • All living organisms are classified based on a binomial nomenclature system devised by Carolus (Carl) Linnaeus.

    • This system is based on rules such as:

    • Homo sapiens

    • Variations include:

      • Homo Sapiens

      • Home sapiens

      • Homosapiens

Historical Classification Systems

  • Function of historically classifying living organisms:

    • Initially categorized into two groups: Plants & Animals.

    • Discovery of unicellular eukaryotes and bacteria led to the development of five kingdoms:

    1. Plants

    2. Animals

    3. Fungi

    4. Protists

    5. Monera (prokaryotes)

    • New discoveries:

    • Distinction of two very different groups of prokaryotes originally called Eubacteria & Archaebacteria, now recognized as Bacteria & Archaea.

    • Organisms with eukaryotic cells grouped as Eukarya.

Current Classification of Life

  • Current groups classified into three Domains:

    1. Bacteria

    2. Archaea

    3. Eukarya

Key Concepts to Remember

  • Understand:

    • Classification of Life using molecular techniques for organism classification based on similarities and differences.

    • Description of prokaryotes with their unique features and shared similarities, for example:

    • Differences between Bacteria and Archaea

    • Structural diversity

    • Metabolic diversity

    • Example of pathogenic and non-pathogenic bacteria.

    • Example of an Archaean.

  • Realize it’s vital not just to recall examples but to set them in context and apply relevant theories.

  • Contextual Note: Scientific work can sometimes exhibit intrinsic bias.

Prokaryotic Diversity

  • Visualization provided in illustrations such as Fig. 26-21, depicting kingdoms and various organisms alongside taxonomical classifications.

    • Fungi - EUKARYA

    • Prokaryotes including Bacteria and Archaea alongside their common ancestor of all life.

  • Various groups illustrated include:

    • Green algae, Land plants, Red algae, Ciliates, Dinoflagellates, and metabolic types of prokaryotes like thermophiles and halophiles.

Pathogenic Prokaryotes

  • Significance of prokaryotes:

    • Approximately half of all known infectious diseases are caused by pathogenic prokaryotes.

    • About 100 bacterial species cause infectious disease in humans; many more are actually beneficial.

  • Within Europe, approximately 33,000 people die annually due to antibiotic-resistant bacteria.

  • By the year 2050, it's predicted that more people will die from antimicrobial resistance than from cancer—approximately 10 million deaths annually.

  • Notably, half of all antibiotics currently used derive from one genus of prokaryote.

Molecular Techniques for Classification

  • Developed by Carl Woese, techniques focus on finding molecular differences in 16S rRNA.

    • Essential question tackled: How do you classify something that cannot be visually observed?

    • Importance of this work discussed in "Life, rearranged" | PNAS.

Differences Between Bacteria & Archaea

  • Evolutionary history:

    • Bacteria and Archaea have evolved separately for billions of years, leading to fundamental differences primarily at the molecular level, including differences in:

    • Cell wall structure

    • Membrane lipids

    • Enzymes used for transcription (RNA polymerase)

    • Structural differences among various other enzymes.

  • In some aspects of molecular biology, Archaea display similarities to Eukarya rather than Bacteria.

Similarities between Bacteria & Archaea

  • Despite long-term separation, both domains:

    • Exhibit prokaryotic cell organization.

    • Consist of unicellular organisms.

    • Include species with diverse surface features and wide metabolic diversity.

Diversity of Prokaryotic Cells

Cell Wall Structure

  • Bacterial cell walls:

    • Mostly composed of peptidoglycan, targeted by many antibiotics.

    • Gram-positive Bacteria: Stain purple due to a thick peptidoglycan layer.

    • Gram-negative Bacteria: Thinner peptidoglycan with a complex lipid outer membrane, which allows the crystal violet stain to be easily rinsed away, revealing the red safranin dye.

Other Surface Features

  • Structures found in both Bacteria & Archaea, but differing in molecular structure:

    • Capsule - Polysaccharide, offering virulence such as in Klebsiella pneumoniae and Streptococcus pneumoniae.

    • Fimbriae - Critical in virulence mechanisms, especially for E. coli.

    • Flagellae - Function as mobility structures, powered by a rotary motor mechanism.

Prokaryotic Metabolism

  • Metabolic types include:

    • Phototrophs (e.g., Cyanobacteria)

    • Chemotrophs (e.g., sulfur bacteria)

    • Heterotrophs - Act as decomposers, useful in sewage treatment.

    • Can undergo aerobic and anaerobic cellular respiration.

    • Participate in essential ecological processes, including nitrogen fixation and nitrification in soil and oceans.

    • Some metabolic capabilities have significance in industrial contexts, such as waste reclamation and oil breakdown.

Overview of Prokaryotic Life

  • Comprehensive exploration shows diversity spanning all biomes.

  • Major classifications of prokaryotic organisms contribute significantly to ecological balance and human health.

Conclusion

  • The understanding of prokaryotic life emphasizes their importance in infection, disease, and ecological roles. Future classifications are likely to evolve as molecular techniques advance, fostering a deeper understanding of the tree of life.*