Cell Theory and Cell Structure

Introduction to Cell Theory

• Cell theory states all organisms consist of one or more cells
• The cell is the smallest unit of life, performing all vital physiological activities.
• Cells arise from pre-existing cells through cell division.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic cells lack a defined nucleus and membrane-bound organelles, with genetic material in a nucleoid.
• Eukaryotic cells have a nucleus and membrane-bound organelles like mitochondria, endoplasmic reticulum, and Golgi apparatus.

Role of the Nucleus

• In eukaryotic cells, the nucleus houses DNA and coordinates activities like growth, metabolism, and protein synthesis.

Ribosomes and Protein Synthesis

• Ribosomes synthesize proteins, translating genetic information from the nucleus.
• Ribosomes are found floating in the cytoplasm or attached to the rough endoplasmic reticulum.

Endomembrane System

• Endoplasmic Reticulum (ER): synthesis of proteins and lipids, calcium storage, and detoxification.
  • Rough ER (with ribosomes)
  • Smooth ER (without ribosomes)
• Golgi Apparatus modifies, sorts, and packages proteins and lipids for secretion or use within the cell.
• Lysosomes contain digestive enzymes to break down waste materials and cellular debris.
• Vesicles transport materials within the cell.

Mitochondria and Chloroplasts

• Mitochondria generate ATP through cellular respiration.
• Chloroplasts, found in plant cells, convert light energy into chemical energy via photosynthesis.
• These organelles are believed to be from endosymbiotic relationships with prokaryotic cells

Components of Biological Membranes

• The biological membrane is a phospholipid bilayer interspersed with proteins.
• Phospholipid Bilayer: Provides a semi-permeable barrier.
• Transmembrane Proteins: Involved in transport, signal transduction, and cell recognition.
• Internal Protein Network: Supports the structure.
• Cell-Surface Markers: Involved in cell recognition and interaction.

Membrane Fluidity

• Membrane fluidity is maintained by the fluid mosaic model, a flexible layer made of lipid and protein molecules.

Membrane Proteins

• Transport Proteins: Facilitate the movement of substances across the membrane.
• Enzymatic Proteins: Accelerate intracellular and extracellular reactions.
• Receptor Proteins: Receive and relay signals.
• Cell Adhesion Proteins: Help cells stick to each other and to the extracellular matrix.

Transport Mechanisms

• Simple Diffusion: Movement of hydrophobic molecules without assistance.
• Facilitated Diffusion: Polar molecules and ions movemolecules and ions assisted by carrier proteins or channels.
• Active Transport: Movement against the concentration gradient requiring energy (e.g., Na+/K+ pump).
• Osmosis: Movement of water through a semi-permeable membrane

Kinetic and Potential Energy

• Kinetic energy is the energy of motion.
• Potential energy is stored energy.

Redox Reactions and Thermodynamics

• Redox reactions involve the transfer of electrons between molecules, crucial for cellular energy production.
  • First Law: Energy cannot be created or destroyed.
  • Second Law: Entropy (disorder) increases in an isolated system.
  • Third Law: Entropy approaches zero as the temperature approaches absolute zero.

Enzyme Catalysis

• Enzymes reduce the activation energy required for reactions, speeding up the reaction rates.
• Enzyme activity can be influenced by temperature, pH, and the presence of inhibitors or activators.

Metabolism and Pathways

• Anabolic Pathways require energy to synthesize complex molecules from simpler ones.
• Catabolic Pathways release energy by breaking down complex molecules into simpler ones.
• Metabolic pathways show a complex interplay of sequential reactions.

Cell Size Limitations

• Cell size is restricted by diffusion of substances. -Surface area -Temperature -Concentration gradient -Distance

Similarities in Cells

• Eukaryotic and prokaryotic cells share common structures. -Genetic material -Cytoplasm -Ribosomes -Plasma Membrane

Bacterial vs. Archaeal Cells

• Archaea membrane lipids include saturated hydrocarbons covalently bonded to glycerol, forming a monolayer membrane.

Eukaryotic Cell Organization

• Eukaryotic cells display complex compartmentalization, using the endomembrane system and a cytoskeleton for support.

Cytoskeleton

• Fiber types: -Actin: Aid in cellular movement -Microtubules: Facilitate cellular movement and organize the cytoplasm -Intermediate Filaments: Provide structural stability

Membrane Fluidity

• The fluid mosaic model describes the dynamic nature of membranes.

Na+/K+ Pump

• Utilizes ATP to maintain ion concentration gradients.

Endocytosis and Exocytosis

• Endocytosis: Engulfing materials.
• Exocytosis: Releasing materials.

Energy Source

• The sun acts as the primary energy source for the biosphere.