Cell Theory and Microscopy

Cell Theory

• The cell theory outlines the fundamental principles of how life is organized
• All living things consist of cells or their products
• Cells are the smallest unit of life
• Cells form from other pre-existing cells

Microscopy

• Light microscopes use visible light and lenses to create magnified images of specimens
• Preparing temporary mounts of cells and tissues, staining, and measuring sizes with an eyepiece graticule are useful skills
• Light microscopes typically include an ocular lens (~10x) combined with objective lenses (~10x, 40x, 100x)

Using Light Microscopes

• Begin by resolving the image at the lowest magnification using the coarse focus
• Increase the magnification by changing the objective lens and fine focus adjustment
• Calculate total magnification by multiplying the magnification of the ocular and objective lenses
• An eyepiece graticule can determine sizes of biological structures

Calculating Magnification

• Use the formula: Magnification = Image size (with ruler) ÷ Actual size (according to scale bar) to calculate linear magnification
• Ensure both image and actual size are of the same units before calculation
• Metric conversions can be used to ensure values are the same:
  • Metre (m): 1(10°)
  • Centi- (cm): 10-2
  • Milli- (mm): 10-3
  • Micro- (um): 10-6
  • Nano- (nm): 10-9

Advances in Microscopy

• Microscopes are scientific tools for visualizing objects not visible to the naked eye
• The two main types are optical (light) microscopes and electron microscopes
• Light microscopes are useful in viewing living colored specimens
• They use glass lenses to bend light and magnify images

Improving Cellular Clarity

• The use of fluorescent labeling enhances the clarity of cellular structures
• Synthetic dyes (e.g., DAPI) can bind to specific cellular compounds to highlight specific structures
• Immunofluorescence staining uses fluorescent-tagged antibodies to target specific cellular components

Electron Microscopes

• Electron microscopes provide much higher magnification and resolution but can only view dead specimens
• Electromagnets focus electrons to produce monochromatic images, to which false color can be applied
• Transmission electron microscopes (TEMs) transmit electrons through the specimen to produce a cross-section image
• Scanning electron microscopes (SEMs) scatter electrons over a surface to create a 3D map

Cryogenic Electron Microscopy

• It involves freezing samples before visualization to achieve image standards comparable to X-ray crystallography
• It allows for determining molecular structures at near-atomic resolution without needing specimen crystallization
• Freeze fracturing can expose internal cellular structures by cracking the frozen specimen along a plane
• Integral membrane proteins within the plasma membrane were visualized using freeze fracturing

Structures Common to All Cells

• All cells contain a plasma membrane, genetic material, ribosomes, and cytosol
• The plasma membrane provides an outer boundary that maintains a different internal chemistry (homeostasis), compared to the external environment
• Genetic material are coded instructions (DNA) that controls the cell's internal activities (metabolism)
• Ribosomes translate the cell’s coded instructions into functional elements (proteins)
• Cytosol contains an internal fluid used as a reaction medium for necessary metabolic processes

Prokaryote Cell Structure

• Prokaryotes are single-celled organisms with a simple cell structure that lacks compartmentalization and membrane-bound organelles
• Their shapes can vary: rods (bacilli), spheres (cocci), spirals (spirilla), commas (vibrio), or corkscrews (spirochetes)
• Prokaryotes are categorized into two domains based on structural and genetic variation

Prokaryotic Biological Domains

• Bacteria comprises a large, diverse group that includes many pathogenic forms
• Archaea includes extremophiles found in extreme environments, but can also inhabit normal habitats
• The nucleoid is the region in the cytosol contains the genetic material (single DNA strand is called the genophore)
• Additional DNA molecules (plasmids) can be exchanged through bacterial conjugation, known as horizontal gene transfer
• Ribosomes are responsible for protein synthesis and are small in size (70S)
• Prokaryotic cells possess a cell wall and glycocalyx (outer slime capsule)
• Pili are hair-like extensions involved in adhesion (attachment pili) or plasmid exchange (sex pili)
• Movement through flagella, can be several whip-like projections

Eukaryote Cell Structure

• Eukaryotes are organisms whose cells contain a nucleus and compartmentalized by membrane-bound organelles
• Eukaryotic cells have a greater level of structural complexity and evolved from prokaryotic cells through endosymbiosis
• Eukaryotes are classified into distinct kingdoms based on structural and functional differences:
  • Animal cells lack a cell wall and use heterotrophic nutrition (ingestion)
  • Plant cells have cell walls (cellulose) and use autotrophic nutrition (photosynthesis)
  • Fungi cells have cell walls (chitin) and use heterotrophic nutrition (absorption)
• Protists are any eukaryotic organism that does not categorize into the animal, plant, or fungal kingdoms

Eukaryotic Cellular Components

• All eukaryotic cells share a nucleus, larger (80S) ribosomes, and membrane-bound organelles
• The organelles include mitochondria, endoplasmic reticulum, Golgi apparatus, and vesicles
• Some plant cells have chloroplasts (photosynthesis) and a big fluid-filled vacuole enveloped by a tonoplast membrane
• Multicellular fungi forms form filamentous hyphae partitioned by septa (internal walls)

Processes of Life in Unicellular Organisms

• All living things execute seven integral survival functions
  • Metabolism are essential chemical reactions
  • Reproduction are offspring produced either sexually or asexually
• Sensitivity: Response to internal and external stimuli
• Homeostasis: Maintain a stable internal environment
  • Excretion removes waste products
  • Nutrition exchanges materials and gases with the environment
  • Growth/Movement: Changes size and shape

Eukaryotic vs. Prokaryotic Cells

• Cell types are categorized based on structure in animals, fungi, and plants, as well as differentiating them between prokaryotic and eukaryotic

Prokaryotic Structural Differences

• Prokaryotes have naked, circular DNA without introns or a nucleus
• They lack compartments and have 70S ribosomes
• Reproduction is asexual by binary fission
• Cells are haploid, small (>10µm), and unicellular

Eukaryotic Structural Differences

• Eukaryotes has DNA with histones in a linear form with introns inside the nucleus
• They possess compartments and 80S ribosomes
• Reproduction can be asexual or sexual
• Cells are haploid or diploid, large (~100µm), and often multicellular

Bacteria and Archaea Differences

• Bacteria have ester-linked lipids and peptidoglycan, while archaea have ether-linked lipids and no peptidoglycan
• Bacteria have naked DNA without introns, making them susceptible to antibiotics
• Archaea have histones, rare introns, and are not susceptible to the same antibiotics

Eukaryotic Cell Structural Differences

• Animal cells ingest heterotrophically, have no cell wall, small temporary vacuoles, are motile with centrioles and lysosomes
• Plant cells are autotrophic, have cellulose cell walls, have large and central permanent vacuoles, non-motile, and chloroplasts/Plastids
• Fungi cells absorb nutrients heterotrophically
• Fungi cell walls are made of chitin
• Fungi vacuoles are large and central and the cell is non-motile but unique organelles are present

Atypical Cell Structures in Eukaryotes

• Specific eukaryotic cells and tissues do not conform to standard organization supporting unique cellular activities
• Striated muscle fibers form when individual muscle cells fuse into long fibers with multiple nuclei surrounded by a continuous plasma membrane and challenges the discrete cell unit idea
• Fungi may have hyphae structures and are used for nutrient absorption and growth
• Aseptate fungal hyphae lack internal walls with continuous cytoplasm and multiple nuclei and challenges living things consisting of autonomous cells

Sieve Tube Elements

• Sieve elements that line the pholem in plants connect via plasmodesmata into supracellular assemblies
• These elements lack nuclei, hold few organelles, and rely on local companion cells for survival
• Phloem sieve tube elements challenge multicellular structure consiting of anatomically independent cells

Red Blood Cells

• Mature red blood cells have no organelles to have more room for hemoglobin
• Red blood cells cannot independently replicate due to missing genetic structure- marrow continually produces new cells
• Red blood cells do not have structure needed for survival, challenging the traditional definition of cell

Cell Type Identification with Microscopes

• Being skilled in identifying cells with microscopes
• Being skilled in identifying cell structure like necleoid region, prokaryotic cell wall, nucleaus, mitrochondrian, chloroplast, sap vacuole, Golgi and plasma membrane in electron and light micrographs
• Light have have a low magnification and resolution and are used to view living structures with color
• Eukaryotic cells appear larger than eukaryotic views and the nucleaus and chloroplast are disernable without staining

Drawing Cellular Structures

• Animal cells: nucleus must be double membrane structure, the ER network show be connected and contain ribosome to indicate if smooth or rough
• Plant cells must have a cell wall, chloroplasts with double mmebrane with flattened stack disks (grana), a lage vacuole occupies a majority of the cell's volume