Chapter 6: The Cell

Basic Features and Types of Cells

Cells are the fundamental units of life. All living organisms are composed of cells, which share certain basic features but can be classified as prokaryotic or eukaryotic based on structural differences.

• Four Basic Features of All Cells:

  • Plasma membrane

  • Cytoplasm

  • Genetic material (DNA)

  • Ribosomes

• Prokaryotic vs. Eukaryotic Cells:

  • Prokaryotic cells lack a nucleus and membrane-bound organelles (e.g., bacteria, archaea).

  • Eukaryotic cells have a nucleus and various membrane-bound organelles (e.g., plants, animals, fungi, protists).

Cell Organelles and Their Functions

Each organelle within a eukaryotic cell has a specific function essential for cell survival and activity.

• Cell Membrane: Semi-permeable barrier controlling entry and exit of substances.

• Cytoplasm: Jelly-like fluid where organelles are suspended.

• Nucleus: Contains genetic material (DNA); controls cell activities.

• Mitochondria: Site of cellular respiration; produces ATP.

• Ribosomes: Synthesize proteins; found free in cytoplasm or on rough ER.

• Chloroplasts: Site of photosynthesis in plant cells.

• Endoplasmic Reticulum (ER):

  • Smooth ER: Lipid synthesis, detoxification.

  • Rough ER: Studded with ribosomes; protein synthesis and modification.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Contain digestive enzymes; break down waste.

• Peroxisomes: Break down fatty acids and detoxify harmful substances.

• Vacuole: Storage of substances; large central vacuole in plant cells.

• Cell Wall: Provides structure and protection (plants, fungi, some protists).

• Cytoskeleton: Network of protein filaments for shape, support, and movement.

  • Microfilaments

  • Intermediate filaments

  • Microtubules

• Centrosomes: Organize microtubules; important in cell division.

• Cilia & Flagella: Movement of cells or substances over cell surface.

• Cell Junctions: Connections between cells for communication and adhesion.

Plant vs. Animal Cells

• Plant cells have a cell wall, chloroplasts, and a large central vacuole; animal cells do not.

• Animal cells have centrioles and lysosomes, which are rare in plant cells.

The Endomembrane System

The endomembrane system is a group of membranes and organelles in eukaryotic cells that work together to modify, package, and transport lipids and proteins.

• Includes the nuclear envelope, ER, Golgi apparatus, lysosomes, vesicles, and plasma membrane.

Microscopy

• Three Parameters of Microscopy:

  • Magnification

  • Resolution

  • Contrast

• Light vs. Electron Microscopy:

  • Light microscopes use visible light; lower resolution but can view living cells.

  • Electron microscopes use electron beams; higher resolution but require dead specimens.

Cell Fractionation

Cell fractionation is a technique to separate cellular components based on size and density, often using centrifugation.

Cell Membranes

• Composition: Phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• Properties: Fluid mosaic model; selectively permeable.

• Membrane Fluidity: Maintained by unsaturated fatty acids and cholesterol.

• Membrane Proteins:

  • Integral proteins: Span the membrane.

  • Peripheral proteins: Attached to membrane surface.

• Functions of Membrane Proteins:

  • Transport

  • Enzymatic activity

  • Signal transduction

  • Cell-cell recognition

  • Intercellular joining

  • Attachment to cytoskeleton or ECM

Membrane Transport

• Passive Transport: Movement of substances down their concentration gradient (e.g., diffusion, osmosis).

• Active Transport: Movement against concentration gradient; requires energy (e.g., sodium-potassium pump).

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

• Endocytosis & Exocytosis: Bulk transport of materials into (endocytosis) or out of (exocytosis) the cell.

  • Types of exocytosis: Constitutive, regulated, and lysosome-mediated.

• Examples: Sodium-potassium pump maintains electrochemical gradients in animal cells.

Chapter 8: Metabolism

Metabolism and Metabolic Pathways

Metabolism encompasses all chemical reactions in a cell, organized into metabolic pathways.

• Types of Metabolic Pathways:

  • Anabolic (build complex molecules)

  • Catabolic (break down molecules)

  • Amphibolic (both anabolic and catabolic)

• Forms of Energy: Kinetic, potential, chemical, thermal, etc.

• Laws of Thermodynamics:

  • First law: Energy cannot be created or destroyed.

  • Second law: Entropy (disorder) increases in spontaneous processes.

• Free Energy (): Determines whether a reaction is spontaneous.

• Exergonic vs. Endergonic Reactions:

  • Exergonic: Release energy ()

  • Endergonic: Require energy ()

• Equilibrium: State where forward and reverse reactions occur at the same rate.

• Cellular Work: Mechanical, transport, and chemical work.

• ATP: Main energy currency of the cell; structure includes adenine, ribose, and three phosphate groups.

• ATP Hydrolysis: Releases energy to drive cellular work.

Enzymes

• Definition: Biological catalysts that speed up reactions by lowering activation energy.

• Mechanism: Bind substrates at active site; form enzyme-substrate complex.

• Regulation: Inhibitors (competitive, noncompetitive), allosteric regulation, feedback inhibition.

Chapter 9: Cellular Respiration

Overview of Cellular Respiration

Cellular respiration is the process by which cells extract energy from glucose and other molecules to produce ATP.

• Three Stages:

  • Glycolysis

  • Citric Acid Cycle (Krebs Cycle)

  • Oxidative Phosphorylation (Electron Transport Chain and Chemiosmosis)

• Redox Reactions: Involve transfer of electrons; oxidation (loss), reduction (gain).

• NAD+: Electron carrier; reduced to NADH during glycolysis and the citric acid cycle.

• Fermentation: Anaerobic process; produces lactic acid or alcohol.

• Obligate vs. Facultative Anaerobes: Obligate cannot survive in oxygen; facultative can use oxygen or not.

Chapter 10: Photosynthesis

Overview of Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy.

• Equation:

• Autotrophs vs. Heterotrophs: Autotrophs produce their own food; heterotrophs consume others.

• Chloroplast Structure: Includes thylakoids (site of light reactions) and stroma (site of Calvin cycle).

• Light Reactions: Convert light energy to chemical energy (ATP, NADPH).

• Calvin Cycle: Uses ATP and NADPH to fix carbon dioxide into sugars; occurs in three phases.

• Electromagnetic Spectrum: Visible light is used in photosynthesis (approx. 400-700 nm).

• Photosynthetic Pigments: Chlorophyll a, chlorophyll b, carotenoids.

• Photosystem I vs. II: Differ in light absorption and role in electron transport chain.

• Alternative Carbon Fixation: C4 and CAM pathways in some plants to minimize water loss.