Lecture 1 + 2: Cells

Cell Definition and Cell Theory

The cell is the basic structural and functional unit of all living organisms. The cell theory is a fundamental concept in biology that states:

• All living things are composed of one or more cells.

• The cell is the basic unit of structure and organization in organisms.

• All cells arise from pre-existing cells.

Example: Both bacteria (unicellular) and humans (multicellular) are made up of cells.

Cell Biology Applications

• Medical research: Understanding diseases at the cellular level.

• Biotechnology: Genetic engineering, cloning, and production of medicines.

• Environmental science: Studying microbial roles in ecosystems.

Prokaryotic vs. Eukaryotic Cells

Cells are classified as prokaryotic or eukaryotic based on their structure.

• Prokaryotic cells: Lack a nucleus and membrane-bound organelles. DNA is found in the nucleoid region. Example: Bacteria, Archaea.

• Eukaryotic cells: Have a true nucleus and membrane-bound organelles (e.g., mitochondria, endoplasmic reticulum). Example: Plants, Animals, Fungi, Protists.

Advantages of compartments (eukaryotes): Compartmentalization allows for specialized functions and increased efficiency.

Disadvantages: More complex regulation and energy requirements.

Comparison Table: Prokaryotic vs. Eukaryotic Cells

Bacteria, Archaea, and Eukarya

• Bacteria: Single-celled prokaryotes with peptidoglycan in their cell walls.

• Archaea: Single-celled prokaryotes without peptidoglycan; often found in extreme environments.

• Eukarya: Organisms with eukaryotic cells (includes plants, animals, fungi, protists).

The Tree of Life and Prokaryotes

• Tree of Life: A model showing evolutionary relationships among all living organisms.

• Significance of prokaryotes: Prokaryotes (bacteria and archaea) represent two of the three domains of life and are among the earliest forms of life.

Prokaryotic Metabolism and Ecological Roles

• Energy acquisition: Prokaryotes obtain energy through various metabolic pathways, including photosynthesis, chemosynthesis, and heterotrophy.

• Ecological significance: Prokaryotes are essential for nutrient cycling (e.g., nitrogen fixation), decomposition, and as symbionts in other organisms.

• Human health: Many prokaryotes are beneficial (gut microbiota), while some can cause disease.

Example: Rhizobium bacteria fix nitrogen in plant roots.

Importance of Prokaryotes to Life on Earth

• Without prokaryotes, essential processes like decomposition and nutrient cycling would not occur, making life as we know it impossible.

• Prokaryotes interact with the human body, aiding digestion and protecting against pathogens.

Lecture 3: Macromolecules

Atoms and Molecules in Organisms

Living organisms are composed of atoms such as carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. These atoms combine to form molecules essential for life.

Types of Chemical Bonds

• Ionic bonds: Transfer of electrons between atoms (e.g., NaCl).

• Covalent bonds: Sharing of electrons between atoms (e.g., H2O).

• Hydrogen bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., between water molecules).

Properties of Water and Hydrogen Bonds

• Cohesion: Water molecules stick together due to hydrogen bonding.

• Adhesion: Water molecules stick to other substances.

• High specific heat: Water resists temperature changes.

• Solvent properties: Water dissolves many substances, facilitating biochemical reactions.

Importance of hydrogen bonds: Stabilize the structure of proteins and DNA; enable water's unique properties.

Osmosis and Tonicity

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

• Hypertonic solution: Higher solute concentration outside the cell; cell loses water and shrinks.

• Hypotonic solution: Lower solute concentration outside; cell gains water and may burst.

• Isotonic solution: Equal solute concentration; no net water movement.

Example: Red blood cells in a hypertonic solution shrink (crenate); in a hypotonic solution, they swell and may lyse.

Chemistry of Carbon

• Tetravalence: Carbon forms four covalent bonds, allowing for diverse organic molecules.

• Ability to form chains and rings: Enables the complexity of biological macromolecules.

Macromolecules: Definition and Classes

• Macromolecule: A large, complex molecule, typically formed by polymerization of smaller subunits (monomers).

• Four classes: Carbohydrates, lipids, proteins, nucleic acids.

Table: Four Classes of Macromolecules

Levels of Protein Structure

• Primary structure: Sequence of amino acids.

• Secondary structure: Local folding (α-helix, β-sheet) stabilized by hydrogen bonds.

• Tertiary structure: 3D shape formed by interactions among R groups.

• Quaternary structure: Association of multiple polypeptide chains.

Enzymes: Function and Mechanism

• Enzymes: Biological catalysts that speed up chemical reactions without being consumed.

• How they work: Lower the activation energy required for reactions.

• Role: Essential for metabolism, DNA replication, and many cellular processes.

Example: Amylase breaks down starch into sugars.

Additional info: Enzyme activity can be affected by temperature, pH, and substrate concentration. Enzymes are highly specific for their substrates.