Cells 1

Introduction to Cells and Life

• Presented by Dr. Rebecca Labard in course BIBS 1201: Molecules, Cells, Genes.

• Overview of key learning outcomes:

  • Understanding the diversity of life and classification.

  • Definition and characteristics of cells.

  • Differences between prokaryotes and eukaryotes.

  • Introduction to endosymbiosis.

Diversity of Life

• Life's diversity is vast, with around 1,800,000 identified species, increasing due to advances in microbiology and genome sequencing.

• Speculation on Earth's total species count ranges from 10 to 100 million.

• Examples of extreme environments include deep oceans and various soils, where high microbial diversity exists.

Classification of Life

• Historical classification based on morphological features and now increasingly on genetic analysis, particularly nucleic acids.

• Example: Two different species of fruit flies were re-evaluated based on genome sequencing, revealing they were the same species due to different mating times related to gene expression.

• 16S rRNA is crucial for bacterial classification, encoding ribosomal RNA and aiding in understanding evolutionary relationships.

Naming and Taxonomy

• Each species has a two-part name (genus and species), e.g., Staphylococcus aureus (golden staph).

• Staphylococcus aureus is known for causing hospital-acquired infections.

• Staining techniques (e.g., Gram stain) classify bacteria as gram-positive or gram-negative based on cell wall composition.

Levels of Classification

• Life is classified into three domains:

  • Bacteria

  • Archaea

  • Eukaryotes

• Archaea discovered in 1977 and categorized separately from bacteria due to genetic differences.

• Archaea are typically found in extreme environments.

Size and Complexity

• Prokaryotes (Bacteria & Archaea) are simpler, typically unicellular.

• Prokaryotes do not have membrane-bound organelles; eukaryotes are more complex and can be unicellular or multicellular.

• Key examples of eukaryotic kingdoms include animalia, plantae, and fungi. The term protist refers to informal unicellular eukaryotes.

Characteristics of Life

• Cells are the smallest unit of life and share key qualities:

  • Reproduction: Cells can reproduce.

  • Growth and Development: Cells undergo stages of development.

  • Response to Environment: Cells can react to stimuli.

  • Metabolism: Cells have biochemical processes such as energy generation (e.g., photosynthesis).

  • Evolution/Adaptation: Organisms evolve in response to environmental changes.

Definition of a Cell

• Cells are the basic organizational units that perform life activities.

• Both prokaryotic and eukaryotic cells share key components:

  • Membrane: Separates interior from exterior.

  • DNA: Genetic material.

  • Ribosomes: Sites of protein synthesis.

Differences Between Cell Types

• Prokaryotic Cells: Smaller, simpler, with no nucleus (DNA in nucleoid), lack membrane-bound organelles.

• Eukaryotic Cells: Larger, more complex, with membrane-bound organelles including a nucleus.

Investigating Bacteria

• Bacteria are diverse in morphology and metabolism; identified by Gram stain properties, morphologies like cocci (spherical), bacilli (rod), and staphylococci (clusters).

• Bacterial cell wall composition varies, and this influences staining responses.

• Some bacteria can form endospores to survive harsh environments, e.g., Clostridium tetani (tetanus).

Archaea Overview

• Similar in size to bacteria but with different membrane compositions and metabolic pathways.

• Archaea thrive in extreme environments and are non-pathogenic; no known archaea cause disease.

Cell Metabolism

• Different types of bacteria can be aerobic or anaerobic, with unique adaptations for energy production, e.g., photosynthetic cyanobacteria.

• Important to note that bacteria's cellular structure involves a cell wall, ribosomes, and in some cases, flagella for motility.

Cell Organelles

• Eukaryotic Organelles: Membrane-bound structures within eukaryotic cells that compartmentalize functions:

  • Mitochondria: Involved in ATP production and energy metabolism; have their own DNA.

  • Chloroplasts: Sites of photosynthesis in plant cells, containing chlorophyll and their own DNA.

Endosymbiotic Theory

• Proposes that eukaryotic cells originated through a symbiotic relationship between ancestral prokaryotic cells.

• Mitochondria and chloroplasts are thought to have evolved from engulfed prokaryotes that provided functional advantages, leading to their adaptation as organelles.

• Evidence includes the presence of DNA and ribosomes in both mitochondria and chloroplasts, and their method of replication analogous to prokaryotic cell division.

Conclusion

• Review of the concepts covered in the lecture, with a recommendation to explore additional resources and practice questions on Moodle.