2.1 Origin of Life and Prokaryotes

Origin of Life on Earth

The study of life's origin explores how life began on early Earth, including the formation of organic molecules and the development of self-sustaining cellular systems.

• Prebiotic Earth Conditions: Early Earth had a reducing atmosphere, rich in gases like methane, ammonia, and water vapor, which facilitated the formation of organic compounds. (Ch. 15.1)

• Miller-Urey Experiment: This experiment simulated early Earth conditions and demonstrated that amino acids and other organic molecules could form spontaneously. (Ch. 15.2)

• Steps Necessary for Life: Life requires the synthesis of organic molecules, assembly into polymers, packaging into protocells, and the development of self-replicating systems such as RNA and ribozymes. (Ch. 15.3)

• Cells as the Smallest Units: Cells are the fundamental units of self-sustaining life.

Domains of Life

All living organisms are classified into three domains based on cellular characteristics and genetic makeup.

• Three Domains: Bacteria, Archaea, and Eukarya (Ch. 1.6)

• Comparison: Archaea and Bacteria are both prokaryotic but differ in membrane composition, genetics, and environmental adaptations.

Diversity and Abundance of Prokaryotes

Prokaryotes are the most abundant and diverse group of organisms, playing essential roles in ecosystems and human health.

• Ecological Roles: Prokaryotes are involved in nutrient cycling, decomposition, and symbiotic relationships. (Ch. 16.1)

• Human Health: Some prokaryotes are beneficial (e.g., gut microbiota), while others can cause disease.

Prokaryotic Cell Structure

Prokaryotes exhibit a variety of shapes and possess specialized structures for survival and adaptation.

• Shapes: Cocci (spherical), bacilli (rod-shaped), spirilla (spiral-shaped)

• Cell Walls and Projections: Most have cell walls (peptidoglycan in bacteria), flagella for movement, and pili for attachment.

Adaptations for Survival

Prokaryotes have evolved numerous adaptations to thrive in diverse and extreme environments.

• Reproductive Rate: Rapid binary fission allows quick population growth.

• Biofilms: Communities of prokaryotes encased in a protective matrix, enhancing survival. (Ch. 16.4)

• Endospores: Dormant, resistant cells formed under harsh conditions.

• Archaea in Extreme Environments: Archaea can survive in extreme heat, salinity, and acidity. (Ch. 16.6)

2.2 Cell Structure

Cell Theory

Cell theory is a foundational concept in biology, stating that all living things are composed of cells, and cells are the basic units of life. (Ch. 4.1)

• Three Tenets: All organisms are made of cells; cells are the basic unit of structure and function; all cells arise from pre-existing cells.

Endosymbiotic Hypothesis

The endosymbiotic hypothesis explains the origin of eukaryotic cells through the engulfment of prokaryotic cells, leading to organelles like mitochondria and chloroplasts. (Ch. 15.4)

• Evidence: Mitochondria and chloroplasts have their own DNA and double membranes.

Evolution and Multicellularity

Multicellularity evolved from single-celled ancestors, allowing for specialized cell functions and complex organisms.

• Advantages: Division of labor, increased size, and adaptation to various environments.

Microscopy and Cell Structure

Microscopes are essential tools for studying cell structure and function.

• Compound Light Microscope: Used to observe cell morphology and organelles.

Prokaryotic vs. Eukaryotic Cells

Cells are classified as prokaryotic or eukaryotic based on structural differences.

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles.

• Eukaryotic Cells: Have a nucleus and various organelles.

• Plant vs. Animal Cells: Plant cells have cell walls, chloroplasts, and large vacuoles; animal cells do not.

Kingdoms of Life

Organisms are grouped into kingdoms based on cell type and other characteristics.

• Kingdoms: Plantae, Fungi, Animalia (Ch. 1.6)

Cellular Components

Cells contain specialized structures that perform distinct functions.

• Nucleus: Contains genetic material (DNA).

• Cell Membrane: Regulates entry and exit of substances.

• Cell Wall: Provides structural support (plants, fungi, bacteria).

• Organelles: Mitochondria (energy production), ribosomes (protein synthesis), lysosomes (digestion), endoplasmic reticulum (protein and lipid synthesis), Golgi apparatus (modification and transport).

2.3 Cell Transport

Fluid-Mosaic Model of Cell Membrane

The fluid-mosaic model describes the structure of the cell membrane as a dynamic arrangement of phospholipids and proteins. (Ch. 5.1)

• Phospholipid Bilayer: Hydrophilic heads face outward, hydrophobic tails face inward.

• Proteins: Integral and peripheral proteins serve as channels, receptors, and enzymes.

• Cholesterol: Maintains membrane fluidity.

Passive Transport

Passive transport moves substances across membranes without energy input, driven by concentration gradients.

• Diffusion: Movement of molecules from high to low concentration.

• Facilitated Diffusion: Transport via membrane proteins.

• Osmosis: Diffusion of water across a selectively permeable membrane.

Osmosis Equation:

Where is water potential, is solute potential, and is pressure potential.

• Tonicity: Refers to the relative concentration of solutes; affects cell volume (isotonic, hypertonic, hypotonic).

Active Transport

Active transport requires energy (usually ATP) to move substances against their concentration gradient.

• Carrier Proteins: Transport specific molecules across the membrane.

• Endocytosis: Uptake of large particles via vesicle formation (includes phagocytosis and pinocytosis).

• Exocytosis: Release of substances from the cell via vesicles.

• Receptor-Mediated Endocytosis: Specific uptake of molecules via receptor binding.

Comparison of Transport Mechanisms

• Passive vs. Active Transport: Passive transport does not require energy and moves substances down their concentration gradient, while active transport requires energy and moves substances against the gradient.

• Endocytosis Types: Phagocytosis (cell eating), pinocytosis (cell drinking), receptor-mediated endocytosis (specific uptake).

Additional info: Academic context and definitions have been expanded for clarity and completeness.