chapters 4 5 6 lecture

Light Microscope:
- Principle: Utilizes visible light to illuminate specimens.
- Mechanism: Light passes through a specimen, through glass lenses, to the viewer's eye.
- Magnification: Up to 1000x.
- Limitations: Cannot provide details of small cell structures due to limits of resolution.
Electron Microscope (EM):
- Developed in the 1950s; uses a beam of electrons instead of light.
- Magnification: Can magnify up to 100,000x.
- Resolution: Capable of resolving structures as small as 2 nanometers.
Types of Electron Microscope:
- Scanning Electron Microscope (SEM): Analyzes cell surface details; utilizes electron beams.
- Transmission Electron Microscope (TEM): Focuses on internal cell structures.
- Differential Interference Contrast Microscopy: Creates images of living cells that appear three-dimensional.

Cells must be large enough to house necessary organelles (e.g., DNA, proteins) and small enough for efficient exchange with surroundings.
Plasma Membrane:
- Functions as a selective barrier between the living cell and its environment.
- Composed of a phospholipid bilayer (hydrophilic heads outward, hydrophobic tails inward).
- Proteins embedded in the bilayer serve various functions (transport, signaling, structure).

Prokaryotic Cells:
- Simpler, smaller (e.g., bacteria).
- Lack a membrane-enclosed nucleus; DNA is coiled in a nucleoid region.
- Surface structures (e.g., cell walls, flagella) provide structural support and mobility.
Eukaryotic Cells:
- More complex and larger; include animal and plant cells.
- Membrane-enclosed nucleus and many organelles (nucleus, ER, Golgi apparatus, lysosomes, etc.).

Nucleus:
- Contains cell’s DNA; controls activities via mRNA synthesis.
- Structure: Nuclear envelope with pores regulates molecule exchange.
Ribosomes:
- Sites of protein synthesis; can be free (in cytosol) or bound (to ER).
Endoplasmic Reticulum (ER):
- Rough ER: Studded with ribosomes; synthesizes proteins and produces membranes.
- Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies certain chemicals.
Golgi Apparatus:
- Receives products from ER; modifies, sorts, and ships them via vesicles.
Lysosomes:
- Contain digestive enzymes; recycle worn-out organelles, digest food, and destroy bacteria.
Vacuoles:
- Storage compartments; sizes and functions vary across plant and animal cells.
Mitochondria:
- Powerhouse of the cell; site of cellular respiration converting food energy into ATP.
- Structure includes an inner membrane folded into cristae to increase surface area.
Chloroplasts (in plant cells):
- Site of photosynthesis; contains chlorophyll.
- Thylakoids (stacks called grana) capture light energy.
Cytoskeleton:
- Network of protein fibers (microtubules, microfilaments, intermediate filaments) supporting cell shape, movement, and organelle transport.

Extracellular Matrix:
- Composed of glycoproteins; supports the plasma membrane and connects cells in tissues.
Types of Cell Junctions:
- Tight Junctions: Prevent leakage of fluids across epithelial cells.
- Anchoring Junctions: Fasten cells into strong sheets.
- Gap Junctions: Channels for communication between adjacent cells.

Fluid Mosaic Model: Describes plasma membrane as a blend of phospholipids and various proteins.
Selective Permeability: Membrane's capacity to allow certain substances to pass while blocking others.
Transport Proteins: Aid in transporting ions and larger molecules across membranes; can function with or without energy.

Passive Transport:
- Movement without energy; includes diffusion and osmosis.
- Osmosis: Diffusion of water across a selectively permeable membrane.
Active Transport:
- Movement of substances against their concentration gradient; requires ATP.
Endocytosis/Exocytosis:
- Endocytosis: Engulfment of materials into the cell.
  - Types include phagocytosis and receptor-mediated.
- Exocytosis: Exporting materials out of the cell.

Energy Transformation:
- Kinetic vs. Potential energy; chemical energy is crucial for cellular functions.
Thermodynamics:
- First Law: Energy cannot be created or destroyed.
- Second Law: Energy transformations increase the disorder in the universe (entropy).
Metabolism: The sum of all chemical reactions in a cell, includes pathways that build and break down molecules.
ATP and Energy Coupling:
- ATP as the primary energy currency of the cell; drives various cellular processes.
Enzymatic Function:
- Enzymes lower activation energy and increase the rate of reactions; specific in their substrates.
Inhibitors:
- Competitive and non-competitive inhibitors regulate enzyme activity through binding interactions.
Feedback Inhibition: The end product of a reaction may inhibit an enzyme involved in its synthesis, thereby controlling metabolic pathways.

Understanding these cellular structures and processes is crucial for insight into biological functions and life itself. Support from microscopy and knowledge of energy flow within cells initiates a fundamental comprehension of life's building blocks.