Biological Foundations: Cells, Evolution, and Molecular Processes

Origin of Life and Biological Evolution

Theories on Spontaneous Generation

Early experiments tested the concept of spontaneous generation:

• Francesco Redi: Rejected spontaneous generation.
• John Needham: Supported spontaneous generation (later refuted).
• Louis Pasteur: Rejected spontaneous generation using swan-neck flasks.
• Lazzaro Spallanzani: Rejected spontaneous generation.

Darwin's Observations

Species vary globally, locally, and over time.

Biological Evolution

Evolution is characterized by descent from a common ancestor and adaptation to the environment.

Hierarchy of Life Organization

1. Species
2. Population
3. Community
4. Ecosystem
5. Biome
6. Biosphere

Essential Biomolecules

Biomolecules are the fundamental building components of life.

• Carbohydrates (Carbs)

  Primary source of energy. Monomer: Monosaccharide.

• Lipids (Fats)

  Composed primarily of Glycerol and Fatty Acids.

• Proteins

  Perform structural functions and make enzymes. Monomer: Amino Acids.

• Nucleic Acids

  Includes DNA and RNA. Monomer: Nucleotides.

Cellular Foundations

Endosymbiotic Theory

Proposes that the first true cells were prokaryotic, which later evolved into eukaryotic cells through symbiotic relationships.

Key Components of the Cell

• Cell Membrane

  Controls what goes in and out of the cell.

• Cytoplasm

  The liquid substance filling the cell.

• Cell Wall

  A layer outside the cell membrane, primarily for support and protection (found in plants, fungi, and bacteria).

• Cytoskeleton

  Provides structural support for the cell.

• Ribosomes

  Non-membrane bound organelles responsible for protein production.

• Nucleus

  Holds the cell's DNA (often metaphorically called "the office").

• Endoplasmic Reticulum (ER)

  Network responsible for transporting molecules.

• Golgi Apparatus

  Modifies, stores, and releases proteins.

• Mitochondria

  The "power plants" of the cell; they make ATP during cellular respiration (requires glucose and O₂).

• Chloroplasts

  Organelles that make glucose through photosynthesis (found in plants and algae).

• Vacuoles

  Storage compartments for water, salts, proteins, and carbohydrates.

• Vesicles

  Small sacs used to transport materials within the cell.

• Lysosomes

  Clean up the cell using digestive enzymes.

• Chromatin

  DNA tightly packed with proteins.

• Nucleolus

  Site for the assembly of ribosomes.

Comparing Prokaryotic and Eukaryotic Cells

• Prokaryotic Cells

  Typically lack a nucleus and membrane-bound organelles. Most possess cell walls.

• Eukaryotic Cells

  Characterized by a true nucleus, mitochondria, ER, Golgi apparatus, and other membrane-bound organelles.

• Shared Components (Both)

  DNA, Ribosomes, Cytoplasm, and Cell Membrane.

Cellular Metabolism and Enzymes

Cellular metabolism refers to all chemical reactions occurring within the cell.

Metabolic Processes

• Metabolic Pathway

  A connected series of chemical reactions.

• Anabolic Reactions (Anabolism)

  Build complex molecules from simpler ones, typically requiring ATP input.

• Catabolic Reactions (Catabolism)

  Break down complex molecules into simpler ones, resulting in the release of energy.

Catalysis

• Catalyst

  A substance that speeds up a chemical reaction without being consumed.

• Enzymes

  Biological catalysts that facilitate specific biochemical reactions.

Transport Across the Cell Membrane

Movement of substances across the cell membrane is categorized based on energy requirement.

Passive Transport

Movement of molecules across the membrane without using cellular energy (moving down the concentration gradient).

• Simple Diffusion

  Small, nonpolar molecules (like gases) pass directly through the membrane easily, moving with the concentration flow.

• Osmosis

  The diffusion of water across a selectively permeable membrane.

• Facilitated Diffusion

  Movement of molecules aided by specific protein channels or carriers.

Active Transport

Movement of materials against a concentration difference, which requires cellular energy (ATP).

• Protein Pump

  A membrane protein that uses ATP hydrolysis (ATP converted to ADP) to actively transport specific ions or molecules across the membrane.

• Endocytosis

  The process where large molecules are taken into the cell by creating vesicles from the cell membrane.

• Exocytosis

  The process where materials (often cell waste or secreted products) are released out of the cell via vesicles fusing with the cell membrane.